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The effects of preharvest shading and postharvest storage temperatures on the quality of ‘Ponkan’ (Citrus reticulata Blanco) mandarin fruits
Scientia Horticulturae 188 (2015) 57–65
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The effects of preharvest shading and postharvest storage temperatures on the quality of ‘Ponkan’ (Citrus reticulata Blanco) mandarin fruits Tan-Cha Lee, Pei-Juan Zhong, Pai-Tsang Chang ∗ Department of Horticultural Science, National Chiayi University, 300 Xuefu Rd., Chiayi City 60004, Taiwan
a r t i c l e
i n f o
Article history: Received 13 January 2015 Received in revised form 10 March 2015 Accepted 13 March 2015 Available online 3 April 2015 Keywords: Citrus Temperature Sunburn Granulation Decay
a b s t r a c t A two-year trial was performed to investigate the effects of using preharvest white shade nets and postharvest storage at 13.5 ◦ C or 25 ◦ C on the physiological responses and quality of ‘Ponkan’ mandarin fruits. A significant reduction in leaf and fruit surface temperatures, PPF, and sunburn was seen when using white shade nets in comparison with the control sample. Trees grown under white netting had a significantly higher juice percentage, less weight loss, lower granulation percentage, and lower percentage decay than the control sample. However, there were no significant differences in peel color, total soluble solids (TSS), and titratable acid (TA) between the control and shading samples after postharvest storage at 13.5 ◦ C or 25 ◦ C. In summary, ‘Ponkan’ mandarin grown with white shading nets exhibited greater sunscald resistance, higher juice percentage, and less weight loss and granulation when stored at 13.5 ◦ C postharvest than the mandarin grown without shading and those stored at 25 ◦ C. © 2015 Elsevier B.V. All rights reserved.
1. Introduction ‘Ponkan’ mandarin (Citrus reticulata Blanco) is a non-climacteric citrus with a high economic value. Appropriate postharvest practices can effectively reduce fruit losses and improve fruit quality, and thus lead to higher profits. However, citrus fruits may exhibit various disorders during postharvest, which limit the storage period and reduce their commercial values (Porat et al., 2000). Many factors contribute to postharvest losses in fresh fruits, such as environmental conditions, mechanical damage during harvesting and handling, and cooling storage (Klein and Perry, 1982; Marcilla et al., 2006; Porat et al., 2004). The most common disorder seen during citrus postharvest storage is decay (Porat et al., 2000, 2004). Many reports indicate that postharvest treatment using fungicidal thiabendazole (TBZ) treatment (Smilanick et al., 2006), hot water sprays (Porat et al., 2000), and coating with low molecular weight chitosan (LMWC) (Chien et al., 2007) can successfully decrease the incidence of decay in citrus fruits during storage. Granulation is another citrus disorder, first reported in ‘Valencia’ oranges by Bartholomew et al. (1935), and also seen in ‘Ponkan’ mandarin (Xingjie, 1990). Bartholomew et al. (1941) stated that granulation is not caused by the segments drying, but instead by the
∗ Corresponding author. Tel.: +886 52717760. E-mail address: [email protected] (P.-T. Chang). http://dx.doi.org/10.1016/j.scienta.2015.03.016 0304-4238/© 2015 Elsevier B.V. All rights reserved.
formation of gel within vesicles. Symptoms of granulation include the dry pulp of segments being discolored and containing low concentrations of TSS and TA (Goto and Araki, 1983; Nakajima, 1976). An earlier study showed that granulation is more severe when the fruit is grown under shaded conditions, especially when covered with black bags (Awasthi and Nauriyal, 1973). Furthermore, later studies indicated that granulation can occur both when the fruits are still on the tree and after harvest, during storage (Hwang et al., 1990). Meanwhile, high temperatures have enhanced the development of granulation in Florida citrus (Ritenour et al., 2004). Previous studies indicated that fruit quality and shelf life are related to preharvest factors, such as carbohydrate content (Goldschmidt, 1999), fruit position and crop load (Volz et al., 1993), and temperature (Ferguson et al., 1999). Muleo et al. (1994) reported that preharvest shading improves fruit water status and increases fruit volume in stone fruits, while another study noted that greater light exposure can increase fruit size and the concentrations of soluble solids in such fruits (Marini et al., 1991; Southwick et al., 1990). In addition, Crisosto et al. (1997) reported that shaded stone fruits had a higher incidence of postharvest disorders and shorter shelf life than sun-exposed ones. These contradictory effects are assumed to be due to the timing and duration of shading in the field (George et al., 1996; Muleo et al., 1994). We have previously reported that white net shading in the field is effective with regard to reducing the incidence of sunscald and lowering canopy temperatures, without affecting the peel color,
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TSS, TA, and TSS/TA ratio of ‘Murcott’ tangor fruits (Tsai et al., 2013). Since ‘Ponkan’ mandarin have a relatively long storage life in Taiwan, it is of interest to examine whether preharvest shading treatment can affect the postharvest physiological responses and quality of this hesperidium fruits. The present study thus positioned white shading nets 1.0 m above ‘Ponkan’ mandarin trees from August until harvest, and then during the postharvest period stored the fruits at two temperatures to study the effects on decay, weight loss, granulation, and changes in quality. 2. Materials and methods 2.1. Site description This study was conducted in a commercial citrus orchard in Shihkang, Taichung, Taiwan, (lat. 24.25◦ N, long. 120.81◦ E, elevation 300 m). The trees were 15-year-old ‘Ponkan’ mandarin (Citrus reticulate Blanco) arranged in a typical open-center training system with similar height of about 2.0 m, and planted with a north to south orientation at a spacing of 2 m and 2 m on the center between rows and within rows, respectively. This area has a subtropical climate, with average annual precipitation of about 2.13 m. The orchard management followed standard horticultural practices, as well as those for disease and pest control.
and then immediately sent to the laboratory and kept at 25 ◦ C for 72 h for curing. Fruits were weighed and selected for uniformity (e.g., size, color, shape, and maturity), visually assessed as to whether free of damage and diseases, and then individually packed into 0.03 mm polyethylene (PE) bags. Four hundred and eighty PE packed fruits with and without shading treatment were then randomly distributed into eight boxes, and four boxes of 60 ‘Ponkan’ mandarin fruit with and without shading were stored at 25 ◦ C or 13.5 ◦ C. 2.6. Determination of weight loss A sample of 10 fruits from each box with four replications stored at 25 ◦ C or 13.5 ◦ C was randomly selected and marked for weight loss determination. The initial averaged fresh weights of the fruits treated with and without shading were recorded before being stored at 25 ◦ C or 13.5 ◦ C. The weight loss of the fresh ‘Ponkan’ mandarin fruits in each treatment was measured by calculating the changes in weight of the fruits stored at 25 ◦ C or 13.5 ◦ C every four weeks. The results were expressed as: ((averaged fresh weight before storage − averaged fresh weight after storage)/(initial averaged fresh weight)) × 100%. 2.7. Decay assessment
2.2. Field experiment The field experimental design was a completely randomized design (CRD) with four replications. The treatments for the ‘Ponkan’ trees were: no shading as control and shading with a 20% shading rate using white nylon nets positioned roughly 100 cm above the citrus trees from August to the end of October. There was one tree per treatment, and field trials were conducted in two consecutive years (2009 and 2010).
During the storage period, each box of mandarin fruits treated with and without shading stored at 25 ◦ C or 13.5 ◦ C was examined every four weeks to detect mold, with samples regarded as infected if a visible lesion was observed. Decay assessment was evaluated as the percentage of the total number of fruits examined that exhibited mold or visible lesions. 2.8. Fruit quality and physiological analysis
2.3. Data collection of shade treatment The photosynthetic photon flux (PPF) inside the shade net and around the control branches was determined on cloudless days from 10:30 to 13:00 during the experiment. Ten readings on mature leaves per replication were taken at random positions along the branch using an LI-189 quantum sensor attached to a LI-6200 portable photosynthesis system (LI-COR, Lincoln, NE). A shielded SK-L200TH probe (Tokyo, Japan) attached to a SKL200TH␣ data logger (Tokyo, Japan) was used to monitor the air temperature inside the shade net and around the control branches every hour. Air temperatures were recorded for every replication from 1 Oct. to 31 Oct. in 2009 and 2010. Leaf and fruit temperatures were monitored on clear days using an infrared temperature sensor (MI 200; Apogee Instruments, Logan, UT). The temperatures of ten leaves and ten fruits per tree were determined during midday (11:00–13:00).
Every four weeks, a sample of 10 unmarked fruits without mold and infection with four replications was removed from the 25 ◦ C and 13.5 ◦ C rooms for quality and physiological analysis (i.e., peel color analysis, granulation percentage, juice percentage, total soluble solids (TSS)%, titratable acid (TA)%, and sugar to acid (TSS/TA) ratio). 2.9. Peel color analysis Color was measured using a tristimulus colorimeter (CR 200; Minolta, Osaka, Japan), with a 5 mm aperture to examine the differences of fruits appearance following the procedure described by Tsai et al. (2013). The readings were then averaged to represent peel color. 2.10. Granulation evaluation
2.4. Sunscald investigation Sunscald was determined when yellow or brown blotches appeared on the citrus peel. We investigated all the fruits on every experimental tree for sunscald symptoms from 1 Sep. to 31 Oct. in 2009 and 2010, with the results expressed as a percentage of sunscald, as follows: (number of fruits with sunscald)/(total fruits) × 100%. 2.5. Storage experiment ‘Ponkan’ mandarin fruits with and without shading were randomly harvested by hand on 23 Nov. 2009 and 08 Nov. 2010,
During the storage period, the same 10 fruits selected every four weeks for peel color analysis were then examined for the degree of granulation evaluation. Each fruit was peeled and the pulp was removed, and each slice of sarcocarp was then visually evaluated for the presence and severity of granulation. The measurement for the granulation severity of a single mandarin fruit was modified from Sharma et al. (2006). A non-granulated mandarin was scored as 0, non-granulation (NG); 1, 10% granulation (G1); 2, 11–25% granulation (G2); 3, 26–50% granulation (G3); and 4, more than 50% granulation (G4) (Fig. 1). The degree of granulation was expressed as the percentage of the total number of fruits examined that showed evidence of granulation.
