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Renae Moran, Jennifer DeEll, and Cindy B.S. Tong

We evaluated regional variation in the Delta Absorbance Meter® index of absorbance difference (IAD) as a measure of harvest maturity and for predicting the occurrence of storage disorders in ‘McIntosh’ apples [Malus ×sylvestris (L.) var. domestica (Borkh.) Mansf.] in 2016 and ‘Honeycrisp’ apples in 2016 and 2017. Apples were grown in Maine (ME), Minnesota (MN), and Ontario (ON), and they were harvested from one orchard in each region, and two to three times each year, followed by cold storage at 0.5 °C for 2 months in 2016 and 4 months in 2017. In 2016, ‘Honeycrisp’ IAD values were similar in ME and ON, but lower than in MN. In 2017, IAD was greater in ME than in the other two regions during the first harvest, and it similar to MN in the latter two harvests and lower in ON than in the other regions. In ‘Honeycrisp’ apples, IAD was more strongly related to starch pattern index (SPI), internal ethylene concentration, and fruit peel blush than to chlorophyll or soluble solids concentration. Soft scald incidence (SSI) of ‘Honeycrisp’ fruit was greater in ME than in MN and ON in both years. In ME, SSI was related to IAD at harvest in both years, but with an inverse relationship with the first harvest and a positive relationship in the second harvest. A positive relationship also occurred in ON in 2017. SSI was not related to IAD at harvest in MN in both years and ON in 2016. Regional similarities in patterns of change in ‘Honeycrisp’ fruit IAD were not consistent from year to year, and this indicates that a single IAD standard should not be used to assess fruit maturity in different regions. In ‘McIntosh’, IAD values were variable among the three regions and were not related to other maturity indicators. IAD was not useful for measuring maturity in ‘McIntosh’ apples, but it was weakly related to core browning incidence.

Free access

Elena de Castro, William V. Biasi, and Elizabeth J. Mitcham

Apple [Malus ×sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. ‘Cripps Pink’] fruit were harvested yearly, at two or three maturity stages, from the same California orchard in 2002 through 2005. Fruit firmness, soluble solids, titratable acidity, background color, and percent blush were correlated with the starch pattern index at harvest. Fruit from each harvest were stored at 0.5 ºC in air or in a controlled atmosphere (CA) with 1.5 or 2 KPa O2 in combination with 1, 3, and 5 KPa CO2. Subsets of fruit were treated with 1 μL·L−1 1-methylcyclopropane for 24 hours at 0 ºC or 2200 μL·L−1 diphenylamine (DPA) for 5 minutes. Ethylene production was measured for 30 days after harvest. Ethylene concentration in the storage atmosphere was also monitored during storage. Fruit quality was evaluated after storage plus 5 days of ripening at 20 ºC. Fruit in a CA with 1 or 3 KPa CO2 maintained firmness and green background color, and produced less ethylene during ripening at 20 ºC than fruit stored in a CA with 5 KPa CO2; however, quality of all CA-stored fruit was better than air-stored fruit. Flesh browning developed only in CA storage, appearing by 2 months and not increasing in incidence with further storage periods. 1-Methylcyclopropane conserved fruit quality in air as well as CA during 4 months of storage, and DPA-treated fruit were firmer after CA storage, but similar after air storage, compared with untreated fruit. Diphenylamine did not control a stem-end scald disorder, which increased with time in storage and affected more than 80% of the fruit after 6 months of air storage.

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Rui Zhou and Bruno Quebedeaux

Photosynthesis and carbohydrate metabolism in apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] source leaves were monitored during a 7-day period after source-sink manipulations by girdling or partial defoliation treatments. In the girdling treatment, sorbitol, sucrose, glucose, and starch accumulated in leaves, and net photosynthetic rates (Pn) at 350 μL·L-1 CO2 decreased during a 7-day period. Pn measured at 1000 μL·L-1 [CO2] was also decreased but the changes were less. Stomatal conductance and intracellular CO2 concentration decreased markedly in leaves of girdled shoots. When shoots were partially defoliated, starch and glucose concentrations in remaining source leaves declined steadily during the 7-day study period. Sorbitol and sucrose concentrations decreased during the first 2 days after defoliation, then increased the following 5 days. Pn of the remaining leaves measured at ambient and elevated CO2 levels were enhanced markedly. Aldose-6-phosphate reductase activity in source leaves increased markedly from 27.5 to 39.2 μmol·h-1·g-1 fresh weight (FW) after partial defoliation but remained unchanged in leaves after girdling. Selective and maximum sucrose phosphate synthase (SPS) activities increased following partial defoliation and decreased following girdling. ADP-glucose pyrophosphorylase activity remained relatively unchanged in the partial defoliation treatments but increased markedly in the girdled-shoot leaves. These results suggested that girdling-induced photosynthetic inhibition is mainly due to stomatal limitation, however, the photosynthesis enhancement by partial defoliation may be due primarily to acceleration of photosynthetic capacity per se. These studies showed that the metabolism of sorbitol, sucrose and starch, three photosynthetic end products in mature apple leaves, was coordinately regulated in source leaves in response to source-sink manipulations.

