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Effects of a photoselective netting system on Fuji and Jonagold apples in a Mediterranean orchard
Scientia Horticulturae 263 (2020) 109104
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Effects of a photoselective netting system on Fuji and Jonagold apples in a Mediterranean orchard
T
Mirella Aoun*, Karen Manja Faculty of Agricultural and Food Sciences (FAFS) American University of Beirut, 508 Wing B-Agriculture Building, PO Box 11-236, Riad El Solh, Beirut, 1107 2020, Lebanon
ARTICLE INFO
ABSTRACT
Keywords: Tree fruit production Nets Apples Postharvest quality Light stress Photosynthesis efficiency Shading factor Codling moth Fruit flies
An assessment of a red photoselective netting system on apple production was conducted in a Mediterranean semi-arid climate. For two seasons, blocks of trees from an early bearing (cv Jonagold) and late bearing (cv Fuji) cultivars were covered to full canopy with red photoselective nets with 20% shading factor and an exclusion mesh size of 5.2 × 2.1 mm in an experimental orchard and compared to uncovered blocks of trees in the same orchard. The influence of nets on microclimate was assessed by measuring light intensity, Photosynthetic active radiation (PAR), Air temperature and relative humidity. An average decrease of 22.8% in light intensity along with a reduction in the average PAR radiation incidence by 23% improved the leaves photosynthesis efficiency with no influence on air temperature and relative humidity. The nets, installed after petal fall, had no significant influence on annual shoot growth and fruit set. At harvest, apples taken from netted trees were better graded than in the control in terms of both quality and quantity. Fruit weight, size and color blush were significantly higher in apples grown under nets compared to uncovered ones in both cultivars. While apple firmness was slightly lower under nets, no significant differences were reported in terms of sugar content and malic acid between both treatments. Nets significantly reduced the population of codling moth and the fruit damages caused by this pest without use of insecticides. Nets also decreased the amount of fruit fly caught in traps. No differences were recorded in terms of powdery mildew occurrence, aphids, mites and leafminer populations between both treatments. At last, nets also protected apples from sunburn and bird damages. To our knowledge, this is the first overall assessment of apple production in a pest-exclusion setting using red photoselective nets.
1. Introduction The need to protect horticultural crops is increasing worldwide. This is due mainly to global climate variability, limited water-resources, and the demand for safer and better quality commodities with less chemicals and environmentally-friendly practices. Protective cultivation is being developed around the world as a promising solution to these challenges. Netting is being tested as an efficient way to protect crops against climate challenges i.e. excessive radiation (light and heat), hail, wind, and against biological challenges i.e. flying pests (insects, bats, birds) and in some cases diseases and to improve quality and yield. For a recent exhaustive review on the use of nets for Tree fruit crops and their impact on the production refer to Manja and Aoun (2019).Tests carried out on apple trees (Lawson et al., 1994; Aoun, 2016; Chouinard et al., 2017) and stone fruit trees (Erez et al., 1992; Lloyd et al., 2005)
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have demonstrated that various types of insect-proof nets can prevent the entry of a number of pests without drastically changing the environment and quality of the fruit produced under nets. A successful example covering large areas (more than 2500 ha in France) is the exclusion system called Alt’Carpo developed in France (Sévérac and Romet, 2007). Used increasingly in organic orchards, Alt’Carpo exclusion nets help to keep the damage caused by codling moths at levels below 0.1% without the use of pesticides (Sauphanor et al., 2012). Recently, and thanks to technological advances with photo-selective plastic filters, colored nets have been developed, which provide differential filtration of solar radiation together with physical protection. In plants, including some fruit trees, it has been demonstrated that changes in light composition in red, far-red and blue spectra affects significantly fruit tree plant responses regulated by light such as CO2 assimilation and anthocyanin synthesis and could be a useful tool for
Corresponding author. E-mail addresses: [email protected], [email protected] (M. Aoun).
https://doi.org/10.1016/j.scienta.2019.109104 Received 1 November 2019; Received in revised form 28 November 2019; Accepted 2 December 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
Scientia Horticulturae 263 (2020) 109104
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sustainable management of yield and quality in modern orchards (Bastías and Grappadelli, 2012; Bastías et al., 2012). However, the potential use and benefit of this technology in fruit tree production remain under-explored and needs to be optimized depending on the species/cultivar and geographical region. In this study, we assessed the use of red photoselective nets in an exclusion system under semi-arid Mediterranean climate and on two worldwide commercial apple cultivars; Fuji (late bearing cultivar) and Jonagold (early bearing cultivar). The specific objectives of this research were to use photoselective nets in a full canopy protective system and to measure and compare the effects of the photoselective netting system on the overall orchard environment and production. Fig. 1. Photoselective red net mounted on a block of Jonagold and Fuji trees in the experimental orchard. The net caged the whole canopies of the trees to create both a shading and pest-exclusion effect and was attached to a wire 0,5 m from the soil to permit access. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
2. Materials and methods 2.1. Experimental site The experiment was conducted in a research apple orchard located at Advancing Research Enabling Communities Center (AREC) of the American University of Beirut in the Bekaa valley of Lebanon (coordinates 33°55′ latitude and 36°04′ longitude, 995 m ASL). The orchard consists of nine apple cultivars planted in 1999 and grafted on 2 types of rootstocks M7 and MM111. The orchard included six rows and two trees per cultivar in a row. It was established with 4.5 m between rows and 3.5 m between trees. The experiment was conducted under a semiarid Mediterranean weather characterized by dry hot summers from May till September (the average temperature recorded in the orchard from May till September 2018 was 23,5ᵒ C ± 0.2 while the average relative humidity was 48.6% ± 0.6) and a mean annual rainfall of 528 mm with a standard deviation of 165 mm.
blocks. One delta trap baited with codling moth (cydia pomonella) pheromone capsule containing a blend of E8, E10 Dodecadionol (Alpha Scents,USA) was set in each treatment at mid-canopy height, within the tree canopy. In addition, one yellow trap (Econex Trypack,Alpha Scents.Inc,Spain) with a diffuser of 3 dietary attractants for Ceratitis capitata, was set in each treatment at 1.5 m from the ground, outside tree canopy. At last, one yellow trap with (Hook TML, Isca, USA), an “attract and kill” of the fruit fly, Ceratitis capitata was put in each treatment. The orchard was managed following an Integrated Pest Management spraying calendar and sprays were performed when the present pest number exceeded the economic threshold level. For insect pest management, no sprays were done in the covered blocks as we relied only on nets for insect pest control in these blocks. The orchard was sprayed by the end of February with a mix of paraffinic oil (Copper oxychloride) and an insecticide in order to control overwintering insects. Before the setup of the experiment in 2017, one insecticidal spray was done in May in the entire orchard before the setting of the nets to control overall insect pest population in order not to correlate their presence with any treatment. This spray was not repeated in 2018. Sprays against Powdery mildew were done only in the month of May after leaf scouting in both treatments.
2.2. Experimental design The experiment took place during two growing seasons between April and October 2017 and 2018. The experiment was conducted on Jonagold and Fuji trees, early and late cultivars, respectively. Eight randomly distributed blocks constitute the set-up of the experiment in the orchard. Four were covered with nets and four were uncovered and constitute the control treatment. Each block contains either two trees (28m2) or four trees (56 m2) of both cultivars for a total of twelve trees covered with nets and twelve uncovered trees (six per cultivar). The N Leno 3640(red) Polysack net (Green.tek, Inc., Janesville, WI, USA) was tested in this experiment. It is a photoselective net, red in color with 20% shading factor and a mesh size of 5.2 × 2.1 mm. The net was mounted on a frame structure composed of four steel tubes (4.25 m) supported by galvanized wires fixed in the ground. A 0.75 m part of each steel tube was fixed in the soil with concrete. The netted frame was caging the whole canopy and was open on two sides at the bottom for about 0.5 m from the soil to allow access (Fig. 1). The nets were spread on when the fruits were 20 mm in diameter in 2017 (May 10) and after petal fall in 2018 (April 18) and were removed at Fuji harvest. Jonagold trees were harvested at mid-(in 2018) or end of August (2017) while Fuji trees at the end of September (2018) or beginning of October (2017) two days after the removal of the nets.
2.4. Microclimatic measurements Temperature, humidity and light intensity were measured from the beginning of May till the end of September in both treatments. Temperature and humidity were recorded each 4 h in 2017 and each hour in 2018, in a 24 h interval using sensors (HOBO Pro V2 data logger, Onset,USA) protected with radiation shields from direct solar radiation, rain and sprays whereas light intensity (in μmoles m − 2s−1) was recorded every two hours using other sensors (HOBO Pendant data logger,Onset,USA). These instruments were installed above the canopy, 2.5 m above the ground level, at the center of a control and a net block. Photosynthetically active radiation (PAR) was quantified once a week in 2017 from June 23 till August 17 and repeated in 2018 to confirm results. The radiation was determined at 1:00 pm on a clear sunny day using a portable light meter (LI-189, LI-COR, USA). Measurements were made at mid canopy layer of one tree per block near sun exposed leaves.
2.3. Agricultural practices and pest management All the trees in the experiment received the same irrigation and fertilization applications. The orchard was irrigated twice a week from May until the end of August and once a week in September. NPK fertilizers were either added in the irrigation system or through foliar applications supplemented with trace elements. Weeding was done monthly using a weed eater. In order to monitor the presence of pests in both treatments (control and nets) and to test the ability of nets to exclude adult insect pests; traps for commercial pests were set in the orchard in the experimental
2.5. Photochemical efficiency of photosystem II In order to obtain quantitative information on photosynthesis in intact leaves of covered and uncovered trees, chlorophyll fluorescence 2
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was assessed using a portable fluorometer (model OS-30p, OptiSciences, Hudson, New Hampshire, USA). Minimum (F˳) and maximum chlorophyll fluorescence (Fm) were measured at 9 a.m. from beginning of June till the end of July in a sunny day condition and variable fluorescence (Fv=Fm–Fo) was generated. The measurements were made on a mature sun-exposed leaf from 5 annual shoots per treatment. The leaves were dark-adapted for 30 min (Reyes-Diaz et al., 2009) using leaf clips with sliding shutters and photochemical efficiency of photosystem II (Fv/Fm) was determined by assessing chlorophyll fluorescence.
according to national standards for apples Libnor, No.477, 2001. The percentage of red blush was also taken into consideration in the grading. Sixty apples per treatment per cultivar were subjected for further assessment. In order to measure flesh firmness, the skin was removed on 2 opposite sides of each apple. Then, a fruit pressure tester (mod. FT 327 (3-27lbs), Italy) fitted with an 11.3 mm diameter head was used to measure the maximum force in lb needed to penetrate the peeled flesh. Drops of the juice that came out from the apple after the flesh firmness test were used to measure soluble solids content (SSC) of each apple using the digital hand- held pocket refractometer (PAL, Atago Co, Japan). After sectioning the apples transversally at the equator position and performing the starch iodine test, starch pattern index (Cornell University chart) was evaluated from 1 to 8, where 1 indicated the least starch to sugar conversion and 8 the most. The second section of the apple was put in a juice extractor (MK-6115, Muller Koch, Germany). The titratable acidity was measured by titrating the diluted extracted juice to an end point of pH 8.1 with 0.1 N NaOH using the auto-titrator formed of pH Module 867, the dosing unit Dossino 800 and Tiamo software (Metrohm, Switzerland). Calculating the apples acidity was performed using the equation: A = V × 0.1 N×0.67 where A is the acid concentration in g/L, V is the NaOH volume spent in the titration, N is the normality of NaOH, 0.67 is a factor to express the malic acid acidity in meq.
