Sprout and stem development from potato tubers of differing physiological age: the role of apical dominance

Abstract

A series of experiments over three years (1984–1987) is described in which tubers of a range of early and maincrop varieties were exposed to two different storage-temperature regimes to give different physiological ages. Tubers exposed to 10–15°C from the break of dormancy and then held at 5° had a final age at planting of ca. 500 day-degrees > 4°C. Tubers held at 5°C throughout storage were physiologically younger, having accumulated only 100 day-degrees > 4°C. These temperature regimes, in the light, were considered to be representative of the treatment of tubers for commercial production of early and maincrop potatoes. For each treatment, the number and lenght of all sprouts longer than 2 mm at planting, and the number of stems produced in the field, were recorded. In a parallel study in 1985–1986, tubers of a single variety, aged in the same way, intact or with the apical sprout removed, were held in the laboratory to give full expression of sprout production. The use of physiologically younger tubers did not necessarily give more sprouts at planting, nor mainstems after planting in the field. However, the younger tubers held in the laboratory did carry significantly more sprouts, and sprout production from additional eyes was induced by desprouting. Overall, younger tubers produced at least one more mainstem than older tubers in only three out of twelve comparisons and, when the total number of stems per tuber was assessed, the younger tubers carried the same number or fewer stems in all cases. It is concluded from this investigation that, although apical dominance plays an important role in determining the number of sprouts produced per tuber, there is a high degree of variation between varieties and seasons, and within batches of tubers, in its expression. Extrapolation from a single variety, and in general from experiments confined to the laboratory, may bot be justified in the prediction of numbers of stems in the field.