Canadian Journal of Plant Science
Response of Bosc and Cold Snap™ pears to thinning with NAA, 6-BA, ACC and S-ABA
Journal: Canadian Journal of Plant Science ManuscriptFor ID CJPS-2017-0258.R2 Review Only Manuscript Type: Article
Date Submitted by the Author: 31-Oct-2017
Complete List of Authors: Cline, John; University of Guelph Ontario Agricultural College, Plant Agriculture Carter, Kathryn; Ontario Ministry of Agriculture, Food and Rural Affairs Gunter, Amanda; University of Guelph, Plant Agriculture Bakker, Catherine; University of Guelph, Plant Agriculture Green, Amanda; Ontario Ministry of Agriculture Food and Rural Affairs
Keywords: Pyrus, chemical thinning, crop load management, plant bioregulators
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Response of Bosc and Cold Snap™ pears to thinning with NAA, 6-BA, ACC and S-ABA.
J.A. Cline1*, K. Carter2 A. Gunter3, C. Bakker3, and A.C. Green4
1 Associate Professor, Tree Fruit Physiology, Department of Plant Agriculture, Ontario Agricultural College, University of Guelph, 1283 Blueline Rd, Simcoe, ON N3Y 4N5 Email: [email protected] 2Tender Fruit and Grape Production Specialist, Ontario Ministry of Agriculture, Food and Rural Affairs, 4890 Victoria Ave N, Vineland Station, ON, L0R 2E0 3 Research Technician, Physiology, Department of Plant Agriculture, Ontario Agricultural College, University of Guelph, 1283 Blueline Rd, Simcoe, ON N3Y 4N5 4Tree Fruit Specialist, For Ontario Review Ministry of Agriculture, Only Food and Rural Affairs, 1283 Blueline Rd, Simcoe, ON N3Y 4N5
* Corresponding author Email:[email protected]
ABSTRACT Adjusting the crop load of European pears [Pyrus communis L.] by hand thinning is currently required to ensure marketable size of most cultivars grown in Ontario. The benefits of chemical thinning pears and their effect on fruit quality and fresh market returns was investigated in a three year study where a series of foliar chemical thinning sprays was applied during the 10 mm fruitlet stage to Bosc and Cold Snap™ pear trees growing in commercial orchards in the Niagara Peninsula, Ontario. Treatments included an untreated and hand thinned control, and two concentrations each of 6 benzyladenine (6 BA; 75 mg L 1 and 150 mg L 1), naphthalene acetic acid (10 mg L 1 and 20 mg L 1), 1 aminocyclopropane carboxylic acid (150 mg L 1 and 300 mg L 1) and s abscisic acid (s ABA; 150 mg L 1 and 300 mg L 1). Overall, all thinning products reduced crop load at least once in the three year study, although this varied by year and cultivar. Higher concentrations were more effective than lower concentrations. Napthalene aceditic acid (both rates), 150 mg L 1 6 BA and 300 mg L 1 s ABA were most consistent. Since the crop load of control trees was not heavy, minimal hand thinning was required and all thinning treatments reduced crop value compared with the untreated trees. There were minimal effects on starch hydrolysis, soluble solids, fruit firmness and skin colour at harvest.
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Abbreviations: 1 aminocyclopropane carboxylic acid (ACC), 6 benzyladenine (6 BA), days after full bloom (DAFB), naphthalene acetic acid (NAA), s abscisic acid (s ABA), trunk cross sectional area (TCSA)
Keywords: Pyrus, chemical thinning, crop load management, plant bioregulators
INTRODUCTION Consumption of fruit, including pears, has been driven by trends toward healthier eating, improved availability ofFor a greater Review variety of fruit, Onlyand innovation by the fruit processing sector. In Canada, nearly all pears are consumed fresh, with a per capita consumption of approximately 2.2 kg/person annually (Statistics Canada 2015). While the demand for fresh pears has been relatively stable (Statistics Canada 2015), with increasing demand for local products, there is potential to expand the production of pears in Ontario, a sector which has seen a long term declining trend due to decreasing profitability and the closing of the primary processing plant in 2008 (OMAFRA 2016). Currently, about 90% of domestic fresh pear consumption comes from imports (Statistics Canada 2016), and it is estimated that a 10% replacement of imports would result in a 3 fold increase in production area in Ontario from a current 250 ha (OMAFRA 2016). Bartlett and Bosc represent 95% of current pear production by area, however, these cultivars are prone to fireblight (E. Amylovora) and as a result growers are hesitant to plant them. There is interest in the recent introduction, AC Harovin Sundown (Cold Snap™) (Shaw, 2017), which is both winter hardy and less susceptible to fire blight (Hunter et al. 2009).
Expanding access to new marketing opportunities requires fruit that can compete with imports, thereby meeting high quality (firmness, soluble solids, acidity levels), fruit size, volume, availability, and food safety criteria. To compete with current imports and expand local pear markets, growers will need to produce target size fruit. Achieving large, high quality fruit with optimum yield often requires substantial fruit thinning in years when fruit set is heavy. Many studies on apples have shown that chemical thinning can improve fruit size and reduce biennial bearing. Several products, including
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naphthalene acetic acid (NAA), ethephon and 6 benzyladenine (6 BA) (applied post bloom) and ammonium thiosulfate and lime sulphur (applied at bloom), have been used to thin pears; the most common post bloom thinner is NAA followed by 6 BA. NAA has been used on other cultivars (McArtney and Well 1995, Meland and Gjerde 1996, Vilardell et al. 2005, Asin et al, 2009) with varying degrees of success. Benzyl adenine has also been used to thin several pear varieties with quite consistent results when applied between 100 and 200 mg L 1 (Stern and Flaishman 2003, Vilardell et al. 2005, Maas and Steeg 2010, Dussi and Sugar 2011, Bound 2015)
Very little research hasFor been conductedReview on the Onlyuse of two new potential thinners, 1 aminocyclopropane carboxylic acid (ACC) and s abscisic acid (s ABA), which are being investigated on apples (Greene et al. 2011; Greene 2012; McArtney and Obermiller 2012; Einhorn and Arrington 2017), for use on pears.
The objective of this research was to determine the effects of foliar applied NAA, 6 BA, 1 ACC and s ABA on fruit set, crop load, fruit size, yield and quality of Cold Snap™ and Bosc pear cultivars. Specific objectives were to evaluate the efficacy of two different concentrations of each chemical thinner applied at ~ 10–12 mm fruit diameter and to determine the economic impact on final crop value after thinning in comparison to untreated and hand thinned control trees.
MATERIALS AND METHODS
Experiment One: Cold Snap™ Cold Snap™ pear trees (planted in 2010 and formerly named Harovin Sundown), grafted on OHFx87 rootstocks and located at a commercial orchard near St. David’s, Ontario (Lat. 43.177582oN, Long. –79.090595oW) were used for this study. Trees were spaced at 0.91 m within and 3.65 m between rows (3011 trees/ha), trained to a vertical axis 3 wire spindle training system, and managed according to standard practices for Ontario (Anonymous, 2014). Treatments were applied using a commercial air blast axial fan sprayer (GB Irrorazione Diserbo, Model Laser P7, Italy) to single tree plots at 1379
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kPa, 750 L/ha, calibrated to deliver approximately 2 L per tree which approximated tree row volume dilute (Sutton and Unrath 1988). To minimize treatment interference caused by spray drift, experimental units were separated by at least one guard tree. The ten treatments were applied to trees in a randomized complete block design with six replications. The same trees were used in 2014, 2015 and 2016. Full bloom occurred 18 May, 8 May, and 6 May in 2014, 2015, and 2016, respectively. Experimental units received one of the following ten treatments: i) untreated control; ii) hand thinned control after ‘June’ drop; iii) 75 mg L 1 of 6 BA (Cilis Plus, Fine Americas Inc., Walnut Creek, CA); iv) 150 mg L 1 of 6 BA; v) 10 mg L 1 of NAA (Fruitone L, Amvac, Los Angeles, CA); vi) 20 mg L 1 of NAA;For vii) 150 Review mg L 1 of s ABA Only (Protone); viii) 300 mg L 1 of s ABA (Protone, Valent BioSciences Corp. Libertyville, IL); ix) 150 mg L 1 of ACC (Valent BioSciences Corp., Libertyville, IL); and x) 300 mg L 1 of ACC. All treatments were applied on 29 May 2014, 23 May 2015 and 26 May 2016 at ~10–12 mm fruitlet diameter. After natural fruit drop, the hand thinned control treatments were hand thinned to commercial levels of 1 2 fruit per flower cluster and spaced approximately 15 cm apart. All treatments included 0.05% Regulaid® non ionic spray adjuvant (2 butoxyethanol, poloxalene, monopropylene glycol, KALO, Inc., Overland Park, USA). Fruit were harvested on 26 September 2014, 25 September 2015 and 27 September 2016.