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Fig. 1. Degree of granulation detected in ‘Ponkan’ mandarin fruits. NG, no granulation 0; G1, granulation severity 1; G2, granulation severity 2; G3, granulation severity 3; G4, granulation severity 4.
2.11. Juice percentage, total soluble solids and titratable acid After granulation detection, the amount of fruit pulps was recorded (g/fruit) along with the juice percentage, while the total soluble solids (TSS), and titratable acid (TA) were measured according to the procedures in Tsai et al. (2013). The juice percentage was expressed as follows: ((juice weight)/total weight (juice + pulp)) × 100%. A few drops of the supernatant were placed on a refractometer (Mater-M, Tokyo, Japan) to measure the TSS expressed as a percentage (%). Titratable acid was determined with 0.1 N sodium hydroxide (NaOH) to pH 8.2, and expressed as the citric acid content (Tsai et al., 2013). The sugar/acid ratio is represented as the percentage sugar/percentage acid. 2.12. Statistical analysis This experiment uses a two-factor factorial design, carried out a completely randomized design, with four replicates per treatment, with each box being a replicate. Data for temperatures, PPF, and sunscald were analyzed by one-way analysis of variance (ANOVA), other data were analyzed by two-way analysis of variance (ANOVA) using SAS (version 9.2; SAS Institute, Cary, NC). Mean value separations were performed using a least significant difference (LSD) test at a 5% significance level (P ≤ 0.05). 3. Results 3.1. Characterization of shading Shading not only effectively reduced the air temperature, but also leaf and fruit surface temperatures, in both 2009 and 2010. In addition, shading significantly lowered PPF as compared with the control sample in both years (Table 1). 3.2. Sunscald occurrence The period of sunscald investigation lasted from 1 Sep. to 31 Oct. in 2009 and 2010. When the fruits were shaded with a white shade net a low rate of sunscald was found in both September and October
2009, at just 3.4%. However, for the control fruits, grown without shading, a significant incidence of sunscald was found in September and October 2009, at 8.3% and 8.7%, respectively as shown in Fig. 2A. Similar results were found when sunscald symptoms were investigated in 2010 (Fig. 2B). A significant percentage of sunscald was found for the control fruits in September and October 2010, at 9.15% and 9.45%, respectively. On the other hand, in 2010, the ‘Ponkan’ mandarin fruits grown with a white shade net only had 2.94% and 3.04% of sunscald in September and October, respectively. 3.3. Granulation evaluation The results of this study indicate that degree of granulation was significantly higher in the control sample (35%) than for the fruits grown underneath white shading net (19%) at harvest in 2009. After the fruits were subjected to temperature conditioning, a significant difference in the degree of granulation was observed between preharvest treatments (Fig. 3A). Although the percentage of granulation was lower next year, similar results were seen in 2010 (Fig. 3B). The level of granulation increased as storage time increased; however, the white net shading treatment examined in this work was effective in reducing the incidence of granulation. 3.4. Weight loss At harvest there was no difference in the average weight between the shading and control samples (data not shown). The weight loss of the ‘Ponkan’ mandarin fruits, as measured in 2009 and 2010, is shown in Fig. 4A and B, respectively. During the storage period, there was no significant difference in weight loss calculated between preharvest treatments until week 12 in 2009 (Fig. 4A). In 2010, the significant difference in weight loss calculated between preharvest treatments was seen after week 8 (Fig. 4B). However, postharvest storage temperatures had a main influence on weight loss. The rate of weight loss increased regardless of shading treatments and storage temperatures in both 2009 and 2010, respectively. Additionally, the weight loss of the fruits stored at 13.5 ◦ C was much lower than that of the fruits stored at 25 ◦ C.
Table 1 Effects of shading of ‘Ponkan’ mandarin branches in 2009 and 2010 on air, leaf and fruit surface temperatures, and PPF. Treatment
Air temperature (◦ C)z
Leaf temperature (◦ C)y
Fruit surface temperature (◦ C)y
PPF (mol m−2 s−1 )x
2009 Control White net
34.5 ± 1.02aw 30.7 ± 0.77b
39.9 ± 1.14a 33.7 ± 0.94b
42.3 ± 1.51a 36.7 ± 0.75b
1731 ± 107a 1271 ± 83b
2010 Control White net
33.8 ± 0.97a 28.8 ± 0.48b
38.9 ± 0.43a 33.6 ± 1.08b
40.9 ± 1.46a 35.2 ± 1.13b
1631 ± 114a 1133 ± 103b
z y x w
Values are means ± SE, for n = 4. Air temperature was measured from 11:00 to 14:00. Values are means ± SE, for n = 10. Leaf and fruit surface temperatures were measured from 11:00 to 13:00. Values are means ± SE, for n = 4. PPF was recorded from 10:30 to 13:00. Values in a column with different letters are statistically different by a least significance difference (LSD) test at P ≤ 0.05.
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12
A. 2009
Control White net
a a
10
8
6
b
b Sunscald percentage %
4
2
0 12
a
B. 2010
a 10
8
6
b
b 4
2
0
September
October Month
Fig. 2. Effects of using a white net on the percentage of sunscald of ‘Ponkan’ mandarin fruits in 2009 and 2010.
3.5. Decay assessment There was no difference in the decay percentage between the preharvest shading and control samples. After the fruits were stored at different storage temperatures, a significant difference in the decay percentage was observed in 2009 and 2010 (Fig. 5). Although the amount of decay increased along with the storage time, there was no significant difference between the control and shading samples in this regard. However, a lower storage temperature (e.g., 13.5 ◦ C) lead to more than 25% less decay as compared to storage at 25 ◦ C after 8 weeks of storage. 3.6. Fruit physicochemical characteristics A significant difference in juice content was found for the fruit samples grown under the white shading nets as compared with
control at harvest in 2009, and similar results were observed for fruits stored at different temperatures regardless of the storage time. Preharvest shading treatment had a significant effect on juice content, but postharvest storage temperatures did not (Table 2). The same results were observed in 2010 (Table 2). The mandarin fruits had no significant differences in TSS and TA when grown with and without a white shading net. In addition, postharvest storage temperature had no significant influences on TSS and TA, either (Table 2). The ‘Ponkan’ mandarin fruits were harvested when ripe, with a greenish peel color. Although the peel color turned to orangish as the storage period increased, there were no significant differences in peel color related to either via preharvest or postharvest treatment (data not shown). As a result, mandarin grown with and without a white shading net and then stored at different temperatures had no significant differences with regard to TSS, TA, or appearance.
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100
80
Control 25 oC White net 25 oC Control 13.5 oC White net 13.5 oC
61
A. 2009
aA aB bA
aA 60 aA 40
bB
aB bA aA
aA
a
Granulation (%)
bA bA b 20
0 60
3rd
59th
31th
Day
50
87th aA
B. 2010
aA
40
bA
aB
30 aA aA
20
aB
bB
bA
a
bA
10
bB
b
bB
0
3rd
59th
31th
87th
Day Fig. 3. Effects of using a white net on the degree of granulation of ‘Ponkan’ mandarin fruits during storage at 13.5 ◦ C and 25 ◦ C in 2009 and 2010z . z Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of storage temperatures.
4. Discussion Shading, a preharvesting application has been reported not only to reduce air temperature, canopy temperature, crop skin temperature, and PPF, but also to affect growth and quality for many commercial crops, such as kiwifruit (Actinidia deliciosa) (Basile et al., 2008), ‘Fuji’ apple (Dussi et al., 2005), Citrus (Jifon and Syvertsen, 2001), plum (Prunus salicina Lindell) (Murray et al., 2005), blueberry (Vaccinium corymbosum L.) (Retamales et al., 2008), ‘Murcott’ tangor (Citrus reticulata × Citrus sinensis) (Tsai et al., 2013), and cut foliages, (Stamps, 2008). Our study found that shading can effectively reduce air, canopy and skin temperatures (Table 1), but has no significant effects on the physicochemical characteristics (e.g., TSS and TA) (Table 2) of the ‘Ponkan’ mandarin fruits in comparison with the control sample, similar to the findings of our previous study, which examined ‘Murcott’ tangor fruits (Tsai et al., 2013). In contrast, shading treatments had a negative effect on soluble solid
concentrations (SSC) and fruit size in stone fruit (George et al., 1996; Murray et al., 2005). Although continuous shading can be disadvantageous with regard to the TSS content, as a reduction in PPF results in lower photosynthate production (Mataa and Tominaga, 1998; Syvertsen, 1984), light radiation can still penetrate the 20% shading rate of the white nylon nets, and thus achieve photosynthesis saturation. There were thus no significant differences in TSS and TA between the control and shading treatments. The current study found a slight occurrence of sunscald in ‘Ponkan’ mandarin fruits in both 2009 and 2010. This is possibly due to the microclimate underneath the shading, and because the level of scattered radiation below the nets was still high enough to cause sunscald (Cohen et al., 1997; Stamps, 2009). In addition, shading increased the juice content of ‘Ponkan’ mandarin fruits at harvest (Table 2) similar to the findings in Jifon and Syvertsen (2001), which examined ‘Ruby Red’ grapefruit (Citrus paradise L.). Previous studies have demonstrated that the stomata of
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10
8
A. 2009
Control 25 oC White net 25 oC Control 13.5 oC White net 13.5 oC
aA bA
aA
6
aA
aB bB
4
aA aA
aB aB aB
Weight loss (%)
aB 2
0 8
3rd
59th
31th
87th aA
Day 6
B. 2010 bA
aA bA
aB
4
bB aA
aB aA
2
bB aB
aB
0
4
8
12
Week Fig. 4. Changes in percentage weight loss of ‘Ponkan’ mandarin fruits grown with a white shading net and the control samples during storage at 13.5 ◦ C and 25 ◦ C in 2009 and 2010z . z Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of storage temperatures.
