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Multiple season-long sprays of ethephon or NAA combined with calcium chloride on Honeycrisp: II. Effect on fruit mineral concentrations and incidence of bitter pit
Scientia Horticulturae 247 (2019) 96–100
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Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti
Multiple season-long sprays of ethephon or NAA combined with calcium chloride on Honeycrisp: II. Effect on fruit mineral concentrations and incidence of bitter pit
T
John A. Cline Department of Plant Agriculture, Ontario Agricultural College, University of Guelph, Simcoe, Ontario, N3Y 4N5, Canada
ARTICLE INFO
ABSTRACT
Keywords: 1-Aminocyclopropane carboxylic acid (ACC) 2-Chloroethylphosphonic acid Naphthaleneacetic acid (NAA) Fruit calcium Tank mix
Honeycrisp apple trees are highly prone to biennial bearing and bitter pit (BP). This 3-y study tested the hypothesis that tank mix sprays of ethephon (ETH), naphthaleneacetic acid (NAA), and 1-aminocyclopropane carboxylic acid (ACC) combined with calcium chloride (CaCl2) can mitigate these production problems. Mature ‘Honeycrisp’ were treated with either three of six applications of 150 mg.L-1 ETH, 5 mg.L-1 NAA or two of five applications of 150 mg.L-1 ACC, all tank-mixed with and without CaCl2 and applied at 10-d intervals starting 21–26 June over three growing seasons. Fruit cortical tissue nutrient concentrations were influenced by applications of CaCl2, ETH, NAA, and ACC. In one year, Ca concentrations were significantly higher in fruit from trees treated with six sprays of ETH or NAA with CaCl2 compared with the untreated control. Compared with untreated trees, fruit Ca concentrations were 115% and 148% higher with three and six applications, respectively. Applications of CaCl2 significantly reduced the incidence and severity of BP post-harvest in two of three years when fruit tissue Ca levels were low. ETH alone also increased the incidence and severity of BP two-fold compared with the control, while early season sprays of NAA reduced BP incidence and severity compared with the untreated control. High and similar levels of BP incidence and severity were observed when six sprays of NAA were applied with or without Ca. Fruit tissue K levels were generally reduced with the addition of CaCl2, and within 1 year, K levels were higher in fruit treated with ACC. Fruit Mg concentrations generally decreased with the addition of Ca or NAA. Six applications of ACC resulted in a 30-fold increase in fruit Mg concentrations compared to the untreated control. Tank mixing CaCl2 with the flower-promoting bio-regulators ETH and NAA proved to effectively reduce BP and increase fruit tissue Ca levels. This approach would offer cost savings when repeat sprays of each are required on a bi-weekly basis.
1. Introduction Producers of ‘Honeycrisp’ face several production challenges, including biennial bearing, susceptibility to low fruit calcium (Ca), and storage disorders. Bitter pit (BP), a physiological disorder associated with low fruit Ca, develops on the tree or in storage (Faust and Shear, 1968; Ferguson and Watkins, 1989; Perring, 1986; Vang-Petersen, 1980). The factors associated with this disorder are not fully known, but several factors are well recognized, including low fruit Ca (Turner et al., 1977), cultivar, fruit weight (Perring and Jackson, 1975), harvest date/ maturity (Prange et al., 2011), crop load (Robinson and Lopez, 2012; Telias et al., 2006; Volz et al., 1993), seed number, water availability, temperature, and mineral status. The association between mineral nutrition and BP incidence appears to be related to the Ca content of the fruit or its various parts (Himilrick and McDuffie; Ferguson and
E-mail address: [email protected]. https://doi.org/10.1016/j.scienta.2018.11.092 Received 17 June 2018; Accepted 30 November 2018 0304-4238/ © 2018 Elsevier B.V. All rights reserved.
Watkins, 1989). Cultivar selection, low crop load, large fruit size, intensive pruning, and excessive potassium (K) and magnesium (Mg) fertilization can increase a plant’s propensity to BP (Himelrick and McDuffie, 1983; Faust, 1989). BP results in significant annual losses wherever ‘Honeycrisp’ is grown. This cultivar, developed by the University of Minnesota and released in 1991 (Luby and Bedford, 1992), is the third most widely planted cultivar by area in Ontario and is being planted at the highest rate of all cultivars in the region (OAG, 2017). ‘Honeycrisp’ is particularly susceptible to BP, in part due to its inherent large fruit size, but also due to genetic reasons not yet fully understood. What is known is that Honeycrisp BP incidence and severity vary by tree age (Bedford, 2001), orchard, rootstock (Kim and Ko, 2004), and crop load (Greene and Weis, 2001). Further, delayed cooling and warmer post-harvest storage conditions favour BP development (DeEll et al., 2016; Li et al.,
Scientia Horticulturae 247 (2019) 96–100
