Potato tuber dormancy and postharvest sprout control

Potato is the third most important food crop in the world and is an excellent source of dietary calories, vitamins, and minerals. At harvest and for an indeterminate period thereafter, potato tubers are in a state of physiological dormancy and will not sprout. Tuber dormancy is lost during storage in a cultivar- and environmentally dependent manner. The onset of sprouting, which follows the loss of tuber dormancy, results in numerous biochemical changes that are detrimental to the processing and nutritional qualities of potatoes. The initiation of tuber dormancy is coincident with the initiation of tuberization. The duration of tuber dormancy is affected by both genetic and pre- and postharvest environmental factors. Endogenous plant hormones are involved in the regulation of tuber dormancy progression. Current evidence suggests that abscisic acid and ethylene are required for dormancy initiation and maintenance, while cytokinins appear to regulate dormancy exit. The exact roles of auxins and gibberellins in tuber dormancy control have yet to be determined, but both are involved in the control of sprout growth that follows dormancy termination. Dormancy initiation and progression are associated with wholesale changes in gene expression. Although the transcript abundances of many genes change dramatically during tuber dormancy, in most cases, the biological significance of these changes has yet to be determined. Dormant tuber meristems are arrested in the G1 position of the cell cycle, and the onset of sprout growth following dormancy exit is accompanied by the resumption of cell cycle progression and expression of genes encoding key proteins involved in cell cycle control. Dormancy progression is also accompanied by changes in chromatin composition involving both DNA cytosine methylation and covalent histone modification. Because of its deleterious effects on tuber quality, successful longterm storage of potatoes requires the control of sprouting. In most commercial storages, sprout control is achieved through the application of sprout inhibitors. The most widely used sprout inhibitors are synthetic chemicals that inhibit sprouting in an herbicidal manner. Several newer natural product-based sprout inhibitors have been introduced whose mechanisms of action are distinct from those of the earlier synthetic sprout inhibitors.