Experiment Two: Bosc Bosc pear trees (planted in 2010), grafted on OHFx97 rootstocks located at a commercial orchard near Virgil, Ontario (Lat. 43.208771oN, Long. –79.160627oW) were used for this study. Trees were spaced at 0.91 m within and 3.65 m between rows (3011 trees/ha), trained to a vertical axis 3 wire spindle training system, and managed according to standard practices for Ontario (Anonymous, 2014). Ten treatments were applied to single whole trees in a randomized complete block design with six replications. Full bloom occurred 20 May, 10 May, and 6 May in 2014, 2015, and 2016, respectively, which generally followed Bosc by 1 2 days. The same trees were used in 2014 and 2015. The experiment was moved to another part of the orchard in 2016 due to widespread fire blight affecting the trees used in 2014 and 2015. Experimental units
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received one of the following ten treatments: i) untreated control; ii) hand thinned control after ‘June’ drop; iii) 75 mg L 1 of 6 BA; iv) 150 mg L 1 of 6 BA; v) 10 mg L 1 of NAA; vi) 20 mg L 1 of NAA; vii) 150 mg L 1 of s ABA; viii) 300 mg L 1 of s ABA, ix) 150 mg L 1 of ACC; and x) 300 mg L 1 of ACC. All treatments were applied on 29 May 2014, 23 May 2015 and 26 May 2016 at ~10–12 mm fruitlet diameter. After natural fruit drop, the hand thinned control treatments were hand thinned to commercial levels of 1 fruit per flower cluster and spaced approximately 15 cm apart. All treatments included 0.05% Regulaid® non ionic spray adjuvant. Fruit were harvested on 1 October 2014, 22 September 2015 and 21 September 2016. For Review Only Horticultural Measurements In both experiments, tree trunk circumference 30 cm above the graft union was measured at the beginning and end of each growing season, from which trunk cross sectional area was calculated. In early May of each year, two main scaffold branches on each of the east and west sides of the tree were selected and marked prior to bloom to determine fruit set by counting the number of flower clusters per branch. In June, after fruit set, the number of fruit set per flower cluster (spur) was counted. These data were used to calculate percent fruit set (number of fruit set divided by number of flowers) and fruit set per flower cluster. Return bloom was rated each spring when trees were in full bloom by visually assessing each tree and assigning a rating from 0 to 5 (0 = no flowers present, 1 = few, 2 = moderate flowering, 3 = average, 4 = high, 5 = very high flowering).
At harvest, the total number and weight of individual fruit per tree were recorded. A fruit sample consisting of 50 (2014, 2015) or 100 (2016) pears with a wide range of different sizes was used to determine the relationship between fruit weight and fruit diameter. A linear regression line of best fit was then used to translate individual fruits into fruit diameters; these were sorted according to nine size categories based on minimum diameters of < 57 mm, 57 mm, 60 mm, 64 mm, 67 mm, 70 mm, 73 mm, 76 mm and > 76 mm. The total weight of fruit in each size category was used to calculate the crop value per tree based on the following prices (CDN $ per kg): <57 mm ($0.00), 57 mm
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($0.26), 60 mm ($1.72), 63 mm ($1.97), 67 mm ($1.97), 70 mm ($2.21), 73 mm ($2.21), 76 mm ($2.21) and >76 mm ($2.21), based on commercial prices provided by the Ontario Tender Fruit Producers’ Marketing Board (2017). The resulting crop value represented gross returns, excluding input, storage or packaging costs. The estimated time to hand thin a mature high density pear orchard in Ontario (age 6+ yrs) is 101 hr/ha at a cost of $1961/ha (adjusted for 2017 changes in minimum wage rates, Tender Fruit Growers, 2016). These costs were excluded from the gross return because in the years the experiments were conducted, very little hand thinning was required to impose the hand thinning treatment. For Review Only Ten sound fruit free of defects were randomly selected from each tree for fruit quality determination. Fruit ground colour of Cold Snap™ was measured using a Konica Minolta Chroma Meter CR 400 (Konica Minolta, Japan). Values are expressed using the CIE L*a*b system where L* is the lightness factor ranging from black (–L*) to white (+L*); a* is a chromaticity coordinate ranging from green (–a*) to red (+a*); and b* is the chromaticity coordinate ranging from blue (–b*) to yellow (+b*). Fruit firmness of Bosc and Cold Snap™ was measured using a Güss fruit texture analyzer (Güss Manufacturing, Strand, South Africa) equipped with an 8 mm stainless steel blunt probe inserted at a velocity of 10 mm.sec 1 to a depth of 8.1 mm and the peak force was recorded. Measurements were taken on opposite sides of the fruit after an approximately 2 mm thick tangential section of peel (1.5–2.0 cm in diameter) was sliced from the equator of the fruit. The mean of these two measurements was used in subsequent data analyses. For each treatment replicate, slices taken from each of the ten fruit were frozen and later thawed to express a composite sample of fruit juice. Total soluble solids were measured using a temperature compensating digital refractometer (Model PR 100, Atago, Japan). The juice was mixed well and then a 1 mL subsample was taken and applied to the test window of the instrument. An additional 5 mL subsample of juice was taken, diluted 1:10 in distilled water, then titrated to pH 8.2 by addition of 0.1 N aqueous NaOH with an auto titrator (model G20, Mettler Toldeo AG, Schwerzenbach, Switzerland) using methods reported elsewhere (Mitcham et al.,
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1996). Initial juice pH was recorded and titratable acidity (TA; expressed as malic acid equivalence) was calculated.
Data were subjected to analysis of variance (ANOVA) using the PROC MIXED statement (version 9.4, SAS Institute, Inc., Cary, NC, USA). Mean separation using the Duncan Multiple Range test was used to separate treatment means (P = 0.05) as fixed effects and blocks as random effects. A Shapiro Wilk test was used to test the assumption that residuals were normally distributed. Scatterplots of studentized residuals were visually observed to test the assumption that errors were not heterogeneous. Lund’sFor test of Review outliers with studentized Only residuals indicated whether outliers were present; if so, they were removed from the analysis. In cases where there were large deviations from these assumptions, data were corrected by log or square root transformation prior to analysis. Single degree of freedom orthogonal comparisons were performed to evaluate each of the thinning products with the untreated control. Because of space constraints, these comparison were not included in the tables.
RESULTS AND DISCUSSION
Environmental Conditions During Fruit Set and Early Development
Daily minimum and maximum temperatures, and rainfall over from 1 May – 13 Jun in St. David’s, Ontario, the closest available weather station to the Cold Snap ™ orchard, are presented in Figure 1. The Bosc orchard was 8.5 km from the Cold Snap™ orchard, and would have experienced relatively similar environmental conditions, and so for the purposes of this discussion environmental conditions for the weather station situated near the Cold Snap™ orchard are only presented. In 2014, five rainfall events occurred within 4d preceding and after bloom (18 May), and air temperature minimum and maximum temperatures fluctuated from 2.8 11.3oC and 14.48 23.9oC, respectively. Conditions for bee activity and pollination during the bloom period were less than ideal. Seven days following treatment application (29 May), only one precipitation event occurred (3 June) and air temperature minimum and maximum temperatures fluctuated
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from 7.1 21.1oC and 18.7.48 29.3oC, respectively. Air temperature above 20oC are considered conducive to uptake and physiological activity of exogenously applied plant bio regulators (Ontario Ministry of Agriculture and Food 2016) and therefore environmental conditions following treatment application should not have limited their physiological effect. In 2015, four rainfall events occurred 4d after bloom (8 May), and air temperature minimum and maximum temperatures fluctuated from 5.2 13.6oC and 19.2 33.5oC, respectively. Conditions for bee activity and pollination during the bloom period were considered good. Seven days following treatment application (23 May), only one precipitation event occurred (27 May) and air temperature minimum and maximum temperaturesFor fluctuated Review from 1.0 19.7 OnlyoC and 19.9 32.0oC, respectively indicating that environmental conditions were excellent tor chemical thinner uptake and physiological activity within the plant. In 2016, one rainfall event occurred 1d after bloom (7 May), and air temperature minimum and maximum temperatures fluctuated from 1.0 8.6oC and 14.5 24.2, respectively. Conditions for bee activity and pollination during the bloom period were considered excellent. Seven days following treatment application (26 May), no precipitation fell and air temperature minimum and maximum temperatures fluctuated from 9.9 20.9oC and 28.2 34.6oC, respectively indicating that environmental conditions were optimal excellent tor chemical thinner physiological activity within the plant.
Experiment 1: Cold Snap™ 2014 Applications of 10 mg L 1 of NAA or 300 mg L 1 of s ABA significantly reduced fruit set, total number of fruit per branch and total number of fruiting sites per branch compared with the untreated control (Table 1). The 10 mg L 1 concentration of NAA resulted in the lowest percentage of flowers that had one fruit per spur. There was no treatment effect on the percentage of flowers that set more than one fruit per flower cluster.
Total fruit yield, number of fruit and crop load of trees treated with 10 mg L 1 of NAA were significantly lower than the untreated control (Table 2). Compared with the untreated control, fruit weight was reduced by the 150 mg L 1 ACC treatment but not by
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the 300 mg L 1 ACC treatment. Crop value was unaffected by the thinning treatments according to ANOVA, but orthogonal contrasts indicated that applications of NAA significantly reduced crop value compared with the control (data not shown).
The total weight of fruit in the nine size categories differed among the treatments (Table 3). Significant treatment differences were observed among the size distribution categories ≤ 60 mm. The 150 mg L 1 ACC treatment resulted in the greatest amount of fruit in the ≤ 57 mm size category (P = 0.03). However, 10 mg L 1 of NAA decreased the weight of fruit in the 57 and 60 mm size categories compared with the untreated and hand thinned controls. For Review Only
None of the fruit quality parameters were affected by the thinning treatments according to ANOVA (data not shown). However, orthogonal contrasts indicated a slight increase in fruit firmness and reduction of soluble solids with applications of s ABA compared with the untreated control (data not shown). The contrasts also indicated a slight increase in fruit density following applications of 6 BA or ACC compared with the untreated control.