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Luiz Argenta, Xuetong Fan, and James Mattheis

The efficacy of the ethylene action inhibitor 1-methylcyclopropene (1-MCP) applied in water to slow ripening of `Golden Delicious' [Malus sylvestris var. domestica (Borkh.) Mansf.] apples was evaluated in comparison with 1-MCP applied as a gas in air. The material was applied by dipping fruit in 1-MCP water solutions (0, 0.03, 0.3 or 3 μM) for 4 min, or by exposing fruit to 1-MCP gas (0, 0.01, 0.1 or 1 μL·L-1) in air for 12 h. Fruit were held in air at 20 °C for 25 days after treatment or stored at 0.5 °C in air for up to 6 months followed by 7 days in air at 20 °C. Application of 1-MCP in water or air delayed the increase in respiration and ethylene production associated with fruit ripening, and reduced the amount of fruit softening, loss of acidity and change in peel color. Treatments applied in water required a concentration 700-fold higher compared to those applied in air to induce similar physiological responses. Fruit responses to 1-MCP varied with treatment concentration, and the maximum effects were obtained at concentrations of 0.1 or 1 μL·L-1 in air and 3 μM in water. Peel color change was impacted less than retention of firmness and titratable acidity for some 1-MCP treatments. Treatment with 1-MCP was less effective for slowing peel degreening when treated fruit were stored at 0.5 °C compared to storage at 20 °C. In 1 of the 3 years of this study, fruit treated with 1-MCP and stored in air at 0.5 °C developed a peel disorder typified by a gray-brown discoloration that is unlike other disorders previously reported for this cultivar.

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Amos Naor, Moshe Flaishman, Raphael Stern, Aharon Moshe, and Amnon Erez

The relative contribution of various temperatures to dormancy completion of lateral vegetative apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] buds was studied quantitatively on whole container-grown trees. Trees were exposed continuously to 10 different temperatures and also to daily alternating temperatures in a 24-hour cycle. In addition, fully chilled vertically and horizontally positioned shoots were compared under forcing conditions. No budbreak occurred in shoots chilled above 12.5 °C. There was a steep increase in budbreak as the chilling temperature fell from 12.5 to 7.5 °C. There was little difference in the level of budbreak on shoots chilled between 7.5 and 0 °C. The relative contribution of temperature to chilling accumulation in apple found in our study differs from what has been proposed for stone fruit and for apple in previous studies, especially at temperatures <6 °C. The length of exposure to forcing conditions required to initiate budbreak diminished as the chilling temperature was reduced. No additional bud-break was apparent on shoots chilled longer than 2100 chilling hours. The chilling requirement found here for lateral vegetative buds is much higher than that needed for terminal vegetative and flower buds. Trees that were exposed to daily alternating temperatures had lower levels of budbreak when the high temperature in the diurnal cycle was greater than 14 °C. Practically no budbreak was apparent on trees that were exposed to diurnal cycles with a high temperature of 20 °C for 8 hours. Budbreak on horizontally positioned trees was more than twice that on the vertically positioned trees, emphasizing the magnitude of the apical dominance effect and its strong masking of the chilling effect on lateral buds in vertically grown apple trees. Based on the data collected here we propose a new response curve for vegetative budbreak in `Golden Delicious·apple, within a temperature range between 0 to 15 °C.

