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Irrigation decision support systems evolving in the domestic temperate tree fruit production industry incorporate measures of soil moisture status, which diverges from classic physiological indicators of edaphic stress. This study used an autonomous sensor-based irrigation system to impose a water deficit (soil matric potential targets of –25, –40, –60, and –80 kPa) on ‘Autumn Gala’, ‘CrimsonCrisp’, and ‘Golden Delicious’ apple (Malus domestica) cultivars grafted to ‘Budagovsky 9’ rootstock in the greenhouse (n 5 60). It was hypothesized that relationships between physiological plant function, assessed via infrared gas exchange and chlorophyll fluorescence, and the soil matric potential may be used to advance emerging irrigation decision support systems. Complications arising from defoliation by day 11 at –60 and –80 kPa indicate the generation of substrate-specific soil–water relationships in research applications of autonomous sensor-based irrigation systems. ‘Autumn Gala’ carbon assimilation rates at –80 kPa declined from day 0 to day 8 (9.93 and 5.86 lmolμm–2 μs –1 carbon dioxide), whereas the transpiration rate was maintained, potentially reducing observed defoliation as other cultivars increased transpiration to maintain carbon assimilation. Correlation matrices revealed Pearson’s r ≤ |0.43| for all physiological metrics considered with soil matric potential. Nevertheless, exploratory regression analysis on predawn leaf water potential, carbon assimilation, transpiration, stomatal conductance, and nonphotochemical quenching exposed speculatively useful data and data shapes that warrant additional study. Nonlinear piecewise regression suggested soil matric potential may useful as a predictor for the rate of change in predawn leaf water potential upon exposure to a water deficit. The critical point bridging the linear spans, –30.6 kPa, could be useful for incorporating in emerging irrigation decision support systems. [ABSTRACT FROM AUTHOR]

Promalin (Valent BioSciences, Libertyville, IL, USA) is a proprietary mixture of gibberellin A4 + 7 and 6-benzyladenine that is widely used in apple production to improve the fruit shape, size, and skin quality. Promalin typically increases fruit size and length. However, the increased growth likely increases the strain in the fruit skin, which may exacerbate microcracking of the cuticle and, consequently, russeting. This study aimed to monitor the growth-stimulating effect of Promalin in three different regions of fruits and investigate whether Promalin affects cuticular microcracking via effects on the deposition of cuticular components or via the accumulation of strain in the cuticle. Four Promalin sprays (20 mg⋅L−1) were applied to runoff; the first was applied at full bloom, and the remaining sprays were applied at approximately weekly intervals thereafter. Fruit surface areas and fruit surface area growth rates of the Promalin-treated fruits were higher than those of the untreated control fruits. Promalin increased the fruit length, but it had no effect on the fruit equatorial diameter. In Promalin-treated fruits, the base of each sepal extended, thickened, and became fleshy as early as 15 days after full bloom (DAFB). Allometric growth analyses revealed higher constant differential growth ratios of the pedicel and calyx length (before 36 DAFB) in Promalin-treated fruits than in control fruits. After 36 DAFB, the difference in constant differential growth ratios between Promalin-treated fruits and control fruits decreased. Cuticle mass per unit area increased with time in all regions of the fruit surface and was slightly (+3.3%) but significantly higher in fruits treated with Promalin than in control fruits. Additionally, the biaxial strain release was slightly and significantly lower in Promalin-treated fruits than in control fruits. When the isolated, cuticle was ablated from the inner surface and dewaxed, strain relaxation in the control fruits was higher than that in the Promalin-treated fruits. It was concluded that Promalin treatment increases the length of the fruit by increasing the lengths of the pedicel and calyx regions early during fruit development. Promalin only slightly increased cuticle deposition and fixation of cuticular strain. Promalin had no effects on microcracking or russeting.

Aminoethoxyvinylglycine (AVG) is widely used in commercial apple (Malus ×domestica Borkh.) production to reduce preharvest fruit drop (PFD) and delay ripening for harvest management. Recently, the maximum allowable concentration of AVG was doubled (up to 264 mg⋅L−1). Reports of the relationship between the AVG concentration and fruit growth, size, and quality have been contradictory. We evaluated the relationship between the AVG concentration and PFD, fruit size, fruit quality, and expression of ethylene signaling-related and cell wall modification-related genes. Experiments were conducted in 2019 and 2020 using mature ‘Red Delicious’ in western North Carolina. The AVG treatments [0 and 132 (AVG-1x) and 264 mg⋅L−1 (AVG-2x)] were applied 3 weeks before the expected harvest. The AVG treatments reduced fruit drop and internal ethylene concentration relative to the control in both years. There was no difference in drop between AVG-1x and AVG-2x applications. Only in 2020 did AVG treatments delay fruit softening and starch hydrolysis and reduce soluble solids concentration. There were no effects on red fruit color development. Fruit size was unaffected by AVG in 2019, but it was reduced in 2020 with the AVG-2x application. AVG reduced ethylene synthesis and altered signaling, evidenced by decreased relative expression of genes related to ethylene signaling (ARGOS1, ARGOS2). AVG applications also reduced the expression of EXPA8;1, suggesting that reduced cell wall disassembly was associated with a reduction in fruit softening. These results indicate that preharvest applications of 132 mg⋅L−1 AVG effectively reduced PFD via altering ethylene evolution and signaling. Use of a higher AVG concentration was of limited benefit. [ABSTRACT FROM AUTHOR]

