Location: Physiology and Pathology of Tree Fruits Research
2017 Annual Report
Objectives
The long-term goal of this project is to develop various tools to assist in quality management of deciduous tree fruits. Specifically, during the next five years we will focus on the following objectives.
Objective 1: Integrate pre- and postharvest environment and commercial horticultural management practices with genomic and metabolomic regulation of apple and pear fruit quality.[C1; PS 1.A]
Sub-objective 1A: Determine how fruit position within the tree impacts pear metabolic profile, superficial scald, postharvest quality, and ripening.
Sub-objective 1B: Determine if inconsistent post-storage ripening of 1-
methylcyclopropene (1-MCP) treated d’Anjou pears is relatable to differential
absorbance (DA) value at harvest.
Sub-objective 1C: Determine if pre-storage light exposure impacts apple peel
metabolic responses to postharvest chilling.
Objective 2: Enable new apple, pear and sweet cherry fruit biomarker-based quality management strategies. [C1; PS 1.A]
Sub-objective 2A: Determine if apple aroma volatile production changes when fruit are stored in environments conducive to development of physiological disorders.
Sub-objective 2B: Develop biomarker-based risk monitoring protocols using existing validated gene expression and metabolic biomarkers for early detection of apple and pear peel and cortex storage disorders.
Sub-objective 2C: Determine if sweet cherry fruit pitting, cracking and browning is relatable to fruit epidermis and wax composition.
The two objectives both rely on metabolomic and genomic techniques to investigate field and postharvest factors that impact fruit quality. The link from sub-objective 2B to 1A reflects biomarkers identified in the previous project period to be validated for apple (2B) as well as applied initially for pear (1A, 2B).
Objective 1 is focused on enhancing knowledge of how field horticulture impacts postharvest fruit quality with emphasis on fruit physiological disorders and ripening. The sub-objectives (1A, 1B) are designed to generate new information regarding the impact of pear field horticulture on fruit quality and ripening metabolism, particularly disorder-related metabolomics and genomics.
Sub-objective 1C also is focused on generating disorder-related metabolomic information for apple fruit sun damage originating prior to harvest.
Application of metabolomic and genomic techniques to disorders arising in the postharvest environment is the basis for Objective 2. Can assessment of apple fruit volatiles accumulating during storage in environments known to cause disorders provide a means to avoid disorder development. (2A) Biomarkers identified for apple disorders in the previous project plan will be validated with multiple fruit lots and cultivars (2B). Disorder metabolism of sweet cherries (2C) will be explored using a metabolomic approach.
Approach
Fruit from commercial orchards will be harvested then stored at ARS-Wenatchee and in commercial CA rooms. Fruit quality, metabolites, and mRNA will be characterized at harvest and after storage using standard methods.
Hypothesis 1A: Fruit position on the tree directly impacts maturation, superficial scald susceptibility, ripening and storability, and associated metabolism. Pears from two extreme light environments within the tree canopy will be grouped based on differential absorbance (DA). Fruit quality and disorders will be assessed at harvest and after storage. Metabolites and mRNA in peel collected from each canopy location/DA group will be analyzed. Results will be mined for metabolites and mRNA associated with physiological disorders.
Hypothesis 1B: Inconsistent post-storage ripening of 1-MCP treated d’Anjou pears is relatable to differential absorbance (DA) value at harvest. Pears will be exposed at harvest to 1-MCP for 16 hours, then stored at 1 degree C. After storage fruit will be evaluated for disorders and fruit quality characterized.
Hypothesis 1C: Apple peel metabolism following cold storage imposition is altered by pre-harvest light exposure. ‘Granny Smith’ apples exposed to direct sunlight will be harvested and sorted by sun damage. Apples will be stored at 1 degree C and after storage, untargeted metabolic profiling of ~800 metabolites will be performed on peel and cortex tissue collected at each sampling date. Multivariate and univariate statistical approaches will be employed to link changes in specific areas of metabolism with sunscald and superficial scald development.
Hypothesis 2A: Apple aroma volatile production changes when fruit are stored in environments conducive to development of physiological disorders. ‘Honeycrisp’ apples stored in controlled atmosphere chambers will be subjected to atmospheres known to cause physiological disorders. Volatile compound samples will be collected after various intervals and after 180 days, fruit will be removed from storage and evaluated for incidence and severity of external disorders.