Ground colour of the fruit was not affected by the thinning treatments based on ANOVA (data not shown). Orthogonal contrasts indicated that: applications of 6 BA resulted in fruit colour that was more red/yellow and less intense than the control; s ABA resulted in blacker, greener and less intense colour than the control; and ACC applications resulted in less black, more red/yellow and less intense colour than the untreated control (data not shown).
2015 Application of chemical thinners resulted in significant differences in fruit set among treatments; however, only applications of 20 mg L 1 of NAA resulted in significantly lower fruit set compared with the untreated control (Table 4). Applications of 150 mg L 1 of 6 BA, 10 or 20 mg L 1 of NAA, 300 mg L 1 of s ABA or 150 mg L 1 of ACC significantly reduced the total number of fruit per branch and total number of fruiting sites per branch
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compared with the untreated control. There was no treatment effect on the percentage of flowers that set one or more fruit, nor on return bloom (data not shown).
Trees sprayed with 150 mg L 1 of 6 BA, 10 or 20 mg L 1 of NAA or 300 mg L 1 of s ABA produced a significantly lower total fruit yield and crop load than untreated control trees (Table 5). All concentrations of 6 BA, NAA and s ABA reduced the total number of fruit; however, fruit weight was unaffected by any of the thinning treatments. Application of chemical thinners did not increase crop value and even resulted in lower values when NAA or 300 mg L 1 of s ABA was applied. For Review Only The weight of fruit in the 57 mm to 70 mm size categories was affected by the thinning treatments (Table 6). Application of 20 mg L 1 of NAA decreased the weight of fruit in the 57 to 70 mm size categories compared with the untreated and hand thinned controls, although the total weight of fruit per tree was also less. NAA at a concentration of 10 mg L 1 had a similar but slightly lesser effect.
Fruit firmness, soluble solids, pH, TA and moisture content were unaffected by the thinning treatments according to ANOVA (data not shown). However, orthogonal contrasts indicated a slight increase in fruit firmness with applications of NAA, s ABA or ACC compared with the untreated control (data not shown).
Ground colour of the fruit was only slightly affected by the thinning treatments (data not shown). Lightness values (L*), chromaticity (b*), chroma (C*) and hue angle did not differ among the treatments. The a* chromaticity coordinate was significantly higher (less green) following applications of 150 mg L 1 of s ABA compared with the untreated control.
2016 Application of ACC and 6 BA in 2015 enhanced return bloom in 2016 compared with the untreated check (data not shown). Application of chemical thinners in 2016 resulted in significant differences in fruit set among treatments (Table 7). All concentrations of
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NAA, s ABA and the 300 mg L 1 concentration of ACC reduced final fruit set compared with the untreated control. All thinning treatments however had similar total numbers of fruit per branch and number of fruiting spurs per branch, with the exception of 150 mg L 1 of 6 BA, which had a significantly higher number of fruit per branch and a higher number of fruiting spurs than the untreated control. Application of 20 mg L 1 of NAA increased the percentage of flowering clusters with no fruit compared with the untreated control. The untreated control had the largest percentage of flowering sites that had four fruit per spur. The percentages of flower clusters with one, two, three or five fruit per cluster were unaffected by the thinning treatments. For Review Only Trees sprayed with 150 mg L 1 of 6 BA produced higher yields, total number of fruit per tree and crop load than the untreated control trees (Table 8). Applications of 300 mg L 1 of ACC also resulted in a greater number of fruit per tree and higher crop load. This, in addition to fruit set measurements and return bloom ratings, indicated that the high concentrations of 6 BA and ACC applied in 2015 enhanced return bloom, and that the 2016 application of these products failed to thin fruit. Fruit weight and crop value were unaffected by the thinning treatments.
The weights of fruit in the < 57 to 64 mm size categories were affected by the thinning treatments (Table 9). Trees that were sprayed with 150 mg L 1 of 6 BA and 150 mg L 1 of ACC produced a higher weight of fruit in the < 57 mm size category compared with the untreated check. Orthogonal contrasts indicated that hand thinning (P = 0.043) and NAA (P = 0.028) treatments reduced the weight of fruit in the 57 mm size category (data not shown). Treating trees with 150 mg L 1 of 6 BA increased the weight of fruit in the 60 mm size category, whereas 20 mg L 1 of NAA reduced the amount of fruit in the 63 mm size category.
Fruit firmness, soluble solids and initial pH were unaffected by the thinning treatments according to ANOVA (data not shown). However, orthogonal contrasts indicated a slight increase in fruit firmness with applications of NAA or s ABA compared with the
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untreated control. TA was significantly lower in fruit from trees treated with 300 mg L 1 of ACC compared with the untreated control (data not shown).
Ground colour of the fruit was slightly affected by the thinning treatments (data not shown). L* values were significantly lower or darker in fruit from the NAA and s ABA treatments compared with the untreated check. Applications of NAA and s ABA also resulted in fruit that were greener (lower chromaticity a* values) than the untreated check. Finally, b*, C*, hue angle and percent of fruit surface with blush did not differ among the treatments. For Review Only Experiment 2: Bosc
2014 Application of NAA or 300 of mg L 1 of ACC significantly reduced fruit set compared with the hand thinned control (Table 1). The highest concentrations of NAA and ACC reduced the total number of fruit per branch, but only the high concentration of NAA reduced the total number of fruiting sites compared with the hand thinned control. The untreated control treatment had the highest percentage of flower clusters that set one fruit. Treatments that had higher fruit set generally had a greater percentage of flower clusters that set two fruit. Treatments that thinned well, such as both rates of NAA, and 300 mg L 1 s ABA had the lowest percentage of flower clusters that set two fruit.
Applications of 20 mg L 1 of NAA reduced total fruit yield compared with the untreated control (Table 2). The highest concentrations of NAA and ACC resulted in the lowest total number of fruit and crop load. Applications of 300 mg L 1 of ACC increased fruit weight. None of the chemical thinners increased crop value compared with the untreated control, indicating that there was no measurable financial benefit of thinning in 2014 based on crop value alone.
The weights of fruit in the < 57 , 60 , 64 and 67 mm size categories were affected by the thinning treatments (Table 3). In general, the magnitude of difference in weight
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within a category was not markedly different than that of the untreated control, with the exception of 300 mg L 1 of ACC, which resulted in the lowest amount of fruit in the above size categories. Orthogonal contrasts indicated that applications of NAA in particular reduced the percentage of fruit in the 60–63 mm size categories compared with the untreated control (data not shown).
Fruit firmness, soluble solids and TA were unaffected by the thinning treatments (data not shown). Initial pH was significantly higher in fruit from trees treated with 150 mg L 1 of 6 BA compared with the untreated check. For Review Only 2015 Application of chemical thinners resulted in significant differences in fruit set between treatments (Table 4). Fruit set, total number of fruit per branch and total number of fruiting sites per branch varied somewhat; however, all treatments except for NAA were similar to the untreated and hand thinned controls. Applications of NAA reduced fruit set, number of fruit per branch and fruiting sites per branch. The hand thinned control treatment, both rates of 6 BA, 10 mg L 1 NAA and 150 mg L 1 s ABA had the greatest percent of flower clusters with 1 fruit, all of which were higher than the untreated control treatment. The untreated control and both concentrations of ACC had the highest percentage of flower clusters that set two fruit. There was no 2014 treatment effects on return bloom (data not shown).
Applications of 150 mg L 1 6 BA, NAA and 300 mg L 1 of s ABA significantly reduced total fruit yield and number of fruit per tree, but increased fruit weight compared with the untreated control (Table 5). These products failed to increase yield or crop value compared with the control, and even resulted in lower crop value when NAA, 150 mg L 1 of 6 BA or 300 mg L 1 of s ABA were applied compared with the control. Crop load was significantly reduced by applications of 150 mg L 1 of 6 BA or NAA. The trees used for this trial were a uniform size, as indicated by the lack of significant differences between treatments in spring trunk cross sectional area (data not shown).
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The weight of fruit in the 60–73 mm and ≥ 76 mm size categories was affected by the thinning treatments (Table 6); 150 mg L 1 of 6 BA and both concentrations of NAA reduced the weight of fruit in the 60 73 mm size categories compared with the untreated control. Both concentrations of NAA also increased the weight of fruit in the ≥ 76 mm size category.
Fruit firmness, soluble solids and TA were unaffected by the thinning treatments (data not shown). Applications of 150 mg L 1 of 6 BA or 20 mg L 1 of NAA resulted in lower juice pH levels compared with the untreated control. For Review Only 2016 Return bloom in 2016 was unaffected by applications of chemical thinners applied the previous year (data not shown). In 2016, chemical thinners resulted in significant differences in fruit set between treatments (Table 7). All chemical thinning treatments, except for the low concentration of s ABA and ACC, significantly reduced fruit set compared with the untreated control. Applications of 20 mg L 1 NAA a resulted in the lowest numbers of fruit per branch. There was no effect on the percentage of flowers that set 1 or more fruit.
