Investigations of Multiple Approaches to Reduce Green Spot Incidence in ‘WA 38’ Apple

Abstract

A pre-harvest apple (Malus × domestica Borkh.) disorder named “green spot” (GS) was recently identified on ‘WA 38’ apples. Previous work indicated a tentative association between GS and fruit mineral imbalance, and an influence of rootstock selection on GS frequency; however, the specific causes, risk factors, and mitigation steps have not been explored. In this study, the role of microclimate, modified using netting or fruit bagging, on GS incidence in ‘WA 38’ apples over two years on two different dwarfing rootstocks, ‘Geneva 41’ (‘G.41’) and ‘Malling 9-Nic29’ (‘M.9’), was investigated. Early season fruit bagging reduced GS appearance, but netting showed mixed results between year and rootstock. Rootstock selection influenced GS incidence, especially in the 2021 season. Fruit mineral analyses highlighted some differences of mineral composition between symptomatic and asymptomatic apples, which helped to corroborate earlier reports; however, within the full context of these results, it is not clear that nutrient imbalance directly influences disorder incidence. Further work to understand the mechanisms behind GS emergence should consider environmental factors, including light, humidity, and wind, as well as anatomical features of ‘WA 38’ fruit, such as lenticel morphology and physiology.

Heat Stress and Water Irrigation Management Effects on the Fruit Color and Quality of ‘Hongro’ Apples

“…Various parameters, including crack location, size, and depth, were used to assess cracking. Spots on the fruit surface [17] were evaluated for size, shape, and coloration to differentiate between different lesion types. Bitter rot symptoms were identified as characteristic brown lesions with a foul odor.…”

A Haplotype-resolved, Chromosome-scale Genome for Malus domestica 'WA 38'

“…2023), maturity at harvest (Serra et al 2023), and an ‘off’ flavor that has been brought up by consumers that may be the result of improper picking times, crop load management, handling/packing practices or other post harvest processes (Mendoza, M., Hanrahan, I., & Bolaños, G., 2020). Most concerning is green spot (Figure 1 C, D, and F), a corking disorder that seems to be unique to ‘WA 38’, but with etiology similar to disorders associated with mineral imbalances such as bitter pit and drought spot (Sheick et al . 2022, 2023).…”

“…However, it inherited undesirable traits as well, such as a propensity for physiological symptoms that may be related to mineral imbalances (Sheick et al 2023;Sallato, Whiting, and Munguia 2021), maturity at harvest 5 , and an 'off' flavor that has been brought up by consumers that may be the result of improper picking times, crop load management, handling/packing practices or other post harvest processes 6 . Most concerning is green spot (Figure 1 C, D, and F), a corking disorder that seems to be unique to 'WA 38', but with etiology similar to disorders associated with mineral imbalances such as bitter pit and drought spot (Sheick et al 2022(Sheick et al , 2023. The propensity for and cause of physiological disorders often differs on a cultivar-by-cultivar basis (Pareek 2019), and a genetic basis for such predispositions is likely (Di Guardo et al 2013;Lum 6 https://treefruit.wsu.edu/article/2022-update-additional-wa-38-harvest-and-storage-considerations/ 5 https://www.actahort.org/members/showpdf?session=1982017 4 Retrieved December 27, 2022, from https://plants.ces.ncsu.edu/plants/malus-domestica/common-name/apples/ 3 https://waapple.org/did-you-know/ 2 https://fruitgrowersnews.com/news/global-apple-market-reached-78m-set-to-continue-moderate-gr owth/ 4 et al 2016; Johnston and Brookfield 2012;Liebhard et al 2003).…”