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2012; Mattheis et al., 2017; Watkins et al., 2004). Recent models aiming to predict BP incidence in ‘Honeycrisp’ determined that 65% of the variation was explained by the current season’s extension shoot length and the nitrogen-to-Ca ratio in fruit peel tissue (Baugher et al., 2017). Ca is mobile in the xylem and moves via the transpiration stream with little movement into the fruit. Consequently, Ca accumulates more in leaves than fruit (Cline et al., 1991; Himelrick and McDuffie, 1983) and apple growers must apply foliar Ca on multiple occasions throughout the growing season. Foliar sprays of Ca remain the gold standard for reducing BP, provided that sufficient elemental Ca is applied to fruit during the fruit growth and development period to raise fruit Ca levels above 4–5 mg/100 g (fresh wt.) (Perring and Jackson, 1975; Turner et al., 1977). Efficacy is based on sufficient elemental Ca being absorbed by the fruit, not the formulation of Ca (Bramlage et al., 1985). Calcium chloride (CaCl2) remains the most effective and cheapest form of Ca available to growers (Biggs and Peck, 2015; Crassweller, 2016; Peryea et al., 2007). In Ontario, a minimum of 12 kg ha−1 per season of elemental Ca applied over a minimum of four foliar sprays are recommended to avoid BP on susceptible cultivars such as ‘Northern Spy,’ ‘Red Delicious,’ and ‘Honeycrisp’ (OMAFRA, 2016). Rosenberger et al. (2004) advise a much lower rate: 3.4 kg ha−1 of elemental Ca per season applied over six dilute sprays. This recommendation followed a study in which reductions in BP incidence of up to 90% were obtained with foliar applications of at least 3.25 kg ha−1 (CaCl2) elemental Ca per season (Rosenberger et al., 2014). In Pennsylvania, a range of minimum of 4.5–16 kg ha−1 per season of elemental Ca over 6–8 sprays is recommended to reduce BP (Crasweller, 2016). For the mid-Atlantic USA, rates up to 26 kg ha−1 of elemental Ca per season are recommended to significantly reduce BP incidence in ‘Honeycrisp’ (Biggs and Peck, 2015). The present study was conducted in light of the global importance of BP in ‘Honeycrisp,’ as well as the issues of high BP incidence and biennial bearing associated with this cultivar. The 3-year study aimed to determine the response of ‘Honeycrisp’ to multiple season-long foliar applications of Ca for mitigation of BP tanked-mixed with ethephon (ETH) and naphthaleneacetic acid (NAA) to enhance return bloom. The potential cost savings in tank mixing these sprays, which are typically applied on a bi-weekly basis, are believed to be considerable. This study specifically tested the hypothesis that CaCl2 tank-mixed with ETH or NAA would be efficacious for improving fruit levels of Ca and reducing BP symptoms.
which equated to tree row volume pesticide dilute (Sutton and Unrath, 1988). To minimize treatment interference caused by spray drift, experimental units were separated by at least two guard trees. Treatments were arranged in a randomized complete block design and consisted of two trees per experimental unit. All orchards were managed according to standard practices for Ontario (OMAFRA, 2016).
2. Materials and methods
2.3. Statistical analysis
An experiment was repeated over three growing seasons to investigate the response of ‘Honeycrisp’ apple trees to tank-mixed foliar sprays of CaCl2 for BP control as well as NAA and ETH to enhance return bloom. Experimental details and treatments have been reported previously (Cline, 2018a, Part 1 of this series). Briefly, ‘Honeycrisp’/ M.9 T337 (1.8 x 4.5 m), planted in 2000 and trained to a vertical axe, were used for this experiment. In 2009 and 2013, the following foliar treatments were applied as follows: i) untreated control; ii) three applications of 150 mg L−1 ETH (Ethrel, Rhône Poulenc, Canada); iii) six applications of 150 mg L−1 ETH; iv) three applications of 5 mg L−1 NAA (Amvac, Newport Beach, CA, USA); and v) six applications of 5 mg L−1 NAA. Treatments 2–5 were applied at 10-d intervals starting on 21–26 June and were each tanked mixed with 6 g·L−1 food grade CaCl2 (94% anhydrous CaCl2, Occidental Chemical Corp. Ludding, MI, US), resulting in a total of nine treatments (Table 1). In 2014, 150 mg/L ACC (Valent BioSciences, Libertyville, IL) (without CaCl2) was applied a total of two (27 June, 10 July) and five times, as indicated in Table 1. All sprays included 0.05% (v/v) Regulaid organosilicone surfactant (Kalo Industries, Overland Park, KS) to improve wetting and uptake. Treatments were applied using a commercial air blast sprayer (GB Irrorazione Diserbo, Model Laser P7, Italy) at 1379 kPa, 388 L/ha,
Data were subject to an analysis of variance (ANOVA) using SAS ver. 9.4 (SAS Institute; Cary, NC, USA) with a significance level of 5% (α = 0.05). A mixed analysis model (PROC GLIMMIX) was used with block as a random effect and treatment as a fixed effect. Further details of the statistical methods are reported previously (Cline, 2019, Part I of this series).
