Differential Sensitivity of Genetically Related Potato Cultivars to Treatments Designed to Alter Apical Dominance, Tuber Set and Size Distribution

The cultivar, Bondi, was selected from a cross between Ranger Russet (maternal parent) and Karaka and is currently being evaluated as a frozen processing cultivar. Relative to Ranger, 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 the relative efficacies of gibberellin (GA), cytokinin (benzyladenine (BA)) and seed aging for altering apical dominance, tuber set and size distribution of these genetically related cultivars. GA applied to cut seed prior to planting hastened emergence, 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. BA marginally hastened plant emergence (Bondi) and decreased apical dominance (both cultivars) only when combined with GA, but had no further effects on tuber set, yields or tuber size distributions in either cultivar. Age-priming Ranger seed for 700 degree days (DD) at 32 °C during storage shifted the tuber size distribution to a much greater extent than 2 mg L −1 GA (optimal concentration) without reducing marketable yield. The combined age and GA treatment resulted in no further shift in size distribution for Ranger beyond that induced by the 700-DD treatment alone, but reduced the marketable yield by 9.6 MT ha −1 . In contrast to GA, the mechanism by which age-priming altered tuber size distribution in Ranger could not be explained by effects on stem number/tuber set relationships alone. Bondi, however, exhibited an even greater shift toward smaller tubers with no reduction in yield with the combined 700-DD/GA (2 mg L −1 ) treatment, reflecting its decreased sensitivity to GA. Moreover, the shift in tuber size distribution induced by aging Bondi seed for 700 DD was approximately equal to that observed by treating seed with 8 mg L −1 GA (optimal concentration). The reduced sensitivity of Bondi to GA was likely inherited from its paternal parent Karaka, which displays similar morphological traits, including high yield of large tubers.