Wednesday, August 10, 2016
Georgia Ballroom (Sheraton Hotel Atlanta)
Seedlings of bedding plants are often exposed to elevated temperature and/or water deficit stress during transportation. Such poor environmental conditions can decrease crop quality and cause crop loss. To mitigate damage from water stress, plants need to reduce transpirational water loss by closing their stomata. Osmotic stress induces stomatal closure similar to water deficit stress in plants and thus could be used to enhance water stress tolerance. Both water stress and osmotic stress trigger abscisic acid-signaling pathway which increases the level of cytosolic calcium in guard cells. Calcium has been known to play an important role during the process of stomatal closure. The objective of our research was to investigate whether osmotic stress and/or exogenous calcium application delayed plant wilting and enhanced water stress tolerance in bedding plant plugs. Seedlings of Impatiens walleriana ‘Xtreme White’, Viola cornuta ‘Sorbet Midnight Glow’ and ‘Sorbet XP Yellow’, and Viola ×wittrockiana ‘Matrix Blue Frost’ were used in this experiment. Osmotic stress inducing chemicals for treatments included CaCl2 and Ca(NO3)2 (calcium), and BaCl2 and Ba(NO3)2 (non-calcium), and they were applied at 50, 100, and 150 mM. As an osmotic stress inducing control, mannitol was drenched on seedlings at 150 and 300 mM. All treatments delayed wilting and extended shelf life up to one day compared to non-treated control in two cultivars of V. cornuta, V. ×wittrockiana (except at 50 mM) and I. walleriana (except at 150 mM). V. ×wittrockiana treated at 50 mM did not show shelf life extension, while all treatments at 150 mM in I. walleriana caused leaf curling and accelerated wilting within six hours after application. No damage was observed in all treatments in violas and pansy. Mannitol application also increased shelf life in all cultivars tested. Our data indicated that treatments inducing osmotic stress seemed to be effective to delay wilting in seedlings of I. walleriana, V. cornuta, and V. ×wittrockiana. To determine whether exogenous calcium application enhanced water stress tolerance, plants were pretreated with aforementioned chemicals 1, 2 and 4 days before water was withheld. The effect of pretreatment of each chemical on enhancing water deficit tolerance is currently being investigated.