Effects of Antitranspirants on Enhancing Temporary Drought Tolerance in Bedding Plants

Bedding plants are often exposed to drought stress during shipping and retailing due to unexpected high temperatures and irregular irrigation.  Such stresses reduce the quality and marketability of bedding plants.  To prevent damage chemicals known as antitranspirants can be applied to the crops prior to shipping or retailing.  Antitranspirants temporarily increase tolerance to drought stress by either physically blocking stomata or physiologically inducing stomatal closure to prevent water loss through transpiration.  Physical antitranspirants containing polymers, resins, or waxes cover the stomata when sprayed on the leaves.  Physiological antitranspirants induce stomatal closure by Sugar Alcohol-based Compounds (SACs) or abscisic acid (ABA), a phytohormone.  However, little is known about the effectiveness of commercially available antitranspirants on enhancing drought tolerance of bedding plants.  Two physical antitranspirants, β-pinene polymer (βP) and vinyl-acrylic polymer (VP), and four physiological antitranspirants, three SACs and a biologically active form of ABA (s-ABA) were applied to Begonia semperflorens, Impatiens hawkeri, Impatiens walleriana, Pelargonium ×hortorum, two cultivars of Petunia ×hybrida, two cultivars of Tagetes erecta, and Tagetes patula.  Physical antitranspirants were sprayed and the physiological antitranspirants were drenched at a half (0.5X), equal to (1X), or twice (2X) the manufacturer’s recommended rate.  s-ABA delayed visual wilting symptoms and extended shelf life of all species and cultivars tested except for geranium.  βP-treated T. erecta showed increased shelf life by 1.2 d.  Longer shelf lives were observed when higher concentrations (2X) of antitranspirants were applied, compared to 0.5X and 1X, as shown in I. walleriana and P. ×hybrida treated with s-ABA at 2X, and in T. erecta treated with βP at 2X, respectively.  Application of antitranspirants at 1X was conducted independently to measure leaf gas exchange in I. hawkeri, P. ×hortorum, and P. ×hybrida.  s-ABA reduced stomatal conductance within 4 h after application, resulting in reduction of water loss and extension of shelf life.  βP also appeared to block stomata within 4 h of application and caused reduced stomatal conductance in I. hawkeri and P. ×hybrida.  The efficacy of βP was, however, less than that of s-ABA.  Our data showed that VP and SACs had little or no effect on relieving drought stress symptoms and s-ABA was the most effective in closing stomata and enhancing temporary drought tolerance.