2.1. Measurement of fruit nutrient levels In 2013 and 2014, a composite sample of 10 fruit between 81 and 83 mm in diameter was collected from each plot immediately prior to harvest to measure the concentrations of P, K, Mg, Ca, Cu, Zn, Mn, B, and Fe within the fruit flesh. Samples for tissue analyses were prepared by removing four longitudinal slices of skin on opposite sides of each fruit using a vegetable peeler. A mandolin was then used to remove 2–4 mm of subdermal cortical tissue from each of the peeled sections, for a total of four slices per fruit. No skin was included in the sample. A stainless-steel cork borer (15.4 mm Ø) was then used to subsample and remove four discs per fruit. The composite sample of 40 discs, weighing approximately 12–15 g, was weighed and frozen until chemical analysis. The tissue was processed fresh, and mineral percentages were quantified through dry ashing followed by inductively coupled plasma optical emission spectrometry (AOAC 985.01) at a provincially accredited commercial laboratory (Lab Services, Guelph, Ontario, Canada). Values are expressed on a fresh weight basis. 2.2. Bitter pit assessment BP was assessed post-harvest in 2009 and in 2013 after fruit were stored for 60 days at 2–4°C) in regular air storage. Inadequate levels of BPdeveloped in fruit to provide a valid assessment in 20,014. In 2009, a uniform size of ∼30 representative fruits per experimental unit was used to determine BP incidence and severity. In 2013, a 50-fruit sample was graded by minimum diameter into six size categories (< 67, 67 ≤ 70, ≥70 ≤ 73, ≥73 ≤ 76, ≥76 ≤ 79, and ≥79 mm). Individual fruit in each category were then rated for BP severity on a 5-point scale based on the number of pits per tree (0,1–5, 6–10, 11–15, > 16–20). The BP severity index (BPSI) was calculated according to Eq. (1). BPSI =
(bitter pit rating ) (number of fruit in rating ) (total number of fruit per sample ) (number of bitter pit rating categories )
(1)
3. Results and discussion Fruit cortical tissue nutrient concentrations were influenced by applications of ETH, NAA, ACC, and Ca (Tables 1 and 2). In 2013, Ca concentrations were significantly higher in fruit from trees treated with six sprays of ETH with CaCl2 (56% increase) or six sprays of NAA (39% increase) with CaCl2 compared to the untreated control. The contrasts also indicated an overall increase in fruit Ca concentration when CaCl2 was tank-mixed with the ETH and NAA sprays, and when the number of applications of either product was increased from three (115% of the control) to six (148% of the control). Fruit Ca concentration in 2014 was unaffected by the treatments according to the ANOVA; however, the contrasts indicated a significant increase in Ca levels when three versus six sprays were applied. 97
Scientia Horticulturae 247 (2019) 96–100
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Table 1 Effect of Ethrel and NAA with or without Calcium Chloride on fruit mineral content at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, ON, 2013. Treatment
Fruit mineral nutrient content (mg per 100 g fresh weight) Pz
Untreated Control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA y
6.44 6.05 5.48 6.96 6.22 5.98 5.23 7.27 6.51 #####
abc abc bc ab abc abc c a abc
** NS NS NS NS
K
Mg
104.7 102.1 105.3 101.1 96.3 107.2 102.2 103.6 97.1 0.0502
4.69 4.53 4.48 4.29 4.28 4.78 4.23 4.27 4.00 #####
* NS NS NS NS
** NS *** NS NS
Ca ab abc abc abc abc a bc abc c
Mn
1.25 1.25 1.37 1.38 1.49 1.42 1.96 1.47 1.74 < 0.0001
c c c c bc c a bc ab
*** ** *** *** *
0.0376 0.0383 0.0374 0.0362 0.0379 0.0389 0.0370 0.0371 0.0366 0.6363 NS NS NS NS NS
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. z ns, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively.
In 2013 and 2014, none of the treatments resulted in significant differences in phosphorus (P) content compared to the untreated control, although there were significant differences among the other treatments. The contrasts indicated a decrease in P concentration when CaCl2 was included in the spray solutions in 2013, and an increase with applications of ACC in 2014. When applied alone, CaCl2 had no effect on fruit P concentrations in previous studies (e.g. Peryea et al., 2007; Telias et al., 2006). Further research will be required to determine the reasons for the reduction in P observed herein. There were no significant differences in fruit K concentration among the treatments in 2013 (P = 0.055); however, the contrasts indicated an overall reduction in K with the addition of CaCl2. This finding is consistent with other studies indicating the competing nature of K, Ca, and Mg cation (Perring, 1986). In 2014, K concentration was higher in fruit from trees treated with ACC, and levels were further increased when the
number of sprays was increased from three to six. There is a lack of data on the effect of multi-season ACC sprays in apple fruit nutrient levels at harvest. It is unlikely that the higher fruit tissue K levels are a result of a K-based by-product in the ACC spray; indeed, even if such a by-product were present, the small amount of total ACC product applied would not have accounted for this increase. Six sprays of NAA plus CaCl2 reduced fruit Mg levels compared to the untreated control in 2013. The contrasts also indicated an overall decrease in Mg content with the addition of CaCl2 or NAA. The decrease in fruit K levels is consistent with other studies where foliar sprays of CaCl2 have been applied (Peryea et al., 2007), and again can be explained by the completive interaction of Mg and Ca ions. In 2014, six applications of ACC resulted in a 30-fold increase in fruit Mg concentrations compared to the untreated control. This increase was magnified with six versus three applications of ACC, and such an
Table 2 Effect of Ethrel and NAA with or without Calcium Chloride on fruit mineral content at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, ON, 2014. Treatment