the leaves on the fruit trees were more open under shading than the control condition, and late shaded citrus trees (from August until harvest) have a higher water content than light-exposure ones due to less evaporation from the shaded leaves (Hilgeman, 1977; Jifon and Syvertsen, 2001). Similar shading periods were applied in the current study in both years, and thus the practice of late shading could improve tree water status, and this is suggested as being a key factor in the higher fruit juice content found in this work for the shaded samples. Many factors are associated with the occurrence of granulation in citrus, including climate, field management practices, harvest timing, and storage conditions (Awasthi and Nauriyal, 1973; Burns and Albrigo, 1998; Hwang et al., 1990). In the present study, we examined the effects of using a white shading net on the occurrence of granulation in the preharvest period. We found that the white shading nets significantly reduced the incidence of granulation as
compared with the control samples (Fig. 3). Awasthi and Nauriyal (1973) reported that being grown under shaded conditions, especially for citrus fruits covered with black bags, resulted in a greater severity of granulation. However, our study showed the opposite effects, which suggests that black bags are more endothermic than white nylon netting, thus resulting in a relatively high temperature during blooming and fruit setting, leading to greater granulation in citrus fruits (Ritenour et al., 2004). On the other hand, the development of granulation has also been reported during storage (Gilfillan and Stevenson, 1977), with Ladaniya (2008) indicating that this is due to weight loss. Our results support this contention, showing that the rate of granulation increased along with weight loss during postharvest storage (Figs. 3 and 4). However, whether the causes of granulation in citrus fruits depend on pre- or postharvest factors requires further clarification.
T.-C. Lee et al. / Scientia Horticulturae 188 (2015) 57–65
100
80
63
A. 2009
Control 25 oC White net 25 oC Control 13.5 oC White net 13.5 oC
aA aA
aA
60
aA aB 40
bB
aB
Decay rate (%)
aB 20 aA 0 100
aA aB aB
3rd
59th
31th
Day
87th aA
B. 2010
aA
80 aA aA 60 aB aB
40 aB aB 20 aA
aA aBaB
0
4
8
12
Week Fig. 5. Decay rate of ‘Ponkan’ mandarin fruits grown with a white shading net and the control samples during storage at 13.5 ◦ C and 25 ◦ C in 2009 and 2010z . z Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of storage temperatures.
The results of this study showed that postharvest storage temperatures had an impact on ‘Ponkan’ mandarin fruits. During the postharvest period, weight loss mostly depends on the storage tem´ 2004), and our study confirmed that peratures (Jemriic´ and Paviˇcic, the weight loss is mainly affected by storage temperatures, regardless of whether preharvest shading is used or not. Furthermore, the fruits stored at 13.5 ◦ C show less weight loss than those stored at 25 ◦ C (Fig. 4), which is likely because the higher storage temperature caused the loss of more moisture. This is important, as the more than 5% weight loss of ‘Ponkan’ mandarin fruits stored at 25 ◦ C from week 8th to week 12th could significantly reduce its market values (Grierson et al., 1978). There are several postharvest decay symptoms seen in citrus, such as green mold, blue mold, and sour rot (Eckert and Eaks, 1989). However, there are also many postharvest methods to inhibit the related microorganisms, and thus maintain fruit quality and extend
storage periods, such as the use of fungicides, modified atmosphere packaging (MAP), and hot water brushing (HWB) (Porat et al., 2000, 2004; Smilanick et al., 2006). In the present study, the decay index was 0% before storage because we visually inspected each experimental fruit to ensure that it was free of damage and disease, and then packed them into individual plastic bags. It is recommended that the storage temperature for mandarins to be between 5 ◦ C and 8 ◦ C (Kader and Arpaia, 2002), and chilling injuries can result in greater incidence of decay in kumquat (Fortunella margarita) fruits (Chalutz et al., 1989). Although, previous studies suggested that while plastic bags can reduce mechanical damage and contamination, and maintain the relative humidity around the fruits (Kader et al., 1989), the excessive moisture inside the package may increase the incidence of decay (Porat et al., 2004). However, our data showed that a relatively low storage temperature (e.g., 13.5 ◦ C) lead to better inhibition of
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Table 2 Effects of shading on juice content, total soluble solids, and titratable acid on ‘Ponkan’ mandarin fruits during storage at 13.5 ◦ C or 25 ◦ C in 2009 and 2010. Treatment
Storage temperature (◦ C)
2009 Control White net 4 weeks Control White net
Juice content (%)z 41.3 ± 4.9by 47.6 ± 3.7a
Total soluble solids (%)z 9.3 ± 0.5a 9.7 ± 0.5a
Titratable acid (%)z 0.6 ± 0.06a 0.58 ± 0.06a
13.5 25 13.5 25
41.0 40.7 44.3 46.8
± ± ± ±
3.7bA 5.5bA 5.7aA 3.0aA
10.1 9.6 10.2 10.3
± ± ± ±
0.5aA 0.3aA 0.4aA 0.7aA
0.56 0.48 0.56 0.53
± ± ± ±
0.08aA 0.07aA 0.11aA 0.11aA
13.5 25 13.5 25
38.3 40.5 42.9 44.4
± ± ± ±
4.2bA 4.9bA 4.5aA 5.2aA
9.9 9.9 10.1 10.1
± ± ± ±
0.8aA 0.4aA 0.6aA 0.5aA
0.38 0.39 0.39 0.36
± ± ± ±
0.08aA 0.07aA 0.07aA 0.03aA
13.5 25 13.5 25
36.1 34.2 40.3 38.6
± ± ± ±
4.1bA 4.8bA 5.2aA 4.1aA
9.4 9.8 9.4 9.1
± ± ± ±
0.5aA 0.8aA 0.7aA 0.9aA
0.33 0.32 0.32 0.29
± ± ± ±
0.07aA 0.05aA 0.08aA 0.08aA
8 weeks Control White net 12 weeks Control White net Source of variance
d.f.
Mean square
Analysis of variance Treatment Temperature Treatment × temperature Error
1 1 1 12
132.25∗ 2.25 6.25 1.92
Treatment
Storage temperature (◦ C)
2010 Control White net 4 weeks Control White net
Juice content (%) 41.45 ± 3.8b 8.89 ± 4.93a
0.0625 0.0225 0.0625 0.0175 Total soluble solids (%) 8.8 ± 0.4a 8.9 ± 0.41a
0.0004 0.0009 0.0002 0.0017 Titratable acid (%) 0.62 ± 0.02a 0.58 ± 0.02a
13.5 25 13.5 25
38.91 38.77 44.01 46.22
± ± ± ±
3.57bA 4.67bA 3.77aA 4.34aA
9.28 9.38 9.35 9.35
± ± ± ±
0.56aA 0.42aA 0.35aA 0.31aA
0.48 0.47 0.43 0.48
± ± ± ±
0.07aA 0.04aA 0.03aA 0.04aA
13.5 25 13.5 25
38.35 36.22 40.22 41.38
± ± ± ±
3.28bA 5.41bA 4.36aA 4.48aA
9.06 8.88 8.89 8.78
± ± ± ±
0.80aA 0.42aA 0.45aA 0.43aA
0.36 0.34 0.31 0.32
± ± ± ±
0.03aA 0.02aA 0.06aA 0.04aA
13.5 25 13.5 25
37.93 31.97 39.63 38.63
± ± ± ±
4.48aA ± 5.28bA 4.01aA 4.19aA
7.98 8.13 8.02 8.32
± ± ± ±
0.52aA 0.34aA 0.58aA 0.45aA
0.32 0.33 0.30 0.31
± ± ± ±
0.01aA 0.03aA 0.03aA 0.02aA
8 weeks Control White net 12 weeks Control White net Source of variance
d.f.
Mean square
Analysis of variance Treatment Temperature Treatment × temperature Error
1 1 1 12
169∗ 9 25 2.25
0.0025 0.0225 0.1225 0.075
0.0022 0.0010 0.0014 0.0026
Values are means ± SE, for n = 4. Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of the temperatures. * P < 0.01. z
y
postharvest decay, regardless of whether preharvest shading was used or not. 5. Conclusions Shading is an effective method that can be used in the field to reduce heat, direct solar radiation, and create microclimate. Although the effects of shading nets and shading periods vary among crops, preharvest shading has already been adopted for some crops to enhance their productivity and quality. In the present study, we demonstrated that white net shading could be used during the late preharvest period in orchards to reduce the
occurrence of sunscald and granulation of ‘Ponkan’ mandarin fruit without affecting fruit maturity and quality at harvest; however, its postharvest quality and shelf-life may be directly related to storage conditions, such as temperature and humidity. A better understanding of the optimal manipulation of preharvest shading, such as the optimal shading materials, and shading periods, is needed help to ensure the best possible quality at harvest, as well as the best conditions during the postharvest period to maintain high quality of fruit. Therefore, in the future, more research is needed to explore the effects of shading on postharvest quality, especially in relation to the use of colored shade nets and different shading periods.
