Drought stress prior to harvest affects postharvest respiration rate and susceptibility to storage rots.

Abstract

Sugarbeets in North Dakota, Minnesota and Michigan are largely grown without supplemental irrigation. Roots harvested from these production regions, therefore, are inevitably drought stressed when natural rainfall is insufficient. Roots from drought stressed plants are currently incorporated into storage piles despite a paucity of information regarding the impact of water stress on root storability. Research, therefore, was carried out to assist storage pile managers in formulating best practices for the postharvest storage of drought-stressed roots by determining the effects of preharvest drought stress on postharvest respiration rate, sucrose loss, invert sugar accumulation and susceptibility to storage rots. Drought stressed roots were obtained by discontinuing watering of greenhouse plants for 7, 14 or 21 days prior to harvest. These watering regimes yielded roots with mild, moderate and severe water stress as determined by their effects on plant photosynthesis and root water content. Storage respiration rate was significantly elevated by severe water stress, with the magnitude of drought-induced elevations in respiration rate increasing as storage duration increased. Moderate and severe water stress additionally increased susceptibility to rot caused by Botrytis cinerea and Penicillium spp., but had no significant effect on root sucrose or invert sugar concentrations. Overall, these results suggest that sugarbeet root storability is minimally affected by mild drought stress but is progressively eroded as both drought stress severity and storage duration increase.