Fruit mineral nutrient content (mg per 100 g fresh weight) P
Untreated control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca 3 sprays of ACC 6 sprays of ACC P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of ACC Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA Effect of 3 vs 6 sprays ACC y
5.63 4.98 5.80 5.81 5.31 5.48 6.56 6.10 6.21 6.74 7.22 0.0010 NS NS NS ** NS NS NS
K abc c abc abc bc bc abc abc abc ab a
Mg
81.3 84.0 88.0 87.7 82.9 86.3 87.3 87.4 83.4 107.1 118.2 < 0.0001
b b b b b b b b b a a
NS NS NS *** NS NS *
3.50 3.98 3.94 3.61 3.42 4.06 3.98 3.71 3.38 4.29 4.86 < 0.0001
c bc bc bc c bc bc bc c ab a
NS ** NS *** NS NS **
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. z ns, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively. 98
Ca
Mn
2.06 2.02 2.07 2.11 1.94 2.18 2.26 1.95 2.10 1.99 2.02 0.1709
0.0320 0.0335 0.0354 0.0347 0.0318 0.0346 0.0360 0.0354 0.0323 0.0376 0.0402 0.0016
NS NS NS NS * NS NS
NS NS NS *** NS NS NS
b b ab ab b ab ab ab b ab a
Scientia Horticulturae 247 (2019) 96–100
J.A. Cline
ETH were applied, the addition of CaCl2 reduced both BP incidence and severity. Six sprays of ETH alone increased the incidence and severity of BP by two-fold compared to the untreated control. Based on the contrasts, three early-season sprays of NAA with or without CaCl2 resulted in lower BP incidence or severity than the untreated control treatment, whereas similar or higher levels of BP incidence and severity were observed when six sprays of NAA were applied, with or without CaCl2. In 2013, the BPSI of fruit smaller than 73 mm was unaffected by the treatments according to the ANOVA, whereas the contrasts indicated a significant reduction in BPSI when CaCl2 was added to the ETH and NAA spray solutions (Table 4). For the larger fruit size categories (and the mean of all size categories), there were significant treatment differences in BPSI, although none of the individual treatments were significantly different from the untreated control. Nevertheless, the contrasts again indicated a highly significant overall reduction in BPSI when applications of CaCl2 were tank-mixed with ETH and NAA. Multiple season-long foliar applications of CaCl2 tanked-mixed with ETH and NAA aiming to mitigate BP and enhance return bloom were effective in improving fruit cortical Ca levels and reducing BP incidence and severity. It is unclear why these effects were not observed in 2014; the 2014 findings may be associated with higher and sufficient fruit Ca levels across all treatments, including the untreated control, to cause Ca deficiency. The yearly differences in fruit Ca levels may have been related to environmental conditions in the orchards, although this seems unlikely given that precipitation and heat accumulation during the growing season were not markedly different between the two years (data not shown). Tank mixing CaCl2 with the flower-promoting bio-regulators ETH and NAA used in this study proved effective at reducing BP and increasing fruit tissue Ca levels. This combined treatment would offer substantial economic savings in situations where repeat sprays of each are required on a bi-weekly basis, as the products could be combined and the number of applications reduced to one pass each time. Cost savings would increase with the number of repeat applications, although three to six sprays are typically adequate, depending on the cultivar and level of treatment required. Furthermore, no leaf or fruit phytotoxicity was observed in this study, and results suggest that tankmixed CaCl2 and ETH and NAA are compatible.
Table 3 Effect of Ethrel and NAA with or without Calcium Chloride on the severity of bitter pit at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, Ontario, 2009. Percent bitter pit incidence (%) Unsprayed Control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA
16.9 2.0 3.6 3.6 2.8 34.0 5.1 18.5 10.4 0.0017
Bitter pit severity index (0-100)x ab b b b b a b ab ab
3.8 0.5 0.8 0.8 0.6 7.5 1.1 4.1 2.1 0.0018
* NS NS **
* NS NS **
*
*
ab b b b b a b ab ab
y
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. x Bitter pit severity index. z NS, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively.
increase could markedly influence post-harvest fruit quality and the incidence of BP (Bramlage et al., 1979). However, the lack of BP observed in the 2014 sample prevented us from evaluating this effect in the present study. Fruit Mn concentrations were unaffected by the treatments in 2013. In 2014, Mn concentrations were higher in fruit from trees treated with six sprays of ACC compared to the untreated control, and the contrasts similarly indicated an overall increase in Mn concentration with applications of ACC. Applications of CaCl2 significantly reduced the incidence and severity of BP post-harvest (Tables 3 and 4). In 2009, when six sprays of
Table 4 Effect of Ethrel and NAA with or without Calcium Chloride on the severity of bitter pit at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, Ontario, 2013. Treatment
Untreated Control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA y
Bitter pit severity index (0-100)x
Percent bitter pit incidence (all size categories)
< 67 mm
67-70 mm
70-73 mm
73-76 mm
76-79 mm
> 79 mm
Mean of all categories
4.2 7.7 4.7 14.2 2.0 22.1 0.0 16.0 2.3 0.0523
2.9 10.4 0.0 6.7 16.7 13.9 13.3 9.0 6.3 0.9081
22.5 6.9 0.0 18.4 5.0 21.6 0.0 15.0 11.6 0.2302
20.3 14.1 6.9 11.4 10.4 15.2 2.6 31.5 5.3 0.0017
12.0 28.5 5.7 6.8 4.5 20.9 0.0 10.0 5.4 0.0128
17.9 16.0 10.0 20.9 7.9 16.5 1.8 25.6 2.8 0.0003
17.1 15.1 6.4 16.0 6.9 17.7 2.1 22.5 4.6 0.0008
*** * NS NS
** NS NS NS
NS NS NS NS
* NS NS NS
*** * NS NS
** NS NS NS
*** NS NS NS
*** NS NS NS
NS
NS
NS
NS
NS
NS
NS
NS
26.3 21.5 9.4 28.8 12.5 24.1 3.2 35.5 8.6 0.0005
abc abc bc ab abc abc c a bc
ab ab b ab b ab b a b
ab a ab ab ab ab b ab ab
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. x Bitter pit severity index (BPSI). z NS, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively.