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References Awasthi, R.P., Nauriyal, J.P., 1973. Effect of age, tree condition, tree aspect, fruit size, rootstock and tree variation on granulation. J. Res. Punjab Agric. Univ. 10, 62–70. Bartholomew, E.T., Sinclair, W.B., Raby, E.C., 1935. Granulation of Valencia orange. Calif. Citrog. 21, 30. Bartholomew, E.T., Sinclair, W.B., Turrell, F.M., 1941. Granulation of Valencia oranges. Univ. Calif. Agric. Exp. Sta. Bull., 647. Basile, B., Romano, R., Giaccone, M., Barlotti, E., Colonna, V., Cirillo, C., Shahak, Y., Forlani, M., 2008. Use of photo-selective nets for hail protection of kiwifruit vines in southern Italy. Acta Hortic. 770, 185–192. Burns, J.K., Albrigo, L.G., 1998. Time of harvest and method of storage affect granulation in grapefruit. HortScience 33, 728–730. Chalutz, E., Lomaniec, E., Waks, J., 1989. Physiological and pathological observations on the post-harvest behaviour of kumquat fruit. Trop. Sci. 29, 199–206. Chien, P.J., Sheu, F., Lin, H.R., 2007. Coating citrus (Murcott tangor) fruit with low molecular weight chitosan increases postharvest quality and shelf life. Food Chem. 100, 1160–1164. Cohen, S., Moreshet, S., LeGuillou, L., Simon, J.G., Cohen, M., 1997. Response of citrus trees to modified radiation regime in semi-arid conditions. J. Exp. Bot. 48, 35–44. Crisosto, C.H., Johnson, R.S., DeJong, T., Day, K.R., 1997. Orchard factors affecting postharvest stone fruit quality. HortScience 32, 820–823. Dussi, M.C., Giardina, G., Sosa, D., González Junyent, R., Zecca, A., Reeb, P., 2005. Shade nets effect on canopy light distribution and quality of fruit and spur leaf on apple cv, Fuji. Span. J. Agric. Res. 3, 253–260. Eckert, J.W., Eaks, I.L., 1989. Postharvest disorders and diseases of citrus fruits. In: Reuther, W., Calavan, E.C., Carman, G.E. (Eds.), The Citrus Industry, vol. 4. University of California Press, Berkeley, USA, pp. 179–260. Ferguson, I.B., Snelgar, W., Bowen, J.H., Woolf, A.B., 1999. Preharvest field heat and postharvest fruit response. Acta Hortic. 485, 149–154. George, A.P., Hieke, S., Rasmussen, T., Ludders, P., 1996. Early shading reduces fruit yield and late shading reduces quality in low-chill peach (Prunus persica (L) Batsch) in subtropical Australia. J. Hortic. Sci. 71, 561–571. Gilfillan, I.M., Stevenson, J.A., 1977. Postharvest development of granulation in South African export oranges. Proc. Intl. Soc. Citricult. 1, 299–303. Goldschmidt, E.E., 1999. Carbohydrate supply as a critical factor for citrus fruit development and productivity. HortScience 34, 1020–1024. Goto, A., Araki, C., 1983. Chemical compositions and internal anatomy of the gelated and granulated juice sacs of Sanbokan (Citrus sulcata Hort Ex Takahashi) fruit. J. Jpn. Soc. Hortic. Sci. 52, 316–324. Grierson, W., Miller, W.M., Wardowski, W.F., 1978. Packingline Machinery for Florida Citrus Packinghouses. University of Florida, Florida, USA, Bulletin 803. Hilgeman, R.H., 1977. Response of citrus trees to water stress in Arizona. Proc. Intl. Soc. Citricult. 1, 70–74. Hwang, Y.S., Huber, D.J., Albrigo, L.G., 1990. Comparison of cell wall components in normal and disordered juice vesicles of grapefruit. J. Am. Soc. Hortic. Sci. 115, 281–287. ´ T., Paviˇcic, ´ N., 2004. Postharvest treatments of Satsuma mandarin (Citrus Jemriic, unshiu Marc.) for the improvement of storage life and quality. Postharvest Biol. Technol. 4, 213–227. Jifon, J.L., Syvertsen, J.P., 2001. Effects of moderate shade on citrus leaf gas exchange, fruit yield, and quality. Proc. Fla. State Hortic. Soc. 114, 177–181. Kader, A.A., Arpaia, M.L., 2002. Postharvest handling systems: subtropical fruits. In: Kader, A.A. (Ed.), Postharvest Technology of Horticultural Crops. University of California, Agriculture and Natural Resources, Oakland, CA, pp. 375–383.
65
Kader, A.A., Zagory, D., Kerbel, E.L., 1989. Modified atmosphere packaging of fruits and vegetables. Crit. Rev. Food Sci. Nutr. 28, 1–30. Klein, B.P., Perry, A.K., 1982. Ascorbic acid and vitamin A activity in selected vegetables from different geographical areas of the United States. J. Food Sci. 47, 941–945. Ladaniya, M.S., 2008. Citrus Fruit Biology, Technology and Evaluation. Elsevier Inc., USA, 18–21, 193–196, 417–444. Marini, R.P., Sowers, D., Marini, M.C., 1991. Peach fruit quality is affected by shade during final swell of fruit growth. J. Am. Soc. Hortic. Sci. 116, 383–389. Marcilla, A., Zarzo, M., Del Río, M.A., 2006. Effect of storage temperature on the flavour of citrus fruit. Span. J. Agric. Res. 4, 336–344. Mataa, M., Tominaga, S., 1998. Effects of shading stage and level on fruit set and development, leaf carbohydrates and photosynthesis in Ponkan (Citrus reticulata Blanco). Jpn. J. Trop. Agric. 42, 103–110. Muleo, R., Masetti, C., Tellini, A., Loreti, F., Morini, S., 1994. Modifications of some characteristics in nectarine fruit induced by light deprival at different times of fruit growth. Adv. Hortic. Sci. 8, 75–79. Murray, X.J., Holcroft, D.M., Cook, N.C., Wand, S.J.E., 2005. Postharvest quality of ‘Laetitia’ and ‘Songold’ (Prunus salicina Lindell) plums as affected by preharvest shading treatments. Postharvest Biol. Technol. 37, 81–92. Nakajima, Y., 1976. Study on dry juice sacs of Hyuganatsu (Citrus tamurana Hort Ex Tanaka) in late stages of fruit development. J. Jpn. Soc. Hortic. Sci. 44, 338–346. Porat, R., Daus, A., Weiss, B., Cohen, L., Fallik, E., Droby, S., 2000. Reduction of postharvest decay in organic citrus fruit by a short hot water brushing treatment. Postharvest Biol. Technol. 18, 151–157. Porat, R., Weiss, B., Cohen, L., Daus, A., Aharoni, N., 2004. Reduction of postharvest rind disorders in citrus fruit by modified atmosphere packaging. Postharvest Biol. Technol. 33, 35–43. Retamales, J.B., Montecino, J.M., Lobos, G.A., Rojas, L.A., 2008. Colored shading nets increase yields and profitability of highbush blueberries. Acta Hortic. 770, 193–197. Ritenour, M.A., Albrigo, L.G., Burns, J.K., Miller, W.M., 2004. Granulation in Florida citrus. Proc. Fla. State. Hortic. Soc. 117, 358–361. Sharma, R.R., Singh, R., Saxena, S.K., 2006. Characteristics of citrus fruits in relation to granulation. Sci. Hortic. 111, 91–96. Smilanick, J.L., Brown, G.E., Eckert, J.W., 2006. Postharvest citrus diseases and their control. In: Wardowski, W.F., Miller, W.M., Hall, D.J., Grierson, W. (Eds.), Fresh Citrus Fruits. , second ed. Florida Science Source, Inc., Longboat Key, FL, USA, pp. 339–396. Stamps, R.H., 2008. Differential effects of colored shade nets on three cut foliage crops. Acta Hortic. 770, 169–176. Stamps, R.H., 2009. Use of colored shade netting in horticulture. HortScience 44, 239–241. Southwick, S.M., Weinbaum, S.A., Muraoka, T.T., Krueger, W.R., Shackel, K.A., Yeager, J.T., 1990. Leaf attributes as indices of fruit quality in prune tree canopies. HortScience 25, 751–754. Syvertsen, J.P., 1984. Light acclimation in citrus leaves. II: CO2 assimilation and light, water, and nitrogen use efficiency. J. Am. Soc. Hortic. Sci. 109, 812–817. Tsai, M.S., Lee, T.C., Chang, P.T., 2013. Comparison of paper bags, calcium carbonate, and shade nets for sunscald protection in ‘Murcott’ tangor fruit. HortTechnology 23, 659–667. Volz, R.K., Ferguson, I.B., Bowen, J.H., Watkins, C.B., 1993. Crop load effects on mineral nutrition, maturity, fruiting and tree growth of ‘Cox’s Orange Pippin’ apple. J. Hortic. Sci. 68, 127–137. Xingjie, T., 1990. Relationship between pectinmethylesterase and polygalacturonase activities and granulation in citrus fruit. In: Proc. Intl. Citrus Symp., Guangzhou, China, pp. 796–798.