Multistep chemical thinning programs have been widely recommended in the eastern United States; however, adoption of bloom thinners is limited. With caustic blossom thinners, narrow effective application timings and concerns related to spring frost damage are barriers for commercial use in this region. If effective and safe, use of hormonal blossom thinners for apple would be an attractive alternative. We evaluated the effects and interactions of bloom thinners [6-benzyladenine (BA) and lime sulfur (LS, or calcium polysulfide) + stylet oil (LS+SO)] and a postbloom thinner (NAA) in the context of a multistep, carbaryl-free thinning program across three locations. Experiments were conducted in 2017 and 2018 on mature ‘Gala’ in North Carolina, Massachusetts, and Pennsylvania, USA. In four of six studies, BA at bloom increased the efficacy of postbloom NAA and reduced crop density (P < 0.08). Postbloom NAA generally increased fruit relative growth rate (RGR) and reduced crop density. However, where NAA failed to reduce crop load, there was a negative influence on RGR. BA and LS+SO increased RGR in one of six studies; however, BA was generally ineffective as a blossom thinner, whereas LS+SO was more effective. Nevertheless, BA applied at bloom may have utility as part of a multistep thinning program. As a part of a multistep thinning program, BA applied at bloom may be useful in increasing efficacy of postbloom applications, particularly when use of caustic blossom thinners is not permitted. [ABSTRACT FROM AUTHOR]

Irrigation decision support systems evolving in the domestic temperate tree fruit production industry incorporate measures of soil moisture status, which diverges from classic physiological indicators of edaphic stress. This study used an autonomous sensor-based irrigation system to impose a water deficit (soil matric potential targets of –25, –40, –60, and –80 kPa) on ‘Autumn Gala’, ‘CrimsonCrisp’, and ‘Golden Delicious’ apple (Malus domestica) cultivars grafted to ‘Budagovsky 9’ rootstock in the greenhouse (n = 60). It was hypothesized that relationships between physiological plant function, assessed via infrared gas exchange and chlorophyll fluorescence, and the soil matric potential may be used to advance emerging irrigation decision support systems. Complications arising from defoliation by day 11 at –60 and –80 kPa indicate the generation of substrate-specific soil–water relationships in research applications of autonomous sensor-based irrigation systems. ‘Autumn Gala’ carbon assimilation rates at –80 kPa declined from day 0 to day 8 (9.93 and 5.86 μmol⋅m–2⋅s–1 carbon dioxide), whereas the transpiration rate was maintained, potentially reducing observed defoliation as other cultivars increased transpiration to maintain carbon assimilation. Correlation matrices revealed Pearson’s r ≤ |0.43| for all physiological metrics considered with soil matric potential. Nevertheless, exploratory regression analysis on predawn leaf water potential, carbon assimilation, transpiration, stomatal conductance, and nonphotochemical quenching exposed speculatively useful data and data shapes that warrant additional study. Nonlinear piecewise regression suggested soil matric potential may useful as a predictor for the rate of change in predawn leaf water potential upon exposure to a water deficit. The critical point bridging the linear spans, –30.6 kPa, could be useful for incorporating in emerging irrigation decision support systems.

Organic apple (Malus ×domestica Borkh.) growers lack effective strategies to manage preharvest drop. For susceptible cultivars, yield losses caused by preharvest drop can exceed 30% at the beginning of harvest. To address this issue, a formulation of aminoethoxyvinylglyine (AVG) designed for organic use was developed and compared with a commercially available AVG formulation. We evaluated the effects and interactions of the AVG formulation and application number on preharvest drop and fruit maturity in 2017 and 2018. We selected 30 pairs of mature ‘Oregon Spur II Red Delicious’/‘M. 111’ trees planted at the Mountain Horticultural Crops Research and Extension Center in Mills River, NC, USA. Trees were planted with spacing of 2.7 × 6.1 m, trained to a central leader, and received plant protectant sprays that adhered to local recommendations throughout the growing season. Both AVG formulations were applied at 132 mg⋅L−1 at 3 or 3 + 1 weeks before the anticipated harvest. An untreated control was also included for comparison. The experiment had six replicates and a randomized complete block design with a 2 × 2 augmented factorial treatment structure. A one-way analysis of variance was performed and single degree of freedom contrasts were used to compare treatment groups of interest. During both years, organic and conventional AVG were equally effective for reducing preharvest drop and delaying fruit softening and starch hydrolysis at harvest. During one year, increasing the number of applications of AVG reduced cumulative fruit drop, delayed fruit softening at harvest, and reduced internal ethylene concentrations. Inconsistencies in responses across years may be explained, in part, by abnormally warm temperatures observed in 2018. AVG approved for organic use appears to be a promising preharvest drop management technology with efficacy similar to that of conventional AVG.

Aminoethoxyvinylglycine (AVG) is widely used in commercial apple (Malus ×domestica Borkh.) production to reduce preharvest fruit drop (PFD) and delay ripening for harvest management. Recently, the maximum allowable concentration of AVG was doubled (up to 264 mg⋅L−1). Reports of the relationship between the AVG concentration and fruit growth, size, and quality have been contradictory. We evaluated the relationship between the AVG concentration and PFD, fruit size, fruit quality, and expression of ethylene signaling-related and cell wall modification-related genes. Experiments were conducted in 2019 and 2020 using mature ‘Red Delicious’ in western North Carolina. The AVG treatments [0 and 132 (AVG-1x) and 264 mg⋅L−1 (AVG-2x)] were applied 3 weeks before the expected harvest. The AVG treatments reduced fruit drop and internal ethylene concentration relative to the control in both years. There was no difference in drop between AVG-1x and AVG-2x applications. Only in 2020 did AVG treatments delay fruit softening and starch hydrolysis and reduce soluble solids concentration. There were no effects on red fruit color development. Fruit size was unaffected by AVG in 2019, but it was reduced in 2020 with the AVG-2x application. AVG reduced ethylene synthesis and altered signaling, evidenced by decreased relative expression of genes related to ethylene signaling (ARGOS1, ARGOS2). AVG applications also reduced the expression of EXPA8;1, suggesting that reduced cell wall disassembly was associated with a reduction in fruit softening. These results indicate that preharvest applications of 132 mg⋅L−1 AVG effectively reduced PFD via altering ethylene evolution and signaling. Use of a higher AVG concentration was of limited benefit.

