Anatomical, Physiological, and Molecular Responses of Sweetpotato Native Periderm to Preharvest Water Deprivation During Early-storage Root Bulking

Abstract

Preharvest irrigation cutoff to promote skin set is a common management practice in irrigated commercial sweetpotato production, but its effects on native periderm, the developmentally formed periderm of intact storage roots before harvest, are poorly understood. We evaluated anatomical, physiological, and molecular responses of native periderm to controlled short-term irrigation/fertigation withdrawal during the early storage root bulking stage (30–50 days after transplanting) in ‘Bayou Belle’, ‘Beauregard’, and ‘Orleans’ sweetpotato. Greenhouse experiments compared well-watered plants with plants subjected to 5 days of withdrawal (WD5) or 10 days of withdrawal (WD10) before harvest. Native periderm structure was characterized from transverse sections stained with phloroglucinol-HCl, and postharvest weight loss was measured for 5 weeks. The relative expressions of IbPAL , IbCCoAOMT , IbCAD , and IbACO were quantified in well-watered and WD10 roots. Withdrawal increased circularity, an index of reduced outer-boundary irregularity, and produced a more continuous native periderm with fewer expansion-associated discontinuities. Percent lignified tissue increased 1.9-fold to 3.6-fold relative to well-watered controls, depending on cultivar and treatment duration. By week 5, cumulative weight loss was 38% to 45% in well-watered roots compared with 21% to 24% after WD5 and 20% to 30% after WD10. IbPAL expression increased 1.6-fold to 3.8-fold across cultivars, whereas IbCCoAOMT , IbCAD , and IbACO responses were genotype-dependent. These coordinated responses are consistent with accelerated native periderm maturation during early bulking and support the use of greenhouse-grown roots as a controlled developmental system. Because nutrient delivery was also interrupted during irrigation withdrawal, the response cannot be attributed to the water status alone; therefore, field validation and experiments that separate water from the nutrient supply are needed.