2.6. Phenology, annual growth and fruit set The apples phenological development was assessed using the BBCHscale (Meier et al., 1994). The weekly stage after fruit set was determined by measuring the average apple’s diameter of both cultivars using a metric ruler. The average annual growth was determined by measuring the length of five annual shoots per tree at the end of annual vegetative growth, in our case beginning of July. Fruit set was determined for each tree by calculating the average number of apples found in five clusters per tree. 2.7. Biotic and abiotic stresses A weekly monitoring of pest presence and damages was performed from May till the end of September on 6 trees covered with nets (3 per cultivar) and 6 uncovered trees (3 per cultivar).
2.9. Statistical analysis Statistical analysis of the data was performed using SPPS version 24 (IBM corp, Armonk, IL, USA). Shapiro-Wilk test was used to assess the data for normal distribution and Levene’s test was used for homogeneity of variances. When the assumptions for normality were not respected, transformations were first applied. If no transformation assumed normality, non-parametric tests were performed including chisquare and Man-Whitney. The influence of the treatment was determined using the independent samples t-test with P = 0.05. Two-way analysis of variance for a completely randomized design was separately performed when the influence of date, cultivar or year were determined in addition of treatment effect. Means of significant effects were separated using Fisher’s protected LSD (least significant differences) at a 5% significance level. Tukey test was used when multiple comparisons were needed in particular to compare averages at multiple dates and hours.
2.7.1. Leaf pests Five annual shoots per tree were scouted: one annual shoot from the inner part of the tree canopy (around the central axis) and four from the outer part of the tree canopy (periphery area) taken from each cardinal direction. Shoots were scouted for powdery mildew (Podosphaera leucotricha) infections and for the presence of rosy (Dysaphis plantaginea), green (Aphis pomi) or woolly aphids (Eriosoma lanigerum) and leafminer (Phyllonorycter spp.). Scouting for mites (Tetranychus ulmi) was done by observing the upper and lower side of one mature leaf/tree found on a shoot that was between the central leader and the periphery area using a 10x lens (Sight Savers, Bausch & Lomb, USA). 2.7.2. Fruit pests Five fruits per tree were scouted randomly: One fruit from the inner and four from the outer canopy taken from each cardinal direction. Damages caused by codling moth, fruit fly, aphids, mites, powdery mildew were recorded.
3. Results
2.7.3. Abiotic and other damages Deformations, sunburn damages and damages caused by birds were also assessed on fruits according to the protocol described above.
3.1. Microclimatic modification Temperature and relative humidity were measured from the beginning of May till the end of September in net and control treatments. In 2017, average temperature (0C) and percent of relative humidity measurements were taken every 4 h in a 24 h- interval while in 2018, average, minimum and maximum temperature and relative humidity were measured every hour in a 24-H. The recorded values were not significant between treatments in both years. Measurements of Photosynthetic Photon Flux Density (PPFD) for light intensity under nets and in the open field were recorded each 2 h in a 24 -hs interval from the beginning of May till the end of September in both seasons. We analyzed the differences between treatments from 6 a.m. until 8 pm when light was detected in the orchard. From 8 a.m. until 4 pm, the net significantly reduced PPFD compared to control with the highest difference recorded at 12 pm (Fig. 2) and an average difference of 22.8%. As expected, in both seasons, Photosynthetic Active Radiation (PAR) radiation was significantly reduced by an average of 23% under the net compared to the control.
2.8. Post-harvest assessment Twenty apples were harvested from each tree in the experiment for a total of 120 apples per cultivar per treatment in order to evaluate the apples physicochemical characteristics at commercial harvest for both cultivars. The harvest was performed at apple commercial maturity for each cultivar taking into consideration the assessment of fruit color, fruit firmness, starch index and seeds color. For both cultivars, apples were picked from the two treatments on the same day. Samples were packed in previously labeled boxes and transported to the American University of Beirut, FAFS, Agriculture Department, research lab where they were subjected to physicochemical analysis. The weight and size of each apple were measured using an analytical balance (AB-204 S,Mettler Toledo, Switzerland) and a caliper respectively. The percentage of the red blush surface of the apple skin was assessed subjectively. Apples were graded based on the size and impurities on the skin 3
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The average fruit set measured as the number of fruits per cluster was not different between the two treatments in both seasons (Table 2). This is to be seen through the fact that nets had no effect on pollination since their set-up happened after pollination occurred. 3.4. Fruit quality 3.4.1. External fruit quality The harvest dates were determined by assessing maturity indices once a week in the harvest intervals of both cultivars. Fruits of the same cultivar were picked on the same day from uncovered and covered trees to assess the effect of net on fruit quality. Nets had a significant positive effect on most of the quality parameters measured at harvest in both cultivars; in particular apple size and weight. The photoselective red nets used also significantly increased red blush percentage; thus fruit skin coloration (Table 3). These results translate well in commercial grading assessment as apples are normally graded according to the size, color and freedom from defects usually found on the fruit skin. Apples were graded according to official national standards (LIBNOR). A significantly higher percentage of apples classified in Grade Extra (highest premium quality grade) were recorded in both cultivars under net. Consequently, a significantly lower percentage of Jonagold and Fuji apples of poor marketable quality sorted to Grade 2 were recorded under net compared to control (Table 4). Jonagold trees had lower total production in 2018 and apple grading was not affected by net.
Fig. 2. Average light intensity (in μmoles m − 2s−1) at different hours of the day during the whole 2017 season in control (uncovered trees) and net (trees covered with red photoselective nets). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
3.2. Photochemical efficiency of photosystem II Nets positively affected photosynthesis efficiency in leaves as maximum quantum yield of Photosystem II primary photochemistry in the dark adapted state (Fv/Fm) and the Fv/Fo ratios significantly increased in leaves of netted trees compared to uncovered control trees (Table 1). According to Murchie and Lawson (2013), the value of Fv/Fm is highly consistent for unstressed leaves, with values of ∼0.83, and correlates to the maximum quantum yield of photosynthesis. Any type of ‘stress’ leading to an inactivation damage of PSII (often referred to as photoinhibition) lowers Fv/Fm. Our results indicate that uncovered control trees are more stressed than netted ones and are less capable to cope with the environmental conditions resulting in reduced photosynthesis.
3.4.2. Internal fruit quality Apples grown under nets were in general softer in both cultivars (Table 5). Starch breakdown was also slightly more advanced in Fuji apples grown under net in 2017 compared to the ones in uncovered control which may suggest fruit ripening acceleration under nets for Fuji cultivar. However, no significant differences were recorded for soluble sugar content and malic acid.
3.3. Seasonal development 3.3.1. Annual growth The average annual shoot length was measured on five annual shoots per tree in the beginning of July when annual growth was completed. The results showed that annual growth remained unaffected by the net presence except for Jonagold in 2018 where annual shoot length was significantly longer under net. A result particular for that year as vegetative growth (here indicated by shoot length) was more important than previous year (Table 2: Total shoot length).
3.5. Biotic and abiotic stresses 3.5.1. Leaf pests The main leaf pests observed during the season were powdery mildew, mites and aphids and to less extent leafminers. Powdery mildew (Podosphaera leucotricha) was observed mainly in May and June with significantly higher incidence on Jonagold (11.6% average of infected leaves in both seasons compared to 1.5% for Fuji). In 2018, the percentage of leaf infected was lower (less than 1%) in both cultivars due to a particular dry weather. In both years, the nets had no significant effect on the percentage of leaves infected by powdery mildew. Nets did not have any effect on mite (Tetranychus urticae) and leafminer (Phyllonorycter spp.) populations in both cultivars and in both seasons: mites were observed in 2017 only, starting the end of June with an average of one mite per leaf observed during the season which was below the threshold level of intervention. As for the leafminer, a maximum of 6% of the leaves observed were infested in 2017 and less than 1% in 2018. There were no significant differences between control and net for these pests. Rosy aphid (Dysaphis plantaginea), green and woolly aphids (Aphis pomi) and (Eriosoma lanigerum) were rarely observed with an incidence below the threshold level.
3.3.2. Fruit set We chose to layout the nets after petal fall to avoid poor pollination resulting in low crop load. Table 1 Photochemical efficiency of photosystem II in control and covered trees.1 Fv/Fm
Fv/Fo
2017 3
Control Net
2
0.78 ± 0.003a 0.80 ± 0.003b
2018
2017
2018
0.77 ± 0.005a 0.80 ± 0.005b
3.60 ± 0.07a 4.06 ± 0.07b
3.52 ± 0.09a 4.02 ± 0.09b
1 Efficiency of photosystem II was determined by assessing chlorophyll fluorescence. Minimum (F˳) and maximum chlorophyll fluorescence (Fm) were measured on dark adapted leaves at 9 a.m. from beginning of June till the end of July in a sunny day condition and variable fluorescence (Fv=Fm–Fo) was generated. The maximum quantum yield of photosystem II (Fv/Fm) and the Fv/ Fo ratios were generated on leaves of trees covered with red photoselective nets (net) and uncovered trees (control). 2 Mean value ± standard error. Different letters represent significant differences between treatments for each ratio at P < 0.05. 3 N = 25 observations per treatment in 2017 and 40 observations per treatment in 2018.