Multistep chemical thinning programs have been widely recommended in the eastern United States; however, adoption of bloom thinners is limited. With caustic blossom thinners, narrow effective application timings and concerns related to spring frost damage are barriers for commercial use in this region. If effective and safe, use of hormonal blossom thinners for apple would be an attractive alternative. We evaluated the effects and interactions of bloom thinners [6-benzyladenine (BA) and lime sulfur (LS, or calcium polysulfide) + stylet oil (LS+SO)] and a postbloom thinner (NAA) in the context of a multistep, carbaryl-free thinning program across three locations. Experiments were conducted in 2017 and 2018 on mature ‘Gala’ in North Carolina, Massachusetts, and Pennsylvania, USA. In four of six studies, BA at bloom increased the efficacy of postbloom NAA and reduced crop density (P < 0.08). Postbloom NAA generally increased fruit relative growth rate (RGR) and reduced crop density. However, where NAA failed to reduce crop load, there was a negative influence on RGR. BA and LS+SO increased RGR in one of six studies; however, BA was generally ineffective as a blossom thinner, whereas LS+SO was more effective. Nevertheless, BA applied at bloom may have utility as part of a multistep thinning program. As a part of a multistep thinning program, BA applied at bloom may be useful in increasing efficacy of postbloom applications, particularly when use of caustic blossom thinners is not permitted.

Abstract. Organic apple (Malus ×domestica Borkh.) growers lack effective strategies to manage preharvest drop. For susceptible cultivars, yield losses caused by preharvest drop can exceed 30% at the beginning of harvest. To address this issue, a formulation of aminoethoxyvinylglyine (AVG) designed for organic use was developed and compared with a commercially available AVG formulation. We evaluated the effects and interactions of the AVG formulation and application number on preharvest drop and fruit maturity in 2017 and 2018. We selected 30 pairs of mature ‘Oregon Spur II Red Delicious’/‘M. 111’ trees planted at the Mountain Horticultural Crops Research and Extension Center in Mills River, NC, USA. Trees were planted with spacing of 2.7 × 6.1 m, trained to a central leader, and received plant protectant sprays that adhered to local recommendations throughout the growing season. Both AVG formulations were applied at 132 mg.L-1 at 3 or 3 + 1 weeks before the anticipated harvest. An untreated control was also included for comparison. The experiment had six replicates and a randomized complete block design with a 2 × 2 augmented factorial treatment structure. A one-way analysis of variance was performed and single degree of freedom contrasts were used to compare treatment groups of interest. During both years, organic and conventional AVG were equally effective for reducing preharvest drop and delaying fruit softening and starch hydrolysis at harvest. During one year, increasing the number of applications of AVG reduced cumulative fruit drop, delayed fruit softening at harvest, and reduced internal ethylene concentrations. Inconsistencies in responses across years may be explained, in part, by abnormally warm temperatures observed in 2018. AVG approved for organic use appears to be a promising preharvest drop management technology with efficacy similar to that of conventional AVG. [ABSTRACT FROM AUTHOR]

Irregular flowering and biennial bearing are challenging in many apple (Malus ×domestica) cultivars such as Honeycrisp. Apple flowering is influenced by many factors including crop load, fruit weight, seed number, and bourse shoot length. However, it is unclear how these factors exert their control. We investigated flowering in ‘Honeycrisp’ and whether flower formation is regulated locally within the spur or if it is under the control of the whole tree system. Treatments consisting of 30 to 240 fruit per tree with one or two fruit per spur were applied, and seed number, fruit weight, bourse shoot length, bourse number, and resulting flower formation measured. In 2013, flowering was affected by fruit number per tree, fruit number per spur and their interaction, and with lower total tree crop loads, spurs bearing two fruit had fewer flowers than those with a single fruit. In 2014, few spurs formed flowers regardless of treatment. In 2013, flowering was unaffected by seed number on single-fruited spurs but flowering inhibition was correlated with fruit weight. In spurs bearing two fruit, flowering was inhibited by higher seed numbers but fruit weight per spur had no effect on flowering. Our data suggest that both whole tree and within-spur characteristics contribute to local flower formation. Therefore, ‘Honeycrisp’ spurs can be considered semiautonomous organs because inhibition of flower formation appears to be related to the depletion of resources both locally within the spurs, and systematically within the whole tree. The main factors associated with flower formation were fruit number per tree, fruit number per spur, bourse shoot length, and bourse number per spur. In contrast to previous reports, our data show that seeds do not play a direct role in regulating flower formation.

Apple (Malus ×domestica) growers can incur significant economic losses when fruit drop before they can be harvested [preharvest fruit drop (PFD)]. In some years and cultivars, more than 30% of potential yield can be lost. Growers frequently apply plant bioregulators to reduce PFD, either via delay in maturity [aminoethoxyvinylglycine (AVG), 1-methylcycolpropene] or via inhibition in production of cell hydrolysis enzymes in the fruit pedicel [naphthalene acetic acid (NAA)]. Finding a physiological indicator of PFD would allow growers to assess the susceptibility of fruit to PFD. Due to its lignification, xylem is believed to be the last tissue to break down in the fruit pedicel, leading to PFD. To determine whether loss in xylem functionality can be used as an indicator of PFD potential, studies were conducted in 2020 and 2021 with ‘Red Delicious’ treated with AVG (132 µL·L−1), NAA (10 µL·L−1), and an ethylene-producing compound [ethephon (150 µL·L−1 in 2020, 200 µL·L−1 in 2021)] to generate a range of PFD potentials. Xylem functionality was assessed in the fruit cortex. Internal ethylene content (IEC), fruit maturity indices, and PFD rates were quantified weekly throughout the harvest period. Expression of genes encoding for cell hydrolysis enzymes (MdEG1 and MdPG2) was quantified to relate xylem functionality to fruit abscission mechanisms. In 2020 and 2021, AVG reduced PFD compared with the untreated control by decreasing IEC. Although ethephon did not result in higher PFD than untreated fruit, NAA reduced PFD in 2020 but not 2021. For all treatments in both years, there was a linear decrease in xylem functionality throughout the measurement period. Cumulative PFD exponentially decreased as xylem functionality neared zero and the climacteric rise in ethylene began. Concurrent with the rise in IEC and PFD was an increase in the expression of MdEG1 and MdPG2 in the fruit pedicel of the control compared with AVG-treated fruit. AVG-treated fruit lost xylem functionality at a similar rate to the untreated control but had lower expression of MdEG1 and MdPG2. These results indicate that xylem functionality is not a sole direct indicator of PFD. The concurrent increase in PFD and expression of MdEG1/MdPG2 supports previous research indicating that these two genes may serve as potential markers for PFD.

