1a. Objectives (from AD-416):
The long-term objective of this project is to develop tools to assist in marker-assisted selection and quality management of deciduous tree fruits. Over the next 5 years this program will focus on the genetic, metabolic and physiological mechanisms underlying fruit texture, aroma, and physiological disorders (Appendix 1) based on the following objectives: Objective 1: Identify genetic factors regulating apple cultivar-specific fruit texture and aroma production. Objective 2: Characterize the physiological basis for external necrotic disorders and identify genetic and/or metabolic markers associated with disorder development. •Sub-objective 2.a. Discover biomarkers that predict, diagnose, and/or distinguish apple superficial scald and soft-scald. •Sub-objective 2.b. Validate prospective biomarkers that predict, diagnose, and/or distinguish apple superficial scald and soft scald. Objective 3: Determine how environmentally-induced changes in apple fruit physiology affect onset of physiological disorders.
1b. Approach (from AD-416):
Research to elucidate genetic regulation of apple fruit texture and aroma will utilize established molecular analytical techniques. All analyses will use resources in place in the research unit. The apple germplasm to be utilized is available via an ongoing collaboration with the Washington State University Apple Breeding Program. This includes reference cultivars as well as a large cross population specifically established for studies related to fruit texture. Metabolomic studies will utilize fruit obtained from commercial and research orchards with chemical analyses conducted using location resources. Chemical analyses (GC- and LC-MS) will be performed using established methods where available with new methods developed as needed. Fruit will be stored using the location’s cold storage and controlled atmosphere facility which consists of 140-2 bushel chambers in which N2, CO2, and air are manipulated to achieve desired proportions in each chamber. Individual chamber temperature control is available for 20 chambers. Field experiments will be primarily conducted in commercial orchards to allow microclimate effects to be evaluated under a range of geographic and horticultural management conditions. Fruit microenvironment prior to harvest will be manipulated using polyethylene bags. Evaluation of fruit epidermis by SEM will utilize equipment in place in the research unit.
3. Progress Report:
Many apple cultivars develop disorders after harvest due to low storage temperature. Symptoms, browning of the peel or internal tissues, can take months to develop, but tissue injury can occur soon after harvest. The processes by which injury and browning occur are not understood, therefore, in 2013 ARS scientists conducted experiments that showed peel and internal browning provoked by low storage temperature is accompanied by increased amounts of unique compounds that could serve as indicators of low temperature injury. This finding supports development of systems to monitor these apple fruit compounds during storage to predict risk of disorder development prior to appearance of symptoms. The information could contribute to development of predictive and diagnostic tests that would enhance marketing for particular fruit lots, and also identify injury caused by low storage temperature. As the pattern of apple fruit ripening and fruit response to storage conditions is variety specific, postharvest characteristics for new varieties is not predictable. To determine best management practices for the new variety ‘Lady Alice’, in 2013 ARS scientists conducted experiments to examine the effect of postharvest technologies currently available to the apple storage industry on ‘Lady Alice’ fruit firmness and physiological disorders. Best outcome for firmness retention and lack of disorders was by treating fruit with an inhibitor of ripening after harvest then storing fruit in air at 33 degrees Fahrenheit. This finding provides information to industry that can contribute to development of postharvest management practices for ‘Lady Alice’ apples.
Leisso, R.S., Buchanan, D.A., Lee, J., Mattheis, J.P., Rudell Jr, D.R. 2013. Cell wall, cell membrane, and volatile metabolism are altered by antioxidant treatment, temperature shifts, and peel necrosis during apple fruit storage. Journal of Agricultural and Food Chemistry. 61:1373-1387.