The effect of timed water stress on quality,total solids and reducing sugar content of potatoes

Potato (Solanum tuberosum L.) solids and reducing sugars were examined before, just after, and two weeks after transient water stress to gain an understanding of tuber changes that occur directly associated with water stress. Russet Burbank and A082260-8 potatoes were grown on Owyhee silt loam at the Malheur Experiment Station, Ontario, Oregon. Potatoes were subjected to a single episode of transient water stress by omitting furrow irrigation in either late June, July, or in early August of 1988 and 1989 to examine variety differences in the short term effects of water stress on changes in solids and reducing sugars in tuber stem ends. Irrigation was managed to maintain soil water potential above -65 kPa at 20 cm depth during tuber initiation through bulking except during transient stress when the soil water potential reached -82 to -110 kPa. Tuber samples were taken from plots and minimally stressed check treatments before stress, at the peak of stress, two weeks after the transient stress period, and after harvest. Tubers were sectioned longitudinally and the percent solids and reducing sugars were determined for samples from the tuber stem end, center, and apical end. Longitudinal tuber strips were fried after harvest to determine fry color. Tuber stem-end fry color did not darken in A082260-8 potatoes subjected to water stress. The line A082260-8 had higher stem-end solids and lower stem-end reducing sugars than Russet Burbank. Neither variety responded to transient water stress or recovery from transient stress with an immediate increase in reducing sugars in any tuber part. Reducing sugars were elevated in harvested tubers, particularly in the stem-ends of Russet Burbank potatoes subjected to water stress. Increases in tuber reducing sugars related to transient water stress were not found during the stress period or immediately after stress, but were present in harvested tubers.