‘Honeycrisp’ is a popular apple cultivar, but it is prone to several disorders, especially bitter pit. Previously reported models for predicting bitter pit are biased, indicating that the models are missing one or more important predictor variables. To identify additional variables that may improve bitter pit prediction, a study was undertaken to investigate the influence of canopy position, spur characteristics, and individual fruit characteristics on bitter pit development. ‘Honeycrisp’ trees from two orchards over 2 years provided four combinations of orchards and years. Fruits were sampled from spurs at different canopy positions and with varying bourse shoot lengths and numbers of fruits and leaves. Following cold storage, bitter pit was assessed in three ways: 1) bitter pit severity was recorded as the number of pits per fruit, 2) bitter pit was recorded as a binomial response (yes, no) for each fruit, and 3) the incidence of bitter pit was recorded as the proportion of fruit developing bitter pit. As a result of the high fruit-to-fruit variation, bitter pit severity was associated with canopy position or spur characteristics to a lesser extent than bitter pit incidence. Bitter pit incidence was generally greater for fruits developing on spurs with only one fruit and spurs from the lower canopy. Binomial data were analyzed with a generalized linear mixed model. Fruit harvested from trees with heavy crop loads, and those developing on spurs with multiple fruit and spurs with long bourse shoots had the lowest probability of developing bitter pit. Regardless of how bitter pit was assessed, bitter pit related positively to fruit weight (FW), but the relationship usually depended on other variables such as canopy position, fruit per spur, and leaves per spur. The advantages of fitting binomial data with logistic regression models are discussed.

Zinc finger–homeodomain (ZF-HD) proteins, a family of plant-specific transcription factors, play an important role in regulating plant growth and development, as well as responses to stress. Although ZF-HDs have been investigated in several model plants, no systematic studies have been reported in apple (Malus ×domestica). In this study, 14 putative ZF-HD genes were identified in the apple genome and characterized using bioinformatics tools. All members harbored complete canonical structures of the ZF-HD motif. Phylogenetic analysis demonstrated that ZF-HD genes in the genome of apple could be classified into four subfamilies, with high intragroup similarities. Gene-structure analysis revealed that although 11 MdZHDs had only one exon, MdZHD6 and MdZHD13 had two exons and MdZHD8 had six exons, suggesting limited variation among the apple ZHD genes. The expression profiles of MdZHD genes revealed their involvement in the growth and development of different tissues. Numerous binding sites for transcription factors, such as MYB, bZIP, and AP2, were found in the promoter region of the putative MdZHD genes. Nearly all putative MdZHDs were predicted to localize in the nucleus. Finally, the expression levels of the MdZHD genes under abiotic stress were examined in apple rootstock Malus hupehensis and the results showed that the expression of 10 MdZHD genes was induced in response to three abiotic stress factors. Exceptionally, the expression of MdZHD11 was not induced in response to any of the abiotic stress treatments, MdZHD12 was only induced in response to salt stress, and MdZHD7 and MdZHD9 were induced in response to both drought and salt stress. The present results provide valuable insights into the putative physiological and biochemical functions of MdZHDs in apple.

The goal of this research was to evaluate resistance of apple rootstocks to late winter deacclimation during a 2-day exposure to warm temperatures in Maine. We measured the cold temperature tolerance of xylem, phloem, and cambium from 0 to −40 °C in 1- and 2-year-old shoot pieces from apple rootstock cultivars and advanced selections ‘M.9 T337’ (M.9), ‘M.7 EMLA’ (M.7), ‘Budagovsky 9’ (B.9), ‘Geneva® 41’ (G.41), ‘Geneva 30’ (G.30), ‘Geneva 935’ (G.935), ‘Geneva 814’ (G.814), G.4013, G.5257, and Vineland 6 (V.6) after a 2-day exposure to warm (22 °C) or cold (2 to 4 °C) temperatures. Injury was measured on a 0 to 10 rating scale based on percentage of discolored cross-sectional xylem and phloem, and cambial length and circumference with brown discoloration, with 0 indicating no browning and 10 indicating browning in the entire tissue. Injury was also measured as intensity of browning on a scale of 0 (no browning) to 5 (dark brown to black). The weighted averages of the two ratings were used to calculate an index of browning. Genotypic variation occurred in the degree of deacclimation, which ranged from none to as much as 15 °C loss in hardiness. Two genotypes, ‘G.41’ and ‘M.9’, showed little change in hardiness in both years they were tested. Two genotypes, G.4013 and ‘G.814’, lost substantial hardiness in both years and may be vulnerable to late winter freeze-thaw events, but were among the hardiest before deacclimation. ‘G.935’ and G.5257 showed a small loss of hardiness, whereas ‘B.9’ lost hardiness in the cambium, but not the xylem, and V.6 lost hardiness after warm exposure, but showed almost no injury at temperatures as cold as −35 °C. The loss of hardiness of these four genotypes that were tested in only one year should be verified with additional testing because of the potential for yearly variation.