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The effects of preharvest shading and postharvest storage temperatures on the quality of ‘Ponkan’ (Citrus reticulata Blanco) mandarin fruits Tan-Cha Lee, Pei-Juan Zhong, Pai-Tsang Chang ∗ Department of Horticultural Science, National Chiayi University, 300 Xuefu Rd., Chiayi City 60004, Taiwan
a r t i c l e
i n f o
Article history: Received 13 January 2015 Received in revised form 10 March 2015 Accepted 13 March 2015 Available online 3 April 2015 Keywords: Citrus Temperature Sunburn Granulation Decay
a b s t r a c t A two-year trial was performed to investigate the effects of using preharvest white shade nets and postharvest storage at 13.5 ◦ C or 25 ◦ C on the physiological responses and quality of ‘Ponkan’ mandarin fruits. A significant reduction in leaf and fruit surface temperatures, PPF, and sunburn was seen when using white shade nets in comparison with the control sample. Trees grown under white netting had a significantly higher juice percentage, less weight loss, lower granulation percentage, and lower percentage decay than the control sample. However, there were no significant differences in peel color, total soluble solids (TSS), and titratable acid (TA) between the control and shading samples after postharvest storage at 13.5 ◦ C or 25 ◦ C. In summary, ‘Ponkan’ mandarin grown with white shading nets exhibited greater sunscald resistance, higher juice percentage, and less weight loss and granulation when stored at 13.5 ◦ C postharvest than the mandarin grown without shading and those stored at 25 ◦ C. © 2015 Elsevier B.V. All rights reserved.
1. Introduction ‘Ponkan’ mandarin (Citrus reticulata Blanco) is a non-climacteric citrus with a high economic value. Appropriate postharvest practices can effectively reduce fruit losses and improve fruit quality, and thus lead to higher profits. However, citrus fruits may exhibit various disorders during postharvest, which limit the storage period and reduce their commercial values (Porat et al., 2000). Many factors contribute to postharvest losses in fresh fruits, such as environmental conditions, mechanical damage during harvesting and handling, and cooling storage (Klein and Perry, 1982; Marcilla et al., 2006; Porat et al., 2004). The most common disorder seen during citrus postharvest storage is decay (Porat et al., 2000, 2004). Many reports indicate that postharvest treatment using fungicidal thiabendazole (TBZ) treatment (Smilanick et al., 2006), hot water sprays (Porat et al., 2000), and coating with low molecular weight chitosan (LMWC) (Chien et al., 2007) can successfully decrease the incidence of decay in citrus fruits during storage. Granulation is another citrus disorder, first reported in ‘Valencia’ oranges by Bartholomew et al. (1935), and also seen in ‘Ponkan’ mandarin (Xingjie, 1990). Bartholomew et al. (1941) stated that granulation is not caused by the segments drying, but instead by the
∗ Corresponding author. Tel.: +886 52717760. E-mail address: [email protected] (P.-T. Chang). http://dx.doi.org/10.1016/j.scienta.2015.03.016 0304-4238/© 2015 Elsevier B.V. All rights reserved.
formation of gel within vesicles. Symptoms of granulation include the dry pulp of segments being discolored and containing low concentrations of TSS and TA (Goto and Araki, 1983; Nakajima, 1976). An earlier study showed that granulation is more severe when the fruit is grown under shaded conditions, especially when covered with black bags (Awasthi and Nauriyal, 1973). Furthermore, later studies indicated that granulation can occur both when the fruits are still on the tree and after harvest, during storage (Hwang et al., 1990). Meanwhile, high temperatures have enhanced the development of granulation in Florida citrus (Ritenour et al., 2004). Previous studies indicated that fruit quality and shelf life are related to preharvest factors, such as carbohydrate content (Goldschmidt, 1999), fruit position and crop load (Volz et al., 1993), and temperature (Ferguson et al., 1999). Muleo et al. (1994) reported that preharvest shading improves fruit water status and increases fruit volume in stone fruits, while another study noted that greater light exposure can increase fruit size and the concentrations of soluble solids in such fruits (Marini et al., 1991; Southwick et al., 1990). In addition, Crisosto et al. (1997) reported that shaded stone fruits had a higher incidence of postharvest disorders and shorter shelf life than sun-exposed ones. These contradictory effects are assumed to be due to the timing and duration of shading in the field (George et al., 1996; Muleo et al., 1994). We have previously reported that white net shading in the field is effective with regard to reducing the incidence of sunscald and lowering canopy temperatures, without affecting the peel color,
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TSS, TA, and TSS/TA ratio of ‘Murcott’ tangor fruits (Tsai et al., 2013). Since ‘Ponkan’ mandarin have a relatively long storage life in Taiwan, it is of interest to examine whether preharvest shading treatment can affect the postharvest physiological responses and quality of this hesperidium fruits. The present study thus positioned white shading nets 1.0 m above ‘Ponkan’ mandarin trees from August until harvest, and then during the postharvest period stored the fruits at two temperatures to study the effects on decay, weight loss, granulation, and changes in quality. 2. Materials and methods 2.1. Site description This study was conducted in a commercial citrus orchard in Shihkang, Taichung, Taiwan, (lat. 24.25◦ N, long. 120.81◦ E, elevation 300 m). The trees were 15-year-old ‘Ponkan’ mandarin (Citrus reticulate Blanco) arranged in a typical open-center training system with similar height of about 2.0 m, and planted with a north to south orientation at a spacing of 2 m and 2 m on the center between rows and within rows, respectively. This area has a subtropical climate, with average annual precipitation of about 2.13 m. The orchard management followed standard horticultural practices, as well as those for disease and pest control.
and then immediately sent to the laboratory and kept at 25 ◦ C for 72 h for curing. Fruits were weighed and selected for uniformity (e.g., size, color, shape, and maturity), visually assessed as to whether free of damage and diseases, and then individually packed into 0.03 mm polyethylene (PE) bags. Four hundred and eighty PE packed fruits with and without shading treatment were then randomly distributed into eight boxes, and four boxes of 60 ‘Ponkan’ mandarin fruit with and without shading were stored at 25 ◦ C or 13.5 ◦ C. 2.6. Determination of weight loss A sample of 10 fruits from each box with four replications stored at 25 ◦ C or 13.5 ◦ C was randomly selected and marked for weight loss determination. The initial averaged fresh weights of the fruits treated with and without shading were recorded before being stored at 25 ◦ C or 13.5 ◦ C. The weight loss of the fresh ‘Ponkan’ mandarin fruits in each treatment was measured by calculating the changes in weight of the fruits stored at 25 ◦ C or 13.5 ◦ C every four weeks. The results were expressed as: ((averaged fresh weight before storage − averaged fresh weight after storage)/(initial averaged fresh weight)) × 100%. 2.7. Decay assessment
2.2. Field experiment The field experimental design was a completely randomized design (CRD) with four replications. The treatments for the ‘Ponkan’ trees were: no shading as control and shading with a 20% shading rate using white nylon nets positioned roughly 100 cm above the citrus trees from August to the end of October. There was one tree per treatment, and field trials were conducted in two consecutive years (2009 and 2010).
During the storage period, each box of mandarin fruits treated with and without shading stored at 25 ◦ C or 13.5 ◦ C was examined every four weeks to detect mold, with samples regarded as infected if a visible lesion was observed. Decay assessment was evaluated as the percentage of the total number of fruits examined that exhibited mold or visible lesions. 2.8. Fruit quality and physiological analysis
2.3. Data collection of shade treatment The photosynthetic photon flux (PPF) inside the shade net and around the control branches was determined on cloudless days from 10:30 to 13:00 during the experiment. Ten readings on mature leaves per replication were taken at random positions along the branch using an LI-189 quantum sensor attached to a LI-6200 portable photosynthesis system (LI-COR, Lincoln, NE). A shielded SK-L200TH probe (Tokyo, Japan) attached to a SKL200TH␣ data logger (Tokyo, Japan) was used to monitor the air temperature inside the shade net and around the control branches every hour. Air temperatures were recorded for every replication from 1 Oct. to 31 Oct. in 2009 and 2010. Leaf and fruit temperatures were monitored on clear days using an infrared temperature sensor (MI 200; Apogee Instruments, Logan, UT). The temperatures of ten leaves and ten fruits per tree were determined during midday (11:00–13:00).
Every four weeks, a sample of 10 unmarked fruits without mold and infection with four replications was removed from the 25 ◦ C and 13.5 ◦ C rooms for quality and physiological analysis (i.e., peel color analysis, granulation percentage, juice percentage, total soluble solids (TSS)%, titratable acid (TA)%, and sugar to acid (TSS/TA) ratio). 2.9. Peel color analysis Color was measured using a tristimulus colorimeter (CR 200; Minolta, Osaka, Japan), with a 5 mm aperture to examine the differences of fruits appearance following the procedure described by Tsai et al. (2013). The readings were then averaged to represent peel color. 2.10. Granulation evaluation
2.4. Sunscald investigation Sunscald was determined when yellow or brown blotches appeared on the citrus peel. We investigated all the fruits on every experimental tree for sunscald symptoms from 1 Sep. to 31 Oct. in 2009 and 2010, with the results expressed as a percentage of sunscald, as follows: (number of fruits with sunscald)/(total fruits) × 100%. 2.5. Storage experiment ‘Ponkan’ mandarin fruits with and without shading were randomly harvested by hand on 23 Nov. 2009 and 08 Nov. 2010,
During the storage period, the same 10 fruits selected every four weeks for peel color analysis were then examined for the degree of granulation evaluation. Each fruit was peeled and the pulp was removed, and each slice of sarcocarp was then visually evaluated for the presence and severity of granulation. The measurement for the granulation severity of a single mandarin fruit was modified from Sharma et al. (2006). A non-granulated mandarin was scored as 0, non-granulation (NG); 1, 10% granulation (G1); 2, 11–25% granulation (G2); 3, 26–50% granulation (G3); and 4, more than 50% granulation (G4) (Fig. 1). The degree of granulation was expressed as the percentage of the total number of fruits examined that showed evidence of granulation.
