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ARS Home » Pacific West Area » Wenatchee, Washington » Physiology and Pathology of Tree Fruits Research » Research » Research Project #438251

Research Project: Enhancement of Apple, Pear, and Sweet Cherry Quality

Location: Physiology and Pathology of Tree Fruits Research

2021 Annual Report

The long-term goal of this project is to develop tools for quality management of deciduous tree fruits. Specifically, during the next five years we will focus on the following objectives. Objective 1: Resolve production and post-harvest environmental and genetic regulation of apple, pear, and sweet cherry quality. [NP306, C1, PS1A] Sub-objective 1A: Identify if interactions among storage temperature protocol, controlled atmosphere establishment date, and inhibition of ethylene action impact apple and pear fruit market quality and development of physiological disorders. Sub-objective 1B: Determine if dynamic control of controlled atmosphere (CA) oxygen concentration can enhance apple fruit post storage volatile production without fruit quality loss. Sub-objective 1C: Determine relationship between sweet cherry cutin composition, gene expression, and surface defects caused by sun stress following harvest. Objective 2: Use of biomarkers to enhance/assist commercial apple and pear management strategies. [NP306, C1, PS1A] Sub-objective 2A: Determine metabolic and genomic changes related to apple and pear fruit maturation and postharvest chilling. Sub-objective 2B: Identify metabolic and genomic changes linked with fruit quality loss and physiological disorder development during cold storage.

Fruit from commercial orchards will be harvested then stored at ARS-Wenatchee in controlled atmosphere (CA) chambers. Fruit quality, metabolites, and RNA will be characterized at harvest and after storage using standard methods. Hypothesis 1A: The manner in which postharvest technologies are imposed results in additive, synergistic, and antagonistic effects on fruit quality and disorder development. Apple and pear fruit from commercial orchards will be stored continuously at 0.5°C or at 10°C for 7 days, then at 0.5°C. Fruit will be exposed to 0 or 1 µL L-1 1-MCP for 16 hours, then in air or a CA initiated 1 or 9 days after harvest. Following 6 to 8 months, fruit will be removed from storage and held 7 days at 20°C to allow post-storage quality loss and disorder development to occur. Hypothesis 1B: The manner in which postharvest technologies are imposed results in additive, synergistic, and antagonistic effects on apple firmness and related gene expression. Tissues from ‘Gala’ apples stored at various temperatures, in air or CA, with or without 1-MCP treatment will be collected over time. Fruit firmness will be assessed at the same time as tissue harvest for transcriptome analysis plus after 7 at 20°C. Hypothesis 1C: Reciprocity is valid for mean oxygen concentration during CA storage and apple fruit post-storage volatile production and quality. Honeycrisp’ apples will be CA stored continuously at 5.1% O2 as well as at 2.5% O2 with repeated periods in air to average 5.1% O2 over the storage period. Control fruit will also be held continuously in air. Fruit removed from storage after 4 and 8 months will be assessed for external disorders on the day of removal, then will be held 7 days at 20°C in air. On day 7, volatile compounds emitted from intact fruit will be collected and analyzed. Hypothesis 1D: Cuticle composition and gene expression will be impacted by sunlight exposure. Sweet cherries will be harvested from the tree periphery and interior or following shading with black cloth. Fruit peel will be assessed for microcracks using microscopy. RNA will be collected from peel sections with contrasting cutin deposition patterns using laser microdissection. Hypothesis 2A: Changes in molecular phenotypes (metabolites and gene activity) can be linked with progression of fruit maturation and low temperatures during storage. Apple and pear cultivars will be harvested over 12 weeks bracketing horticultural maturity. Fruit maturity, metabolite and RNA content will be assessed using standard methods. Maturity dependent responses to abiotic stress will consist of holding fruit at 20 or 1°C for 48 hours. Hypothesis 2B: Specific changes in apple and pear cell membrane components are provoked by high carbon dioxide, low oxygen CA leading to higher risk of developing carbon dioxide related storage disorders. Apples treated or not with DPA will be stored in CA at 0.5% O2 and up to 5% CO2. Fruit quality and disorders will be assessed after storage as will fruit metabolites and RNA.