The organic acid concentration in apple (Malus ×domestica) juice is a major component of hard cider flavor. The goal of this study was to determine if the malic acid markers, Ma1 and Q8, could classify the titratable acidity concentration in cider apple accessions from the United States Department of Agriculture Malus germplasm collection into descriptive classifications. Our results indicate that for diploid genotypes, the Ma1 marker alone and the Ma1 and Q8 markers analyzed together could be used to predict cider apple acidity (P < 0.0001). Alone, the Ma1 marker categorized acidity into low (5.8 g⋅L−1) groups. The combination of Ma1 and Q8 markers provided more specificity, which would be useful for plant breeding applications. This work also identified a significant difference (P = 0.0132) in acidity associated with ploidy. On average, the triploids accessions had 0.33 g⋅L−1 higher titratable acidity than the diploid accessions. Based on the results of this work, we propose a genetics-based classification system for cider apples with the acidity component defined by the Ma1 and Q8 markers.

Harvesting labor is the largest annual variable operating expense for apple (Malus ×domestica) orchard enterprises and is subject to escalating costs and shortages. In Europe, much of the cider apple harvesting is done with machinery, greatly reducing production costs. However, despite a rapid increase in hard cider production in North America over the past 15 years, mechanical cider apple harvesting has not been widely implemented. In this study, we compared mechanical with hand harvesting costs for model 5-, 15-, and 60-acre cider apple orchards located in New York using a partial budget model. Scale-appropriate harvesters were identified for use at each farm scale. Sensitivity analyses were used to test the cost differential for using each piece of machinery on varying orchard sizes and to model changes in labor costs. Across all orchard scales, we found that mechanically harvesting cider apples was more profitable than hand harvesting, with larger operations breaking even sooner and realizing greater returns than operations using hand harvesting. Mechanical harvesting costs broke even with hand harvesting in years 16, 7, and 5 and by year 30 reduced cumulative harvesting costs by 23%, 52%, and 53% in our 5-, 15-, and 60-acre model orchards, respectively. Increasing the orchard size resulted in greater returns from mechanical harvesting. Using the machinery in the 15-acre orchard scenario on a 30-acre farm resulted in costs breaking even with hand harvesting in year 3; by year 30, the cumulative costs resulted in 66% lower harvesting costs than hand labor. Mechanical harvesting remained profitable when labor wages were decreased and became more profitable in scenarios with increasing wages. For example, in the 60-acre orchard, mechanical harvesting cost 41% less than hand harvesting with a 2% annual compounding decrease in labor wages; with 2% annual compounding increase in labor wages, the mechanical harvesting cost was 63% less than hand harvesting. In addition to the cost savings, mechanical harvesting allows for harvesting cider apples with fewer logistical challenges, such as contracting, housing, and transporting migrant labor.

Mechanical hedging was evaluated at Washington State University Northwestern Washington Research and Extension Center, Mount Vernon, WA, in 2019 and 2020 on eight cider apple (Malus ×domestica) cultivars with four bearing habits: tip—Golden Russet, Harrison; spur—Brown Snout, Cap of Liberty; semispur—Tom Putt, Campfield; and crab—Puget Spice, Hewe’s Virginia Crab. Trees were planted on ‘Geneva 935’ (Malus hybrid) rootstock in one replicate block in 2014 and the second replicate block in 2016 and the central leader of all trees was headed in 2017 to equalize tree size and stage of development. Summer hedging was carried out on all cultivars on 16 July in 2019 and 7 July in 2020. The response of different cultivars was evaluated both years by measuring canopy area removed, shoot biomass removed, and fruit removed, and the amount of time to hedge was measured. Additionally, fruit diameter and fruit yield per tree were measured at harvest both years, and fruit weight was measured at harvest only in 2020. The hedger traveled at an average speed of 1.32 mph; it took 6 seconds on average to hedge both sides of one tree when in-row spacing was 6 ft and took 1.25 minutes to maneuver around the end of a row. The estimated time to hedge 1 acre was 1.45 hours when the hedger traveled at 116 ft/min and the orchard had 10 rows spaced 12 ft apart. Biomass removed on an area and weight basis was less in 2020 than in 2019, whereas yield per tree was 2.6 times greater in 2020 than 2019, and cultivars within a bearing habit differed in these responses to hedging both years. Fruit damaged by the hedger was assessed but observed to be negligible for all cultivars. Yield per tree was negatively correlated with fruit diameter (P < 0.001) and positively correlated with the number of fruit removed per tree (P < 0.025). Further research is needed to assess the long-term effects of hedging on biomass removal, yield, and biennialism to determine whether summer mechanical hedging is a cost-effective and suitable method for managing cider apple orchards.

‘Honeycrisp’ apple is susceptible to bitter pit, which is associated with fruit mineral nutrient composition. Rootstock genotypes can affect nutrient acquisition, distribution, and fruit yields, which all affect fruit nutrient composition and bitter pit susceptibility. However, the changes of these traits among different rootstock genotypes in response to abiotic stress under semiarid conditions are relatively unknown. The objective of this study was to evaluate the influence of different rootstocks and irrigation on nutrient uptake and partitioning with ‘Honeycrisp’ apple grown in an irrigated, semiarid environment. ‘Honeycrisp’ apple trees were grafted on four different rootstocks, Geneva 41 (‘G.41’), Geneva 890 (‘G.890’), M.9-T337 (‘M.9’), and Budagovsky 9 (‘B.9’), and these were planted at high density (3000 trees/ha). Irrigation was applied as either a water-limited treatment where volumetric soil water content was maintained near 50% field capacity (FC) and a well-watered control where soil water content was maintained near 100% FC. ‘G.890’, the most vigorous rootstock, had lower nitrogen and higher potassium content in leaves, while ‘B.9’, the least vigorous rootstock, had lower potassium and higher nitrogen content. Rootstock genotype did not affect calcium uptake. Interestingly, water-limited conditions increased the nutrient content in root and stems but not in leaves. Water-limited trees partitioned more nitrogen and calcium to roots, while well-watered trees in the control partitioned more nutrients to the stems. Fruit size was the largest for ‘G.890’ and smallest for ‘B.9’. Both ‘G.41’ and ‘G.890’ had higher bitter pit incidence, which was associated with higher potassium content in leaves and fruit. These results suggest that rootstock-induced vigor and irrigation can both contribute to nutrient imbalances in leaves and fruit that could affect the development of physiological disorders in ‘Honeycrisp’ apple.

