Potato Seed-tuber Age Affects Mobilization of Carbohydrate Reserves During Plant Establishment

Abstract

During the early stages of growth, developing sprouts rely heavily upon tuber carbohydrate reserves. Strong sprouts are produced from young potato (Solaman tuberosum L.) seed-tubers, whereas tubers of advanced physiological age produce sprouts with reduced vigour. Single-eye seedcores from 7- and 19-month-old seed-tubers were sprouted in order to study the effect of tuber age on carbohydrate reserve mobilization. Following 24 d of growth, the same amount of total shoot dry matter was produced from both ages of seedcores. However, d. wt of individual shoots from older seedcores was 93 % lower than that from younger cores, reflecting a significant loss in apical dominance with age. Furthermore, core d. wt loss per unit gain in plant d. wt was greater from 19-month-old seedcores, indicating an age-related decrease in the efficiency of reserve mobilization over the growth interval. During sprouting, rates of starch hydrolysis and subsequent increases in total soluble carbohydrates were similar for both tuber ages. Reducing sugars (mg g d. wt−1) accumulated faster in older than in younger cores; non-reducing sugars (mainly sucrose) decreased 53% in older seedcores over the 24 d growth interval. Non-reducing sugar content (mg g d. wt−1, mg core−1) of younger cores remained constant. The results suggest that older cores are either less efficient at converting glucose to sucrose (the main translocatable carbohydrate in potatoes) or have higher rates of sucrose hydrolysis (e.g. increased invertase activity) compared with younger tuber tissues during sprouting.