99
abc abc abc ab bc abc c a c
ab ab b ab ab ab b a b
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Acknowledgements
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Multiple season-long sprays of ethephon or NAA combined with calcium chloride on Honeycrisp: II. Effect on fruit mineral concentrations and incidence of bitter pit
T
John A. Cline Department of Plant Agriculture, Ontario Agricultural College, University of Guelph, Simcoe, Ontario, N3Y 4N5, Canada
ARTICLE INFO
ABSTRACT
Keywords: 1-Aminocyclopropane carboxylic acid (ACC) 2-Chloroethylphosphonic acid Naphthaleneacetic acid (NAA) Fruit calcium Tank mix
Honeycrisp apple trees are highly prone to biennial bearing and bitter pit (BP). This 3-y study tested the hypothesis that tank mix sprays of ethephon (ETH), naphthaleneacetic acid (NAA), and 1-aminocyclopropane carboxylic acid (ACC) combined with calcium chloride (CaCl2) can mitigate these production problems. Mature ‘Honeycrisp’ were treated with either three of six applications of 150 mg.L-1 ETH, 5 mg.L-1 NAA or two of five applications of 150 mg.L-1 ACC, all tank-mixed with and without CaCl2 and applied at 10-d intervals starting 21–26 June over three growing seasons. Fruit cortical tissue nutrient concentrations were influenced by applications of CaCl2, ETH, NAA, and ACC. In one year, Ca concentrations were significantly higher in fruit from trees treated with six sprays of ETH or NAA with CaCl2 compared with the untreated control. Compared with untreated trees, fruit Ca concentrations were 115% and 148% higher with three and six applications, respectively. Applications of CaCl2 significantly reduced the incidence and severity of BP post-harvest in two of three years when fruit tissue Ca levels were low. ETH alone also increased the incidence and severity of BP two-fold compared with the control, while early season sprays of NAA reduced BP incidence and severity compared with the untreated control. High and similar levels of BP incidence and severity were observed when six sprays of NAA were applied with or without Ca. Fruit tissue K levels were generally reduced with the addition of CaCl2, and within 1 year, K levels were higher in fruit treated with ACC. Fruit Mg concentrations generally decreased with the addition of Ca or NAA. Six applications of ACC resulted in a 30-fold increase in fruit Mg concentrations compared to the untreated control. Tank mixing CaCl2 with the flower-promoting bio-regulators ETH and NAA proved to effectively reduce BP and increase fruit tissue Ca levels. This approach would offer cost savings when repeat sprays of each are required on a bi-weekly basis.
1. Introduction Producers of ‘Honeycrisp’ face several production challenges, including biennial bearing, susceptibility to low fruit calcium (Ca), and storage disorders. Bitter pit (BP), a physiological disorder associated with low fruit Ca, develops on the tree or in storage (Faust and Shear, 1968; Ferguson and Watkins, 1989; Perring, 1986; Vang-Petersen, 1980). The factors associated with this disorder are not fully known, but several factors are well recognized, including low fruit Ca (Turner et al., 1977), cultivar, fruit weight (Perring and Jackson, 1975), harvest date/ maturity (Prange et al., 2011), crop load (Robinson and Lopez, 2012; Telias et al., 2006; Volz et al., 1993), seed number, water availability, temperature, and mineral status. The association between mineral nutrition and BP incidence appears to be related to the Ca content of the fruit or its various parts (Himilrick and McDuffie; Ferguson and
E-mail address: [email protected]. https://doi.org/10.1016/j.scienta.2018.11.092 Received 17 June 2018; Accepted 30 November 2018 0304-4238/ © 2018 Elsevier B.V. All rights reserved.
Watkins, 1989). Cultivar selection, low crop load, large fruit size, intensive pruning, and excessive potassium (K) and magnesium (Mg) fertilization can increase a plant’s propensity to BP (Himelrick and McDuffie, 1983; Faust, 1989). BP results in significant annual losses wherever ‘Honeycrisp’ is grown. This cultivar, developed by the University of Minnesota and released in 1991 (Luby and Bedford, 1992), is the third most widely planted cultivar by area in Ontario and is being planted at the highest rate of all cultivars in the region (OAG, 2017). ‘Honeycrisp’ is particularly susceptible to BP, in part due to its inherent large fruit size, but also due to genetic reasons not yet fully understood. What is known is that Honeycrisp BP incidence and severity vary by tree age (Bedford, 2001), orchard, rootstock (Kim and Ko, 2004), and crop load (Greene and Weis, 2001). Further, delayed cooling and warmer post-harvest storage conditions favour BP development (DeEll et al., 2016; Li et al.,
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2012; Mattheis et al., 2017; Watkins et al., 2004). Recent models aiming to predict BP incidence in ‘Honeycrisp’ determined that 65% of the variation was explained by the current season’s extension shoot length and the nitrogen-to-Ca ratio in fruit peel tissue (Baugher et al., 2017). Ca is mobile in the xylem and moves via the transpiration stream with little movement into the fruit. Consequently, Ca accumulates more in leaves than fruit (Cline et al., 1991; Himelrick and McDuffie, 1983) and apple growers must apply foliar Ca on multiple occasions throughout the growing season. Foliar sprays of Ca remain the gold standard for reducing BP, provided that sufficient elemental Ca is applied to fruit during the fruit growth and development period to raise fruit Ca levels above 4–5 mg/100 g (fresh wt.) (Perring and Jackson, 1975; Turner et al., 1977). Efficacy is based on sufficient elemental Ca being absorbed by the fruit, not the formulation of Ca (Bramlage et al., 1985). Calcium chloride (CaCl2) remains the most effective and cheapest form of Ca available to growers (Biggs and Peck, 2015; Crassweller, 2016; Peryea et al., 2007). In Ontario, a minimum of 12 kg ha−1 per season of elemental Ca applied over a minimum of four foliar sprays are recommended to avoid BP on susceptible cultivars such as ‘Northern Spy,’ ‘Red Delicious,’ and ‘Honeycrisp’ (OMAFRA, 2016). Rosenberger et al. (2004) advise a much lower rate: 3.4 kg ha−1 of elemental Ca per season applied over six dilute sprays. This recommendation followed a study in which reductions in BP incidence of up to 90% were obtained with foliar applications of at least 3.25 kg ha−1 (CaCl2) elemental Ca per season (Rosenberger et al., 2014). In Pennsylvania, a range of minimum of 4.5–16 kg ha−1 per season of elemental Ca over 6–8 sprays is recommended to reduce BP (Crasweller, 2016). For the mid-Atlantic USA, rates up to 26 kg ha−1 of elemental Ca per season are recommended to significantly reduce BP incidence in ‘Honeycrisp’ (Biggs and Peck, 2015). The present study was conducted in light of the global importance of BP in ‘Honeycrisp,’ as well as the issues of high BP incidence and biennial bearing associated with this cultivar. The 3-year study aimed to determine the response of ‘Honeycrisp’ to multiple season-long foliar applications of Ca for mitigation of BP tanked-mixed with ethephon (ETH) and naphthaleneacetic acid (NAA) to enhance return bloom. The potential cost savings in tank mixing these sprays, which are typically applied on a bi-weekly basis, are believed to be considerable. This study specifically tested the hypothesis that CaCl2 tank-mixed with ETH or NAA would be efficacious for improving fruit levels of Ca and reducing BP symptoms.