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Richard P. Marini, John A. Barden, John A. Cline, Ronald L. Perry, and Terence Robinson

The influence of rootstock on average fruit weight was evaluated for a subset of data from a multilocation NC-140 apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] rootstock trial. Data for eight dwarf rootstocks were collected at four locations for 2 years. Analysis of covariance was used to evaluate the effect of rootstock on average fruit weight when crop density or number of fruit per tree was included in the linear model as a covariate. When number of fruit harvested per tree was used as a covariate, average fruit weight was not affected by rootstock in either year in Ontario. In Michigan and Virginia, rootstock and number of fruit per tree, but not the rootstock × number of fruit interaction, were significant, so common slopes models were used to estimate least squares means for average fruit weight. In general, trees on M.27 and P.1 produced the smallest fruit, and trees on B.9, M.9 EMLA, and Mac.39 produced the largest fruit. In New York the interaction of rootstock × number of fruit was significant, so least squares means were estimated at three levels of number of fruit per tree. Both years, at all levels of number of fruit, trees on M.26 EMLA produced the smallest fruit and trees on M.27 EMLA produced the largest fruit. Average fruit weight was most affected by number of fruit per tree when Mark was the rootstock. In general, results were similar when crop density was used as the covariate, except that trees on M.27 EMLA did not produce small fruit in Michigan and Ontario.

Free access

Susan Lurie, Amnon Lers, Zohar Shacham, Lilian Sonego, Shaul Burd, and Bruce Whitaker

Untreated control, 1-methylcyclopropene (1-MCP)-treated, and heated fruit of the superficial scald-susceptible `Granny Smith' cultivar of apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] were compared with respect to scald incidence, internal ethylene concentration (IEC), α-farnesene metabolism, expression of the genes AFS1, which encodes α-farnesene synthase, the final, rate-limiting enzyme in the α-farnesene biosynthetic pathway, and HMG2 and HMG3, which encode isozymes of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the proposed rate-limiting enzyme in the mevalonate pathway of isoprenoid synthesis. The incidence of scald in untreated `Granny Smith' apples after 16 weeks at 0 °C plus 1 week at 20 °C was 100%; 1-MCP treatment prevented scald development, whereas heat treatment delayed and reduced scald development. 1-MCP also inhibited both α-farnesene and IEC, suggesting that ethylene induces transcription of key genes involved in α-farnesene biosynthesis. Heat treatment reduced levels of α-farnesene and and its oxidation products, conjugated trienols (CTols), but not to the extent of 1-MCP. Internal ethylene concentrations in heated apples did not differ from those in the controls. In both control and heated fruit, a sharp increase in AFS1 mRNA during the first 4 weeks of storage preceded an increase in α-farnesene and a subsequent increase in CTols. AFS1 transcript was absent from 1-MCP-treated apples for the first 10 weeks of storage, and even at 16 weeks was lower than in heated and untreated control fruit. Levels of the HMG2 and HMG3 transcripts varied during storage and among treatments, and were not correlated with the incidence of scald. HMG2 mRNA transcript accumulation was low at harvest and increased in abundance during storage in all treatments, with the greatest increase occurring in 1-MCP-treated fruit. In contrast, HMG3 transcript was constitutively present at all storage times, although it too was slightly more abundant in 1-MCP-treated fruit.

Free access

Zhiguo Ju and Eric A. Curry

Effects of α-farnesene biosynthesis precursors on α-farnesene and ethylene production were studied using Lovastatin-treated or nontreated `Delicious' and `Granny Smith' apples [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]. In nontreated fruit, α-farnesene was detected only in fruit peel (≈3 mm) and not in the more proximal cortical tissue. α-Farnesene was not detectable in preclimacteric fruit peel at harvest. Mevalonic acid lactone (MAL) or farnesyl pyrophosphate (FPP) induced α-farnesene production when fed to preclimacteric peel tissue, but hydroxymethylglutaric acid (HMG) did not. Fruit stored at 0 °C for 30 days (climacteric fruit) produced α-farnesene, and addition of HMG, MAL, or FPP further increased α-farnesene production. When treated at harvest with Lovastatin at 1.25 mmol·L-1 and stored at 0 °C for 30 days, fruit produced ethylene but did not produce α-farnesene. Whereas MAL and FPP induced α-farnesene production in peel sections from these fruit, HMG did not. Induction of α-farnesene by precursor feeding was concentration-dependent and had no effect on ethylene production. Cortical tissue sections from climacteric fruit did not produce α-farnesene unless HMG, MAL, or FPP were fed during incubation. Including Lovastatin at 0.63 mmol·L-1 in the feeding solution eliminated HMG induced α-farnesene production, but did not affect MAL or FPP-induced α-farnesene production. Neither precursor feeding nor Lovastatin treatment affected ethylene production in cortical tissues. Chemical name used: [1S-[1a (R°), 3α, 7β, 8β (2S°, 4S°), 8αβ]]-1,2,3,7,8,8α-hexahydro-3,7-dimethyl-8-[2-(tetrahydro-4-hydroxy-6-oxo-2H-pyran-2-yl)ethyl]-1-naphthalnyl 2-methylbutanoate (Lovastatin).

