The Canon of Potato Science: 41. Sprouting

Abstract

What is it? Sprouting is the visible growth of shoot meristem tissue in the “eyes” of potato tubers which occurs after dormancy has ended. It is the major visible milestone in determining tuber physiological age. The earliest observable stage of sprouting, when only small white buds are visible, is often termed “pipping” or “peeping”. Sprouts have multiple nodes, with meristematic tissue and leaf primordia present at each node as well as at the distal end. Since potato tubers are modified shoot tissue, the apical (“rose-end”) eye is first to sprout, followed by sprouting at the lateral eyes as apical dominance diminishes. Potato sprouts are negatively geotropic and usually develop adventitious roots on the basal portions. Branching of the sprout occurs when apical dominance within the sprout is overcome, either after the sprout is sufficiently large, or following damage to the apex. Repeated damage to the apical ends of sprouts and branches can lead to excessive branching at the eye, forming a tightly-packed rosette of sprouts. Internal sprouts are normal sprouts which penetrate the originating tuber or an adjacent tuber due to close proximity, pile pressure or rosetting. Sprouts grown in darkness are etiolated, with undeveloped leaf primordia. They are usually white to colourless (i.e. without chlorophyll), although the sprouts of some cultivars have pink, red or purple pigmentation. Dark-grown sprouts will continue to elongate with time, and may reach a meter in length as they seek light. In lighted conditions the leaves expand and chlorophyll develops. Sprouts grown in lighted conditions have relatively short internodes, with well-developed leaves and functioning chlorophyll. Emerged sprouts from planted tubers are termed shoots, and subsequently develop into fully-functioning potato plants. Physiologically young tubers will not sprout due to innate dormancy of the meristematic tissue in the eyes. After innate dormancy has ended, sprouting can be delayed by cool storage conditions (enforced dormancy), but will eventually end and