Postharvest Apple Research Updates - from Outside Ontario

The following is a collection of scientific abstracts from colleagues around North America that may be of interest to the Ontario apple industry.

Development of Stem-end Internal Browning and Cracking in Cold Stored 'Gala' Apples Is Related to Fruit Size

- J. Lee, J. Matthies, and D. Ruddell (USDA-ARS, Wenatchee, WA)

'Gala' apple fruit can be susceptible to the development of stem-end browning and cracking (splitting) disorders during cold storage. Previous work indicated fruit stem-end browning incidence increases with fruit size. The objective of this work was to further investigate the effect of fruit size on the development of stem-end browning, cracking and other physiological characteristics of 'Gala' apples previously held in cold storage. Fruit segregated at harvest based on size (small: 120-175 g; large: 250-350 g) were stored at 0.5 °C in air for up to 6 months. Large fruit developed more stem-end browning and cracking compared with small fruit during cold storage, and browning and cracking incidence and severity increased during shelf life. Large fruit had lower internal ethylene concentration after 6 months plus 0 or 7 days at 20 °C. However, large fruit had higher respiration rate during storage and after the shelf life period. Fruit stem-end lightness (L*) and hue angle (ho) declined during and after cold storage, with L* and ho decreasing significantly more for large fruit. While small fruit fresh weight and circumference decreased during storage, large fruit circumference increased along with cracking incidence but fresh weight decreased during storage. These physiological changes appear to contribute to the susceptibility of larger fruit to stem-end browning and cracking more so than smaller fruit. (Proc. ASHS, 2012)

Characteristics of a 'Gala' Apple Fruit Internal Browning Storage Disorder

- J. Matthies, J. Lee, and D. Ruddell (USDA-ARS, Wenatchee, WA)

Factors contributing to development of an internal browning storage disorder developing primarily at the stem-end in 'Gala' apple fruit were investigated. Initial storage temperature, storage duration, controlled atmosphere (CA) CO2 concentration, delayed CA establishment, use of diphenylamine (DPA) and/or 1-methylcyclopropene (SmartFresh), and fruit weight were evaluated. Browning can occur during storage or during a subsequent 7 day shelf-life period. Large fruit are at increased risk of browning development. Browning develops in fruit stored at 0.5 °C in air or CA (1.5% O2, 1-5% CO2). Storage at 0.5 °C for 7 days in 17% O2 + 3% CO2 then air or CA does not enhance browning development. In 2 of 3 crop years, SmartFresh-treated fruit developed browning sooner compared to controls. DPA does not control browning development regardless of storage environment or use of SmartFresh. Cooling fruit to 0.5 °C after 7 days at 10 °C reduces or eliminates browning development regardless of SmartFresh use. Delayed SmartFresh treatment does not impact browning development but results in poor quality if fruit are held 7 days at 10 °C prior to 0.5 °C. The results indicate this disorder may result from chilling injury, and that chemical inhibition of ethylene action can enhance fruit susceptibility. Prompt treatment with SmartFresh and cooling fruit to 10 °C for the initial 7 days after harvest can reduce or prevent disorder development while maintaining fruit quality comparably to fruit treated with SmartFresh and cooled to 0.5 °C after harvest. (Proc. ASHS, 2012)

Evaluating the Synchronicity of Flesh and Peel Ripening in Standard and New Cultivars of Apples

- P.M.A. Toivonen, Y. Mostofi, C.R. Hampson, and P.A. Wiersma (AAFC - Summerland, BC)

Generally internal ethylene concentration (IEC) and starch clearing index (SCI) are used to evaluate apple maturity for harvest in North America. These two methods provide good information on the flesh maturation of apples. Chlorophyll decline in apple peel was recognized as a potential criterion for maturity assessment in the early 1990s, but has not been practical to use because of the time required to extract chlorophyll from the peel. Recently, non-destructive instruments measuring apple peel chlorophyll using spectral reflectance of two chlorophyll-related near infrared bands has enabled instantaneous assessment of peel chlorophyll and thus allows interpretation of maturity. In this study, 'Royal Gala', 'Golden Delicious', 'Fuji (strain Nagano 1)', Aurora Golden Gala™, Nicola™, SPA493, and SPA365 were monitored for changes in IEC, SCI, and chlorophyll content during maturation in Fall 2011. Decline in chlorophyll content was linear with advance in maturity for all cultivars tested. In most cultivars of apples tested, the IEC, SCI, and chlorophyll changes were well synchronized. This indicates that that non-destructive chlorophyll assessment may be an alternate tool for monitoring apple maturation and could also enable mapping of orchards to improve uniformity of maturity at harvest. In some apples, however, changes in chlorophyll content were not well synchronized with IEC and SCI changes. For an apple such as 'Fuji', it may mean that the harvest criteria using non-destructive technology should be adjusted specifically for that cultivar. In other cultivars, for which peel and flesh maturation is even more asynchronous, at least in Fall 2011, suggesting that there may be concerns for maturation in those cultivars that need further investigation. (Proc. ASHS, 2012)

