MODIFYING TUBER SIZE DISTRIBUTION, LOW TEMPERATURE SWEETENING AND TOLERANCE TO HEAT STRESS IN PROCESSING POTATOES (Solanum tuberosum L.)
Herman, Derek James
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Controlling tuber size distribution and the propensity for low temperature sweetening (LTS) of processing potatoes are key to optimizing quality and maximizing crop value. My research focused on (1) developing methods to increase tuber set and shift tuber size distribution in cv. Bondi, (2) investigating how low O2 storage modulates LTS of cvs. Innovator and Russet Burbank, (3) screening cultivars for tolerance to heat stress for retention of LTS-resistant phenotype and (4) determining the mechanism by which heat stress abolishes resistance to LTS. Bondi produces vigorous foliar growth, low tuber set and high yields of large tubers that frequently exceed optimum size for seed and processing markets. We evaluated several methods for altering apical dominance, tuber set and size distribution of Bondi and its maternal parent Ranger Russet. Gibberellic acid (GA) applied to cut seed prior to planting reduced apical dominance, increased tuber set and decreased average tuber size; however, the optimal concentration to maximally shift tuber size distribution without decreasing marketable yield was 4-5-fold greater for Bondi than Ranger. The reduced sensitivity of Bondi to GA was likely inherited from its paternal parent Karaka, which displays similar morphological and developmental traits, indicative of high levels of endogenous GA. Russet Burbank and Innovator are frozen processing cultivars with inherently different susceptibilities to LTS. Here we show how low O2 storage modulates cold-induced sweetening to reveal metabolic differences in LTS metabolism intrinsic to these cultivars. While storage of tubers in 2.5 kPa O2 greatly attenuated the initial LTS responses for both cultivars, the effect was only temporary in Innovator. Low O2 attenuated LTS by inhibiting invertase. Heat stress exacerbated cold-induced sweetening of Ranger and Russet Burbank tubers (LTS-susceptible cultivars), and abolished the inherent LTS-resistance of Sage Russet, GemStar Russet, POR06V12-3 and A02138-2 tubers. Heat stress rendered invertase cold-inducible in the LTS-resistant but non-heat tolerant cultivars/clones. Payette and its maternal parent EGA09702-2, however, demonstrated considerable tolerance to heat stress for retention of LTS-resistance. Payette’s heat tolerance was conferred by the lack of cold-induction of invertase, similar to InnateR Russet Burbank (W8) tubers, where silenced invertase activity conferred robust tolerance to heat stress.