Location: Physiology and Pathology of Tree Fruits Research
2018 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
Progress was made on both objectives and their sub-objectives, all of which fall under National Program 306, Component I, Foods. Progress on this project focuses on Problem 1.A, define, measure, and preserve/enhance/reduce attributes that impact quality and marketability.
Sub-objective 1A: We made significant progress in determining how fruit position within the tree impacts ‘Anjou’ pear metabolic profile, physiological disorders, and postharvest quality. Fruit grown on the outside of the tree canopy mature and ripen differently compared with pears from the tree interior. Exterior and interior fruit also are different metabolically, detectable by fruit chemical and gene expression analyses, at harvest and throughout storage. These differences could lead to new fruit sorting techniques that would enhance ripening uniformity after packing.
Sub-objective 1B: New sorting to advance ripening uniformity after storage was developed. The cause of inconsistent post-storage ripening of 1-methylcyclopropene (1-MCP) treated Anjou pears is relatable to differential absorbance (DA) value at harvest. DA value reflects peel metabolic condition, and we determined fruit with an advanced DA value ripened sooner after 1-MCP treatment (1-MCP inhibits ripening) compared with fruit with less advanced DA value.
Sub-objective 1C: We made significant progress identifying peel compounds that are present in sun-damaged fruit prior to development of visible sun injury. The presence of these compounds may provide a means to non-destructively sort fruit that will develop injury symptoms prior to symptom development.
Sub-objective 2A: We confirmed that aroma volatile production is impacted by sub-optimal storage conditions suggesting monitoring apple volatiles during storage may be useful to predict fruit stress that leads to browning disorders.
Sub-objective 2B: Also in the area of disorder prediction, we confirmed that peel chemistry and gene expression can be utilized for risk-assessment of an apple peel browning disorder. The test can indicate disorder risk months prior to symptom development, and supply chain temperature management is critical to reducing disorder risk.
Sub-objective 2C: We identified physical and chemical differences in fruit surface and peel properties consistent with injury susceptibility to determine if sweet cherry postharvest disorders are relatable to fruit epidermis and wax composition.
Accomplishments
1. The apple peel disorder, superficial scald, is predictable months before symptoms occur. This disorder causes brown discoloration in the peel and typically occurs when fruit are displayed at retail with little or no refrigeration. ARS scientists in Wenatchee, Washington, in collaboration with industry partners, demonstrated an analytical procedure to measure specific peel components can provide an indication of superficial scald risk months in advance of browning development. The test was performed by industry personnel, demonstrating efficacy in a commercial environment. Use of this information provides industry with a means to identify specific fruit lots with high or low disorder risk and can contribute to an improved warehouse marketing plan.
Review Publications
Rudell Jr, D.R., Sullivan, N.L., Mattheis, J.P., Musacchi, S. 2017. Metabolic profiling variations within D’Anjou pear fruit from different canopy positions. HortScience. 52(11):1501–1510. https://doi.org/10.21273/HORTSCI12375-17.
Mattheis, J.P. 2017. Controlled atmosphere pO2 alters ripening dynamics of 1-MCP treated ‘d’Anjou’ pear (Pyrus communis L.) fruit. HortScience. 52(10):1385–1389. https://doi.org/10.21273/HORTSCI12286-17.
Poirier, B.C., Buchanan, D.A., Rudell Jr, D.R., Mattheis, J.P. 2018. Differential partitioning of triterpenes and triterpene esters in apple peel. Journal of Agricultural and Food Chemistry. https://doi.org/10.1021/acs.jafc.7b04509.