which equated to tree row volume pesticide dilute (Sutton and Unrath, 1988). To minimize treatment interference caused by spray drift, experimental units were separated by at least two guard trees. Treatments were arranged in a randomized complete block design and consisted of two trees per experimental unit. All orchards were managed according to standard practices for Ontario (OMAFRA, 2016).
2. Materials and methods
2.3. Statistical analysis
An experiment was repeated over three growing seasons to investigate the response of ‘Honeycrisp’ apple trees to tank-mixed foliar sprays of CaCl2 for BP control as well as NAA and ETH to enhance return bloom. Experimental details and treatments have been reported previously (Cline, 2018a, Part 1 of this series). Briefly, ‘Honeycrisp’/ M.9 T337 (1.8 x 4.5 m), planted in 2000 and trained to a vertical axe, were used for this experiment. In 2009 and 2013, the following foliar treatments were applied as follows: i) untreated control; ii) three applications of 150 mg L−1 ETH (Ethrel, Rhône Poulenc, Canada); iii) six applications of 150 mg L−1 ETH; iv) three applications of 5 mg L−1 NAA (Amvac, Newport Beach, CA, USA); and v) six applications of 5 mg L−1 NAA. Treatments 2–5 were applied at 10-d intervals starting on 21–26 June and were each tanked mixed with 6 g·L−1 food grade CaCl2 (94% anhydrous CaCl2, Occidental Chemical Corp. Ludding, MI, US), resulting in a total of nine treatments (Table 1). In 2014, 150 mg/L ACC (Valent BioSciences, Libertyville, IL) (without CaCl2) was applied a total of two (27 June, 10 July) and five times, as indicated in Table 1. All sprays included 0.05% (v/v) Regulaid organosilicone surfactant (Kalo Industries, Overland Park, KS) to improve wetting and uptake. Treatments were applied using a commercial air blast sprayer (GB Irrorazione Diserbo, Model Laser P7, Italy) at 1379 kPa, 388 L/ha,
Data were subject to an analysis of variance (ANOVA) using SAS ver. 9.4 (SAS Institute; Cary, NC, USA) with a significance level of 5% (α = 0.05). A mixed analysis model (PROC GLIMMIX) was used with block as a random effect and treatment as a fixed effect. Further details of the statistical methods are reported previously (Cline, 2019, Part I of this series).
