Genotypic Variation in Chrysanthemum Stomatal Malfunction following Growth at High Humidity and Its Implications for Postharvest Performance

Abstract

Prolonged periods of high relative air humidity (RH) during cultivation can cause an impaired closure response of stomata. This phenomenon is called stomatal malfunction and can cause excessive water loss. Especially in cut flowers, this is a problem because of the negative consequences for postharvest water balance. This study tested whether humidity-induced stomatal malfunction differs among Chrysanthemum morifolium genotypes and whether it translates into poorer postharvest water balance. Nine genotypes were grown at 60% or 90% RH in one experiment, and in another, two genotypes were grown at 60% RH, after which plants with fully expanded leaves were exposed to 90% RH for 0, 1 or 5 days. Desiccation responses were quantified using excised-leaf transpiration time courses. Leaf morphological traits were recorded, and transpiration was modeled as a function of relative water content of the leaves to capture key features of stomatal closure, including maximum and minimum transpiration, onset of closure, closure rate, and residual transpiration. High RH consistently delayed the onset of closure and increased residual transpiration, but the magnitude of these effects varied among genotypes, demonstrating clear genetic variation in sensitivity. Fully expanded leaves that developed at low RH before short-term exposure to high RH also showed malfunction, indicating that malfunction can develop after leaves have fully expanded. A postharvest assay in the most sensitive genotype showed that 5 days of high RH exposure applied to cut vegetative stems in nutrient solution before transferring them to a 40% RH environment caused rapid fresh weight loss and wilting. Supplying abscisic acid through the nutrient solution during high RH exposure reduced water loss but did not prevent malfunctioning completely. Together, these results identify genotype-dependent susceptibility to humidity-induced stomatal malfunction in chrysanthemum. This supports cultivar selection and breeding as practical routes to improve postharvest quality under humid production conditions.