3.5.2. Fruit pests The percentage of apples infected by codling moth (Cydia pomonella) was significantly greater in control compared to the netted ones for both cultivars and in both seasons (Table 6) The percentage of fallen fruits infested by codling moth was also significantly greater in control (Table 6) and a cumulative higher number of codling moths were caught during the season in control delta trap compared to net 4
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Table 2 Fruit set and shoot length in control and net for each apple cultivar.1 Shoot length (cm)
2017 Control2 Net Total 2018 Control Net Total
Fruit set (Number of fruits/cluster)
Jonagold
Fuji
Jonagold
Fuji
8.43 ± 0.915a3 8.28 ± 0.915a 8.36 ± 0.915a
7.94 ± 0.916a 9.28 ± 0.916a 8.61 ± 0.916a
2.17 ± 0.110a1 2.47 ± 0.110 a 2.32 ± 0.110 a
2.40 ± 0.1144a 2.74 ± 0.1144 a 2.57 ± 0.1144 a
12.35 ± 0.915a 18.77 ± 0.915b 15.56 ± 0.915b
20.53 ± 0.916a 18.20 ± 0.916a 19.37 ± 0.916b
1.80 ± 0.110 a 1.87 ± 0.110 a 1.84b ± 0.110b
2.94 ± 0.1144 a 2.74 ± 0.1144 a 2.84 ± 0.1144 a
1 The average annual growth was determined by measuring the length of five annual shoots per tree at the end of annual vegetative growth, in our case beginning of July. Fruit set was determined for each tree by calculating the average number of apples found in five clusters per tree. 2 Mean value ± standard error. Different letters represent significant differences at P < 0.05 within a cultivar. 3 N = 30 clusters per treatment per cultivar.
Table 3 Postharvest exterior assessment of Jonagold and Fuji fruits.1 Size (mm)
2017 Control3 Net 2018 Control Net 1 2 3
Weight (g)
Red blush (%)
Jonagold
Fuji
Jonagold
Fuji
Jonagold
Fuji
67.44 ± 0.42a2 69.00 ± 0.39b
65.53 ± 0.28a 67.7 ± 0.36b
133.18 ± 2.25a 141.18 ± 2.17b
124.94 ± 1.63a 134.6 ± 1.84b
23.71 ± 1.67a 33.54 ± 1.8b
31.79 ± 1.13a 42.00 ± 0.96b
66.72 ± 0.44a 67.49 ± 0.53a
60.407 ± 0.37a 64.278 ± 0.55b
131.57 ± 2.45a 139.27 ± 3.15b
96.68 ± 1.41a 117.45 ± 2.41b
58.52 ± 1.72a 63.67 ± 1.68b
N/A N/A
Mean size, weight and red blush percentage of apples in trees covered with nets and uncovered trees (control). Mean value ± standard error. Different letters represent significant differences for each parameter at P < 0.05 within a cultivar. N = 120 apples per treatment.
(Table 7). These results were recorded despite the fact that insecticides were sprayed in control and no sprays were used under nets and were obtained with both cultivars and in both seasons confirming the efficacy of nets usage in preventing codling moth attack and apple fruit infestation. It should be noted that the photoselective nets used in our experiment were set in an exclusion layout to cover the entire tree canopy. The cumulative number of male fruit flies caught in yellow traps containing attract and kill pheromone gel during the whole season was found higher in control compared to net (Table 7). Also, the cumulative number of female fruit flies caught in control yellow trap containing dietary attractants during the whole season was higher in control compared to net. However, no fruit flies damages were observed on fruits.
3.5.3. Abiotic and other damages Sunburn, bird damage and fruit deformation were observed on apples in control treatment at harvest but not under nets. At harvest, in the control treatment, 12% and 19 % of Fuji apples had sunburn damage in 2017 and 2018 respectively while no damage was found on apples observed from net treatment. Bird damages were also observed sporadically in control treatment but not under net. 4. Discussion 4.1. Microclimatic modification and its impact on photosynthesis efficiency The reduction in PAR under nets corresponds with the expected shade induced by the nets used having a shading factor of 20%. PAR reduction was also reported by other studies using different shading
Table 4 Count of apples in commercial grades for Jonagold and Fuji cv.1 Grade Extra
Grade 1
Jonagold
2017 Control2 Net 2018 Control Net
Fuji
Grade 2
Jonagold
Fuji
Jonagold
Fuji
%
Count
%
Count
%
Count
%
Count
%
Count
%
Count
7% a 18% b
8 22
11% a 23% b
13 28
72% a 76% a
87 91
75% a 72% a
90 86
21% a 6% b
25 7
14% a 5% b
17 6
24% a 20% a
29 24
5% a 12% b
6 14
60% a 66% a
72 79
46% a 56% a
55 67
16% a 14% a
19 17
49% a 32% b
59 39
1 Apples were sorted in 3 grades from higher to lower: Grade Extra, Grade 1 and Grade 2. Apples were sorted at harvest from trees covered with nets and from uncovered trees (control). 2 N = 120 apples per treatment.
5
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Table 5 Postharvest interior assessment of Jonagold and Fuji cv.1 Firmness (lb)
2017 Control3 Net 2018 Control Net 1 2 3
Starch index
Soluble Sugar Content (ᵒBrix)
Malic acid (g/L)
Jonagold
Fuji
Jonagold
Fuji
Jonagold
Fuji
Jonagold
Fuji
10.24 ± 0.12a2 9.49 ± 0.10b
10.7 ± 0.1a 10.08 ± 0.1b
6.5 ± 0.11a 6.5 ± 0.08a
5.0 ± 0.12a 5.6 ± 0.14b
14.7 ± 0.1a 14.2 ± 0.1b
16.8 ± 0.1a 17 ± 0.1a
4.56 ± 0.10a 4.382 ± 0.11a
4.95 ± 0.15a 4.78 ± 0.11a
10.37 ± 0.20a 9.53 ± 0.22a
11.23 ± 0.14a 10.68 ± 0.11b
6.87 ± 0.11a 6.63 ± 0.07a
5.0 ± 0.16a 5.1 ± 0.15a
16.92 ± 0.12a 15.45 ± 0.07b
19.47 ± 0.23a 18.41 ± 0.17a
4.77 ± 0.20a 4.44 ± 0.09a
4.90 ± 0.13a 4.47 ± 0.07b
Mean firmness, starch index, soluble solid content and malic acid of cv. Jonagold apples covered with nets and uncovered trees(control). Mean value ± standard error. Different letters represent significant differences for each parameter at P < 0.05 within cultivar. N = 60 apples per treatment except for malic acid, N = 20–25 apples per treatment.
photoselecvtive nets positively affected photochemical efficiency of PSII in leaves. According to Murchie and Lawson (2013), any type of ‘stress’ leading to an inactivation damage of PSII (often referred to as photoinhibition) lowers Fv/Fm. Our results indicate that uncovered control trees are more stressed than netted ones and are less capable to cope with the environmental conditions resulting in reduced photosynthesis. Our results are in line with the ones reported by Jutamanee and Onnom (2016) who used shade nets as plastic roofs on mango trees. According to Jutamanee and Onnom (2016), the reduction of high solar energy caused by the plastic roof mitigated the inactivation of the primary photochemistry associated with PSII. Medina et al. (2002) have also reported that shading net (50%) was effective in preventing photoinhibition especially in summer where higher PAR levels and higher temperatures in control increase susceptibility to photoinhibition. The recorded air temperature and relative humidity values were not significant between treatments in both years. This result is in line with the ones reported by Corvalán et al. (2014) who did not record any difference in air temperature and relative humidity using photoselective red nets with 20% shading on grapevines. Kalcsits et al. (2017) who tested red shade nets with similar shading factor to ours on apples also reported that netting did not influence the overall orchard temperature and humidity and suggested that previous studies who reported differences did not use radiation shields to protect sensors which may have resulted in a temperature difference between control and net.
Table 6 Percentages of apples attacked by codling moth and apples fallen on the orchard floor due to codling moth infestation.1 % of infestation
2017 Control3 Net 2018 Control Net
% of fallen fruits with codling moth infestation under trees of both cultivars
Jonagold
Fuji
12%a2 5%b
26%a 4%b
34% 11%b
15%a 5%b
10%a 0%b
32%a 11%b
1
The percentage of fruits attacked by codling moth was determined by dividing the number of apples with codling moth infestation over the total number of apples observed per treatment and per cultivar for each year. As for fallen fruits with codling moth infestation, the percentage was calculated by dividing the total number of apples on the ground presenting a codling moth infestation over the total number of apples found on the ground after fruit drop under Jonagold and Fuji trees in the orchard in the experimental blocks. 2 Different letters represent significant differences at P < 0.05 within a cultivar in a year. 3 N = 165 for Jonagold cv; 210 and 240 for Fuji cv in 2017 and 2018 respectively. N represents the total number observed in a season at a weekly scouting of 5 apples/trees until harvest. Table 7 The cumulative number of male codling moth, male fruit fly and female fruit fly caught in traps during the season.1 Male codling moths 2017 Control Net 2018 Control Net
53 17 31 11
2
Male fruit flies
Female fruit flies
38 11
205 100
44 17
N/A N/A
4.2. Seasonal development: Fruit set and annual growth The results observed confirm previous work when photoselective red nets were used (Giaccone et al., 2012; Vuković et al., 2017). One should expect a fruit thinning potential and influence on reproductive growth when trees are covered before or during bloom time (Kelderer et al., 2014). Fruit set was significantly poorer in 2018 for Jonagold cultivar; Jonagold trees significantly invested in vegetative growth that same year as shown in the length of annual shoot growth (Table 2). The results showed that in general annual growth remained unaffected by the net presence for the exception of Jonagold in 2018. A result that could be particular for that year when vegetative growth was more important than reproductive growth as observed in the field and in comparison with previous year (Table 2). That the net had no significant impact on the length of annual shoot can be explained by the fact that the trees already started vegetative growth when the nets were installed in the orchard. In addition, our nets had a relatively low shading factor (20%) to limit vegetative growth stimulation (Shahak, 2014).