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Fig. 1. Degree of granulation detected in ‘Ponkan’ mandarin fruits. NG, no granulation 0; G1, granulation severity 1; G2, granulation severity 2; G3, granulation severity 3; G4, granulation severity 4.
2.11. Juice percentage, total soluble solids and titratable acid After granulation detection, the amount of fruit pulps was recorded (g/fruit) along with the juice percentage, while the total soluble solids (TSS), and titratable acid (TA) were measured according to the procedures in Tsai et al. (2013). The juice percentage was expressed as follows: ((juice weight)/total weight (juice + pulp)) × 100%. A few drops of the supernatant were placed on a refractometer (Mater-M, Tokyo, Japan) to measure the TSS expressed as a percentage (%). Titratable acid was determined with 0.1 N sodium hydroxide (NaOH) to pH 8.2, and expressed as the citric acid content (Tsai et al., 2013). The sugar/acid ratio is represented as the percentage sugar/percentage acid. 2.12. Statistical analysis This experiment uses a two-factor factorial design, carried out a completely randomized design, with four replicates per treatment, with each box being a replicate. Data for temperatures, PPF, and sunscald were analyzed by one-way analysis of variance (ANOVA), other data were analyzed by two-way analysis of variance (ANOVA) using SAS (version 9.2; SAS Institute, Cary, NC). Mean value separations were performed using a least significant difference (LSD) test at a 5% significance level (P ≤ 0.05). 3. Results 3.1. Characterization of shading Shading not only effectively reduced the air temperature, but also leaf and fruit surface temperatures, in both 2009 and 2010. In addition, shading significantly lowered PPF as compared with the control sample in both years (Table 1). 3.2. Sunscald occurrence The period of sunscald investigation lasted from 1 Sep. to 31 Oct. in 2009 and 2010. When the fruits were shaded with a white shade net a low rate of sunscald was found in both September and October
2009, at just 3.4%. However, for the control fruits, grown without shading, a significant incidence of sunscald was found in September and October 2009, at 8.3% and 8.7%, respectively as shown in Fig. 2A. Similar results were found when sunscald symptoms were investigated in 2010 (Fig. 2B). A significant percentage of sunscald was found for the control fruits in September and October 2010, at 9.15% and 9.45%, respectively. On the other hand, in 2010, the ‘Ponkan’ mandarin fruits grown with a white shade net only had 2.94% and 3.04% of sunscald in September and October, respectively. 3.3. Granulation evaluation The results of this study indicate that degree of granulation was significantly higher in the control sample (35%) than for the fruits grown underneath white shading net (19%) at harvest in 2009. After the fruits were subjected to temperature conditioning, a significant difference in the degree of granulation was observed between preharvest treatments (Fig. 3A). Although the percentage of granulation was lower next year, similar results were seen in 2010 (Fig. 3B). The level of granulation increased as storage time increased; however, the white net shading treatment examined in this work was effective in reducing the incidence of granulation. 3.4. Weight loss At harvest there was no difference in the average weight between the shading and control samples (data not shown). The weight loss of the ‘Ponkan’ mandarin fruits, as measured in 2009 and 2010, is shown in Fig. 4A and B, respectively. During the storage period, there was no significant difference in weight loss calculated between preharvest treatments until week 12 in 2009 (Fig. 4A). In 2010, the significant difference in weight loss calculated between preharvest treatments was seen after week 8 (Fig. 4B). However, postharvest storage temperatures had a main influence on weight loss. The rate of weight loss increased regardless of shading treatments and storage temperatures in both 2009 and 2010, respectively. Additionally, the weight loss of the fruits stored at 13.5 ◦ C was much lower than that of the fruits stored at 25 ◦ C.
Table 1 Effects of shading of ‘Ponkan’ mandarin branches in 2009 and 2010 on air, leaf and fruit surface temperatures, and PPF. Treatment
Air temperature (◦ C)z
Leaf temperature (◦ C)y
Fruit surface temperature (◦ C)y
PPF (mol m−2 s−1 )x
2009 Control White net
34.5 ± 1.02aw 30.7 ± 0.77b
39.9 ± 1.14a 33.7 ± 0.94b
42.3 ± 1.51a 36.7 ± 0.75b
1731 ± 107a 1271 ± 83b
2010 Control White net
33.8 ± 0.97a 28.8 ± 0.48b
38.9 ± 0.43a 33.6 ± 1.08b
40.9 ± 1.46a 35.2 ± 1.13b
1631 ± 114a 1133 ± 103b
z y x w
Values are means ± SE, for n = 4. Air temperature was measured from 11:00 to 14:00. Values are means ± SE, for n = 10. Leaf and fruit surface temperatures were measured from 11:00 to 13:00. Values are means ± SE, for n = 4. PPF was recorded from 10:30 to 13:00. Values in a column with different letters are statistically different by a least significance difference (LSD) test at P ≤ 0.05.
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12
A. 2009
Control White net
a a
10
8
6
b
b Sunscald percentage %
4
2
0 12
a
B. 2010
a 10
8
6
b
b 4
2
0
September
October Month
Fig. 2. Effects of using a white net on the percentage of sunscald of ‘Ponkan’ mandarin fruits in 2009 and 2010.
3.5. Decay assessment There was no difference in the decay percentage between the preharvest shading and control samples. After the fruits were stored at different storage temperatures, a significant difference in the decay percentage was observed in 2009 and 2010 (Fig. 5). Although the amount of decay increased along with the storage time, there was no significant difference between the control and shading samples in this regard. However, a lower storage temperature (e.g., 13.5 ◦ C) lead to more than 25% less decay as compared to storage at 25 ◦ C after 8 weeks of storage. 3.6. Fruit physicochemical characteristics A significant difference in juice content was found for the fruit samples grown under the white shading nets as compared with
control at harvest in 2009, and similar results were observed for fruits stored at different temperatures regardless of the storage time. Preharvest shading treatment had a significant effect on juice content, but postharvest storage temperatures did not (Table 2). The same results were observed in 2010 (Table 2). The mandarin fruits had no significant differences in TSS and TA when grown with and without a white shading net. In addition, postharvest storage temperature had no significant influences on TSS and TA, either (Table 2). The ‘Ponkan’ mandarin fruits were harvested when ripe, with a greenish peel color. Although the peel color turned to orangish as the storage period increased, there were no significant differences in peel color related to either via preharvest or postharvest treatment (data not shown). As a result, mandarin grown with and without a white shading net and then stored at different temperatures had no significant differences with regard to TSS, TA, or appearance.
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100
80
Control 25 oC White net 25 oC Control 13.5 oC White net 13.5 oC
61
A. 2009
aA aB bA
aA 60 aA 40
bB
aB bA aA
aA
a
Granulation (%)
bA bA b 20
0 60
3rd
59th
31th
Day
50
87th aA
B. 2010
aA
40
bA
aB
30 aA aA
20
aB
bB
bA
a
bA
10
bB
b
bB
0
3rd
59th
31th
87th
Day Fig. 3. Effects of using a white net on the degree of granulation of ‘Ponkan’ mandarin fruits during storage at 13.5 ◦ C and 25 ◦ C in 2009 and 2010z . z Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of storage temperatures.
4. Discussion Shading, a preharvesting application has been reported not only to reduce air temperature, canopy temperature, crop skin temperature, and PPF, but also to affect growth and quality for many commercial crops, such as kiwifruit (Actinidia deliciosa) (Basile et al., 2008), ‘Fuji’ apple (Dussi et al., 2005), Citrus (Jifon and Syvertsen, 2001), plum (Prunus salicina Lindell) (Murray et al., 2005), blueberry (Vaccinium corymbosum L.) (Retamales et al., 2008), ‘Murcott’ tangor (Citrus reticulata × Citrus sinensis) (Tsai et al., 2013), and cut foliages, (Stamps, 2008). Our study found that shading can effectively reduce air, canopy and skin temperatures (Table 1), but has no significant effects on the physicochemical characteristics (e.g., TSS and TA) (Table 2) of the ‘Ponkan’ mandarin fruits in comparison with the control sample, similar to the findings of our previous study, which examined ‘Murcott’ tangor fruits (Tsai et al., 2013). In contrast, shading treatments had a negative effect on soluble solid
concentrations (SSC) and fruit size in stone fruit (George et al., 1996; Murray et al., 2005). Although continuous shading can be disadvantageous with regard to the TSS content, as a reduction in PPF results in lower photosynthate production (Mataa and Tominaga, 1998; Syvertsen, 1984), light radiation can still penetrate the 20% shading rate of the white nylon nets, and thus achieve photosynthesis saturation. There were thus no significant differences in TSS and TA between the control and shading treatments. The current study found a slight occurrence of sunscald in ‘Ponkan’ mandarin fruits in both 2009 and 2010. This is possibly due to the microclimate underneath the shading, and because the level of scattered radiation below the nets was still high enough to cause sunscald (Cohen et al., 1997; Stamps, 2009). In addition, shading increased the juice content of ‘Ponkan’ mandarin fruits at harvest (Table 2) similar to the findings in Jifon and Syvertsen (2001), which examined ‘Ruby Red’ grapefruit (Citrus paradise L.). Previous studies have demonstrated that the stomata of
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10
8
A. 2009
Control 25 oC White net 25 oC Control 13.5 oC White net 13.5 oC
aA bA
aA
6
aA
aB bB
4
aA aA
aB aB aB
Weight loss (%)
aB 2
0 8
3rd
59th
31th
87th aA
Day 6
B. 2010 bA
aA bA
aB
4
bB aA
aB aA
2
bB aB
aB
0
4
8
12
Week Fig. 4. Changes in percentage weight loss of ‘Ponkan’ mandarin fruits grown with a white shading net and the control samples during storage at 13.5 ◦ C and 25 ◦ C in 2009 and 2010z . z Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of storage temperatures.