Applications of 150 mg L 1 of 6 BA, NAA and 300 mg L 1 of ACC significantly reduced total fruit yield compared with the untreated check, and both concentrations of s ABA, in addition to the other treatments resulted in reduced yield compared with the hand thinned control (Table 8). All thinning treatments, except for the low concentration of ACC, also reduced total number of fruit per tree. NAA, s ABA and the high concentrations of 6 BA and ACC significantly reduced crop load compared with the untreated and hand thinned controls. Fruit weight was significantly higher for trees sprayed with the high concentration of 6 BA or the low concentration of NAA compared with the untreated control. The orthogonal contrasts also indicated a positive effect on fruit size following application of 6 BA or s ABA (data not shown). No product applied in this study resulted in an increased yield compared with the control. Application of chemical thinners did not increase crop value, and even resulted in lower values than
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the control when NAA, s ABA, or 150 mg L 1 of 6 BA were applied. The trees used in this trial were of a uniform size, as indicated by the lack of significant differences between treatments in spring trunk cross sectional area (data not shown).
Application of chemical thinners had a significant effect on the weight of fruit in all size categories (Table 9). Overall, 150 mg L 1 of 6 BA, both concentrations of NAA and 300 mg L 1 of ACC resulted in the lowest weight of fruit in most size categories. Applications of NAA overthinned severely in every instance.
Soluble solids and TAFor were unaffected Review by the thinningOnly treatments (data not shown). Although non significant according to ANOVA, orthogonal contrasts indicated a slight decrease in fruit firmness following the application of 6 BA compared with the untreated control (data not shown).
Overall, the response of Bosc and Cold Snap™ to the chemical thinners used in this study varied by cultivar and year. NAA appeared to be the most consistent thinner of the four treatments studied, although all products had some effect in at least one of the study years. The response to NAA in the present study is consistent with that of Vilardell et al. (2005) in Spain, who found that Conference pears treated with 10–20 mg L 1 of NAA reduced fruit set, but that the effect on fruit size varied among years. In Norway, Meland and Gjerde (1996) found that petal fall sprays of 10–30 mg L 1 of NAA thinned three of four local cultivars tested, but that fruit fresh firmness of two cultivars was reduced by NAA. In contrast, McArtney and Wells (1995) found that 7.5 mg L 1 of NAA applied 15 days after full bloom (DAFB) had no effect on fruit set or weight of Doyenné du Comice but reduced flesh firmness at harvest by 1.96 N (6%). Asin et al. (2009) also found variable results when thinning with NAA. Overall, there appears to be cultivar and year to year variation in the response of pears to fruitlet thinning with NAA. In the present study, NAA did not influence fruit quality at harvest.
6 BA has also been used to thin several pear varieties, but its use on Bosc or Cold Snap™ has not been reported. In the current study, 6 BA reduced crop load of Cold
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Snap™ in 2015 and Bosc in all years at the higher concentration of 150 mg L 1, but had less or no effect at 75 mg L 1. Fruit size was only improved in 2015 for Bosc at the 150 mg L 1 rate. In Australia, Bound (2015) found that 100–150 mg L 1 of 6 BA thinned and improved the fruit size of Packhams Triumph when applied between 10–40 DAFB. In Spain, Vilardell et al. (2005) found that 200 mg L 1 of 6 BA reduced fruit set of Conference by 73% compared with untreated trees, decreased the number of fruit per tree and increased fruit weight. Maas and Steeg (2010) observed that 150 mg L 1 of 6 BA was optimal for thinning Conference. In another joint study conducted in Argentina and the USA on Williams pear, Dussi and Sugar (2011) found that 6 BA applied between 100 and 150 Formg L 1 at Review 10–13 mm fruitlet Only diameter reduced fruit set as well as the number of fruit and time needed for hand thinning. In addition, they found that 6 BA increased fruit size and yield of large sized fruit compared with the control. In Israel, Stern and Flaishman (2003) found 100 mg L 1 of 6 BA effectively thinned Spadona and Coscia pears when applied at 10 mm fruitlet diameter. Increases in fruit size were also observed due to reductions in crop load and stimulation of fruit cell division. However, there was no effect of BA on fruit shape, seed number or return bloom (data not shown). The rather poor response of 6 BA in the present study does not appear to be associated with cool air temperatures following application (Figure 1). One explanation is that concentrations higher than 150 mg L 1 may be required to thin Cold Snap™ and Bosc. A cytokinin induced effect on cell division and concomitant increase in fruit size, independent of crop load, was likely not detected either because it failed to thin or because Cold Snap™ and Bosc pears do not respond to 6 BA similarly as apples (Wismer et al. 1995).
ACC is a precursor to ethylene metabolism and is involved in fruit abscission and ripening. Comparable research of ACC conducted on apples (Greene et al. 2011;; McArtney and Obermiller 2012; Schupp et al. 2012; McArtney et al. 2014) has not be been performed on pears. In the present study, ACC at a concentration of 300 mg L 1 markedly reduced the crop load of Bosc in two out of three years, but not that of Cold Snap™ compared with the untreated control. ACC also improved fruit size when applied to Bosc once in the three year study period. Given the positive response of ACC, further
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research is required to determine optimal concentrations for pears and to test other application timings.
Abscisic acid, a plant hormone found naturally in plants, is involved in several physiological responses including leaf stomatal control. By regulating stomatal movement, it can influence the carbohydrate status within a plant by reducing photosynthesis during the time the stomata are closed. This can trigger fruitlet abscission in apples (Greene et al. 2011) and therefore merits testing of s ABA on pears as a potential thinner. In the present study, s ABA at concentrations of 150 mg L 1 and 300 mg L 1 reducedFor the crop Review load of Bosc inOnly one of three study years, and Cold Snap™ at a concentration of 300 mg L 1 in one of three study years. Greene (2012) found that 500 mg L 1 of s ABA applied at bloom, petal fall and 10 mm fruitlet diameter resulted in significant fruit thinning of Bartlett pears, where application at 10 mm nearly defruited the trees. In the same study, concentrations of s ABA between 50 and 500 mg L 1 applied at the 10 mm fruitlet stage resulted in a quadratic and highly significant thinning response. S ABA also enhanced return bloom (data not shown), but this may have been a result of the decreased crop load effect of using s ABA. The authors also observed that s ABA generally resulted in larger fruit, greater flesh firmness and higher soluble solids. Extensive leaf yellowing and leaf abscission were noted after s ABA application, especially when applied at concentrations of 250 mg L 1 or higher, which was considered commercially unacceptable. 6 BA was unable to reverse or modify the leaf yellowing and abscission caused by s ABA, as it has been shown to do in other plant species including Malus. In the present study, leaf yellowing or drop was observed after application of s ABA.
CONCLUSIONS
Fruit set was not heavy in 2014–2016 and very little hand thinning was required. Consequently, there were few statistically significant differences between the untreated control and the hand thinned control for any of the parameters measured in this study. All of the thinning treatments had some effect on fruiting characteristics of Cold Snap™
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and Bosc pears. Overall, both cultivars responded similarly to the thinning treatments, with the exception of Cold Snap™ in 2016. Results suggest that the 2015 application of 150 mg L 1 of 6 BA or 300 mg L 1 of ACC enhanced return bloom of Cold Snap™ in 2016 and that applications in 2016, except for 300 mg L 1 of ACC on Bosc, failed to thin. Applications of 10 or 20 mg L 1 NAA consistently resulted in the lowest fruit set compared with the control; however, 150 mg L 1 of 6 BA and 300 mg L 1 of s ABA also resulted in significant reductions in fruit set, number of fruit, number of fruit per spur and crop load. These treatments also resulted in some improvement in fruit size but decreased yield and crop value. No negative effects on fruit quality were observed from any of the thinning treatments.For AlthoughReview 6 BA, NAA Only and s ABA displayed some thinning efficacy, there was no economic benefit in applying them to Bosc or Cold Snap™ in this study because of the subsequent reduction in yield, in which lower yields were not offset by the greater number of larger sized fruit.
ACKNOWLEDGEMENTS This project was funded in part through Growing Forward 2 (GF2), a federal provincial territorial initiative. The Agricultural Adaptation Council assists in the delivery of GF2 in Ontario. Funding was also provided by the University of Guelph, N.M. Bartlett and Vineland Growers Co operative Inc. We acknowledge the assistance of J. Heyens, L. Coello, G. Boerema, A. Cline and P. Cline, N. Querques and J. Muysson with data collection and J. Fedorkow, J. Thwaite, and N. Thwaite for providing their commercial orchards for experimentation.