Growers need reliable information on costs and returns they can expect for a cider apple (Malus ×domestica) orchard suitable for mechanization because specialty cider apples can only be used for making cider, and returns are expected to be lower than for fresh table apples. This study estimates the costs, returns, and net profit that growers may realize by planting cider apples in either a freestanding or tall spindle system that use a mechanical harvester (both systems) and mechanical hedger (tall spindle system only). Results show that both production systems have positive net returns during full production, and their respective break-even returns are lower than the current market price, demonstrating that both systems are potentially profitable investments. Results also show that the tall spindle system is potentially more profitable due to the advantages of earlier start of fruiting and higher crop yield. The estimated net returns of the tall spindle system during full production are nearly 4 times higher than that of a freestanding system. At a discount rate of 10%, the net present value (NPV) of the tall spindle system is positive and payback period is 13 years, whereas the NPV of the freestanding system is negative. The discount rate represents the time value of money and reflects the perception of risk for the investment. The break-even discount rates (i.e., NPV = 0) are ≈6.88% for the freestanding system and 10.78% for the tall spindle system. Sensitivity scenarios found that when all else was constant, profitability increased as market price, crop yield, and production area increase and also when the cost of the harvester decreased. Because mechanical harvesters are expensive, profitability tends to be more favorable for larger farms due to economies of scale. Also, a high picking efficiency is important because fruit that falls on the ground is considered crop yield loss and reduces the gross income from cider apples.

‘Honeycrisp’ (Malus ×domestica) apples were harvested from a total of 17 mid-Atlantic orchards during 2018 and 2019 to verify a previously published bitter pit prediction model. As in the previous study, bitter pit incidence was associated with low calcium (Ca) levels and high ratios of nitrogen (N), potassium (K), and/or magnesium (Mg) to Ca in the fruit peel and excessive terminal shoot growth. The best two-variable model for predicting bitter pit developed with the 2018–19 data set contained boron (B) and the ratio of Mg to Ca (R2 = 0.83), which is different from previous models developed with data from three individual years (2015–17). When used to predict the bitter pit incidence of the 2018–19 data, our previous best model containing the average shoot length (SL) and the ratio of N to Ca underestimated the incidence of bitter pit. The model is probably biased because one or more important variables related to bitter pit have not yet been identified. However, the model is accurate enough to identify orchards with a low incidence of bitter pit.

Blossom thinning can confer significant benefits to apple growers, including increased fruit size and annual bearing. However, current blossom thinning practices can damage spur leaves and/or fruit. We evaluated the use of short duration forced heated air treatments [thermal shock (TS)] as a blossom thinning strategy for ‘York Imperial’. Using a variable-temperature heat gun, TS treatments were applied to solitary blossoms 24 hours after pollination. Effects of output temperature (five levels) and treatment duration (four levels) were evaluated using a completely randomized design with a factorial treatment structure. Short duration treatments (0.5 and 1.0 seconds) were ineffective for arresting pollen tube growth in vivo. TS temperature required to inhibit stylar pollen tube growth was inconsistent across years. In 2014, TS temperatures ≥56 °C inhibited pollen tubes from reaching the style base at 2.0 and 4.0 second durations. However, in 2015, TS temperatures ≥81 °C at 4.0 seconds prevented pollen tubes from reaching the style base. Inconsistent effects of TS across years were attributed to treatments being applied too late due to optimal conditions for pollen tube growth during the intervening 24-hour period after pollination. Excessive injury to spur leaf tissue was observed at temperatures higher than 84 °C and 70 °C (2.0 and 4.0 seconds, respectively). Pollen tube growth was reduced or arrested at temperature and duration combinations that caused minimal visible injury to spur leaves. Identifying and exploiting structural differences between apple blossoms and vegetative spur leaves may provide insight for the future development of TS or other attempts at developing selective thinning technologies.

The use of short-duration applications of thermal energy (thermal shock; TS) as an apple blossom thinning strategy was investigated. Effects of TS temperature and timing on stigmatic receptivity, pollen tube growth in vivo, and visible leaf injury were evaluated in multiple experiments on ‘Crimson Gala’. TS treatments were applied to blossoms and spur leaves using a variable temperature heat gun. TS temperatures ≥86 °C had a strong inhibitory effect on pollen tube growth on the stigmatic surface and in the style. TS temperatures >79 °C reduced average pollen tube length to less than the average style length. Timing of TS treatment (0 or 24 hours after pollination) was not an influential factor, indicating that effective TS temperatures reduced pollen tube growth up to 24 hours after the pollination event. The onset of thermal injury to vegetative tissues occurred at similar TS temperatures that inhibited pollen tube growth in vivo. Excessive leaf injury (>33%) was observed at 95 °C, suggesting relatively narrow differences in thermal sensitivity between reproductive and vegetative tissues. Inconsistent TS temperatures and/or responses were observed in some experiments. Ambient air temperature may have influenced heat gun output temperatures and/or plant susceptibility. While results suggest some promise, additional work is required to validate and further develop this concept.

‘Brown Snout’ cider apple (Malus ×domestica) is desired by cider makers for its relatively high levels of phenolics, and over-the-row machine harvesting of ‘Brown Snout’ has been demonstrated to provide similar yield to hand harvest at a significantly lower cost. The purpose of this study was to determine if there is a measurable impact of harvest method on the phenolic profile of ‘Brown Snout’ juice and cider to better inform equipment adoption recommendations. Using a redox titration assay, the titratable tannin content (± SE) of juice (0.19% ± 0.01%) and cider (0.19% ± 0.01%) were found not to differ due to harvest method. Using a protein precipitation assay, juice from machine-harvested fruit was found to have lower levels of total tannins [231 ± 36 mg·L−1 catechin equivalents (CE)] than juice from hand-harvested fruit (420 ± 14 mg·L−1 CE). However, the total tannins of cider did not differ due to harvest method, the overall average for machine and hand harvest was 203 ± 22 mg·L−1 CE. The total phenolics of juice and cider did not differ due to harvest method (1415 ± 98 mg·L−1 CE and 1431 ± 73 mg·L−1 CE, respectively). Discriminant analysis based on an average of 33 tentatively identified phenolic compounds, as measured by ultra-high performance liquid chromatography coupled with quadrupole time of flight mass spectrometry, showed no separation due to harvest method in juice or cider. In conclusion, over-the-row machine harvesting of ‘Brown Snout’ resulted in a final product of similar quality at reduced labor costs, and thus shows potential for increasing the commercial sustainability of cider apple operations.