1 For each pest, a trap was set in a control block and another under a net block. Traps were scouted twice a week from mid-May to mid-September for codling moth and from mid-August to mid-September for fruit flies. 2 Numbers represent the cumulative count of male or female pest found in a trap during the season.
nets (Retamales et al., 2006; Solomakhin and Blanke, 2007, 2010). The 20–23% shade caused by nets used in this study seemed to be beneficial for trees under high daylight intensity. Indeed, this shading factor positively affected the efficiency of photosystem II, increased apple skin coloration and reduced sunburn damage. According to (Sivakumar and Jifon, 2018), maximum net CO2 assimilation of most C3 species saturates at relatively low irradiance (600–900 μmol/m²/s), which is only 30–40% of full sunlight (1500–2000 μmol/m2/s) on a typical growing season day. The excess radiation normally causes heat stress and a reduction in net photosynthesis. Our results show that 20% shading
4.3. Fruit quality Nets had a significant positive effect on most of the quality parameters measured at harvest; these results are in agreement with those 6
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reported by other authors working with red photoselective nets on apple, pomegranate and peach trees (Brkljača et al., 2016; Corollaro et al., 2015; Meena et al., 2016; Shahak et al., 2004). The positive impact of nets on fruit quality could be attributed to the light scattering and reflection capacity of photoselective nets that can alter plant responses. The increase in weight and size may be the result of less stressful climatic conditions under nets as shown by the chlorophyll fluorescence measurements. An increase in net CO2 assimilation under nets led to an increase in carbohydrate availability for fruit growth as suggested by Bastías et al. (2012). The photoselective red nets used in this study increased fruit skin coloration significantly. This increase may be due to the fact that red photoselective nets enrich red and far-red spectral regions of the light reaching the trees which may alter plant responses regulated by light such as fruit skin color. Color development in apples is related to anthocyanin synthesis, which is stimulated by red and far-red spectral regions (Bastías and Grappadelli, 2012). Apples grown under nets were in general softer in both cultivars (Table 5). This is in line with the results reported by Corollaro et al. (2015) who noticed a lower cell density of apples grown under photoselective red nets. They observed larger cells with a higher volume of air spaces which decreases the resistance to compression. Loreti et al. (1993) indicated that limited solar radiation affects the formation and composition of cell walls as they become more elastic, swell more and contain more water. Starch breakdown was also slightly more advanced in Fuji apples grown under net in 2017 compared to the ones in uncovered control which may suggest fruit ripening acceleration under nets for Fuji cultivar.
experimented here (incomplete exclusion system on rows covered with photoselective nets) is a promising tool for a better quality fruit and an overall tree health with the opportunity of significantly reducing the need for pesticides (no insecticides used under net). The 20% shading caused by nets in a semi-arid climate positively affected the photosynthesis efficiency. In addition, nets significantly protected against major insect pests while improving fruit quality in particular fruit size, weight and skin coloration. Apples under net were better graded than apples in control. Overall, netting system could be proposed as an integrated solution for sustainable apple production in a strategy to address today challenges in tree fruit production. These challenges include increased biotic and abiotic stresses due to climate variability and, at the same time, the growing demand for safe, low-chemical residues products. CRediT authorship contribution statement Mirella Aoun: Conceptualization, Methodology, Validation, Writing - review & editing, Supervision, Project administration. Karen Manja: Formal analysis, Investigation, Resources. Declaration of Competing Interest None. Acknowledgements This study was supported through a seed fund from the Faculty of Agricultural and Food Sciences (FAFS) at the American University of Beirut (AUB). The authors wish to thank all those who helped in making this work possible in particular, Dr Yussef Abou Jawdah who helped in IPM management, Dr Samer Kharroubi who helped in statistical analysis, Mr Nicolas El-Hajj who helped in the design and set-up of the netting system, Mr Andre Bou Haidar, Ms Rachel Sfeir and other graduates who helped in data collection.
4.4. Biotic and abiotic stresses There were no significant differences between control and net for leaf pests. Chouinard et al. (2017) also did not report any significant differences in mobile forms of Tetranychus urticae in both control and exclusion net. The results obtained with codling moths for both cultivars an in both seasons confirm the efficacy of nets usage in preventing codling moth attack and apple fruit infestation when the whole canopy is covered with a relatively small mesh size nets (in this case 5.2 × 2.1 mm). These results are in line with previous studies performed by Alaphilippe et al. (2016); Romet et al. (2010); and Sauphanor et al. (2012) who reported the ability of exclusion nets to control codling moth and reduce fruit attack caused by this pest. According to Sauphanor et al. (2012), the moderate efficacy of the Alt’Carpo netting may be mainly the result of the confined space around the trees altering the reproduction of the moth, complemented by a partial prevention of moth penetration and egg lying. Male moths flying between rows and on top of the trees, which is the main location for female calling and prospecting prior to mating may explain why male moths are not entering inside nets Sauphanor et al. (2012). The results showing reduction of fruit flies caught in traps under nets are in line with the ones reported by Lloyd et al. (2005) and confirm the ability of nets when used in an exclusion setting to significantly reduce pest populations (Candian et al., 2019). The protection from sunburn damages and birds damages confirm the potential of the net to protect against these damages and suggest that a 20% shading factor is efficient under hot Mediterranean summer weather to protect from sunburn damages while improving fruit quality.
References Alaphilippe, A., Capowiez, Y., Severac, G., Simon, S., Saudreau, M., Caruso, S., Vergnani, S., 2016. Codling moth exclusion netting: an overview of French and Italian experiences. IOBC/WPRS Bull. 112, 31–35. Aoun, M., 2016. Évaluation de filets monoparcelle pour la protection des pommiers contre les insects ravageurs sans utilisation d’insecticides. CETAB Retrieved from. www.cetab.org/publications. Bastías, R.M., Grappadelli, L., 2012. Light quality management in fruit orchards: physiological and technological aspects. Chil. J. Agric. Res. 72 (4), 574–581. Retrieved from. https://search.proquest.com/docview/1370728956/fulltext/ 6591B2E949B74921PQ/1?accountid=8555. Bastías, R.M., Manfrini, L., Grappadelli, L.C., 2012. Exploring the potential use of photoselective nets for fruit growth regulation in apple. Chil. J. Agric. Res. 72 (2), 224–231. Retrieved from. https://search.proquest.com/docview/1291056827?pq-origsite= gscholar. Brkljača, M., Rumora, J., Vuković, M., Jemrić, T., 2016. The effect of photoselective nets on fruit quality of apple cv.‘Cripps Pink’. Agriculturae Conspectus Scientificus 81 (2), 87–90. Candian, V., Pansa, M.G., Santoro, K., Spadaro, D., Tavella, L., Tedeschi, R., 2019. Photoselective exclusion netting in apple orchards: effectiveness against pests and impact on beneficial arthropods, fungal diseases and fruit quality. Pest Manag. Sci. https://doi.org/10.1002/ps.5491. Chouinard, G., Veilleux, J., Pelletier, F., Larose, M., Philion, V., Cormier, D., 2017. Impact of exclusion netting row covers on arthropod presence and crop damage to ‘Honeycrisp’apple trees in North America: a five-year study. Crop. Prot. 98, 248–254. https://doi.org/10.1016/j.cropro.2017.04.008. Corollaro, M., Manfrini, L., Endrizzi, I., Aprea, E., Demattè, M., Charles, M., Grappadelli, L., 2015. The effect of two orchard light management practices on the sensory quality of apple: fruit thinning by shading or photo-selective nets. J. Hortic. Sci. Biotechnol. 90 (1), 99–108. https://doi.org/10.1080/14620316.2015.11513159. Corvalán, N., Bastías, R., Umanzor, C., Serra, I., 2014. Grapevine root and shoot growth responses to photoselective nets: preliminary results. Acta Hortic. 1136, 89–94. https://doi.org/10.17660/ActaHortic.2016.1136.12. Giaccone, M., Forlani, M., Basile, B., 2012. Tree vigor, fruit yield and quality of nectarine trees grown under red photoselective anti-hail nets in southern Italy. Acta Hortic. 962, 287–293. https://doi.org/10.17660/ActaHortic.2012.962.53. Erez, A., Wysoki, M., Yablowitz, Z., Korchinski, R., 1992. High density plantings for
5. Conclusions Two years data collection and analysis on two important cultivars in today apple production seem to indicate that the netting system 7
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M. Aoun and K. Manja protected cultivation of fruit crops; net to protect against insects. Acta Hortic. 349, 89–110. https://doi.org/10.17660/ActaHortic.1993.349.14. Jutamanee, K., Onnom, S., 2016. Improving photosynthetic performance and some fruit quality traits in mango trees by shading. Photosynthetica 54 (4), 542–550. https:// doi.org/10.1007/s11099-016-0210-1. Kalcsits, L., Musacchi, S., Layne, D.R., Schmidt, T., Mupambi, G., Serra, S., Sankaran, S., 2017. Above and below-ground environmental changes associated with the use of photoselective protective netting to reduce sunburn in apple. Agric. For. Meteorol. 237, 9–17. https://doi.org/10.1016/j.agrformet.2017.01.016. Kelderer, M., Lardschneider, E., Rainer, A., 2014. Crop regulation with single row netting structures and their influence on crop quality. Paper presented at the Eco fruit. Proceeding of 16th International Conference on Organic-Fruit Growing. Lawson, D.S., Reissig, W.H., Nyrop, J.P., Brown, S.K., 1994. Management of arthropods on columnar apple-trees using exclusionary cages. Crop. Prot. 13 (5), 346–356. https://doi.org/10.1016/0261-2194(94)90049-3. Lloyd, A., Hamacek, E., George, A., Nissen, R., Waite, G., 2005. Evaluation of exclusion netting for insect pest control and fruit quality enhancement in tree crops. Acta Hortic. 694, 253–258. https://doi.org/10.17660/ActaHortic.2005.694.41. Loreti, F., Morini, S., Muleo, R., Masetti, C., Vitagliano, C., 1993. Effect of solar radiation deprival on selected parameters of peach fruits. Adv. Hortic. Sci. 105–108. https:// doi.org/10.1400/14218. Manja, K., Aoun, M., 2019. The use of nets for tree fruit crops and their impact on the production: a review. Sci. Hort. 246, 110–122. https://doi.org/10.1016/j.scienta. 2018.10.050. Medina, C.L., Souza, R.P., Machado, E.C., Ribeiro, R.V., Silva, J.A., 2002. Photosynthetic response of citrus grown under reflective aluminized polypropylene shading nets. Sci. Hortic. 96 (1), 115–125. https://doi.org/10.1016/S0304-4238(02)00085-7. Meena, V., Kashyap, P., Nangare, D., Singh, J., 2016. Effect of coloured shade nets on yield and quality of pomegranate (Punica granatum) cv. Mridula in semi-arid region of Punjab. Indian Journal of Agricultural Sciences 86 (4), 500–505. Meier, U., Graf, H., Hack, H., Hess, M., Kennel, W., Klose, R., Mappes, D., Seipp, D., Stauss, R., Streif, J., Vandenboom, T., 1994. Phänologische Entwicklungsstadien desKernobstes (Malus domstica Borkh. Und Pyrus communisL.) des Steinobstes (Prunus-Arten), der Johannisbeere(Ribes-Arten) und der Erdbeere (Fragaria x ananassaDuch.). Nachrichtenbl. Deut. Pflanzenschutzd. 46 (7), 141–153. Murchie, E.H., Lawson, T., 2013. Chlorophyll fluorescence analysis: a guide to good practice and understanding some new applications. J. Exp. Bot. 64 (13), 3983–3998.
