Location: Physiology and Pathology of Tree Fruits Research
2020 Annual Report
Accomplishments
1. Improving pear quality by identifying metabolites associated with ripening consistency. Pear fruit quality inconsistency can contribute to significant annual losses due to spoilage. This variability can be detected in the natural pear chemistry affecting flavor, appearance, and texture. Changes in chemistry revealed sun exposure may be a prominent source of inconsistency based on fruit on-tree position. Differences in natural fruit chemistry and final product following storage indicates this variability would likely impact every cold chain management decision. Findings indicate that sorting of pears before they enter the cold chain potentially on the basis of levels of specific natural peel chemicals will enhance fruit quality consistency.
2. Reducing apple cold chain losses caused by excess sun exposure. Exposure to excessive sunlight can contribute to 10-25% annual losses due to multiple disorders in many of the world’s most productive apple growing regions including the western United States. Our results demonstrate that heat events in the orchard contribute to sunscald development, a common source of postharvest losses of susceptible apple varieties. Results reveal physical changes to apple peel surface that may confer resistance to solar stress that leads to sun related postharvest disorders. We identified novel peel chemicals associated with risk of delayed sunscald as well as fruit quality and ripening. Monitoring amounts of these compounds may have potential to non-destructively sort apples according to sunscald risk at harvest. This information would allow producers to store fruit with low sunscald risk and to sell high-risk fruit before the disorder develops soon after harvest.
3. New management strategies for apple superficial scald control. Superficial scald (scald), a postharvest browning disorder of apple peel, continues to contribute to annual fruit quality loss, especially in markets where residues of scald control compounds are restricted. We have identified gene activity that, after the chilling injury that causes scald occurs, may be useful to define storage management practices to prevent scald. Our results reveal that chilling injury is cumulative and preventable with optimal controlled atmosphere (low oxygen, high carbon dioxide relative to air) storage conditions started within the first week following harvest. We have demonstrated that post-storage crop-protectant or hot water treatment effectively controls scald if the chilling injury that induces scald has been controlled. Monitoring levels of natural compounds in fruit associated with scald risk may indicate if this criterion is met and post-storage treatments will be effective. These findings indicate novel strategies for reducing or eliminating scald from both crop protectant restricted, and organic cold chains are possible using existing commercial technologies.
4. ‘Honeycrisp’ apple bitter pit is reduced by 1-MCP and/or short-term controlled atmosphere (CA) storage. The apple physiological disorder bitter pit is an unsightly cosmetic defect on the fruit surface which results from several factors existing in orchards prior to harvest. Bitter pit symptoms often do not arise until the fruit have been harvested and placed into cold storage. Bitter pit prevention typically relies on application of calcium sprays and crop load management prior to harvest. ARS scientists collaborating with Washington State University 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 CA with low oxygen and high carbon dioxide content relative to air for 1 or more weeks beginning within 2 days of harvest. Both 1-MCP and CA of 1 week or more reduced bitter pit in most orchard lots with the combination of 1-MCP then CA 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 CA storage rooms. 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.
5. Knowledge of gene expression differences among tree fruit varieties enhances efforts to discover and utilize genes as biomarkers. One way to enhance postharvest tree fruit quality is to apply existing technology with greater precision and accuracy using biomarkers – fruit compounds that predict future fruit quality. ARS scientists in Wenatchee, Washington, in collaboration with scientists at Washington State University, the Pennsylvania State University, and the California State University, have conducted studies to identify new fruit quality biomarkers which are in this case genes. The research identified genes that are unique among fruit varieties of the same type, for example genes that make ‘d’Anjou’ different from ‘Bartlett’ pears and ‘Granny Smith’ different from ‘Golden Delicious’ apples. Scientists can now also explore larger-scale genetic differences that can help explain differences in ripening among some apple and pear varieties, information that may be useful in designing modified storage protocols specific for the needs of each type of apple and pear.
Review Publications
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. https://doi.org/10.1016/j.postharvbio.2019.111062.
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. https://doi.org/10.1016/j.postharvbio.2020.111164.