Anthracnose canker, caused by Neofabraea malicorticis, threatens the sustainability of cider apple (Malus ×domestica) production in the maritime climate of western Washington. In the short-term, the disease reduces overall orchard productivity and in the long-term it reduces an orchard’s economic life span. The disease is difficult to manage using cultural practices, and information on fungicide efficacy is limited and contradictory. To address this situation, a 2-year study was conducted to evaluate efficacy of zinc (4.49 lb/acre), basic copper sulfate (2.49 lb/acre), captan (2.94 lb/acre), thiophanate-methyl (0.69 lb/acre), pyraclostrobin plus boscalid (0.38 lb/acre), and combinations of these fungicides to manage anthracnose canker infection in young cider apple trees cultivated in a maritime climate. Trees used in the first year of the study (2016) were found to be infected by anthracnose canker on receipt, so the first year was a measure of disease control and the second year (2017) was a measure of disease prevention. In 2016, when fungicide treatments were applied every 3 weeks from March through October, none of the treatments evaluated inhibited the development of new infections or the expansion of existing cankers (77% increase in canker size on average for all treatments). In 2017, when fungicide treatments were applied every 3 weeks from February through April, two to three new cankers were observed 3 weeks after final treatment application for all treatments. Results from this study demonstrate that the current fungicides recommended for control of anthracnose canker are not reliably effective in the orchard environment of northwest Washington. Future studies should assess the fungicides evaluated in this study applied in rotation with additional systemic fungicides.

PREMISE: During plant domestication, traits can be subject to a variety of types of selection, ranging from strong directional selection for traits such as seed or fruit size to diversifying selection for traits like color or flavor. These types of selection interact with other evolutionary processes including genetic bottlenecks and interspecific gene flow to generate different levels of genetic diversity across the genome and at target genes in domesticated lineages, but little is known about the impacts of these processes in perennial fruit crops. METHODS: We used sequence capture by hybridization to examine patterns of diversity at a suite of candidate domestication and anonymous background genes in domesticated apple (Malus ×domestica) in comparison to its wild relatives Malus sieversii and Malus orientalis. RESULTS: We found no change in average diversity at these candidate domestication genes across the three species. However, a subset of the genes did exhibit patterns of very high or very low diversity in M. ×domestica compared to its progenitor, M. sieversii. Of the genes with characterized function, the low‐diversity genes mainly contributed to fruit quality traits like color and flavor, predicted to be under conscious, directional selection relatively late in the domestication process, while the high‐diversity genes included a variety of functions. CONCLUSIONS: Overall, these results are consistent with predictions based on the likely timing and nature of selection during domestication and open new avenues for understanding genes with high diversity in a perennial crop compared to its wild relatives. [ABSTRACT FROM AUTHOR]

We report a complete chloroplast genome sequence of Malus sieversii. The CP genome was 160,223 bp in length with a typical quadripartite structure. Length of large single-copy (LSC) was 88,334 bp, whereas small single-copy (SSC) was 19,179 bp in length. A pair of inverted repeats (IR) were 26,355 bp. In total, 128 genes were found including 83 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The phylogenetic analysis on concatenated data set retrieved from 78 protein-coding genes revealed that M. sieversii was closely related with both M. ×domestica and M. sylvestris.

Thousands of apple trees were planted in Wyoming's orchards and homesteads in the 1800s, many of which are still alive today. Unfortunately, cultivar identity of these trees has mostly been lost or obscured. The purpose of this research was to identify heritage apple cultivars in Wyoming using genetic fingerprinting (microsatellite) techniques and to use this information to make recommendations on candidate coldhardy cultivars for specialty crop and breeding programs. Leaf samples were collected from 510 heritage apple trees from 91 sites in 19 locales across Wyoming. Known cultivars from the U.S. Department of Agriculture (USDA)-National Plant Germplasm System, Seed Savers Exchange, and Washington State University apple collections were used as standards to determine cultivar identities. Overall, 328 (64%) of the previously unidentified apples trees were identified to 47 known cultivars. Fifteen of these known cultivars comprised more than 80% of the samples that were identified, with all 15 of those cultivars developed in states and countries with average temperatures or winter conditions similar to Wyoming. Seventy-one of the heritage trees were identified as the Wealthy cultivar. Other commonly identified cultivars were Haralson, Patten's Greening, Yellow Transparent, Northwestern Greening, and McMahon. It is likely that a combination of popularity and cultivar origin affected the choice of cultivars that were grown in Wyoming. Although most original Wyoming heritage apple trees are reaching the end of their life span, many surviving trees continue to produce fruit. This strongly suggests that despite lower resistance to certain pathogens than many modern cultivars, these heritage trees should be considered for use today. The results provide insights into possible cultivars that could be grown in Wyoming and also in other states with similar harsh growing conditions. [ABSTRACT FROM AUTHOR]