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Robert A. Saftner, William S. Conway, and Carl E. Sams

Effects of postharvest pressure infiltration of distilled water, CaCl2 solutions at 0.14 or 0.27 mol·L-1 without and with subsequent fruit coating treatments of preclimacteric `Golden Delicious' [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf. `Golden Delicious'] apples on volatile levels, respiration, ethylene production, and internal atmospheres after storage at 0 °C for 1 to 6 months, and during subsequent shelf life at 20 °C were investigated. Over 30 volatiles were detected, most of the identified volatiles were esters; the rest were alcohols, aldehydes, ethers, a ketone, and a sesquiterpene. Pressure infiltration of water and increasing concentrations of CaCl2 resulted progressively in reduced total volatile levels, respiration, ethylene production, and internal O2 levels and increased CO2 levels in fruit following 2 to 4 months storage in air at 0 °C. Total volatile levels, respiration, ethylene production, and internal atmospheres of CaCl2-treated apples at 0.14 mol·L-1 gradually recovered to nontreated control levels following 2 weeks of shelf life at 20 °C and/or storage at 0 °C in air for more than 4 months. Following the calcium treatments with a shellac- or wax-based coating had similar but stronger and more persistent effects on volatile levels, respiration, ethylene production, and internal atmospheres than those found in fruit treated with CaCl2 alone. Calcium infiltration did not change the composition of volatile compounds found in fruit. Results suggest that pressure infiltration of `Golden Delicious' apples with CaCl2 solutions transiently inhibited volatile levels, respiration, and ethylene production, in part, by forming a more-or-less transient barrier to CO2 and O2 exchange between the fruit tissue and the surrounding atmosphere.

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B.R. Bondada, C.E. Sams, D.E. Deyton, and J.C. Cummins

Environmental factors such as rainfall may reduce the efficacy of foliar-applied soybean [Glycine max (L.) Merrill] oil in reducing pest mortality. Greenhouse studies were conducted to investigate the influence of rain on the retention of soybean oil and the influence of soybean oil and rainfall on surface morphology of apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] and peach [Prunus persica (L.) Batsch (Peach Group)] leaves and stems. `Contender' peach and `Golden Delicious'/Malling 27 apple trees were grown in 19 L pots in a greenhouse (23 ± 9 °C) and sprayed with soybean oil (1%) emulsified with the adjuvants Latron B-1956 or K1. Twenty-four hours after treatment, the trees were subjected to simulated rainfall of 0.0, 0.25, 1.25, or 2.54 cm. A negative linear relationship existed between rainfall and oil retention. Peach leaves receiving 0.25, 1.25, and 2.54 cm rainfall retained 81%, 38%, and 18% of the applied oil, respectively. Oil retention by apple leaves was also negatively related to rainfall. For both species, a negative linear relationship existed between oil retention on stems and rainfall. There was no effect of emulsifier on retention of 1% soybean oil after rain on apple leaves or on the retention of 8% to 11% soybean oil on the stems of apple and peach. Scanning electron microscopy revealed that epicuticular wax occurred as striations on apple and peach leaves. The wax morphology on peach and apple stems appeared as thin plates and platelets, respectively. The wax morphology of leaves and stems of both trees was not affected either by the soybean oil emulsions or rain. Both emulsions induced stomatal closure in leaves and peach stems, however, stomates opened after rainfall of 1.25 or 2.54 cm. The lenticels appeared to be unaffected by either emulsion. Results illustrate that rainfall of 2.54 cm washed off a major portion of the applied oil. Thus, respraying may be needed under natural climatic conditions with rainfall ≥2.54 cm to restore the efficacy of applied soybean oil.