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LITERATURE CITED
Anonymous. 2014. Publication 360: Guide to Fruit Production. Published by the Ministry of Agriculture, Food and Rural Affairs. Queen’s Printer for Ontario, Toronto, Ontario. 365 p. Asín, L., Vilardell, P., Bonany, J. and Alegre, S. 2009. September. Effect of 6 BA, NAA and their mixtures on fruit thinning and fruit yield in 'Conference' and 'Blanquilla'pear cultivars. Acta Hort. 884:379 382. Bound, S.A. 2015. Optimising crop load and fruit quality of ‘Packham’s Triumph’ pear with ammonium thiosulfate, ethephon and 6 benzyladenine. Sci. Hort. 192:187 196. Dussi, M.C. and Sugar, D. 2010. Fruit thinning and fruit size enhancement with 6 benzyldadenine application to ‘Williams’ pear. Acta Hort. 909:403 407. Einhorn, T.C. and Arrington,For M., Review 2017. ABA and Shading Only Induce ‘Bartlett’ Pear Abscission and Inhibit Photosynthesis but Are Not Additive. J. Plant Growth Reg. 35:1 9. Greene, D.W., Schupp, J.R. and Winzeler, H.E. 2011. Effect of abscisic acid and benzyladenine on fruit set and fruit quality of apples. HortScience 46:604 609. Greene, D.W. 2012. Influence of abscisic acid and benzyladenine on fruit set and fruit quality of Bartlett pears. HortScience 47:1607 1611. Greene, D.W., Schupp, J.R. and Winzeler, H.E. 2011. Effect of abscisic acid and benzyladenine on fruit set and fruit quality of apples. HortScience 46:604 609. Hunter, D.M., Kappel, F., Quamme, H.A., Bonn, W.G. and Slingerland, K.C. 2009. ‘Harovin Sundown’ Pear. HortScience 44:1461 1463. Maas, F.M. and Van der Steeg, P.A.H. 2010. Crop load regulation in 'Conference' pears. Acta Hort. 909:367 379. McArtney, S.J., Abrams, S.R., Woolard, D.D. and Petracek, P.D. 2014. Effects of S Abscisic Acid and (+) 8′ Acetylene Abscisic Acid on Fruit Set and Stomatal Conductance in Apple. HortScience 49:763 768. McArtney, S.J. and Wells, G.H. 1995. Chemical thinning of Asian and European pear with ethephon and NAA. N.Z. J. Crop and Hort. Sci. 23:73 84. McArtney, S.J. and Obermiller, J.D. 2012. Use of 1 aminocyclopropane carboxylic acid and metamitron for delayed thinning of apple fruit. HortScience 47:1612 1616. Meland, M. and Gjerde, B. 1996. Thinning apples and pears in a Nordic climate II. The effect of NAA, ethephon and lime sulfur on fruit quality of four pear cultivars. Norwegian J. Agr. Sci. 10:453 468 Mitcham, B., Cantwell, M. and Kader, A. 1996. Methods for determining quality of fresh commodities. Perishables handling newsletter, 85, pp.1 5. Ontario Ministry of Agriculture, Food and Rural Affairs. 2016. Pears: Area, Production, Farm Value, Price and Yield, Ontario, 1979 – 2016. [Online]. Available: http://www.omafra.gov.on.ca/english/stats/hort/pear.htm [26 April 2017] Ontario Tender Fruit Producers’ Marketing Board. 2017. Growing Forward 2 brings new life to Ontario pear growing. [Online]. Avalable: http://www.ontariotenderfruit.ca/news.php?id=4o3s1z5x5u9p [30 June 2017] Schupp, J.R., Kon, T.M. and Winzeler, H.E. 2012. 1 aminocyclopropane carboxylic acid shows promise as a chemical thinner for apple. HortScience 47:1308 1311.
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Shaw, H. 2017. Canada’s own hybrid pear could feed a growing appetite for the fruit and local produce. Financial Post February 13, 2017. [Online]. Available: http://business.financialpost.com/news/retail marketing/canadas own hybrid pear could feed a growing appetite for the fruit and local produce [26 April 2017] Statistics Canada. 2015. Statistical Overview of the Canadian Fruit Industry – 2015. [Online]. Available: http://www.agr.gc.ca/eng/industry markets and trade/statistics and market information/by product sector/horticulture industry/horticulture sector reports/statistical overview of the canadian fruit industry 2015/?id=1480709682930 [26 April 2017] Stern, R.A. and Flaishman, M.A. 2003. Benzyladenine effects on fruit size, fruit thinning and return yield of ‘Spadona’and ‘Coscia’pear. Sci. Hort. 98:499 504. Sutton, T.B. and Unrath, C.R. 1988. Evaluation of the tree row volume model for full season pesticide application on apples. Plant disease 72:629 632. Tender Fruit Growers of Ontario. 2016. Tender fruit establishment and production costs. J. Molenhuis, K.For Carter, K.Review Slingerland, S. MarshallOnly and L. Osborne (eds). 49 p. [ Online]. Available: http://ontariotenderfruit.ca/uploads/file/2016 Ontario Tender Fruit Establishment Production Costs.pdf [17 Oct 2017]. Vilardell, P., Carbó, J., Casals, M., Bonany, J., Asín, L. and Dalmau, R. 2005. Effect of 6 BA and NAA as thinning agents of 'Conference' pear. Acta Hort. 884:379 32 Wismer, P.T., Proctor, J.T.A. and Elfving, D.C., 1995. Benzyladenine affects cell division and cell size during apple fruit thinning. J. Amer. Soc. Hort Sci. 120:802 807
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50 FB T A 40
30
20
10
0 For Review Only FB T B 40
30 C)/Rainfall(mm) o 20
10
0 Temperature( FB T C 40
30
20
10
0 01 May 08 May 15 May 22 May 29 May 05 Jun 12 Jun
Figure 1. Daily maximum (solid line) and minimum (dashed line) air temperature and rainfall (bar) during 1 May to 13 June in 2014 (A), 2015 (B) and 2016 (C), St. Davids, Ontario. FB and T indicate time of full bloom and thinner applications. Data source: Weather Innovations Consulting LP, Chatham, ON.
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ns ns ns 1.7 0.0 0.0 6.1 0.0 0.0 2.8 0.0 0.0 0.0 0.0 0.0 0.7 1.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.3 0.0 0.0 0.5 0.0 0.0 3.1 0.9 0.0 2.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.8 0.0 0.0 1.1 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.6 0.0 0.0
cd bcd bcd abc abc d d abc abc cd abcd a a cd
ab 2 2 3 4 5 1.5 4.9 6.4 6.6 8.4 8.5 10.3 14.2 26.4 25.9 10.3 16.8 33.0 10.9 28.1 19.8 10.9 18.3 10.5
abc abc bcd bcd cde cde a a bcde ab abcd e e abc abc
de Bosc Cold Snap Cold Percentage Percentage offlowers cluster withnumber with set of fruit
88.1 79.7 70.9 98.5 71.9 89.7 83.3 60.6 88.6 87.0 67.9 80.8 83.3 16.3 0.4 0.0 0.0 93.6 93.4 91.6 88.7 88.0 78.0 95.1 cd cd ab d d cd bcd bcd a a bcd bcd bcd bcd bcd bcd abc ab a bc e bc cd de abc abc ab sites fruiting fruiting 3.8 3.3 5.8 2.5 2.9 4.0 6.3 4.0 4.3 3.9 4.6 5.8 6.9 4.5 1.1 4.4 3.2 2.0 4.8 5.7 (no/branch) 1
Canadian Journal of Plant Science cde cde cde cde a a e e de cde cde ab bcd bcd bcde bcd bcd abc ab a bc e bc cde de abc abc abc abc https://mc.manuscriptcentral.com/cjps-pubs *** *** *** *** ** ns ns ns *** *** *** ns ns fruit Total Total 4.1 4.2 7.8 2.2 3.6 4.5 7.4 5.0 4.8 4.5 6.5 6.8 8.2 4.9 1.3 5.0 3.8 2.3 5.8 6.1 (no./branch) For Review Only abc abc a a ab c c bc abc abc abc abc bc ab a ab a bc d bc bc cd ab abc abc
* * flower Fruit set Fruit number of number of clusters) 56.0 73.5 70.0 30.5 32.8 35.3 65.2 54.8 35.2 74.2 )
0.0002 <0.0001 <0.0001 0.2262 0.2984 0.7188 . . -1 *** L 300 150 150 300 34.3 23.5 150 300 N/A 45.9 N/A 150 300 46.5 60.7 (mg a a Rate fruit/100 (no.