https://doi.org/10.1093/jxb/ert208. Retamales, J., Montecino, J., Lobos, G., Rojas, L., 2006. Colored shading nets increase yields and profitability of highbush blueberries. Acta Hortic. 770, 193–197. https:// doi.org/10.17660/ActaHortic.2008.770.22. Reyes-Diaz, M., Alberdi, M., de la Luz Mora, M., 2009. Short-term aluminum stress differentially affects the photochemical efficiency of photosystem II in highbush blueberry genotypes. J. Am. Soc. Hortic. Sci. 134 (1), 14–21. Romet, L., Severac, G., Warlop, F., 2010. Overview of “ALT’CARPO” concept and its development in France. Proceedings of the 14th International Conference on Organic Fruit-Growing (Vol. 22, P. e24) Retrieved from. https://www.ecofruit.net/2010/26_ RP_L_Romet_G_Severac_F_Warlop_S176bis182.pdf. Sauphanor, B., Severac, G., Maugin, S., Toubon, J.F., Capowiez, Y., 2012. Exclusion netting may alter reproduction of the codling moth (Cydia pomonella) and prevent associated fruit damage to apple orchards. Entomol. Exp. Appl. 145 (2), 134–142. https://doi.org/10.1111/j.1570-7458.2012.01320.x. Shahak, Y., 2014. Photoselective netting: an overview of the concept, research and development and practical implementation in agriculture. Acta Hortic. 1015, 155–162. https://doi.org/10.17660/ActaHortic.2014.1015.17. Shahak, Y., Gussakovsky, E.E., Gal, E., Ganelevin, R., 2004. ColorNets: crop protection and light-quality manipulation in one technology. Acta Hortic. 609–616. https://doi. org/10.17660/ActaHortic.2004.636.76. Sévérac, G., Romet, L., 2007. Des arbres bien enveloppés avec Alt’Carpo. L’Arboriculture Frutière 620–621. Sivakumar, D., Jifon, J., 2018. Influence of photoselective shade nettings on postharvest quality of vegetables. Preharvest Modulation of Postharvest Fruit and Vegetable Quality. pp. 121–138. https://doi.org/10.1016/B978-0-12-809807-3.00005-6. 2018. Solomakhin, A., Blanke, M., 2010. The microclimate under colored hailnets affects leaf and fruit temperature, leaf anatomy, vegetative and reproductive growth as well as fruit coloration in apple. Ann. Appl. Biol. 156 (1), 121–136. https://doi.org/10. 1111/j.1744-7348.2009.00372.x. Solomakhin, A.A., Blanke, M.M., 2007. Overcoming adverse effects of hailnets on fruit quality and microclimate in an apple orchard. J. Sci. Food Agric. 87 (14), 2625–2637. https://doi.org/10.1002/jsfa.3022. Vuković, M., Brkljača, M., Rumora, J., Fruk, M., Jatoi, M.A., Jemrić, T., 2017. Vegetative and reproductive traits of young peaches and nectarines grown under red photoselective net. Agriculturae Conspectus Scientificus 81 (3), 181–185.
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Effects of a photoselective netting system on Fuji and Jonagold apples in a Mediterranean orchard
T
Mirella Aoun*, Karen Manja Faculty of Agricultural and Food Sciences (FAFS) American University of Beirut, 508 Wing B-Agriculture Building, PO Box 11-236, Riad El Solh, Beirut, 1107 2020, Lebanon
ARTICLE INFO
ABSTRACT
Keywords: Tree fruit production Nets Apples Postharvest quality Light stress Photosynthesis efficiency Shading factor Codling moth Fruit flies
An assessment of a red photoselective netting system on apple production was conducted in a Mediterranean semi-arid climate. For two seasons, blocks of trees from an early bearing (cv Jonagold) and late bearing (cv Fuji) cultivars were covered to full canopy with red photoselective nets with 20% shading factor and an exclusion mesh size of 5.2 × 2.1 mm in an experimental orchard and compared to uncovered blocks of trees in the same orchard. The influence of nets on microclimate was assessed by measuring light intensity, Photosynthetic active radiation (PAR), Air temperature and relative humidity. An average decrease of 22.8% in light intensity along with a reduction in the average PAR radiation incidence by 23% improved the leaves photosynthesis efficiency with no influence on air temperature and relative humidity. The nets, installed after petal fall, had no significant influence on annual shoot growth and fruit set. At harvest, apples taken from netted trees were better graded than in the control in terms of both quality and quantity. Fruit weight, size and color blush were significantly higher in apples grown under nets compared to uncovered ones in both cultivars. While apple firmness was slightly lower under nets, no significant differences were reported in terms of sugar content and malic acid between both treatments. Nets significantly reduced the population of codling moth and the fruit damages caused by this pest without use of insecticides. Nets also decreased the amount of fruit fly caught in traps. No differences were recorded in terms of powdery mildew occurrence, aphids, mites and leafminer populations between both treatments. At last, nets also protected apples from sunburn and bird damages. To our knowledge, this is the first overall assessment of apple production in a pest-exclusion setting using red photoselective nets.
1. Introduction The need to protect horticultural crops is increasing worldwide. This is due mainly to global climate variability, limited water-resources, and the demand for safer and better quality commodities with less chemicals and environmentally-friendly practices. Protective cultivation is being developed around the world as a promising solution to these challenges. Netting is being tested as an efficient way to protect crops against climate challenges i.e. excessive radiation (light and heat), hail, wind, and against biological challenges i.e. flying pests (insects, bats, birds) and in some cases diseases and to improve quality and yield. For a recent exhaustive review on the use of nets for Tree fruit crops and their impact on the production refer to Manja and Aoun (2019).Tests carried out on apple trees (Lawson et al., 1994; Aoun, 2016; Chouinard et al., 2017) and stone fruit trees (Erez et al., 1992; Lloyd et al., 2005)
⁎
have demonstrated that various types of insect-proof nets can prevent the entry of a number of pests without drastically changing the environment and quality of the fruit produced under nets. A successful example covering large areas (more than 2500 ha in France) is the exclusion system called Alt’Carpo developed in France (Sévérac and Romet, 2007). Used increasingly in organic orchards, Alt’Carpo exclusion nets help to keep the damage caused by codling moths at levels below 0.1% without the use of pesticides (Sauphanor et al., 2012). Recently, and thanks to technological advances with photo-selective plastic filters, colored nets have been developed, which provide differential filtration of solar radiation together with physical protection. In plants, including some fruit trees, it has been demonstrated that changes in light composition in red, far-red and blue spectra affects significantly fruit tree plant responses regulated by light such as CO2 assimilation and anthocyanin synthesis and could be a useful tool for
Corresponding author. E-mail addresses: [email protected], [email protected] (M. Aoun).
https://doi.org/10.1016/j.scienta.2019.109104 Received 1 November 2019; Received in revised form 28 November 2019; Accepted 2 December 2019 0304-4238/ © 2019 Elsevier B.V. All rights reserved.
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sustainable management of yield and quality in modern orchards (Bastías and Grappadelli, 2012; Bastías et al., 2012). However, the potential use and benefit of this technology in fruit tree production remain under-explored and needs to be optimized depending on the species/cultivar and geographical region. In this study, we assessed the use of red photoselective nets in an exclusion system under semi-arid Mediterranean climate and on two worldwide commercial apple cultivars; Fuji (late bearing cultivar) and Jonagold (early bearing cultivar). The specific objectives of this research were to use photoselective nets in a full canopy protective system and to measure and compare the effects of the photoselective netting system on the overall orchard environment and production. Fig. 1. Photoselective red net mounted on a block of Jonagold and Fuji trees in the experimental orchard. The net caged the whole canopies of the trees to create both a shading and pest-exclusion effect and was attached to a wire 0,5 m from the soil to permit access. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
2. Materials and methods 2.1. Experimental site The experiment was conducted in a research apple orchard located at Advancing Research Enabling Communities Center (AREC) of the American University of Beirut in the Bekaa valley of Lebanon (coordinates 33°55′ latitude and 36°04′ longitude, 995 m ASL). The orchard consists of nine apple cultivars planted in 1999 and grafted on 2 types of rootstocks M7 and MM111. The orchard included six rows and two trees per cultivar in a row. It was established with 4.5 m between rows and 3.5 m between trees. The experiment was conducted under a semiarid Mediterranean weather characterized by dry hot summers from May till September (the average temperature recorded in the orchard from May till September 2018 was 23,5ᵒ C ± 0.2 while the average relative humidity was 48.6% ± 0.6) and a mean annual rainfall of 528 mm with a standard deviation of 165 mm.
blocks. One delta trap baited with codling moth (cydia pomonella) pheromone capsule containing a blend of E8, E10 Dodecadionol (Alpha Scents,USA) was set in each treatment at mid-canopy height, within the tree canopy. In addition, one yellow trap (Econex Trypack,Alpha Scents.Inc,Spain) with a diffuser of 3 dietary attractants for Ceratitis capitata, was set in each treatment at 1.5 m from the ground, outside tree canopy. At last, one yellow trap with (Hook TML, Isca, USA), an “attract and kill” of the fruit fly, Ceratitis capitata was put in each treatment. The orchard was managed following an Integrated Pest Management spraying calendar and sprays were performed when the present pest number exceeded the economic threshold level. For insect pest management, no sprays were done in the covered blocks as we relied only on nets for insect pest control in these blocks. The orchard was sprayed by the end of February with a mix of paraffinic oil (Copper oxychloride) and an insecticide in order to control overwintering insects. Before the setup of the experiment in 2017, one insecticidal spray was done in May in the entire orchard before the setting of the nets to control overall insect pest population in order not to correlate their presence with any treatment. This spray was not repeated in 2018. Sprays against Powdery mildew were done only in the month of May after leaf scouting in both treatments.