2.1. Measurement of fruit nutrient levels In 2013 and 2014, a composite sample of 10 fruit between 81 and 83 mm in diameter was collected from each plot immediately prior to harvest to measure the concentrations of P, K, Mg, Ca, Cu, Zn, Mn, B, and Fe within the fruit flesh. Samples for tissue analyses were prepared by removing four longitudinal slices of skin on opposite sides of each fruit using a vegetable peeler. A mandolin was then used to remove 2–4 mm of subdermal cortical tissue from each of the peeled sections, for a total of four slices per fruit. No skin was included in the sample. A stainless-steel cork borer (15.4 mm Ø) was then used to subsample and remove four discs per fruit. The composite sample of 40 discs, weighing approximately 12–15 g, was weighed and frozen until chemical analysis. The tissue was processed fresh, and mineral percentages were quantified through dry ashing followed by inductively coupled plasma optical emission spectrometry (AOAC 985.01) at a provincially accredited commercial laboratory (Lab Services, Guelph, Ontario, Canada). Values are expressed on a fresh weight basis. 2.2. Bitter pit assessment BP was assessed post-harvest in 2009 and in 2013 after fruit were stored for 60 days at 2–4°C) in regular air storage. Inadequate levels of BPdeveloped in fruit to provide a valid assessment in 20,014. In 2009, a uniform size of ∼30 representative fruits per experimental unit was used to determine BP incidence and severity. In 2013, a 50-fruit sample was graded by minimum diameter into six size categories (< 67, 67 ≤ 70, ≥70 ≤ 73, ≥73 ≤ 76, ≥76 ≤ 79, and ≥79 mm). Individual fruit in each category were then rated for BP severity on a 5-point scale based on the number of pits per tree (0,1–5, 6–10, 11–15, > 16–20). The BP severity index (BPSI) was calculated according to Eq. (1). BPSI =
(bitter pit rating ) (number of fruit in rating ) (total number of fruit per sample ) (number of bitter pit rating categories )
(1)
3. Results and discussion Fruit cortical tissue nutrient concentrations were influenced by applications of ETH, NAA, ACC, and Ca (Tables 1 and 2). In 2013, Ca concentrations were significantly higher in fruit from trees treated with six sprays of ETH with CaCl2 (56% increase) or six sprays of NAA (39% increase) with CaCl2 compared to the untreated control. The contrasts also indicated an overall increase in fruit Ca concentration when CaCl2 was tank-mixed with the ETH and NAA sprays, and when the number of applications of either product was increased from three (115% of the control) to six (148% of the control). Fruit Ca concentration in 2014 was unaffected by the treatments according to the ANOVA; however, the contrasts indicated a significant increase in Ca levels when three versus six sprays were applied. 97
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Table 1 Effect of Ethrel and NAA with or without Calcium Chloride on fruit mineral content at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, ON, 2013. Treatment
Fruit mineral nutrient content (mg per 100 g fresh weight) Pz
Untreated Control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA y
6.44 6.05 5.48 6.96 6.22 5.98 5.23 7.27 6.51 #####
abc abc bc ab abc abc c a abc
** NS NS NS NS
K
Mg
104.7 102.1 105.3 101.1 96.3 107.2 102.2 103.6 97.1 0.0502
4.69 4.53 4.48 4.29 4.28 4.78 4.23 4.27 4.00 #####
* NS NS NS NS
** NS *** NS NS
Ca ab abc abc abc abc a bc abc c
Mn
1.25 1.25 1.37 1.38 1.49 1.42 1.96 1.47 1.74 < 0.0001
c c c c bc c a bc ab
*** ** *** *** *
0.0376 0.0383 0.0374 0.0362 0.0379 0.0389 0.0370 0.0371 0.0366 0.6363 NS NS NS NS NS
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. z ns, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively.
In 2013 and 2014, none of the treatments resulted in significant differences in phosphorus (P) content compared to the untreated control, although there were significant differences among the other treatments. The contrasts indicated a decrease in P concentration when CaCl2 was included in the spray solutions in 2013, and an increase with applications of ACC in 2014. When applied alone, CaCl2 had no effect on fruit P concentrations in previous studies (e.g. Peryea et al., 2007; Telias et al., 2006). Further research will be required to determine the reasons for the reduction in P observed herein. There were no significant differences in fruit K concentration among the treatments in 2013 (P = 0.055); however, the contrasts indicated an overall reduction in K with the addition of CaCl2. This finding is consistent with other studies indicating the competing nature of K, Ca, and Mg cation (Perring, 1986). In 2014, K concentration was higher in fruit from trees treated with ACC, and levels were further increased when the
number of sprays was increased from three to six. There is a lack of data on the effect of multi-season ACC sprays in apple fruit nutrient levels at harvest. It is unlikely that the higher fruit tissue K levels are a result of a K-based by-product in the ACC spray; indeed, even if such a by-product were present, the small amount of total ACC product applied would not have accounted for this increase. Six sprays of NAA plus CaCl2 reduced fruit Mg levels compared to the untreated control in 2013. The contrasts also indicated an overall decrease in Mg content with the addition of CaCl2 or NAA. The decrease in fruit K levels is consistent with other studies where foliar sprays of CaCl2 have been applied (Peryea et al., 2007), and again can be explained by the completive interaction of Mg and Ca ions. In 2014, six applications of ACC resulted in a 30-fold increase in fruit Mg concentrations compared to the untreated control. This increase was magnified with six versus three applications of ACC, and such an
Table 2 Effect of Ethrel and NAA with or without Calcium Chloride on fruit mineral content at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, ON, 2014. Treatment
Fruit mineral nutrient content (mg per 100 g fresh weight) P
Untreated control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca 3 sprays of ACC 6 sprays of ACC P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of ACC Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA Effect of 3 vs 6 sprays ACC y