S-ABA S-ABA Statisticalsignificance NAA 20 NAA 10 6-BA 150 6-BA 6-BA 75 6-BA NAA NAA S-ABA S-ABA 150 38.2 10 20 11.8 36.0
Table 1. Fruit 1. Table set andclustering datafrom Snap and Boscpear Cold treestreated chemical thinners with in Data 2014. collected were from fourbranchesrepresentative tree. per control Untreated Hand-thinned N/A control 46.5 value P control Untreated Hand-thinned N/A control 6-BA 6-BA 75 41.8 Treatment Statisticalsignificance ACC ACC ACC ACC = = respectively. 0.001 P P = = and0.01, P P = 0.05, = P P Canadian Journal of Plant Science https://mc.manuscriptcentral.com/cjps-pubs For Review Only
0.0203 0.0004 0.0008 0.0003 0.0019 0.2581 0.6194 . value ns, *, *, ns, **,***, indicates not significant,and significant differences at a P Note: Note: Meanscolumn a within sharing sharing not not lowercased a italic letterdiffer the significant P at
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b 9.03 4.16 7.21 8.90 8.27 7.27 8.81 11.32 11.61 10.91 20.06 15.52 21.13 25.42 14.03 10.65 14.42 16.11 20.41 13.22 ab abc ab abc a abc abc a c bc bc ab bc c abc bc abc abc bc a Crop
183 160 172 158 161 181 138 149 169 160 214 199 188 194 194 180 185 177 188 200 ) (g) ($/tree) a c ab ab ab ab b a a ab ab e e cde cde de cde bcde abc abc ab a abcd bcde 0.9 3.8 3.5 3.2 3.0 2.4 4.3 4.2 3.7 3.3 1.7 2.1 1.9 2.1 2.7 3.2 3.4 4.4 3.1 2.5 Bosc Cold Snap Cold c a a ab ab ab bc a a ab ab c bc c bc bc ab ab a ab bc offruit Load weight tree per 28.8 35.5 28.2 38.8 40.5 56.5 57.3 73.7 55.5 38.5 Canadian Journal of Plant Science
7.0 12.3 23.0 48.2 21.3 41.3 17.4 18.0 39.0 14.7 37.3 20.6 27.8 21.6 52.7 48.3 22.8 19.0 47.0 39.7 18.6 20.8 16.1 21.8 23.7 31.0 32.2 39.5 31.0 22.7 https://mc.manuscriptcentral.com/cjps-pubs a a b a a a a a a a a a a bc bc c bc bc ab ab a ab bc
Total ** ** *** ** * ns ** *** * * Total Yielld number Crop Fruit value 6.2 6.9 5.4 7.2 7.9 7.6 (kg/tree) tonnes/ha (no./tree) (no./TCSA 10.3 10.7 13.1 For Review Only10.3 - )
0.0027 0.0016 <0.0001 0.0218 0.0518 0.0083 0.0012 0.0005 0.0127 0.0322 1 150 300 150 300 6.0 4.9 150 300 150 300 6.8 7.2 N/A 7.6 N/A Rate yield (mgL
c c
Means column a within sharing sharing not not lowercased a italic letterdiffer the Psignificant at Table 2. Total 2. Table numberyield, tree, per ofcrop fruit load,crop fruit weight, valueand trunk-cross area sectional in to response chemical thinning treatments Cold to applied Snap™ andBosc pears in 2014 control Untreated Hand-thinnedcontrol N/A 6.3 P control Untreated Hand-thinnedcontrol N/A P Treatment Note: level according level to Duncan's range multiple test. ACC ACC ACC ACC = = P =and0.01, P P = 0.05, = P P Canadian Journal of Plant Science https://mc.manuscriptcentral.com/cjps-pubs For Review Only Trunk cross-sectional area. Gross returnswith no inputcosts included. ns, *, *, ns, **, ***, indicates nonsignificant,and significant differences at 0.001 respectively. 0.001 a b c Page 25 of 39 Page 26 of 39 >76 >76 mm mm 0.1393 0 0 76 mm mm 0.149 3 3 73 1.9 1.7 1.1 1.1 0.1 0.4 2.3 1.4 0.3 mm mm 0.130 2 2 ns ns ns ns 70 0.6 0.8 0.6 0.4 0.5 0.2 0.4 0.0 1.1 0.4 0.5 0.3 0.9 0.5 0.4 0.2 0.5 0.2 0.3 0.3 2.0 1.7 0.6 0.2 0.4 0.1 2.2 0.7 0.4 0.1 0.1 0.7 0.7 0.2 0.4 0.5 0.1 0.3 0.1 mm mm 0.413 ab cd ab c 3 3 ns 67 1.2 1.1 0.9 2.5 1.3 0.2 2.1 0.6 0.8 0.7 0.8 mm mm 0.118 Bosc Bosc ab c bc d bc d Cold Snap Snap Cold 7 7 64 1.3 0.8 1.3 1.2 0.9 1.3 1.0 1.4 0.3 0.9 1.1 0.8 0.8 1.1 0.6 0.5 0.4 0.1 0.2 mm mm 0.055 ab b ab cd ab ab c ab c bc ab bc ab a a ** ns 0.9 0.8 0.9 0.9 0.2 0.7 1.1 0.6 1.0 1.4 Weightfruit(kg/tree) of minimum each for category size a a ab ab c a a c ab c ab c bc ab c a a Canadian Journal of Plant Science * * 1.1 1.0 0.4 0.2 0.9 0.3 0.8 0.4 0.8 1.1 0.3 0.8 0.9 0.3 0.8 1.5 https://mc.manuscriptcentral.com/cjps-pubs b b b ab c bc b b ab ab b b ab b b b b a a ab For Review Only * 0 0 9 3 1 6 6 3 3 3 3 1 1 5 5 7 7 6 6 4 4 4 4 1. 0. 0. 0. 0. 0. 1. 0. 1. 0. 0. 2. 1. <57 mm mm <57 mm 57 mm 60 - ) 0.0348 0.0131 0.0039 1 75 10 20 150 300 150 150 300 N/A N/A Rate (mgL a value harvested fruit harvested sorted were size nine into classes accordingto their The weight. minimum separate diameter to fruit used the are indicatedbelow forcategory.respective each Table 3. Influence 3. Table of chemical thinning treatments fruit size on distribution ofCold and Snap Boscpears in 2014. For each treatment, all Treatment control Untreated Hand-thinnedcontrol N/A P control Untreated Hand-thinnedcontrol N/A 6-BA 6-BA 6-BA 6-BA 75 6-BA NAA NAA S-ABA S-ABA Statisticalsignificance ACC ACC 0.4771 0 0 0.913 2 2 2.5 0.7 0.0 1.7 0.9 0.3 1.2 0.6 0.4 1.3 0.9 0.3 2.1 1.1 0.2 2.2 0.9 0.5 1.8 1.1 0.6 0.487 5 5 3.0 2.0 1.1 1.3 1.8 2.0 1.6 0.105 a a d d cd bc d cd a-d a-d d d 8 8 2.9 0.9 1.0 1.4 1.2 1.9 0.7 0.000 = = respectively. 0.001 P a a cd cd bc d bc d ab d d 3 3 2.0 0.5 0.4 1.0 0.9 1.4 0.2 =and0.01, 0.001 P P a a cd d d a-d a-d bc d ab d d = 0.05, = P P 9 9 0.000 Canadian Journal of Plant Science 9 9 0.5 1.1 0.2 0.3 0.2 0.2 0.2 0.6 0.2 0.3 0.4 0.9 0.0 0.1 https://mc.manuscriptcentral.com/cjps-pubs 0.556 a a bc bc bc bc ab c c For * Review ns *** Only ** *** ns ns ns ns 4 4 2 2 2 2 1 1 1 1 2 2 0 0 0. 0. 0. 0. 0. 0. 0. 0.0332 10 20 150 300 150 150 300 a Means column a within sharing sharing not not lowercased a italic letterdiffer the Psignificant at Page 27 of 39 Page 28 of 39 3 3 4 6 ns ns ns ns ns ns 1.4 0.0 0.0 0.6 0.0 0.0 5.0 0.0 0.0 0.0 0.0 0.0 0.4 0.0 0.0 0.0 0.0 0.0 1.8 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 1.1 0.0 0.0 0.5 0.0 0.0 0.3 0.0 0.0 0.0 0.0 0.0 2.2 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.8 0.0 0.0 0.8 0.0 0.0 3.4 0.0 0.4 0.8146 . . 0.1542 . 