2.2. Experimental design The experiment took place during two growing seasons between April and October 2017 and 2018. The experiment was conducted on Jonagold and Fuji trees, early and late cultivars, respectively. Eight randomly distributed blocks constitute the set-up of the experiment in the orchard. Four were covered with nets and four were uncovered and constitute the control treatment. Each block contains either two trees (28m2) or four trees (56 m2) of both cultivars for a total of twelve trees covered with nets and twelve uncovered trees (six per cultivar). The N Leno 3640(red) Polysack net (Green.tek, Inc., Janesville, WI, USA) was tested in this experiment. It is a photoselective net, red in color with 20% shading factor and a mesh size of 5.2 × 2.1 mm. The net was mounted on a frame structure composed of four steel tubes (4.25 m) supported by galvanized wires fixed in the ground. A 0.75 m part of each steel tube was fixed in the soil with concrete. The netted frame was caging the whole canopy and was open on two sides at the bottom for about 0.5 m from the soil to allow access (Fig. 1). The nets were spread on when the fruits were 20 mm in diameter in 2017 (May 10) and after petal fall in 2018 (April 18) and were removed at Fuji harvest. Jonagold trees were harvested at mid-(in 2018) or end of August (2017) while Fuji trees at the end of September (2018) or beginning of October (2017) two days after the removal of the nets.
2.4. Microclimatic measurements Temperature, humidity and light intensity were measured from the beginning of May till the end of September in both treatments. Temperature and humidity were recorded each 4 h in 2017 and each hour in 2018, in a 24 h interval using sensors (HOBO Pro V2 data logger, Onset,USA) protected with radiation shields from direct solar radiation, rain and sprays whereas light intensity (in μmoles m − 2s−1) was recorded every two hours using other sensors (HOBO Pendant data logger,Onset,USA). These instruments were installed above the canopy, 2.5 m above the ground level, at the center of a control and a net block. Photosynthetically active radiation (PAR) was quantified once a week in 2017 from June 23 till August 17 and repeated in 2018 to confirm results. The radiation was determined at 1:00 pm on a clear sunny day using a portable light meter (LI-189, LI-COR, USA). Measurements were made at mid canopy layer of one tree per block near sun exposed leaves.
2.3. Agricultural practices and pest management All the trees in the experiment received the same irrigation and fertilization applications. The orchard was irrigated twice a week from May until the end of August and once a week in September. NPK fertilizers were either added in the irrigation system or through foliar applications supplemented with trace elements. Weeding was done monthly using a weed eater. In order to monitor the presence of pests in both treatments (control and nets) and to test the ability of nets to exclude adult insect pests; traps for commercial pests were set in the orchard in the experimental
2.5. Photochemical efficiency of photosystem II In order to obtain quantitative information on photosynthesis in intact leaves of covered and uncovered trees, chlorophyll fluorescence 2
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was assessed using a portable fluorometer (model OS-30p, OptiSciences, Hudson, New Hampshire, USA). Minimum (F˳) and maximum chlorophyll fluorescence (Fm) were measured at 9 a.m. from beginning of June till the end of July in a sunny day condition and variable fluorescence (Fv=Fm–Fo) was generated. The measurements were made on a mature sun-exposed leaf from 5 annual shoots per treatment. The leaves were dark-adapted for 30 min (Reyes-Diaz et al., 2009) using leaf clips with sliding shutters and photochemical efficiency of photosystem II (Fv/Fm) was determined by assessing chlorophyll fluorescence.
according to national standards for apples Libnor, No.477, 2001. The percentage of red blush was also taken into consideration in the grading. Sixty apples per treatment per cultivar were subjected for further assessment. In order to measure flesh firmness, the skin was removed on 2 opposite sides of each apple. Then, a fruit pressure tester (mod. FT 327 (3-27lbs), Italy) fitted with an 11.3 mm diameter head was used to measure the maximum force in lb needed to penetrate the peeled flesh. Drops of the juice that came out from the apple after the flesh firmness test were used to measure soluble solids content (SSC) of each apple using the digital hand- held pocket refractometer (PAL, Atago Co, Japan). After sectioning the apples transversally at the equator position and performing the starch iodine test, starch pattern index (Cornell University chart) was evaluated from 1 to 8, where 1 indicated the least starch to sugar conversion and 8 the most. The second section of the apple was put in a juice extractor (MK-6115, Muller Koch, Germany). The titratable acidity was measured by titrating the diluted extracted juice to an end point of pH 8.1 with 0.1 N NaOH using the auto-titrator formed of pH Module 867, the dosing unit Dossino 800 and Tiamo software (Metrohm, Switzerland). Calculating the apples acidity was performed using the equation: A = V × 0.1 N×0.67 where A is the acid concentration in g/L, V is the NaOH volume spent in the titration, N is the normality of NaOH, 0.67 is a factor to express the malic acid acidity in meq.
2.6. Phenology, annual growth and fruit set The apples phenological development was assessed using the BBCHscale (Meier et al., 1994). The weekly stage after fruit set was determined by measuring the average apple’s diameter of both cultivars using a metric ruler. The average annual growth was determined by measuring the length of five annual shoots per tree at the end of annual vegetative growth, in our case beginning of July. Fruit set was determined for each tree by calculating the average number of apples found in five clusters per tree. 2.7. Biotic and abiotic stresses A weekly monitoring of pest presence and damages was performed from May till the end of September on 6 trees covered with nets (3 per cultivar) and 6 uncovered trees (3 per cultivar).
2.9. Statistical analysis Statistical analysis of the data was performed using SPPS version 24 (IBM corp, Armonk, IL, USA). Shapiro-Wilk test was used to assess the data for normal distribution and Levene’s test was used for homogeneity of variances. When the assumptions for normality were not respected, transformations were first applied. If no transformation assumed normality, non-parametric tests were performed including chisquare and Man-Whitney. The influence of the treatment was determined using the independent samples t-test with P = 0.05. Two-way analysis of variance for a completely randomized design was separately performed when the influence of date, cultivar or year were determined in addition of treatment effect. Means of significant effects were separated using Fisher’s protected LSD (least significant differences) at a 5% significance level. Tukey test was used when multiple comparisons were needed in particular to compare averages at multiple dates and hours.
2.7.1. Leaf pests Five annual shoots per tree were scouted: one annual shoot from the inner part of the tree canopy (around the central axis) and four from the outer part of the tree canopy (periphery area) taken from each cardinal direction. Shoots were scouted for powdery mildew (Podosphaera leucotricha) infections and for the presence of rosy (Dysaphis plantaginea), green (Aphis pomi) or woolly aphids (Eriosoma lanigerum) and leafminer (Phyllonorycter spp.). Scouting for mites (Tetranychus ulmi) was done by observing the upper and lower side of one mature leaf/tree found on a shoot that was between the central leader and the periphery area using a 10x lens (Sight Savers, Bausch & Lomb, USA). 2.7.2. Fruit pests Five fruits per tree were scouted randomly: One fruit from the inner and four from the outer canopy taken from each cardinal direction. Damages caused by codling moth, fruit fly, aphids, mites, powdery mildew were recorded.
3. Results
2.7.3. Abiotic and other damages Deformations, sunburn damages and damages caused by birds were also assessed on fruits according to the protocol described above.
3.1. Microclimatic modification Temperature and relative humidity were measured from the beginning of May till the end of September in net and control treatments. In 2017, average temperature (0C) and percent of relative humidity measurements were taken every 4 h in a 24 h- interval while in 2018, average, minimum and maximum temperature and relative humidity were measured every hour in a 24-H. The recorded values were not significant between treatments in both years. Measurements of Photosynthetic Photon Flux Density (PPFD) for light intensity under nets and in the open field were recorded each 2 h in a 24 -hs interval from the beginning of May till the end of September in both seasons. We analyzed the differences between treatments from 6 a.m. until 8 pm when light was detected in the orchard. From 8 a.m. until 4 pm, the net significantly reduced PPFD compared to control with the highest difference recorded at 12 pm (Fig. 2) and an average difference of 22.8%. As expected, in both seasons, Photosynthetic Active Radiation (PAR) radiation was significantly reduced by an average of 23% under the net compared to the control.
2.8. Post-harvest assessment Twenty apples were harvested from each tree in the experiment for a total of 120 apples per cultivar per treatment in order to evaluate the apples physicochemical characteristics at commercial harvest for both cultivars. The harvest was performed at apple commercial maturity for each cultivar taking into consideration the assessment of fruit color, fruit firmness, starch index and seeds color. For both cultivars, apples were picked from the two treatments on the same day. Samples were packed in previously labeled boxes and transported to the American University of Beirut, FAFS, Agriculture Department, research lab where they were subjected to physicochemical analysis. The weight and size of each apple were measured using an analytical balance (AB-204 S,Mettler Toledo, Switzerland) and a caliper respectively. The percentage of the red blush surface of the apple skin was assessed subjectively. Apples were graded based on the size and impurities on the skin 3
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The average fruit set measured as the number of fruits per cluster was not different between the two treatments in both seasons (Table 2). This is to be seen through the fact that nets had no effect on pollination since their set-up happened after pollination occurred. 3.4. Fruit quality 3.4.1. External fruit quality The harvest dates were determined by assessing maturity indices once a week in the harvest intervals of both cultivars. Fruits of the same cultivar were picked on the same day from uncovered and covered trees to assess the effect of net on fruit quality. Nets had a significant positive effect on most of the quality parameters measured at harvest in both cultivars; in particular apple size and weight. The photoselective red nets used also significantly increased red blush percentage; thus fruit skin coloration (Table 3). These results translate well in commercial grading assessment as apples are normally graded according to the size, color and freedom from defects usually found on the fruit skin. Apples were graded according to official national standards (LIBNOR). A significantly higher percentage of apples classified in Grade Extra (highest premium quality grade) were recorded in both cultivars under net. Consequently, a significantly lower percentage of Jonagold and Fuji apples of poor marketable quality sorted to Grade 2 were recorded under net compared to control (Table 4). Jonagold trees had lower total production in 2018 and apple grading was not affected by net.
Fig. 2. Average light intensity (in μmoles m − 2s−1) at different hours of the day during the whole 2017 season in control (uncovered trees) and net (trees covered with red photoselective nets). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
3.2. Photochemical efficiency of photosystem II Nets positively affected photosynthesis efficiency in leaves as maximum quantum yield of Photosystem II primary photochemistry in the dark adapted state (Fv/Fm) and the Fv/Fo ratios significantly increased in leaves of netted trees compared to uncovered control trees (Table 1). According to Murchie and Lawson (2013), the value of Fv/Fm is highly consistent for unstressed leaves, with values of ∼0.83, and correlates to the maximum quantum yield of photosynthesis. Any type of ‘stress’ leading to an inactivation damage of PSII (often referred to as photoinhibition) lowers Fv/Fm. Our results indicate that uncovered control trees are more stressed than netted ones and are less capable to cope with the environmental conditions resulting in reduced photosynthesis.
3.4.2. Internal fruit quality Apples grown under nets were in general softer in both cultivars (Table 5). Starch breakdown was also slightly more advanced in Fuji apples grown under net in 2017 compared to the ones in uncovered control which may suggest fruit ripening acceleration under nets for Fuji cultivar. However, no significant differences were recorded for soluble sugar content and malic acid.
