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ARS Home » Pacific West Area » Wenatchee, Washington » Physiology and Pathology of Tree Fruits Research » Research » Research Project #438827

Research Project: Developmental Genomics and Metabolomics Influencing Temperate Tree Fruit Quality

Location: Physiology and Pathology of Tree Fruits Research

Project Number: 2094-43000-008-013-T
Project Type: Trust Fund Cooperative Agreement

Start Date: Oct 1, 2020
End Date: Sep 30, 2022

Over 11 million ‘WA38’ (traded as Cosmic Crisp®) trees have been planted in the last 5 years in WA with an estimated total industry investment of $500 million. In our previous project (AP-14-103A), a disorder on ‘WA38’ apples called “green spot” (due to symptom appearance) was reported from Sunrise WSU experimental orchard. In 2016 and 2017, 32% and 26% green spot incidences respectively were recorded in that orchard. The disorder is turning out to be more widespread than first expected, arising in many regions, and could, potentially, lead to significant crop losses without a better understanding of how to manage and mitigate the symptom development. The causes and timing of symptom appearance are not yet understood. Symptoms become apparent in the orchard between the end of July and the beginning of August and can be diverse, ranging from undefined green patterns on the peel or well-defined superficial circular green spots (of different sizes) to corking spots immediately under the surface as the disorder becomes more severe. We have developed a protocol using fruit bags to determine when, yet unknown conditions trigger events that will lead to the disorder. We will determine if stressors like light, overcooling water, and spray applications contribute to disorder incidents and pinpoint the disorder inception. To do this, we will bag apples weekly/every 10 days from fruit set all along the summer, removing them one month/3 weeks prior to harvest, so as to exclude light during key growth periods in combination with other environmental factors. We will analyze peel chemistry to track when the fruit first reacts to the disorder-provoking stress and, subsequently, can no longer control its effects, then, link those events with environmental conditions. Then, we can suggest management practices that can be deployed around those events to mitigate or eliminate the disorder. Expected outcomes include a determination of factors contributing to green spot incidence and development and strategies for reducing or eliminating the disorder. Objectives: 1. Determine the effect of bagging fruit on the intensity of green spot appearance. 2. Determine green spot onset in relation to events or management factors along the season.

We will determine the timing of the appearance of green spot symptoms in an experimental orchard containing fruit bagged at different times during the season to determine the nature of the environmental events that triggered symptom development. Fruitlets from one tree replication at each time point at which the symptoms become apparent will be utilized for metabolomic analysis sampling. Apple peel will be the key tissue of this investigation. Furthermore, a final sampling for analysis will be collected at harvest to compare the metabolomic profiles of fruit that were bagged before the green spot onset with fruit that were left unbagged throughout the growing season (Figure 1). Metabolomic profiling of symptomatic fruit vs asymptomatic fruit, in bagged or control replications, will help us determine which biochemical pathways are impacted in green spot fruit. Furthermore, metabolomic profiles of fruit at harvest can be compared to mid-season fruitlets to see if biochemical differences correlated with green spot symptoms can be detected earlier in the season.