0.5809 ab cd cd d d cd bcd bcd d d cd a a abc abc 2 2 ns *** *** 9.3 6.2 8.7 7.6 4.4 6.9 6.2 6.6 5.6 3.1 7.4 2.6 8.9 11.1 10.7 22.1 16.3 10.0 25.3 20.0 0.5945 0.0002 bcd bcd a a a a a a a abc abc a a ab d d cd Percentage Percentage offlowers with numberset of fruit 1 1 Bosc 89.4 93.2 88.5 87.6 86.4 92.4 95.6 93.9 83.3 93.3 77.9 92.7 93.0 96.6 92.6 87.8 97.5 90.3 74.0 76.2 Cold Snap Cold ab bc bc bc c bc bc ab a a ab a a a ab abc abc bc c ab ab ab a a * * *** ** ns 5.0 3.2 3.2 3.5 1.8 3.2 3.0 4.1 5.4 4.3 6.0 7.2 5.7 4.6 3.1 2.0 5.6 5.1 5.6 6.8 ab bcd bcd bcd bcd abcd d d bcd bcd cd abc abc a a abc ab ab abc abc bcd bcd cd d d abc abc bc ab a a ** ** fruit sites fruiting Total Total 5.8 3.5 3.6 4.2 2.0 3.5 3.2 4.4 6.4 4.6 7.4 7.9 6.2 5.0 3.4 2.3 5.8 5.5 6.8 9.0 (no./branch) (no./branch) Canadian Journal of Plant Science a a abc abc cd abc abc d d cd cd bc abc abc ab abc abc abc abc bcd bcd cd d d d d cd bcd bcd ab a a https://mc.manuscriptcentral.com/cjps-pubs *** *** *** *** flower 0.0007 0.0069 0.0043 0.7421 clusters) Fruit Set Fruit number of number of 46.8 45.8 33.5 27.5 19.8 14.5 25.7 28.3 49.5 55.7 ) For Review Only -1 0.0005 0.0039 0.0154 0.0002 75 47.3 75 20 18.4 10 40.8 10 20 300 37.1 150 50.8 300 74.7 150 40.6 150 53.0 150 150 300 150 300 N/A 58.8 N/A N/A 68.7 N/A Rate fruit/100 (no. a a Means column a within sharing sharing not not lowercased a italic letterdiffer the Psignificant at Table 4. Fruit 4. Table set andclustering datafrom Snap and Boscpear Cold treestreated chemical thinners with in Data 2015. collected were from four representative branches pertree. control Untreated Hand-thinnedcontrol P control Untreated Hand-thinnedcontrol P 6-BA 6-BA Note: 6-BA NAA multiple range multiple test. NAA ACC S-ABA ACC S-ABA Statisticalsignificance ACC ACC = = respectively. 0.001 P =and0.01, P P = 0.05, = P P Canadian Journal of Plant Science https://mc.manuscriptcentral.com/cjps-pubs For Review Only ns, *, *, ns, **,***, indicates nonsignificant,and significant differences at a Page 29 of 39 Page 30 of 39 ab abc abc bc cd d abc cd abc a b Crop value per tree per 27.05 23.19 22.16 19.85 17.41 11.96 20.44 17.33 23.96 27.67 38.73 37.18 a ab 44.43 26.99 a bcd 35.48 abc 0.0005 a a 15.78 e c 41.41 a bc bc c 38.81 a bc a 24.03 de bc b 25.18 cde bc (g) ($/tree) 263 184 207 201 193 195 251 197 224 204 ) a e e e 228 210 abc 198 a a 199 c ab abc 191 198 de 226 bcd bcd 213 bcd cde 198 213 ab a ab ab ab c ab c bc Bosc Cold Snap Cold 1.8 1.6 3.7 4.7 1.3 4.3 3.7 2.5 3.2 3.4 2.7 4.2 4.8 3.9 4.2 4.2 2.0 4.0 2.2 2.7 d d a a a ab a a a a cd ab cd bc Canadian Journal of Plant Science https://mc.manuscriptcentral.com/cjps-pubs 27.7 53.2 cd 55.8 bcd 42.0 de 88.2 99.5 96.6 45.0 93.8 51.7 65.7 103.5 115.5 a a d d ab a a a a a cd ab cd bc *** *** *** *** ns *** *** *** *** ** *** fruit number Crop fruit Total Total For Mean Review Only (kg/tree) (no./tree) (no./TCSA 7.2 21.1 17.3 19.0 20.9 18.7 11.0 18.2 11.7 13.1 - ) <0.0001 <0.0001 <0.0001 0.3888 1 75 11.1 abc 20 10 150 11.0 abc 150 300 8.8 bcd 300 150 9.9 bc 44.2 cde 150 12.3 ab 62.2 abc 300 300 14.4 a 73.0 ab 150 Rate yield offruit Load weight (mgL c c value NAA NAA S-ABA Statisticalsignificance 10 20 8.5 cd 6.2 d 37.7 de 29.2 e S-ABA Treatment NAA-FruitoneL Table 5. Total 5. Table numberyield, tree, per ofcrop fruit load,crop fruit weight, valueand trunk cross-sectional in response area to chemical thinning treatments toapplied Cold Snap™ andBosc2015. in pears control Untreated Hand-thinnedcontrol 6-BA 6-BA N/A N/A 12.1 14.5 ab a 61.7 77.2 abc S-ABA a P control Untreated Hand-thinnedcontrol N/A N/A NAA-FruitoneL Statisticalsignificance 6-BA 6-BA 6-BA S-ABA 75 150 ACC ACC ACC ACC = = 0.001 P <0.0001 =and0.01, P P = 0.05, = P P Canadian Journal of Plant Science https://mc.manuscriptcentral.com/cjps-pubs For Review Only <0.0001 <0.0001 <0.0001 0.0022 Means column a within sharing sharing not not lowercased a italic letterdiffer the Psignificant at Page 31 of 39 c bc abc abc a ab abc bc bc abc ns >76 >76 mm mm 0.3560 0.0317 Page 32 of 39 76 1.8 0.5 1.8 0.6 mm mm 0.8302 0.3973 73 mm mm 0.0037 reach treatment, harvested all fruit were *** *** ns ns <0.0001 Bosc Bosc 1.8 abc 1.8 ab 1.3 0.9 2.7 1.8 cde 3.1 bcd 3.1 bc 1.9 0.9 Cold Snap Snap Cold 0.0002 0.0008 0.1254 <0.0001 0.0003 Weightfruit(kg/tree) of minimum each for category size ** *** *** *** ** ns * 0.6 cde 1.2 0.8 ab bc 1.8 1.4 a bcd 1.5 1.0 0.9 2.2 a 1.0 bc ab ab 0.1 ab 3.2 0.1 1.7 2.0 1.9 b a 0.0 2.2 ab b ab 0.8 ab b 0.4 0.6 5.9 4.2 ab 1.7 0.2 1.4 cd 1.2 4.0 ab 0.1 a ab cd 1.1 1.5 a 2.7 1.5 ab d 1.3 bc a 5.0 0.5 4.8 1.4 de bcd 1.9 4.0 0.3 a e 3.3 1.8 a ab 2.2 ab 1.4 e ab bcd 3.9 1.5 2.9 cde 3.8 2.7 4.9 ab 3.1 bc 2.8 0.7 de bc bc a bcd 1.4 bc 2.0 e 2.4 5.1 2.1 3.8 5.5 bc 0.2 1.8 1.5 a abc a 2.2 2.6 c 2.9 4.0 3.2 4.0 1.4 bc ab 1.5 2.6 3.2 1.4 0.0098 0.0002 Canadian Journal of Plant Science ** *** *** *** https://mc.manuscriptcentral.com/cjps-pubs For Reviewns Only ns ns 0.4 0.5 abc 0.5 0.7 a 1.2 ab 1.8 a 2.4 ab 2.4 a 2.2 1.4 1.6 0.6 0.2 bc 0.3 de 0.5 c 0.8 cd 1.1 bc 1.4 1.3 2.6 0.2 0.2 0.4 0.3 0.0 0.0 0.0 0.0 0.9 0.6 0.6 0.4 0.6 ab 0.2 ab 1.7 bc 1.0 a 0.8 bc 1.9 bcd 1.6 a 1.2 ab abc 2.6 1.5 a bcd 0.2 2.0 0.1 2.3 0.1 0.7 ab a 0.0 0.2 2.1 0.4 1.9 0.0 0.1 0.1 1.0 0.2 1.0 0.3 1.8 1.5 0.5 0.3 0.2 0.6 0.1 bc 0.9 0.1 c 0.5 0.4 c cde abc 0.4 0.1 0.7 cde bc e 0.4 c 0.9 0.3 cd c 0.8 1.2 cd 0.5 bc 1.2 d 1.3 bc 0.7 1.6 c 1.2 0.6 1.1 3.5 2.6 0.7 2.6 <57 <57 mm mm mm 57 mm 60 mm 64 mm 67 mm 70 0.1640 0.0021 <0.0001 - ) 0.1667 0.0642 1 75 10 20 300 150 300 150 150 150 300 150 300 Rate (mgL a a value Statisticalsignificance S-ABA Table 6. Influence 6. Table of chemical thinning treatments fruit size on distribution ofCold Snap™ and Boscpears in fruit.Fo2015 into sorted sizeclasses nine to their according weight. minimumThe separate to diameter used the fruit are indicatedbelow for respective each category. Treatment control Untreated Hand-thinnedcontrol 6-BA N/A N/A 75 value P control Untreated Hand-thinnedcontrol 6-BA 6-BA N/A N/A NAA NAA S-ABA S-ABA Statisticalsignificance P 6-BA NAA NAA S-ABA 150 10 20 ACC ACC ACC ACC Canadian Journal of Plant Science https://mc.manuscriptcentral.com/cjps-pubs For Review Only Means column a within sharing sharing not not lowercased a italic letterdiffer the Psignificant at Page 33 of 39 Page 34 of 39 ns ns 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 0.8 0.6438 0.0153 ns ns ns 0.5345 0.3713 73.6 26.4 0.0 0.0 0.0 79.0 21.2 0.0 0.0 0.0 86.6 13.4 0.0 0.0 0.0 82.1 17.9 0.0 0.0 0.0 89.4 9.1 1.6 0.0 0.0 82.5 10.4 7.1 0.0 0.0 93.6 6.5 0.0 0.0 0.0 82.5 76.6 16.6 22.2 1.0 1.3 0.0 0.0 0.0 0.0 77.5 77.5 17.6 3.6 1.4 b 75.8 75.8 18.0 5.4 0.0 b 65.5 65.5 71.8 24.6 19.9 3.8 7.7 90.6 6.0 4.9 0.7 a 80.2 b 3.4 14.9 1.2 4.1 b 0.9 b 72.0 72.0 20.5 6.4 1.1 b 81.3 81.3 16.2 2.1 70.6 25.7 0.0 3.6 b 0.0 b 74.6 74.6 11.9 13.4 0.0 b 100.0 0.0 0.0 0.0 0.0 Bosc Cold Snap Cold 0.4157 d d b b cde cde ab g g def fg bcd bcd efg a a b b bcd bc bc def bc a *** *** ns ns 2.7 4.4 0.1 2.0 0.6 3.3 1.4 2.1 3.9 5.5 3.6 3.6 3.2 3.2 0.0002 b b bcd bcd b b f