PRE AND POSTHARVEST PHYSIOLOGY AND ETIOLOGY OF PHYSIOLOGICAL DISORDERS IN �HONEYCRISP� APPLES

Objective 1Experimentally determine how specific rootstocks alter physiological disorders and how physiological disorders in turn alter fruit quality. (Year 1)Our first objective focuses on understanding the relationship between rootstocks, environment, fruit quality, and physiological disorder development in the apple cultivar 'Honeycrisp'.Rational. In contrast to research on bitter pit, the rootstock effect on soft scald development have not been addressed except for our preliminary study from this year. Our hypothesis that rootstock is the main driver of scion mineral nutrient concentrations, affecting vigor and yield and importantly fruit susceptibility to physiological disorders. We expect that rootstocks with high bitter pit susceptibility will have lower soft scald incidence during storage.Sub objective A. Study the effects of different Geneva, Malling and Budagovsky rootstocks on the interaction between bitter pit and soft scald.Subobjective B. Study the regional effects of rootstocks on bitter pit and soft scald interaction.Objective 2Understand the mechanisms of bitter pit and soft scald development in relation to endogenous hormones and minerals balance. (Year 1)Rational. The effects of mineral nutrient profile and balance in relation to rootstock and the interaction between soft scald and bitter pit has not yet been explored. Some research examining the effects of different rootstocks on the scion hormones concentration were investigated by the Co-PIs Robinson and Fazio in previous work. However, the relationship between hormone concentration at different stages of fruit development and physiological disorder development during storage remain has not been studied. We hypothesize that the influence of rootstock on hormone concentrations, such as abscisic acid (ABA), may reduce bitter pit and enhance soft scald development or vice versa. In addition, mineral nutrient balance in the fruit as influenced by rootstock could contribute to development of both physiological disorders.Subobjective A. Understand the effects of mineral balance in relation to rootstock on the interaction between bitter pit and softs scald.Subobjective B. Study the effects of the hormonal balance during fruit development starting from fruit set until harvest in relation to rootstock and physiological disorder development in the field and during storage.Objective 3Characterize the variation in fruit physiological disorders and model the relationships among environments, orchard management, storage temperature manipulation, and fruit quality. (Year 2). Rationale: Prediction models for both bitter pit and soft scald based on their interaction are needed but such relationships have not yet been studied in relation to pre and postharvest factors. No studies have identified the interaction between the two disorders in 'Honeycrisp' fruit and their mechanisms through the different fruit development stages and through postharvest storage. An integrative model to predict bitter pit and soft scald. Based on our preliminary data and results of the first objective, we will build a preliminary model to predict bitter pit and soft scald during storage based on their interaction of rootstock genotype and abiotic factors.