5.63 4.98 5.80 5.81 5.31 5.48 6.56 6.10 6.21 6.74 7.22 0.0010 NS NS NS ** NS NS NS
K abc c abc abc bc bc abc abc abc ab a
Mg
81.3 84.0 88.0 87.7 82.9 86.3 87.3 87.4 83.4 107.1 118.2 < 0.0001
b b b b b b b b b a a
NS NS NS *** NS NS *
3.50 3.98 3.94 3.61 3.42 4.06 3.98 3.71 3.38 4.29 4.86 < 0.0001
c bc bc bc c bc bc bc c ab a
NS ** NS *** NS NS **
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. z ns, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively. 98
Ca
Mn
2.06 2.02 2.07 2.11 1.94 2.18 2.26 1.95 2.10 1.99 2.02 0.1709
0.0320 0.0335 0.0354 0.0347 0.0318 0.0346 0.0360 0.0354 0.0323 0.0376 0.0402 0.0016
NS NS NS NS * NS NS
NS NS NS *** NS NS NS
b b ab ab b ab ab ab b ab a
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ETH were applied, the addition of CaCl2 reduced both BP incidence and severity. Six sprays of ETH alone increased the incidence and severity of BP by two-fold compared to the untreated control. Based on the contrasts, three early-season sprays of NAA with or without CaCl2 resulted in lower BP incidence or severity than the untreated control treatment, whereas similar or higher levels of BP incidence and severity were observed when six sprays of NAA were applied, with or without CaCl2. In 2013, the BPSI of fruit smaller than 73 mm was unaffected by the treatments according to the ANOVA, whereas the contrasts indicated a significant reduction in BPSI when CaCl2 was added to the ETH and NAA spray solutions (Table 4). For the larger fruit size categories (and the mean of all size categories), there were significant treatment differences in BPSI, although none of the individual treatments were significantly different from the untreated control. Nevertheless, the contrasts again indicated a highly significant overall reduction in BPSI when applications of CaCl2 were tank-mixed with ETH and NAA. Multiple season-long foliar applications of CaCl2 tanked-mixed with ETH and NAA aiming to mitigate BP and enhance return bloom were effective in improving fruit cortical Ca levels and reducing BP incidence and severity. It is unclear why these effects were not observed in 2014; the 2014 findings may be associated with higher and sufficient fruit Ca levels across all treatments, including the untreated control, to cause Ca deficiency. The yearly differences in fruit Ca levels may have been related to environmental conditions in the orchards, although this seems unlikely given that precipitation and heat accumulation during the growing season were not markedly different between the two years (data not shown). Tank mixing CaCl2 with the flower-promoting bio-regulators ETH and NAA used in this study proved effective at reducing BP and increasing fruit tissue Ca levels. This combined treatment would offer substantial economic savings in situations where repeat sprays of each are required on a bi-weekly basis, as the products could be combined and the number of applications reduced to one pass each time. Cost savings would increase with the number of repeat applications, although three to six sprays are typically adequate, depending on the cultivar and level of treatment required. Furthermore, no leaf or fruit phytotoxicity was observed in this study, and results suggest that tankmixed CaCl2 and ETH and NAA are compatible.
Table 3 Effect of Ethrel and NAA with or without Calcium Chloride on the severity of bitter pit at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, Ontario, 2009. Percent bitter pit incidence (%) Unsprayed Control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA
16.9 2.0 3.6 3.6 2.8 34.0 5.1 18.5 10.4 0.0017
Bitter pit severity index (0-100)x ab b b b b a b ab ab
3.8 0.5 0.8 0.8 0.6 7.5 1.1 4.1 2.1 0.0018
* NS NS **
* NS NS **
*
*
ab b b b b a b ab ab
y
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. x Bitter pit severity index. z NS, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively.
increase could markedly influence post-harvest fruit quality and the incidence of BP (Bramlage et al., 1979). However, the lack of BP observed in the 2014 sample prevented us from evaluating this effect in the present study. Fruit Mn concentrations were unaffected by the treatments in 2013. In 2014, Mn concentrations were higher in fruit from trees treated with six sprays of ACC compared to the untreated control, and the contrasts similarly indicated an overall increase in Mn concentration with applications of ACC. Applications of CaCl2 significantly reduced the incidence and severity of BP post-harvest (Tables 3 and 4). In 2009, when six sprays of
Table 4 Effect of Ethrel and NAA with or without Calcium Chloride on the severity of bitter pit at harvest of 'Honeycrisp' apples. University of Guelph, Simcoe Research Station, Ontario, 2013. Treatment
Untreated Control 3 sprays of Ethrel 3 sprays of Ethrel + Ca 3 sprays of NAA 3 sprays of NAA + Ca 6 sprays of Ethrel 6 sprays of Ethrel + Ca 6 sprays of NAA 6 sprays of NAA + Ca P value Contrastsz Effect of Ca Effect of Ethrel Effect of NAA Effect of 3 vs 6 sprays Ethrel Effect of 3 vs 6 sprays NAA y
Bitter pit severity index (0-100)x
Percent bitter pit incidence (all size categories)
< 67 mm
67-70 mm
70-73 mm
73-76 mm
76-79 mm
> 79 mm
Mean of all categories
4.2 7.7 4.7 14.2 2.0 22.1 0.0 16.0 2.3 0.0523
2.9 10.4 0.0 6.7 16.7 13.9 13.3 9.0 6.3 0.9081
22.5 6.9 0.0 18.4 5.0 21.6 0.0 15.0 11.6 0.2302
20.3 14.1 6.9 11.4 10.4 15.2 2.6 31.5 5.3 0.0017
12.0 28.5 5.7 6.8 4.5 20.9 0.0 10.0 5.4 0.0128
17.9 16.0 10.0 20.9 7.9 16.5 1.8 25.6 2.8 0.0003
17.1 15.1 6.4 16.0 6.9 17.7 2.1 22.5 4.6 0.0008
*** * NS NS
** NS NS NS
NS NS NS NS
* NS NS NS
*** * NS NS
** NS NS NS
*** NS NS NS
*** NS NS NS
NS
NS
NS
NS
NS
NS
NS
NS
26.3 21.5 9.4 28.8 12.5 24.1 3.2 35.5 8.6 0.0005
abc abc bc ab abc abc c a bc
ab ab b ab b ab b a b
ab a ab ab ab ab b ab ab
Mean values followed by the same letter are not significantly different according to Tukey's HSD test at P = 0.05. x Bitter pit severity index (BPSI). z NS, *, **, ***, indicates not significant, and significant differences at P = 0.05, P = 0.01, and P = 0.001 respectively.
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abc abc abc ab bc abc c a c
ab ab b ab ab ab b a b
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Acknowledgements
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