the leaves on the fruit trees were more open under shading than the control condition, and late shaded citrus trees (from August until harvest) have a higher water content than light-exposure ones due to less evaporation from the shaded leaves (Hilgeman, 1977; Jifon and Syvertsen, 2001). Similar shading periods were applied in the current study in both years, and thus the practice of late shading could improve tree water status, and this is suggested as being a key factor in the higher fruit juice content found in this work for the shaded samples. Many factors are associated with the occurrence of granulation in citrus, including climate, field management practices, harvest timing, and storage conditions (Awasthi and Nauriyal, 1973; Burns and Albrigo, 1998; Hwang et al., 1990). In the present study, we examined the effects of using a white shading net on the occurrence of granulation in the preharvest period. We found that the white shading nets significantly reduced the incidence of granulation as
compared with the control samples (Fig. 3). Awasthi and Nauriyal (1973) reported that being grown under shaded conditions, especially for citrus fruits covered with black bags, resulted in a greater severity of granulation. However, our study showed the opposite effects, which suggests that black bags are more endothermic than white nylon netting, thus resulting in a relatively high temperature during blooming and fruit setting, leading to greater granulation in citrus fruits (Ritenour et al., 2004). On the other hand, the development of granulation has also been reported during storage (Gilfillan and Stevenson, 1977), with Ladaniya (2008) indicating that this is due to weight loss. Our results support this contention, showing that the rate of granulation increased along with weight loss during postharvest storage (Figs. 3 and 4). However, whether the causes of granulation in citrus fruits depend on pre- or postharvest factors requires further clarification.
T.-C. Lee et al. / Scientia Horticulturae 188 (2015) 57–65
100
80
63
A. 2009
Control 25 oC White net 25 oC Control 13.5 oC White net 13.5 oC
aA aA
aA
60
aA aB 40
bB
aB
Decay rate (%)
aB 20 aA 0 100
aA aB aB
3rd
59th
31th
Day
87th aA
B. 2010
aA
80 aA aA 60 aB aB
40 aB aB 20 aA
aA aBaB
0
4
8
12
Week Fig. 5. Decay rate of ‘Ponkan’ mandarin fruits grown with a white shading net and the control samples during storage at 13.5 ◦ C and 25 ◦ C in 2009 and 2010z . z Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of storage temperatures.
The results of this study showed that postharvest storage temperatures had an impact on ‘Ponkan’ mandarin fruits. During the postharvest period, weight loss mostly depends on the storage tem´ 2004), and our study confirmed that peratures (Jemriic´ and Paviˇcic, the weight loss is mainly affected by storage temperatures, regardless of whether preharvest shading is used or not. Furthermore, the fruits stored at 13.5 ◦ C show less weight loss than those stored at 25 ◦ C (Fig. 4), which is likely because the higher storage temperature caused the loss of more moisture. This is important, as the more than 5% weight loss of ‘Ponkan’ mandarin fruits stored at 25 ◦ C from week 8th to week 12th could significantly reduce its market values (Grierson et al., 1978). There are several postharvest decay symptoms seen in citrus, such as green mold, blue mold, and sour rot (Eckert and Eaks, 1989). However, there are also many postharvest methods to inhibit the related microorganisms, and thus maintain fruit quality and extend
storage periods, such as the use of fungicides, modified atmosphere packaging (MAP), and hot water brushing (HWB) (Porat et al., 2000, 2004; Smilanick et al., 2006). In the present study, the decay index was 0% before storage because we visually inspected each experimental fruit to ensure that it was free of damage and disease, and then packed them into individual plastic bags. It is recommended that the storage temperature for mandarins to be between 5 ◦ C and 8 ◦ C (Kader and Arpaia, 2002), and chilling injuries can result in greater incidence of decay in kumquat (Fortunella margarita) fruits (Chalutz et al., 1989). Although, previous studies suggested that while plastic bags can reduce mechanical damage and contamination, and maintain the relative humidity around the fruits (Kader et al., 1989), the excessive moisture inside the package may increase the incidence of decay (Porat et al., 2004). However, our data showed that a relatively low storage temperature (e.g., 13.5 ◦ C) lead to better inhibition of
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T.-C. Lee et al. / Scientia Horticulturae 188 (2015) 57–65
Table 2 Effects of shading on juice content, total soluble solids, and titratable acid on ‘Ponkan’ mandarin fruits during storage at 13.5 ◦ C or 25 ◦ C in 2009 and 2010. Treatment
Storage temperature (◦ C)
2009 Control White net 4 weeks Control White net
Juice content (%)z 41.3 ± 4.9by 47.6 ± 3.7a
Total soluble solids (%)z 9.3 ± 0.5a 9.7 ± 0.5a
Titratable acid (%)z 0.6 ± 0.06a 0.58 ± 0.06a
13.5 25 13.5 25
41.0 40.7 44.3 46.8
± ± ± ±
3.7bA 5.5bA 5.7aA 3.0aA
10.1 9.6 10.2 10.3
± ± ± ±
0.5aA 0.3aA 0.4aA 0.7aA
0.56 0.48 0.56 0.53
± ± ± ±
0.08aA 0.07aA 0.11aA 0.11aA
13.5 25 13.5 25
38.3 40.5 42.9 44.4
± ± ± ±
4.2bA 4.9bA 4.5aA 5.2aA
9.9 9.9 10.1 10.1
± ± ± ±
0.8aA 0.4aA 0.6aA 0.5aA
0.38 0.39 0.39 0.36
± ± ± ±
0.08aA 0.07aA 0.07aA 0.03aA
13.5 25 13.5 25
36.1 34.2 40.3 38.6
± ± ± ±
4.1bA 4.8bA 5.2aA 4.1aA
9.4 9.8 9.4 9.1
± ± ± ±
0.5aA 0.8aA 0.7aA 0.9aA
0.33 0.32 0.32 0.29
± ± ± ±
0.07aA 0.05aA 0.08aA 0.08aA
8 weeks Control White net 12 weeks Control White net Source of variance
d.f.
Mean square
Analysis of variance Treatment Temperature Treatment × temperature Error
1 1 1 12
132.25∗ 2.25 6.25 1.92
Treatment
Storage temperature (◦ C)
2010 Control White net 4 weeks Control White net
Juice content (%) 41.45 ± 3.8b 8.89 ± 4.93a
0.0625 0.0225 0.0625 0.0175 Total soluble solids (%) 8.8 ± 0.4a 8.9 ± 0.41a
0.0004 0.0009 0.0002 0.0017 Titratable acid (%) 0.62 ± 0.02a 0.58 ± 0.02a
13.5 25 13.5 25
38.91 38.77 44.01 46.22
± ± ± ±
3.57bA 4.67bA 3.77aA 4.34aA
9.28 9.38 9.35 9.35
± ± ± ±
0.56aA 0.42aA 0.35aA 0.31aA
0.48 0.47 0.43 0.48
± ± ± ±
0.07aA 0.04aA 0.03aA 0.04aA
13.5 25 13.5 25
38.35 36.22 40.22 41.38
± ± ± ±
3.28bA 5.41bA 4.36aA 4.48aA
9.06 8.88 8.89 8.78
± ± ± ±
0.80aA 0.42aA 0.45aA 0.43aA
0.36 0.34 0.31 0.32
± ± ± ±
0.03aA 0.02aA 0.06aA 0.04aA
13.5 25 13.5 25
37.93 31.97 39.63 38.63
± ± ± ±
4.48aA ± 5.28bA 4.01aA 4.19aA
7.98 8.13 8.02 8.32
± ± ± ±
0.52aA 0.34aA 0.58aA 0.45aA
0.32 0.33 0.30 0.31
± ± ± ±
0.01aA 0.03aA 0.03aA 0.02aA
8 weeks Control White net 12 weeks Control White net Source of variance
d.f.
Mean square
Analysis of variance Treatment Temperature Treatment × temperature Error
1 1 1 12
169∗ 9 25 2.25
0.0025 0.0225 0.1225 0.075
0.0022 0.0010 0.0014 0.0026
Values are means ± SE, for n = 4. Means with different lowercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the effect of treatments. Means with different uppercase letters indicate that the significant difference (P < 0.05) is related to comparisons of the influence of the temperatures. * P < 0.01. z
y
postharvest decay, regardless of whether preharvest shading was used or not. 5. Conclusions Shading is an effective method that can be used in the field to reduce heat, direct solar radiation, and create microclimate. Although the effects of shading nets and shading periods vary among crops, preharvest shading has already been adopted for some crops to enhance their productivity and quality. In the present study, we demonstrated that white net shading could be used during the late preharvest period in orchards to reduce the
occurrence of sunscald and granulation of ‘Ponkan’ mandarin fruit without affecting fruit maturity and quality at harvest; however, its postharvest quality and shelf-life may be directly related to storage conditions, such as temperature and humidity. A better understanding of the optimal manipulation of preharvest shading, such as the optimal shading materials, and shading periods, is needed help to ensure the best possible quality at harvest, as well as the best conditions during the postharvest period to maintain high quality of fruit. Therefore, in the future, more research is needed to explore the effects of shading on postharvest quality, especially in relation to the use of colored shade nets and different shading periods.