3.3. Seasonal development 3.3.1. Annual growth The average annual shoot length was measured on five annual shoots per tree in the beginning of July when annual growth was completed. The results showed that annual growth remained unaffected by the net presence except for Jonagold in 2018 where annual shoot length was significantly longer under net. A result particular for that year as vegetative growth (here indicated by shoot length) was more important than previous year (Table 2: Total shoot length).
3.5. Biotic and abiotic stresses 3.5.1. Leaf pests The main leaf pests observed during the season were powdery mildew, mites and aphids and to less extent leafminers. Powdery mildew (Podosphaera leucotricha) was observed mainly in May and June with significantly higher incidence on Jonagold (11.6% average of infected leaves in both seasons compared to 1.5% for Fuji). In 2018, the percentage of leaf infected was lower (less than 1%) in both cultivars due to a particular dry weather. In both years, the nets had no significant effect on the percentage of leaves infected by powdery mildew. Nets did not have any effect on mite (Tetranychus urticae) and leafminer (Phyllonorycter spp.) populations in both cultivars and in both seasons: mites were observed in 2017 only, starting the end of June with an average of one mite per leaf observed during the season which was below the threshold level of intervention. As for the leafminer, a maximum of 6% of the leaves observed were infested in 2017 and less than 1% in 2018. There were no significant differences between control and net for these pests. Rosy aphid (Dysaphis plantaginea), green and woolly aphids (Aphis pomi) and (Eriosoma lanigerum) were rarely observed with an incidence below the threshold level.
3.3.2. Fruit set We chose to layout the nets after petal fall to avoid poor pollination resulting in low crop load. Table 1 Photochemical efficiency of photosystem II in control and covered trees.1 Fv/Fm
Fv/Fo
2017 3
Control Net
2
0.78 ± 0.003a 0.80 ± 0.003b
2018
2017
2018
0.77 ± 0.005a 0.80 ± 0.005b
3.60 ± 0.07a 4.06 ± 0.07b
3.52 ± 0.09a 4.02 ± 0.09b
1 Efficiency of photosystem II was determined by assessing chlorophyll fluorescence. Minimum (F˳) and maximum chlorophyll fluorescence (Fm) were measured on dark adapted leaves at 9 a.m. from beginning of June till the end of July in a sunny day condition and variable fluorescence (Fv=Fm–Fo) was generated. The maximum quantum yield of photosystem II (Fv/Fm) and the Fv/ Fo ratios were generated on leaves of trees covered with red photoselective nets (net) and uncovered trees (control). 2 Mean value ± standard error. Different letters represent significant differences between treatments for each ratio at P < 0.05. 3 N = 25 observations per treatment in 2017 and 40 observations per treatment in 2018.
3.5.2. Fruit pests The percentage of apples infected by codling moth (Cydia pomonella) was significantly greater in control compared to the netted ones for both cultivars and in both seasons (Table 6) The percentage of fallen fruits infested by codling moth was also significantly greater in control (Table 6) and a cumulative higher number of codling moths were caught during the season in control delta trap compared to net 4
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Table 2 Fruit set and shoot length in control and net for each apple cultivar.1 Shoot length (cm)
2017 Control2 Net Total 2018 Control Net Total
Fruit set (Number of fruits/cluster)
Jonagold
Fuji
Jonagold
Fuji
8.43 ± 0.915a3 8.28 ± 0.915a 8.36 ± 0.915a
7.94 ± 0.916a 9.28 ± 0.916a 8.61 ± 0.916a
2.17 ± 0.110a1 2.47 ± 0.110 a 2.32 ± 0.110 a
2.40 ± 0.1144a 2.74 ± 0.1144 a 2.57 ± 0.1144 a
12.35 ± 0.915a 18.77 ± 0.915b 15.56 ± 0.915b
20.53 ± 0.916a 18.20 ± 0.916a 19.37 ± 0.916b
1.80 ± 0.110 a 1.87 ± 0.110 a 1.84b ± 0.110b
2.94 ± 0.1144 a 2.74 ± 0.1144 a 2.84 ± 0.1144 a
1 The average annual growth was determined by measuring the length of five annual shoots per tree at the end of annual vegetative growth, in our case beginning of July. Fruit set was determined for each tree by calculating the average number of apples found in five clusters per tree. 2 Mean value ± standard error. Different letters represent significant differences at P < 0.05 within a cultivar. 3 N = 30 clusters per treatment per cultivar.
Table 3 Postharvest exterior assessment of Jonagold and Fuji fruits.1 Size (mm)
2017 Control3 Net 2018 Control Net 1 2 3
Weight (g)
Red blush (%)
Jonagold
Fuji
Jonagold
Fuji
Jonagold
Fuji
67.44 ± 0.42a2 69.00 ± 0.39b
65.53 ± 0.28a 67.7 ± 0.36b
133.18 ± 2.25a 141.18 ± 2.17b
124.94 ± 1.63a 134.6 ± 1.84b
23.71 ± 1.67a 33.54 ± 1.8b
31.79 ± 1.13a 42.00 ± 0.96b
66.72 ± 0.44a 67.49 ± 0.53a
60.407 ± 0.37a 64.278 ± 0.55b
131.57 ± 2.45a 139.27 ± 3.15b
96.68 ± 1.41a 117.45 ± 2.41b
58.52 ± 1.72a 63.67 ± 1.68b
N/A N/A
Mean size, weight and red blush percentage of apples in trees covered with nets and uncovered trees (control). Mean value ± standard error. Different letters represent significant differences for each parameter at P < 0.05 within a cultivar. N = 120 apples per treatment.
(Table 7). These results were recorded despite the fact that insecticides were sprayed in control and no sprays were used under nets and were obtained with both cultivars and in both seasons confirming the efficacy of nets usage in preventing codling moth attack and apple fruit infestation. It should be noted that the photoselective nets used in our experiment were set in an exclusion layout to cover the entire tree canopy. The cumulative number of male fruit flies caught in yellow traps containing attract and kill pheromone gel during the whole season was found higher in control compared to net (Table 7). Also, the cumulative number of female fruit flies caught in control yellow trap containing dietary attractants during the whole season was higher in control compared to net. However, no fruit flies damages were observed on fruits.
3.5.3. Abiotic and other damages Sunburn, bird damage and fruit deformation were observed on apples in control treatment at harvest but not under nets. At harvest, in the control treatment, 12% and 19 % of Fuji apples had sunburn damage in 2017 and 2018 respectively while no damage was found on apples observed from net treatment. Bird damages were also observed sporadically in control treatment but not under net. 4. Discussion 4.1. Microclimatic modification and its impact on photosynthesis efficiency The reduction in PAR under nets corresponds with the expected shade induced by the nets used having a shading factor of 20%. PAR reduction was also reported by other studies using different shading
Table 4 Count of apples in commercial grades for Jonagold and Fuji cv.1 Grade Extra
Grade 1
Jonagold
2017 Control2 Net 2018 Control Net
Fuji
Grade 2
Jonagold
Fuji
Jonagold
Fuji
%
Count
%
Count
%
Count
%
Count
%
Count
%
Count
7% a 18% b
8 22
11% a 23% b
13 28
72% a 76% a
87 91
75% a 72% a
90 86
21% a 6% b
25 7
14% a 5% b
17 6
24% a 20% a
29 24
5% a 12% b
6 14
60% a 66% a
72 79
46% a 56% a
55 67
16% a 14% a
19 17
49% a 32% b
59 39
1 Apples were sorted in 3 grades from higher to lower: Grade Extra, Grade 1 and Grade 2. Apples were sorted at harvest from trees covered with nets and from uncovered trees (control). 2 N = 120 apples per treatment.
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Table 5 Postharvest interior assessment of Jonagold and Fuji cv.1 Firmness (lb)
2017 Control3 Net 2018 Control Net 1 2 3
Starch index
Soluble Sugar Content (ᵒBrix)
Malic acid (g/L)
Jonagold
Fuji
Jonagold
Fuji
Jonagold
Fuji
Jonagold
Fuji
10.24 ± 0.12a2 9.49 ± 0.10b
10.7 ± 0.1a 10.08 ± 0.1b
6.5 ± 0.11a 6.5 ± 0.08a
5.0 ± 0.12a 5.6 ± 0.14b
14.7 ± 0.1a 14.2 ± 0.1b
16.8 ± 0.1a 17 ± 0.1a
4.56 ± 0.10a 4.382 ± 0.11a
4.95 ± 0.15a 4.78 ± 0.11a
10.37 ± 0.20a 9.53 ± 0.22a
11.23 ± 0.14a 10.68 ± 0.11b
6.87 ± 0.11a 6.63 ± 0.07a
5.0 ± 0.16a 5.1 ± 0.15a
16.92 ± 0.12a 15.45 ± 0.07b
19.47 ± 0.23a 18.41 ± 0.17a
4.77 ± 0.20a 4.44 ± 0.09a
4.90 ± 0.13a 4.47 ± 0.07b
Mean firmness, starch index, soluble solid content and malic acid of cv. Jonagold apples covered with nets and uncovered trees(control). Mean value ± standard error. Different letters represent significant differences for each parameter at P < 0.05 within cultivar. N = 60 apples per treatment except for malic acid, N = 20–25 apples per treatment.
photoselecvtive nets positively affected photochemical efficiency of PSII in leaves. According to Murchie and Lawson (2013), any type of ‘stress’ leading to an inactivation damage of PSII (often referred to as photoinhibition) lowers Fv/Fm. Our results indicate that uncovered control trees are more stressed than netted ones and are less capable to cope with the environmental conditions resulting in reduced photosynthesis. Our results are in line with the ones reported by Jutamanee and Onnom (2016) who used shade nets as plastic roofs on mango trees. According to Jutamanee and Onnom (2016), the reduction of high solar energy caused by the plastic roof mitigated the inactivation of the primary photochemistry associated with PSII. Medina et al. (2002) have also reported that shading net (50%) was effective in preventing photoinhibition especially in summer where higher PAR levels and higher temperatures in control increase susceptibility to photoinhibition. The recorded air temperature and relative humidity values were not significant between treatments in both years. This result is in line with the ones reported by Corvalán et al. (2014) who did not record any difference in air temperature and relative humidity using photoselective red nets with 20% shading on grapevines. Kalcsits et al. (2017) who tested red shade nets with similar shading factor to ours on apples also reported that netting did not influence the overall orchard temperature and humidity and suggested that previous studies who reported differences did not use radiation shields to protect sensors which may have resulted in a temperature difference between control and net.