f cde cde ef bc def bc bc a bc c bc bc bcd bc bc bc cd bcd cde cde bc bc bcd b b a *** *** fruit sites fruiting Percentage offlowers with numberset of fruit Total Total 3.7 5.2 0.1 2.3 0.7 3.8 1.7 2.3 4.8 7.1 4.9 4.9 4.5 4.5 7.4 2.8 2.1 3.7 3.7 2.6 3.5 4.4 4.2 4.2 Canadian Journal of Plant Science (no./branch) (no./branch) 1 2 3 4 5 p p and Boscpear treestreated chemical thinners with in Data 2016. collected were from https://mc.manuscriptcentral.com/cjps-pubs 0.0009 ab ab bcd bc ab e e cde cde de ab cde cde ab ab a dc d bcd bcd cd a a abc a a a *** *** flower Fruit set Fruit number of number of clusters) *** *** *** *** ns ns ns * ns 0.7 4.8 19.8 30.0 12.5 31.3 13.8 16.2 For Review Only 34.2 38.0 0.0004 - ) 1 20 10 75 75 44.2 10 10 20 22.0 13.7 300 150 300 150 N/A 150 150 49.4 Rate fruit/100 (no. (mgL a a value value Statisticalsignificance NAA-FruitoneL S-ABA S-ABA NAA-FruitoneL 6-BA 150 6-BA 6-BA 6-BA L NAA-Fruitone L NAA-Fruitone S-ABA S-ABA significance Statistical 150 300 29.0 28.6 6-BA 6-BA 75 Table 7. Fruit 7. Table set andclustering datafrom Sna Cold Untreated control control Untreated control Hand-thinned N/A N/A 40.0 53.7 P control Untreated Hand-thinnedcontrol N/A fourbranchesrepresentative tree. per Treatment ACC ACC ACC ACC ACC 150 300 44.4 26.6 : Means : a columnwithin sharing sharing not not lowercased a italic letterdiffer the significant P at value ns, *, *, ns, **,***, indicates nonsignificant,and significant differences at multiple range multiple test. Note a P Page 35 of 39 Page 36 of 39 b *** *** 32.94 a 19.93 bc 19.41 bc 20.03 bc 18.14 bc 16.73 16.73 16.01 12.23 19.85 18.26 12.07 17.15 18.51 13.55 21.05 0.4475 a a 5.31 de ab a 13.52 cd ab b b 28.34 ab ab ab b b 0.88 e b b ab 28.93 ab * * (g) ($/tree) 258 240 255 249 217 220 234 212 212 242 ) a cd ab bcd bc bc bc 142 ab ab 156 a a bc bc d d a a a Bosc Cold Snap Cold 0.4 1.3 0.7 1.1 1.9 0.9 1.1 0.1 1.9 2.0 3.6 3.6 3.9 3.9 cd b b bc b a a b b b b a a a 144 d d a a a Canadian Journal of Plant Science 9.8 2.2 40.3 24.2 37.7 61.7 36.2 37.0 64.8 64.5 71.8 71.8 bc cd 65.0 bc 158 64.8 bc 60.7 de cd 86.8 ab 178 cd de 171 174 https://mc.manuscriptcentral.com/cjps-pubs ef bcd bcd de bcd abc abc cd bcd bcd bcd a bcd #### bcd bcd abc ab 94.3 a f f ab a ** ** *** *** ns ns *** *** *** *** fruit number Crop fruit value Total Total Mean Crop (kg/tree) (no./tree) (no./TCSA For Review Only 2.4 9.3 6.2 9.2 8.4 8.9 0.4 13.4 15.2 13.7 - ) 0.0017 <0.0001 <0.0001 0.0931 1 20 75 75 8.4 cd 53.7 cd de 155 300 150 150 300 N/A 150 150 15.7 Rate yield offruit load weight tree per (mgL c c value value 6-BA 6-BA 6-BA NAA NAA S-ABA S-ABA significance Statistical 10 20 150 11.2 300 11.0 7.1 10.8 d 39.0 d e 187 NAA 10 6-BA 6-BA 6-BA S-ABA 75 Statisticalsignificance 150 Treatment S-ABA Table 8. Total 8. Table numberyield, tree, per ofcrop fruit load,crop fruit weight, valueand trunk cross-sectional in response area to chemical thinning treatments toapplied Cold Snap™ andBosc2016. in pears control Untreated control Hand-thinned N/A N/A 9.4 11.4 cd 53.3 cd de 172 P control Untreated Hand-thinnedcontrol N/A NAA ACC ACC ACC ACC ACC 150 300 12.1 14.8 = = 0.001 P =and0.01, P P = 0.05, = P P Canadian Journal of Plant Science https://mc.manuscriptcentral.com/cjps-pubs For Review Only <0.0001 <0.0001 <0.0001 0.0430 <0.0001 Means column a within sharing sharing not not lowercased a italic letterdiffer the Psignificant at < value Trunk cross-sectional area. Gross returnswith no inputcosts included. ns, *, *, ns, **, ***, indicates nonsignificant,and significant differences at respectively. a c P b Note: 0.05 according0.05 level Duncan's to range multiple test. Page 37 of 39 Page 38 of 39 ab a a bc 5 5 ns ns 0.1 0.1 1.2 0.173 ab c 3.32 4 4 0.3 0.3 0.7 0.325 8 8 0.7 0.7 0.5 0.489 b c 1.36 cd 1.76 a b 3.39 a 3.20 a 4.79 5 5 1.4 1.4 0.9 0.636 ns ns ns bc d 1.25 ab c 1.89 Bosc Bosc Cold Snap Snap Cold 2 2 0.101 ab ab 1.9 bc 0.9 bc 1.2 a 0.9 ab 1.4 2.2 c 1.0 c 1.1 1.4 ab 1.0 0.7 c 0.2 ab 0.8 1.7 1.6 c 0.9 ab 0.2 1.3 c 0.4 1.3 1.2 1.1 1.3 a 2.0 0.4 2.1 1.1 0.6 1.1 1.3 1.7 0.7 1.0 0.5 0.6 0.9 0.7 0.2 0.6 0.4 0.1 0.7 3 3 ab 0.65 8 8 ab 1.28 4 4 a 1.66 a 2.83 a 3.59 a 2.40 ab 1.76 0.6 0.4 0.8 Weightfruit(kg/tree) of minimum each for category size ab c bc d 2.0 cd 1.3 bc d 1.2 bc d 1.6 bc d bc 1.9 d 1.6 Canadian Journal of Plant Science 3 3 7 7 bc 4 4 a 0.2 0.0 0.3 https://mc.manuscriptcentral.com/cjps-pubs ab c ab c a- d 1.7 d 1.0 d a d d a 2.4 bcd d cd 0.8 ab abc bc 1.6 ab 2.4 *** *** ** * ns 3 3 9 9 5 5 ab 0.1 0.0 For Review Only 0.1 a b b c 1.6 c b 0.8 c 1.0 a 2.5 b c 1.0 c b 0.8 c 1.5 c 1.1 a 2.2 a b 2.0 1 1 b 5 5 0 0 a 0.0002 0.0002 0.0002 0.0018 0.0224 0.0 0.0 0.1 1.5 1.3 1.6 1.5 3.4 0.7 0.8 3.3 2.6 1.0 <57 mm mm <57 mm 57 mm 60 mm 64 mm 67 mm 70 mm 73 mm 76 mm >76 ) -1 *** 75 75 L a N/A (mg 150 150 N/A N/A Rate value value are indicated are for below each category.respective 6-BA 6-BA 75 NAA NAA S-ABA 10 150 Table 9. Influence 9. Table of chemical thinning treatments fruit size on distribtutionof Snap™ Cold and Bosc infruit. pears For2016 each treatment,harvested all fruit sorted were into size nine classestheir according to The weight. minimum used separate to diameter the fruit Treatment control Untreated N/A Hand-thinned control P control Untreated Hand-thinned N/A control 6-BA 6-BA 6-BA NAA S-ABA 20 300 significance Statistical ACC ACC ACC 150 300 ab c ab ab ab c bc ab ** ab c 2.43 bc d 3.19 ** ab c 1.96 b c 1.78 bc 2.26 ab 3.21 b c 1.59 c 2.21 ab 3.17 = = respectively. 0.001 P bc d 0.67 c 2.27 bc d 1.04 bc d 1.14 =and0.01, P P = 0.05, = P P 6 6 ab 0.62 1 1 a 1.39 ab 2.43 a 3.17 ab 2.37 ab 2.63 9 9 ab 0.56 6 6 b 0.51 5 5 b 0.06 d 0.17 c 0.04 d 0.04 d 0.05 8 8 b 0.03 d 0.24 c 0.81 cd 0.38 cd 0.87 3 3 b 0.33 cd 0.54 c 0.92 cd 1.02 0.2 0.8 0.2 0.1 0.0 0.0 0.1 ab c ab c Canadian Journal of Plant Science 2 2 0 0 ab 2 2 c 1 1 0 0 c 0 0 c 5 5 c 0.1 0.3 0.0 0.1 0.0 0.0 0.0 https://mc.manuscriptcentral.com/cjps-pubs 6 6 bc 1 1 a 0 0 c 4 4 bc 0 0 c 2 2 bc 0 0 c 0.0 0.2 0.0 0.0 0.0 0.0 0.0 For Review Only *** *** * * * ** *** *** 3 3 b 9 9 a 0 0 b 0 0 b 1 1 b 0 0 b 0 0 b 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0005 0.0137 0.0259 0.0185 0.0024 0.0000 0.0000 0.0038 0.0051 20 10 300 150 150 300 150 a Means column a within sharing sharing not not lowercased a italic letterdiffer the Psignificant at Page 39 of