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References Awasthi, R.P., Nauriyal, J.P., 1973. Effect of age, tree condition, tree aspect, fruit size, rootstock and tree variation on granulation. J. Res. Punjab Agric. Univ. 10, 62–70. Bartholomew, E.T., Sinclair, W.B., Raby, E.C., 1935. Granulation of Valencia orange. Calif. Citrog. 21, 30. Bartholomew, E.T., Sinclair, W.B., Turrell, F.M., 1941. Granulation of Valencia oranges. Univ. Calif. Agric. Exp. Sta. Bull., 647. Basile, B., Romano, R., Giaccone, M., Barlotti, E., Colonna, V., Cirillo, C., Shahak, Y., Forlani, M., 2008. Use of photo-selective nets for hail protection of kiwifruit vines in southern Italy. Acta Hortic. 770, 185–192. Burns, J.K., Albrigo, L.G., 1998. Time of harvest and method of storage affect granulation in grapefruit. HortScience 33, 728–730. Chalutz, E., Lomaniec, E., Waks, J., 1989. Physiological and pathological observations on the post-harvest behaviour of kumquat fruit. Trop. Sci. 29, 199–206. Chien, P.J., Sheu, F., Lin, H.R., 2007. Coating citrus (Murcott tangor) fruit with low molecular weight chitosan increases postharvest quality and shelf life. Food Chem. 100, 1160–1164. Cohen, S., Moreshet, S., LeGuillou, L., Simon, J.G., Cohen, M., 1997. Response of citrus trees to modified radiation regime in semi-arid conditions. J. Exp. Bot. 48, 35–44. Crisosto, C.H., Johnson, R.S., DeJong, T., Day, K.R., 1997. Orchard factors affecting postharvest stone fruit quality. HortScience 32, 820–823. Dussi, M.C., Giardina, G., Sosa, D., González Junyent, R., Zecca, A., Reeb, P., 2005. Shade nets effect on canopy light distribution and quality of fruit and spur leaf on apple cv, Fuji. Span. J. Agric. Res. 3, 253–260. Eckert, J.W., Eaks, I.L., 1989. Postharvest disorders and diseases of citrus fruits. In: Reuther, W., Calavan, E.C., Carman, G.E. (Eds.), The Citrus Industry, vol. 4. University of California Press, Berkeley, USA, pp. 179–260. Ferguson, I.B., Snelgar, W., Bowen, J.H., Woolf, A.B., 1999. Preharvest field heat and postharvest fruit response. Acta Hortic. 485, 149–154. George, A.P., Hieke, S., Rasmussen, T., Ludders, P., 1996. Early shading reduces fruit yield and late shading reduces quality in low-chill peach (Prunus persica (L) Batsch) in subtropical Australia. J. Hortic. Sci. 71, 561–571. Gilfillan, I.M., Stevenson, J.A., 1977. Postharvest development of granulation in South African export oranges. Proc. Intl. Soc. Citricult. 1, 299–303. Goldschmidt, E.E., 1999. Carbohydrate supply as a critical factor for citrus fruit development and productivity. HortScience 34, 1020–1024. Goto, A., Araki, C., 1983. Chemical compositions and internal anatomy of the gelated and granulated juice sacs of Sanbokan (Citrus sulcata Hort Ex Takahashi) fruit. J. Jpn. Soc. Hortic. Sci. 52, 316–324. Grierson, W., Miller, W.M., Wardowski, W.F., 1978. Packingline Machinery for Florida Citrus Packinghouses. University of Florida, Florida, USA, Bulletin 803. Hilgeman, R.H., 1977. Response of citrus trees to water stress in Arizona. Proc. Intl. Soc. Citricult. 1, 70–74. Hwang, Y.S., Huber, D.J., Albrigo, L.G., 1990. Comparison of cell wall components in normal and disordered juice vesicles of grapefruit. J. Am. Soc. Hortic. Sci. 115, 281–287. ´ T., Paviˇcic, ´ N., 2004. Postharvest treatments of Satsuma mandarin (Citrus Jemriic, unshiu Marc.) for the improvement of storage life and quality. Postharvest Biol. Technol. 4, 213–227. Jifon, J.L., Syvertsen, J.P., 2001. Effects of moderate shade on citrus leaf gas exchange, fruit yield, and quality. Proc. Fla. State Hortic. Soc. 114, 177–181. Kader, A.A., Arpaia, M.L., 2002. Postharvest handling systems: subtropical fruits. In: Kader, A.A. (Ed.), Postharvest Technology of Horticultural Crops. University of California, Agriculture and Natural Resources, Oakland, CA, pp. 375–383.
65
Kader, A.A., Zagory, D., Kerbel, E.L., 1989. Modified atmosphere packaging of fruits and vegetables. Crit. Rev. Food Sci. Nutr. 28, 1–30. Klein, B.P., Perry, A.K., 1982. Ascorbic acid and vitamin A activity in selected vegetables from different geographical areas of the United States. J. Food Sci. 47, 941–945. Ladaniya, M.S., 2008. Citrus Fruit Biology, Technology and Evaluation. Elsevier Inc., USA, 18–21, 193–196, 417–444. Marini, R.P., Sowers, D., Marini, M.C., 1991. Peach fruit quality is affected by shade during final swell of fruit growth. J. Am. Soc. Hortic. Sci. 116, 383–389. Marcilla, A., Zarzo, M., Del Río, M.A., 2006. Effect of storage temperature on the flavour of citrus fruit. Span. J. Agric. Res. 4, 336–344. Mataa, M., Tominaga, S., 1998. Effects of shading stage and level on fruit set and development, leaf carbohydrates and photosynthesis in Ponkan (Citrus reticulata Blanco). Jpn. J. Trop. Agric. 42, 103–110. Muleo, R., Masetti, C., Tellini, A., Loreti, F., Morini, S., 1994. Modifications of some characteristics in nectarine fruit induced by light deprival at different times of fruit growth. Adv. Hortic. Sci. 8, 75–79. Murray, X.J., Holcroft, D.M., Cook, N.C., Wand, S.J.E., 2005. Postharvest quality of ‘Laetitia’ and ‘Songold’ (Prunus salicina Lindell) plums as affected by preharvest shading treatments. Postharvest Biol. Technol. 37, 81–92. Nakajima, Y., 1976. Study on dry juice sacs of Hyuganatsu (Citrus tamurana Hort Ex Tanaka) in late stages of fruit development. J. Jpn. Soc. Hortic. Sci. 44, 338–346. Porat, R., Daus, A., Weiss, B., Cohen, L., Fallik, E., Droby, S., 2000. Reduction of postharvest decay in organic citrus fruit by a short hot water brushing treatment. Postharvest Biol. Technol. 18, 151–157. Porat, R., Weiss, B., Cohen, L., Daus, A., Aharoni, N., 2004. Reduction of postharvest rind disorders in citrus fruit by modified atmosphere packaging. Postharvest Biol. Technol. 33, 35–43. Retamales, J.B., Montecino, J.M., Lobos, G.A., Rojas, L.A., 2008. Colored shading nets increase yields and profitability of highbush blueberries. Acta Hortic. 770, 193–197. Ritenour, M.A., Albrigo, L.G., Burns, J.K., Miller, W.M., 2004. Granulation in Florida citrus. Proc. Fla. State. Hortic. Soc. 117, 358–361. Sharma, R.R., Singh, R., Saxena, S.K., 2006. Characteristics of citrus fruits in relation to granulation. Sci. Hortic. 111, 91–96. Smilanick, J.L., Brown, G.E., Eckert, J.W., 2006. Postharvest citrus diseases and their control. In: Wardowski, W.F., Miller, W.M., Hall, D.J., Grierson, W. (Eds.), Fresh Citrus Fruits. , second ed. Florida Science Source, Inc., Longboat Key, FL, USA, pp. 339–396. Stamps, R.H., 2008. Differential effects of colored shade nets on three cut foliage crops. Acta Hortic. 770, 169–176. Stamps, R.H., 2009. Use of colored shade netting in horticulture. HortScience 44, 239–241. Southwick, S.M., Weinbaum, S.A., Muraoka, T.T., Krueger, W.R., Shackel, K.A., Yeager, J.T., 1990. Leaf attributes as indices of fruit quality in prune tree canopies. HortScience 25, 751–754. Syvertsen, J.P., 1984. Light acclimation in citrus leaves. II: CO2 assimilation and light, water, and nitrogen use efficiency. J. Am. Soc. Hortic. Sci. 109, 812–817. Tsai, M.S., Lee, T.C., Chang, P.T., 2013. Comparison of paper bags, calcium carbonate, and shade nets for sunscald protection in ‘Murcott’ tangor fruit. HortTechnology 23, 659–667. Volz, R.K., Ferguson, I.B., Bowen, J.H., Watkins, C.B., 1993. Crop load effects on mineral nutrition, maturity, fruiting and tree growth of ‘Cox’s Orange Pippin’ apple. J. Hortic. Sci. 68, 127–137. Xingjie, T., 1990. Relationship between pectinmethylesterase and polygalacturonase activities and granulation in citrus fruit. In: Proc. Intl. Citrus Symp., Guangzhou, China, pp. 796–798.