Table 6 Percentages of apples attacked by codling moth and apples fallen on the orchard floor due to codling moth infestation.1 % of infestation
2017 Control3 Net 2018 Control Net
% of fallen fruits with codling moth infestation under trees of both cultivars
Jonagold
Fuji
12%a2 5%b
26%a 4%b
34% 11%b
15%a 5%b
10%a 0%b
32%a 11%b
1
The percentage of fruits attacked by codling moth was determined by dividing the number of apples with codling moth infestation over the total number of apples observed per treatment and per cultivar for each year. As for fallen fruits with codling moth infestation, the percentage was calculated by dividing the total number of apples on the ground presenting a codling moth infestation over the total number of apples found on the ground after fruit drop under Jonagold and Fuji trees in the orchard in the experimental blocks. 2 Different letters represent significant differences at P < 0.05 within a cultivar in a year. 3 N = 165 for Jonagold cv; 210 and 240 for Fuji cv in 2017 and 2018 respectively. N represents the total number observed in a season at a weekly scouting of 5 apples/trees until harvest. Table 7 The cumulative number of male codling moth, male fruit fly and female fruit fly caught in traps during the season.1 Male codling moths 2017 Control Net 2018 Control Net
53 17 31 11
2
Male fruit flies
Female fruit flies
38 11
205 100
44 17
N/A N/A
4.2. Seasonal development: Fruit set and annual growth The results observed confirm previous work when photoselective red nets were used (Giaccone et al., 2012; Vuković et al., 2017). One should expect a fruit thinning potential and influence on reproductive growth when trees are covered before or during bloom time (Kelderer et al., 2014). Fruit set was significantly poorer in 2018 for Jonagold cultivar; Jonagold trees significantly invested in vegetative growth that same year as shown in the length of annual shoot growth (Table 2). The results showed that in general annual growth remained unaffected by the net presence for the exception of Jonagold in 2018. A result that could be particular for that year when vegetative growth was more important than reproductive growth as observed in the field and in comparison with previous year (Table 2). That the net had no significant impact on the length of annual shoot can be explained by the fact that the trees already started vegetative growth when the nets were installed in the orchard. In addition, our nets had a relatively low shading factor (20%) to limit vegetative growth stimulation (Shahak, 2014).
1 For each pest, a trap was set in a control block and another under a net block. Traps were scouted twice a week from mid-May to mid-September for codling moth and from mid-August to mid-September for fruit flies. 2 Numbers represent the cumulative count of male or female pest found in a trap during the season.
nets (Retamales et al., 2006; Solomakhin and Blanke, 2007, 2010). The 20–23% shade caused by nets used in this study seemed to be beneficial for trees under high daylight intensity. Indeed, this shading factor positively affected the efficiency of photosystem II, increased apple skin coloration and reduced sunburn damage. According to (Sivakumar and Jifon, 2018), maximum net CO2 assimilation of most C3 species saturates at relatively low irradiance (600–900 μmol/m²/s), which is only 30–40% of full sunlight (1500–2000 μmol/m2/s) on a typical growing season day. The excess radiation normally causes heat stress and a reduction in net photosynthesis. Our results show that 20% shading
4.3. Fruit quality Nets had a significant positive effect on most of the quality parameters measured at harvest; these results are in agreement with those 6
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reported by other authors working with red photoselective nets on apple, pomegranate and peach trees (Brkljača et al., 2016; Corollaro et al., 2015; Meena et al., 2016; Shahak et al., 2004). The positive impact of nets on fruit quality could be attributed to the light scattering and reflection capacity of photoselective nets that can alter plant responses. The increase in weight and size may be the result of less stressful climatic conditions under nets as shown by the chlorophyll fluorescence measurements. An increase in net CO2 assimilation under nets led to an increase in carbohydrate availability for fruit growth as suggested by Bastías et al. (2012). The photoselective red nets used in this study increased fruit skin coloration significantly. This increase may be due to the fact that red photoselective nets enrich red and far-red spectral regions of the light reaching the trees which may alter plant responses regulated by light such as fruit skin color. Color development in apples is related to anthocyanin synthesis, which is stimulated by red and far-red spectral regions (Bastías and Grappadelli, 2012). Apples grown under nets were in general softer in both cultivars (Table 5). This is in line with the results reported by Corollaro et al. (2015) who noticed a lower cell density of apples grown under photoselective red nets. They observed larger cells with a higher volume of air spaces which decreases the resistance to compression. Loreti et al. (1993) indicated that limited solar radiation affects the formation and composition of cell walls as they become more elastic, swell more and contain more water. Starch breakdown was also slightly more advanced in Fuji apples grown under net in 2017 compared to the ones in uncovered control which may suggest fruit ripening acceleration under nets for Fuji cultivar.
experimented here (incomplete exclusion system on rows covered with photoselective nets) is a promising tool for a better quality fruit and an overall tree health with the opportunity of significantly reducing the need for pesticides (no insecticides used under net). The 20% shading caused by nets in a semi-arid climate positively affected the photosynthesis efficiency. In addition, nets significantly protected against major insect pests while improving fruit quality in particular fruit size, weight and skin coloration. Apples under net were better graded than apples in control. Overall, netting system could be proposed as an integrated solution for sustainable apple production in a strategy to address today challenges in tree fruit production. These challenges include increased biotic and abiotic stresses due to climate variability and, at the same time, the growing demand for safe, low-chemical residues products. CRediT authorship contribution statement Mirella Aoun: Conceptualization, Methodology, Validation, Writing - review & editing, Supervision, Project administration. Karen Manja: Formal analysis, Investigation, Resources. Declaration of Competing Interest None. Acknowledgements This study was supported through a seed fund from the Faculty of Agricultural and Food Sciences (FAFS) at the American University of Beirut (AUB). The authors wish to thank all those who helped in making this work possible in particular, Dr Yussef Abou Jawdah who helped in IPM management, Dr Samer Kharroubi who helped in statistical analysis, Mr Nicolas El-Hajj who helped in the design and set-up of the netting system, Mr Andre Bou Haidar, Ms Rachel Sfeir and other graduates who helped in data collection.
4.4. Biotic and abiotic stresses There were no significant differences between control and net for leaf pests. Chouinard et al. (2017) also did not report any significant differences in mobile forms of Tetranychus urticae in both control and exclusion net. The results obtained with codling moths for both cultivars an in both seasons confirm the efficacy of nets usage in preventing codling moth attack and apple fruit infestation when the whole canopy is covered with a relatively small mesh size nets (in this case 5.2 × 2.1 mm). These results are in line with previous studies performed by Alaphilippe et al. (2016); Romet et al. (2010); and Sauphanor et al. (2012) who reported the ability of exclusion nets to control codling moth and reduce fruit attack caused by this pest. According to Sauphanor et al. (2012), the moderate efficacy of the Alt’Carpo netting may be mainly the result of the confined space around the trees altering the reproduction of the moth, complemented by a partial prevention of moth penetration and egg lying. Male moths flying between rows and on top of the trees, which is the main location for female calling and prospecting prior to mating may explain why male moths are not entering inside nets Sauphanor et al. (2012). The results showing reduction of fruit flies caught in traps under nets are in line with the ones reported by Lloyd et al. (2005) and confirm the ability of nets when used in an exclusion setting to significantly reduce pest populations (Candian et al., 2019). The protection from sunburn damages and birds damages confirm the potential of the net to protect against these damages and suggest that a 20% shading factor is efficient under hot Mediterranean summer weather to protect from sunburn damages while improving fruit quality.
References Alaphilippe, A., Capowiez, Y., Severac, G., Simon, S., Saudreau, M., Caruso, S., Vergnani, S., 2016. Codling moth exclusion netting: an overview of French and Italian experiences. IOBC/WPRS Bull. 112, 31–35. Aoun, M., 2016. Évaluation de filets monoparcelle pour la protection des pommiers contre les insects ravageurs sans utilisation d’insecticides. CETAB Retrieved from. www.cetab.org/publications. Bastías, R.M., Grappadelli, L., 2012. Light quality management in fruit orchards: physiological and technological aspects. Chil. J. Agric. Res. 72 (4), 574–581. Retrieved from. https://search.proquest.com/docview/1370728956/fulltext/ 6591B2E949B74921PQ/1?accountid=8555. Bastías, R.M., Manfrini, L., Grappadelli, L.C., 2012. Exploring the potential use of photoselective nets for fruit growth regulation in apple. Chil. J. Agric. Res. 72 (2), 224–231. Retrieved from. https://search.proquest.com/docview/1291056827?pq-origsite= gscholar. Brkljača, M., Rumora, J., Vuković, M., Jemrić, T., 2016. The effect of photoselective nets on fruit quality of apple cv.‘Cripps Pink’. Agriculturae Conspectus Scientificus 81 (2), 87–90. Candian, V., Pansa, M.G., Santoro, K., Spadaro, D., Tavella, L., Tedeschi, R., 2019. Photoselective exclusion netting in apple orchards: effectiveness against pests and impact on beneficial arthropods, fungal diseases and fruit quality. Pest Manag. Sci. https://doi.org/10.1002/ps.5491. Chouinard, G., Veilleux, J., Pelletier, F., Larose, M., Philion, V., Cormier, D., 2017. Impact of exclusion netting row covers on arthropod presence and crop damage to ‘Honeycrisp’apple trees in North America: a five-year study. Crop. Prot. 98, 248–254. https://doi.org/10.1016/j.cropro.2017.04.008. Corollaro, M., Manfrini, L., Endrizzi, I., Aprea, E., Demattè, M., Charles, M., Grappadelli, L., 2015. The effect of two orchard light management practices on the sensory quality of apple: fruit thinning by shading or photo-selective nets. J. Hortic. Sci. Biotechnol. 90 (1), 99–108. https://doi.org/10.1080/14620316.2015.11513159. Corvalán, N., Bastías, R., Umanzor, C., Serra, I., 2014. Grapevine root and shoot growth responses to photoselective nets: preliminary results. Acta Hortic. 1136, 89–94. https://doi.org/10.17660/ActaHortic.2016.1136.12. Giaccone, M., Forlani, M., Basile, B., 2012. Tree vigor, fruit yield and quality of nectarine trees grown under red photoselective anti-hail nets in southern Italy. Acta Hortic. 962, 287–293. https://doi.org/10.17660/ActaHortic.2012.962.53. Erez, A., Wysoki, M., Yablowitz, Z., Korchinski, R., 1992. High density plantings for
5. Conclusions Two years data collection and analysis on two important cultivars in today apple production seem to indicate that the netting system 7
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