AVG Combined with NAA Control Preharvest Drop of 'McIntosh' Apples Better than Either Chemical Alone

- T.L.Robinson, S.A. Hoying, M. Miranda' and K. Lungerman (Cornell University, NY)

In some years aminoethoxyvinylglycine (AVG, trade name ReTain) imperfectly controls pre-harvest drop of 'McIntosh' apple. These years are warm with daytime temperatures over 35 °C (95 °F) in August. In 2008-2011, we evaluated whether the combination of AVG and napthaleneacetic acid (NAA) would give better preharvest drop control of 'McIntosh' apple than AVG or NAA alone. AVG (832 g ReTain/ha or 416 g ReTain/ha) was applied 3, 2 or 1 week before normal harvest. At either the 2 or 1 week before normal harvest, a combination of AVG and 20 mg/L NAA was also applied. Pre-harvest fruit drop from untreated control trees exceeded 20% by 21 Sept. and by the end of September had reached 60% drop. The traditional drop control treatment of 20 mg/L NAA applied alone on 7 Sept. did not reduce drop at any date. AVG applied alone reduced fruit drop if applied 3 or 2 weeks before normal harvest but not when applied 1 week before harvest. The addition of 20 mg/L NAA to the AVG sprays, either 2 or 1 week before harvest, improved pre-harvest drop control compared to AVG alone. The combination spray applied 2 weeks before harvest resulted in the lowest pre-harvest drop of any treatment. However, if AVG+NAA was applied 1 week before harvest then its efficacy was reduced but was still similar to AVG alone applied 3 or 2 weeks before harvest. When a reduced rate of AVG (416 g/ha) was combined with NAA, the efficacy in preventing drop was very similar to the full rate of AVG. A hypothesis to explain the improved drop control of 'McIntosh' apples from combining NAA and ReTain is: when NAA is used alone to control pre-harvest drop, it controls the genes associated with abscission zone formation but as a negative side effect it stimulates ethylene production which advances ripening including color formation and softening. With 'McIntosh', the high production of ethylene often overwhelms the stop drop effect of NAA. In contrast, ReTain acts by controlling ethylene biosynthesis but in hot years, pre-harvest drop of 'McIntosh' is not adequately controlled indicating that abscission zone genes are not totally under the control of ethylene and that ReTain does not control these genes adequately under stress conditions. When NAA and ReTain are sprayed together, NAA controls the genes associated with abscission better than ReTain while ReTain blocks the production of ethylene caused by NAA. (Proc. ASHS, 2012)

Effects of repeated 1-MCP treatments on ripening and superficial scald of 'Cortland' and 'Delicious' apples

- X. Lua, J.F. Nock, Y. Maa, X. Liu, and C.B. Watkins (Cornell University, NY)

Postharvest 1-methylcyclopropene (1-MCP) can maintain fruit quality and inhibit development of superficial scald, a physiological storage disorder found in apple fruit, but the extent of the inhibition can vary by cultivar. In this study, we investigated whether multiple applications of 1-MCP, which are now permitted by a label modification of the commercial 1-MCP product, SmartFresh, might improve scald control. 'Cortland' and 'Delicious' apples were untreated, treated on the day of harvest with the antioxidant inhibitor of scald, diphenylamine (DPA), or with 1 ppm 1-MCP at different intervals after harvest. Treatment times (days) were 1, 4, 7, 1 + 4, 4 + 7, 1 + 4 + 7, 7 + 14, 7 + 28, 7 + 42, or 7 + 84. Internal ethylene concentrations (IECs), flesh firmness, and accumulations of (precursors to superficial scald) ?-farnesene and conjugated trienols (CTols) were measured at harvest, at the time of treatment, and at intervals during air storage at 0.5 °C for up to 36 weeks. Scald was completely inhibited by DPA and all 1-MCP treatments in 'Delicious'. However, effective control of scald in 'Cortland' was obtained with 1-MCP treatments within the first 4 days of harvest, either alone or in combination. Scald control with delayed 1-MCP treatments resulted in poorer scald control that was comparable to that obtained with DPA. IECs and œ-farnesene accumulation were similar in untreated and DPA treated fruit, but inhibited by 1-MCP. However, differences among 1-MCP treatments became more evident with increasing storage periods. Inhibition of IECs and œ-farnesene accumulation was greater in fruit treated on days 1, 4, 1 + 4, 4 + 7, 1 + 4 + 7, than on day 7 alone. A second application of 1-MCP on day 14 to fruit treated on day 7 increased inhibition of IECs, ?-farnesene and CTol accumulations, but increasing delays before the second 1-MCP treatment resulted in progressively less inhibition of these factors. Similar effects of treatment on IECs, œ-farnesene and CTol accumulations were found for both cultivars, even though no scald was detected in treated 'Delicious' apples. The results indicate that initial 1-MCP treatments should be applied to faster ripening cultivars such as 'Cortland' within a few days of harvest. (Postharvest Biol. Technol., 2013)


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