Hypothesis 2B: Metabolic and gene expression superficial scald based risk assessment can be used to indicate when scald risk in a storage room is elevated.‘Granny Smith’ and ‘Delicious’ apples, and Anjou pears will be stored in CA at 1 degree C. Superficial scald will be evaluated following various lengths of storage. Storage atmospheres will be evaluated for volatile compounds determined to be useful for scald risk assessment.
Hypothesis 2C: Pitting and cracking incidence of sweet cherries is associated with altered epidermal metabolic profile compared with undamaged fruit. ‘Rainier’ sweet cherries will be subjected to uniform bruising using a steel ball dropped onto the fruit. Micro-cracking and stomata/lenticel number will be estimated by staining fresh whole fruit with acridine orange and counting micro-cracks at five random positions on each fruit using florescence microscopy. Waxes extracted from fruit will be analyzed using HPLC-QTOF-MS. Metabolic differences linked with cracking and epidermal defects will be identified using untargeted metabolic profiling methods developed for apple.
Progress Report
1A: Determine how fruit position within the tree impacts pear metabolic profile, superficial scald, postharvest quality, and ripening: ‘d’Anjou pears were harvested at commercial maturity from the internal and external portions of large, open-vase trained trees. Harvested pears were categorized according to chlorophyll content estimated using a differential absorbance (DA) meter. Pears were stored up to 8 months controlled atmosphere (CA), removing and evaluating the peel metabolome and fruit quality at two, four, eight months and quality, and again, seven days after each storage pull out. Pear metabolism, including that related to fruit quality and ripening, was impacted primarily by fruit location on the tree and remained different through eight months CA storage. Lack of consistent ripening and quality continues to contribute to significant industry losses during storage and the results to date indicate that differences in fruit development arising from fruit position on the tree prior to harvest are reflected in overall fruit metabolism at harvest and after storage and ripening. Some of the metabolites identified are novel and have potential for use as markers for sorting pears at harvest based on where the fruit developed on the tree.
1B: Determine if inconsistent post-storage ripening of 1-methylcyclopropene (1-MCP) treated d’Anjou pears is relatable to DA value at harvest: ‘d’Anjou pears were sorted at harvest into four DA classes and then treated with the ripening inhibitor 1-MCP at zero or 300 parts per billion (ppb) 1-MCP. Fruit were stored at one degrees Celsius (C) in air for up to nine months and assessed after removal from cold storage plus seven days at 20 degrees C. 1-MCP treated fruit were greenest after storage compared with controls, but no differences in softening due to DA value at harvest or 1-MCP treatment were present. DA class at harvest contributed to superficial scald risk after both storage durations, but 1-MCP impacts on scald were dependent on DA class only after six months storage. The results indicate use of DA value at harvest to determine which fruit to treat with 1-MCP for long-term storage has some potential to predict fruit quality after storage.
1C: Determine if pre-storage light exposure impacts apple peel metabolic responses to postharvest chilling: Apple sunscald is a principal source of crop loss for susceptible cultivars in western regions of the U.S. While sunscald results from high light and/or heat in the orchard, the damage typically only appears after one or more months in cold storage. We determined biochemical changes in apple peel that are associated with conditions that lead to sunscald. Monitoring levels of these chemicals could be used to segregate fruit that will or will not develop sunscald. It was determined using four different varieties of apples that peel chemistry is different on the sun exposed and unexposed side of each fruit at harvest in the absence of sunscald symptoms. A means for imaging the presence of a specific class of metabolites associated with sunscald risk was developed and testing is underway. This information may lead to new postharvest management practices that allow fruit that will develop sunscald to be marketed prior to symptom development.
2A: Determine if apple aroma volatile production changes when fruit are stored in environments conducive to development of physiological disorders: ‘Honeycrisp’ apples were stored at one degree C (disorder risk high) or two and a half degrees C (disorder risk low) in air or CA (two percent oxygen, 1 percent carbon dioxide) through eight months. Volatile compounds collected from fruit during storage were analyzed and fruit quality was assessed after fruit were removed from storage. Volatiles produced by fruit stored at the two temperatures in air exhibited several production patterns. These results indicate storage temperature alters ripening-associated volatile production of ‘Honeycrisp’ apples stored in air. For fruit stored in CA, volatile production also showed several volatile production patterns, and there was similarity of volatile content in samples collected at different dates for the two temperatures. This result indicates CA ameliorates some of the influence of storage temperature on volatile production but alters the pattern over time. Differences in volatiles attributed to temperature during air and CA storage accompanied differences in fruit disorder incidence indicating potential for storage room gas samples as indicators of disorder risk.