• Premise of the study: Patterns of genetic diversity in domesticated plants are affected by geographic region of origin and cultivation, intentional artificial selection, and unintentional genetic bottlenecks. While bottlenecks are mainly associated with the initial domestication process, they can also affect diversity during crop improvement. Here, we investigate the impact of the improvement process on the genetic diversity of domesticated apple in comparison with other perennial and annual fruit crops. • Methods: Apple cultivars that were developed at various times (ranging from the 13th through the 20th century) and 11 of the 15 apple cultivars that are used for 90% of the apple production in the United States were surveyed for genetic diversity based on either 9 or 19 simple sequence repeats (SSRs). Diversity was compared using standard metrics and model-based approaches based on expected heterozygosity (He) at equilibrium. Improvement bottleneck data for fruit crops were also collected from the literature. • Key results: Domesticated apples showed no significant reduction in genetic diversity through time across the last eight centuries. Diversity was generally high, with an average He > 0.7 for apples from all centuries. However, diversity of the apples currently used for the bulk of commercial production was lower. • Conclusions: The improvement bottleneck in domesticated apples appears to be mild or nonexistent, in contrast to improvement bottlenecks in many annual and perennial fruit crops, as documented from the literature survey. The low diversity of the subset of cultivars used for commercial production, however, indicates that an improvement bottleneck may be in progress for this perennial crop. [ABSTRACT FROM AUTHOR]

The objective of these studies was to evaluate the efficacy of several concentrations of 1-aminocyclopropane carboxylic acid (ACC) for thinning apple at the standard growth stage for chemical thinning timing and a late thinning growth stage. ACC was applied at concentrations of 0, 100, 300, or 500 mg·L-1 to 'Golden Delicious'/ Bud.9 apple trees at 10 mm or 20 mm fruit diameter. Treatments were applied to the point of drip to individual whole trees in a completely randomized design with five (2010) and six (2011) replications. When ACC was applied at 20 mm, there was a linear dose relationship between concentration and fruit thinning in both years. ACC was ineffective at 10 mm. The naturally occurring compound ACC shows potential for use as a reliable late chemical thinner for apple. [ABSTRACT FROM AUTHOR]

A comparison of field tolerance of 25 apple (Malus × domestica) cultivars and 39 apple rootstocks to the pathogens Marssonina eoronaria and Alternaria alternata apple pathotype was performed. Although most apple cultivars grown in China were susceptible or highly susceptible to both pathogens causing two diseases, considerable variation in the level of resistance to both pathogens was observed. Only three cultivars, Qinguan, Jiguan, and Xiangyanghong, exhibited resistance to both pathogens. Among the rootstocks tested, 30 of 39 (77%) were susceptible or highly susceptible to M. coronaria and 32 (82%) were susceptible to the A. alternata apple pathotype. Four rootstocks, 'P.22', 'SH12', 'Za'ai 76', and 'Qingdao598', were resistant to both pathogens. The correlation between resistance to both pathogens was highly significant in the 74 apple cultivars and rootstocks tested suggesting common genetic resistance factors to these two pathogens. Data represented horizontal resistance in the germplasm. The resistant local germplasm should be used in disease resistance breeding programs. [ABSTRACT FROM AUTHOR]

During storage, many apple (Malus ×domestica Borkh.) genotypes lose their desirable textural qualities, but some like 'Honeycrisp', maintain their sensory Crispness and Firmness. To understand this differential response of genotypes to postharvest changes in texture, reliable and quantifiable methods of texture measurement are needed. This study integrated data from a snapping test, confocal laser scanning microscopy (CLSM), and sensory panels to study postharvest textural changes and to predict sensory textural attributes of Firmness, Crispness, Mealiness, and Juiciness. Three separate analyses on fresh, stored, and combined fresh and stored fruit data yielded different predictors for the same sensory attributes. Change in Crispness during storage was successfully predicted by change in Work during storage. Cell number and size were related to fresh fruit texture and its maintenance during storage. Unique textural properties of 'Honeycrisp' were found to be inherited by its progeny. [ABSTRACT FROM AUTHOR]

The incidence of the physiological apple scab races 1-7 was determined in Swedish apple growing districts between 1999 and 2002. Thirteen apple cultivars, selections or Malus species grafted on rootstock B9 were used as indicator plants. The plants were divided into three lots: one was planted in the field, one was used for growth chamber/greenhouse experiments and one was potted and used as a portable screening orchard. Plants in the growth chamber experiments were inoculated with conidial suspensions (2-3 × 105 conidia ml -¹) from different parts of Sweden. Three weeks after inoculation, the apple scab symptoms were assessed. Race 1 was found in all experiments, while race 5 was absent. Race 4 was only found in samples from the southeastern locations Balsgård and Kivik. The presence of apple scab on Malus baccata jackii was observed in several places for the first time in Sweden. In the orchard trial (Kivik, southeast Sweden, 2001-2002), the trees were interplanted with the susceptible cultivar 'Mutsu'. During the second year, races 1-4 and lesions on M. baccata jackii were found. The portable screening orchard was used as a new method for detection of apple scab races. The indicators were placed in an old, unpruned orchard at Alnarp in 2002. Races 1-3 were observed, plus scab lesions on M. baccata jackii. This method might be feasible for future detection of apple scab races. In conclusion, the apple scab races 1-4 and 6-7 were found in different parts of Sweden while race 5 was absent. Race 7 was observed for the first time in Sweden. [ABSTRACT FROM AUTHOR]

'Macoun'/B.9 apple (Malus ×domestica Borkh.) trees were planted in May 1998 in ± compost or ± monoammonium phosphate (MAP) for a total of four preplant treatments: 1) 90 g phosphorus (P) per tree, 2) 128 kg compost per tree, 3) 90 g P and 128 kg compost per tree, and 4) and an untreated control. MAP did not increase tree growth or yield in any year of the study. Compost increased canopy width into the sixth year after planting, and increased tree height and trunk cross-sectional area (TCA) into the seventh year. Annual yield was increased by compost in the fifth and seventh years, but not fourth or sixth year after planting. Compost increased cumulative yield in the sixth and seventh years. [ABSTRACT FROM AUTHOR]

The article focuses on a research related to the Malus domestica variety of midseason apple, also called Eris. It discusses qualities of the Eris apple variety such as high total soluble solids content (TSS), antioxidant power, and flavor. It also mentions that it has the same degree of resistance with the cultivar Red Chief variety to serious apple pests and diseases.