MODELING THE EFFECTS OF POTATO SEED-TUBER AGE ON PLANT ESTABLISHMENT

Four physiological ages of potato (Solanum tuberosum L. 'Russet Burbank') seed-tubers were produced by varying the time of storage at 15-degrees-C. Age was quantified as the accumulated degree-days (dd) above 4-degrees-C over the 199-d storage interval, and plant emergence and establishment were then modelled in controlled environment studies. As age advanced, time to 50% sprout emergence decreased, reaching a minimum at 589 dd, and then increased with further aging. Apical dominance was also reduced, as evident from a linear increase in the number of sprouts per seedpiece with advancing age. Earlier emergence from older seed-tubers led to significantly more leaves, leaf area, and leaf and stem dry weights per plant compared with younger seed-tubers early in the study; however, this advantage in plant establishment was eventually lost as time progressed through 33 d, resulting in significant age by time interactions on each yield component. Unit leaf rate, and relative growth rates with respect to leaf area and plant dry weight, thus decreased linearly with advancing tuber age over the course of the study. Leaf area ratio of plants from older tubers was greater than that from younger tubers early in the study, but this difference decreased with time. Seed-tuber age affected LAR through altering the leaf weight ratio (efficiency of partitioning dry weight to leaves), not the specific leaf area. Yield component analysis showed that the number of leaves per stem and the leaf area per leaf accounted for 85 and 12 % of the total variation in plant dry weight, respectively. Because plant establishment was clearly more advanced, there may be potential for utilizing aged Russet Burbank seed-tubers to improve grade and earliness and increase yield in areas with short growing seasons.