2B: Develop biomarker-based risk monitoring protocols using existing validated gene expression and metabolic biomarkers for early detection of apple and pear peel and flesh storage disorders: Apple superficial scald continues to be a significant annual source of loss, especially when apples are marketed as organic and no postharvest chemical treatments are applied to control the disorder. Identifying factors that improve superficial scald mitigation during the later portion of the supply chain following effective controlled atmosphere storage is critical as symptoms can develop while fruit are in the marketing chain. Experiments in 2016-17 demonstrated existing superficial scald risk assessment biomarkers, both metabolites and expressed genes, identified high risk fruit lots during simulated distribution, delivery and retail. Additionally, supply chain temperature was shown to have a profound impact on reducing superficial scald with one degree C being far more effective than typical distribution/supply chain temperatures of three degrees C.
Overall, monitoring scald risk assessment biomarker levels during the initial months of CA storage is an effective approach to indicating whether storage conditions such as oxygen levels or any delay until establishing storage atmosphere elevated the scald risk for fruit from that storage room. Fruit producers can use this technique to screen commercial CA rooms for scald risk and manage inventory to reduce risk.
2C: Determine if sweet cherry fruit pitting, cracking and browning is relatable to fruit epidermis and wax composition: Surface browning is a common problem for most yellow or blush sweet cherry cultivars. Rapid cooling of fruit using low temperature water, hydrocooling, has been suspected to exacerbate browning development in susceptible cultivars. Studies conducted in 2017 indicated microcracks and browning formed and/or expanded as a result of hydrocooling of susceptible fruit. Microscopic assessment indicated more microcracks formed on regions of the surface with less sun exposure, and nuclei of cells surrounding microcracks without browning were intact and present, meaning cells likely were alive, while nuclei were absent (cells dead) when tissue was brown. The information to date indicates microscopic assessment may provide insight to determination of sweet cherry surface browning and supports the hypothesis that hydrocooling exacerbates skin browning risk.
Accomplishments
1. ‘Honeycrisp’ apple bitter pit is reduced by 1-methylcyclopropene and/or short term controlled atmosphere (CA) storage. The apple physiological disorder bitter pit is an unsightly peel cosmetic defect that results from several factors existing in orchards prior to harvest. Bitter pit symptoms often do not arise until fruit have been harvested and placed into cold storage. ARS scientists in Wenatchee, Washington, collaborating with sceintists at Washington State University, showed bitter pit incidence is reduced by storing apples in a controlled atmosphere with low oxygen and high carbon dioxide content relative to air for as little as 1 week after harvest. The efficacy for bitter pit reduction of a week of CA immediately after harvest may allow producers to reduce disorder potential while allowing fruit to be marketed early in the harvest season.
Review Publications
Mattheis, J.P., Rudell, D.R., Hanrahan, I. 2017. Impacts of 1-Methylcyclopropene and controlled atmosphere established during conditioning on development of bitter pit in ‘Honeycrisp’ apples. HortScience. 52:132-137. doi:10.21273/HoRTSCI11368-16.
Leisso, R.S., Mattheis, J.P., Rudell, D.R. 2017. Controlled atmosphere storage, temperature conditioning, and antioxidant treatment alter postharvest 'Honeycrisp' metabolism. HortScience. 52(3):423–431. doi:10.21273/HORTSCI11436-16.
Gapper, N.E., Hertog, M., Lee, J., Buchanan, D.A., Leisso, R.S., Giovannoni, J.J., Johnston, J.W., Shaffer, R.J., Micolai, B.M., Mattheis, J.P., Watkins, C.B., Rudell Jr, D.R. 2017. Delayed response to cold stress is characterized by successive metabolic shifts culminating in apple fruit peel necrosis. Biomed Central (BMC) Plant Biology. 17:77. https://doi.org/10.1186/s12870-017-1030-6.
Honaas, L.A., Kahn, E.M. 2017. A practical examination of RNA isolation methods for European pear (Pyrus communis). BMC Research Notes. doi: 10.1186/s13104-017-2564-2.