Progress Report
In support of Sub-objective 1A, ‘Fuji’, ‘Gala’, and ‘Granny Smith’ apples were cooled to 34 or 50 degrees F within 24 hours of receipt after harvest. Fruit cooled to 50 degrees F were held seven days, then cooled to 34 F. At 48 hours after receipt, some fruit at both temperatures were exposed to a controlled atmosphere (CA) containing 1% oxygen and 1% carbon dioxide. After nine days, additional fruit were exposed to the CA. All fruit was held up to eight months in air or CA, then removed from cold storage and held in air at 68 degrees F for seven days. Delayed cooling to 34 degrees F, storage in and delay of CA as well as storage duration impacted development of physiological disorders with the impacts varying for each cultivar. Overall, delayed cooling with rapid initiation of CA has positive impacts on physiological disorder incidence while lacking negative impacts on fruit quality (sugar and acid content, firmness. The research shows that the manner in which postharvest technologies are imposed results in additive, synergistic, and antagonistic effects on apple firmness and related gene expression, ‘Gala’ gene expression patterns relatable to various storage regimes (cooling and CA delay, inhibition of ethylene action or not) were identified. Additionally, we developed an improved method to quantify gene expression using variations of the ‘Gala’ reference genome, the blueprint of ‘Gala’ genes. Further, the ‘Gala’ gene expression results were used to develop a workflow to enhance analysis of apple gene expression data in general. For Sub-objective 1B, ‘Honeycrisp’ apples were stored in CA with oxygen held at 1.5% continuously or with various periods in air followed by a return to 1.5%. Over eight months, production of volatile compounds that contribute to fruit aroma was found to be related to the average CA oxygen content. A simple relationship between average CA oxygen content and poststorage volatile production was not observed due in part to an effect of fruit storage duration. After four months, the impact of CA oxygen content was different than what was observed after eight months. No loss of other aspects of fruit quality (sugar and acid content, firmness, physiological disorders) due to CA oxygen content was observed. The hypothesis that poststorage volatile production can be manipulated by CA oxygen content without loss of fruit quality (sugar and acid content, firmness, disorders) is supported by these initial results. In support of Sub-objective 1C, a cultivar of sweet cherry, ‘TipTop’, that has a yellow skin with areas of red, was harvested at commercial maturity and skin from the blush (sun exposed) and non-blush (shaded) portions was collected. Using a novel analytical protocol developed locally, many unique compounds were identified and quantified, and skin composition was shown to differ between blush-side and shade-side. Research progress also continued for Sub-objective 2A. Fine-scale harvest and pilot gene expression analysis was completed for apple cultivars ‘Granny Smith’ and ‘Red Delicious’. Fruit quality, both at harvest and during the postharvest period, was related to shifts in gene expression across a 10-week window centered on commercial harvest date, revealing 66 shared genes that had activity correlated with starch clearing and superficial scald development. This comparative, multi-cultivar approach reduced the candidate gene list by an order of magnitude. Additionally, an analysis of ‘d’Anjou’ pear maturity genes previously identified showed differential co-expression is a feature of maturity-dependent gene expression. This indicates that gene-to-gene relationships may be useful biomarkers to predict maturation progression. These patterns were observed with a very fine contrast of maturity, suggesting utility to predict small differences in postharvest ripening capacity. Research progress for Sub-objective 2B included assessing carbon dioxide sensitivity, a factor limiting CA storage tolerance for apple cultivars. ‘Honeycrisp’ apples harvested 2 weeks before and at commercial harvest maturity and half were drenched with a commercial antioxidant that can prevent carbon dioxide injury. The ‘Honeycrisp’ results were compared with 15 other cultivars representing different sensitivities to carbon dioxide related and other internal and external disorders. ‘Honeycrisp’ can develop internal browning related to carbon dioxide sensitivity as well as soggy breakdown, an internal browning disorder often confused with carbon dioxide sensitivity and softscald, a closely related peel disorder. All cultivars were stored at 34 degrees F for four months under high carbon dioxide (5%) and ultralow oxygen (0.5%) to promote carbon dioxide-induced disorders. At four months, disorder symptoms were present typical of carbon dioxide injury in control fruit, however, disorders were also present on some cultivars that had been treated with an antioxidant indicating a cause from some factor other than carbon dioxide. Analysis of healthy tissue as well as from tissue with physiological disorder symptoms showed distinctive patterns relatable to the factors that caused fruit injury. These results support the hypothesis that apple fruit disorders can be diagnosed by analysis of affected tissues, an objective technique that could be useful for industry to assure disorder cause is identified.

1. New genomic tool to assess genetic relationships among apple and pear cultivars. Apple and pear genes, including the ‘d’Anjou’ genome that was sequenced locally, were classified into gene families using a software co-developed by ARS researchers and collaborator personnel in Wenatchee, Washington. For pear, the analysis has helped reveal genes missing from some pear cultivar genomes. This information also allowed comparative analysis of ‘d‘Anjou’ genes revealing half the maturity-related genes previously identified by ARS researchers are different compared to those for ‘Bartlett’. This finding is important in the search for genes that can explain the different maturity-dependent postharvest quality characteristics of European pear cultivars.

Review Publications
Mattheis, J.P., Rudell Jr, D.R. 2020. ‘Honeycrisp’ apple (Malus domestica Borkh.) fruit response to controlled atmosphere storage with the low oxygen limit established by monitoring chlorophyll fluorescence. HortScience. 56(2):173-176.
Honaas, L.A., Hargarten, H.L., Hadish, J., Ficklin, S., Serra, S., Musacchi, S., Wafula, E., Mattheis, J.P., dePamphilis, C., Rudell Jr, D.R. 2021. Transcriptomics of differential ripening in ‘d’Anjou pear (Pyrus communis L.). Frontiers in Plant Science. 12. Article 609684.
Argenta, L.C., de Freitas, S.T., Mattheis, J.P., Vieira, M.J., Ogoshi, C. 2021. Characterization and quantification of postharvest losses of apple fruit stored under commercial conditions. HortScience. 56(5):608-616.
McTavish, C.K., Poirier, B.C., Torres, C.A., Mattheis, J.P., Rudell Jr, D.R. 2020. A convergence of sunlight and cold chain: The influence of sun exposure on postharvest apple peel metabolism. Postharvest Biology and Technology. 164. Article 111164.
Poirier, B.C., Mattheis, J.P., Rudell Jr, D.R. 2019. Extending ‘Granny Smith’ apple superficial scald control following long-term ultra-low oxygen controlled atmosphere storage. Postharvest Biology and Technology. 161. Article 111062.
Sanchez-Contreras, J., Rudell Jr, D.R., Mattheis, J.P., Torres, C.A. 2021. Sphingolipids associated with flesh browning onset and development in ‘Cripps Pink’ apples (Malus domestica Borkh.). Postharvest Biology and Technology. 180. Article 111623.
Lwin, H., Rudell Jr, D.R., Lee, J. 2021. Metabolism and cold chain performance of ‘Chuhwangbae’ Asian pears as impacted by 1-MCP treatment. Scientia Horticulturae. 288. Article 110357.