Location: Physiology and Pathology of Tree Fruits Research
2016 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 2, 4, 8 months and quality again 7 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 8 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.
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: ‘d’Anjou’ pears harvested from trees pruned in winter or fall and the following summer were sorted into 3 DA classes and then treated with the ripening inhibitor 1-MCP at 0 or 300 ppb 1-MCP. Fruit were stored at 1 degree Celsius in air for 7 months and assessed after removal from cold storage plus 7 days at 20 degrees Celsius. 1-MCP treated fruit were less ripe after storage compared with controls, and differences in ripening were observed among 1-MCP treated fruit from the 3 DA classes only for fruit pruned in fall and the following summer. The results indicate tree canopy management may be an additional factor influencing postharvest ripening of ‘d’Anjou’ pears during and after cold storage.
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 1 degree Celsius (disorder risk high) or 2.5 degrees Celsius (disorder risk low) in air or CA (2% oxygen, 1% carbon dioxide) through 8 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 were differentiated by 3 patterns of production and all volatile samples were distinct at and across storage durations. These results indicate storage temperature alters ripening- associated volatile production of ‘Honeycrisp’ apples stored in air. For fruit stored in CA, volatile production was distinguished by 5 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 disorder incidence indicating potential for storage room volatile samples as indicators of disorder risk and/or development.
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: ‘Granny Smith’ and ‘Delicious’ apples were stored in multiple commercial CA storage rooms for up to 3 months upon which they were transferred to a common CA storage room for 3 more months or air storage at 5 degrees Celsius. Common CA storage fruit were placed in air at 5 degrees Celsius at 6 months. Air at 5 degrees Celsius was used to simulate supply chain conditions. Scald risk assessment biomarker levels were monitored monthly in all fruit until 10 months. All apples developed scald after 3 months in air at 5 degrees Celsius, albeit with different severity. CA room conditions had the greatest impact on eventual scald incidence or severity as well as biomarker levels. ‘Delicious’ fruit with the highest biomarker levels later had the highest scald incidence during the simulated supply following 3 months of CA storage. Biomarker levels were highest at 2 months among ‘Delicious’ apples from a CA room that eventually developed the highest incidence of scald. The ‘Delicious’ CA room with the highest biomarker levels and poorest scald control had the highest oxygen levels during storage. For ‘Granny Smith’, CA rooms with the highest biomarker levels had the highest scald severity, but not incidence, during the simulated supply chain after 6 months storage. Elevated biomarker levels and scald severity appeared to be most linked with the delay between fruit entering the CA room and establishing the CA atmosphere. 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: A method of visually assessing microcracks in sweet cherry peel surface and extracting wax was developed. Visual comparison of healthy and very superficially browned ‘Skylar Rae’, a yellow blushed cultivar that is susceptible to superficial browning of the skin, indicated that micro-cracks were enlarged on damaged skin and epidermal cell nuclei were absent compared to healthy skin. Results indicate that the faint browning resulted from death of the top layer of epidermal cells around microcracks. This may be the result of infiltration of water and solutes during rapid commercial cooling after harvest. Natural peel wax was extracted from ‘Skylar Rae’ and, a number of compounds previously not known to be present in sweet cherry were identified. Additional analysis of wax extracts is underway in samples collected from healthy and brown fruit. The information to date indicates microscopic assessment may provide insight to determination of sweet cherry surface browning.
Accomplishments
1. Apple fruit superficial scald risk can be objectively estimated long before symptom development. Apple fruit superficial scald results from chilling stress during the first month after harvest and results in dark, sunken peel tissue after 3-6 months of cold storage. Low oxygen controlled atmosphere (CA) storage can control superficial scald but is not always effective across orchard lots and production seasons. ARS scientists in Wenatchee, Washington, have identified natural compounds that accumulate in the peel of apples that can serve as early predictors of scald prior to symptom development. When elevated scald risk has been detected based on biomarker accumulation, storage room oxygen levels can be reduced or fruit can be marketed prior to symptom development. This research provides new tools for apple producers to avoid superficial scald throughout the supply chain.
2. ‘Honeycrisp’ apple bitter pit is reduced by 1-MCP and controlled atmosphere (CA) storage. The apple physiological disorder bitter pit is an unsightly cosmetic defect on the fruit surface and results from several factors existing in orchards prior to harvest. Bitter pit symptoms often do not arise until fruit have been harvested and stored for 1 to 2 months. Bitter pit prevention typically relies on application of calcium sprays and crop load management prior to harvest. ARS scientists in Wenatchee, Washington, conducted studies to evaluate postharvest technologies as an additional means to reduce bitter pit development. Apples were exposed to the ripening inhibitor 1-methylcyclopropene (1-MCP) and/or stored in a controlled atmosphere with low oxygen and high carbon dioxide content relative to air. Both 1-MCP and CA reduced bitter pit in some orchard lots with the combination of 1-MCP then CA established rapidly after harvest providing the best bitter pit prevention. This postharvest prevention protocol can be readily adopted by commercial producers as all technology necessary is currently in place in most apple warehouses having controlled atmosphere storage rooms.
ARS scientists in Wenatchee, Washigton, have established contacts with orchardists, warehouse and field personnel regarding postharvest aspects of apple, pear and sweet cherry biology. These contacts occur on a regular basis. Contacts included interactions at industry sponsored meetings and round table discussions, and frequent contact with individuals around the nation via electronic or voice communication. Information provided to industry personnel growers is based upon findings from this project concerning postharvest biology of apples, pears and sweet cherries for the postharvest management of organic and conventional fruit.
Review Publications
Lee, J., Mattheis, J.P., Rudell Jr, D.R. 2016. Storage temperature and 1-MCP treatment affect storage disorders and physiological attributes of ‘Royal Gala’ apples. HortScience. 51:84-93.
Argenta, L.C., Mattheis, J.P., Fan, X., Amarante, C.V. 2016. Managing ‘Bartlett’ pear fruit ripening with 1-methylcyclopropene reapplication during cold storage. Postharvest Biology and Technology. 113:125-130.
Guan, Y., Peace, C., Rudell Jr, D.R., Verma, S., Evans, K. 2015. QTLs detected for individual sugars and soluble solids content in apple. Molecular Breeding. doi: 10.1007/s11032-015-0334-1.
Rickard, B.J., Rudell Jr, D.R., Watkins, C.B. 2016. Ex ante economic evaluation of technologies for managing postharvest physiological disorders. HortScience. 51(5):537-542.
