Effect of ABA Rates and Application Frequency On Growth of Bell Pepper and Watermelon Transplants

In many southern regions of the U.S., high temperatures and temporary soil drying conditions can be detrimental during transplanting and stand establishment of vegetable crops. Our previous research suggested that abscisic acid (ABA) was an effective tool to modulate transplant shoot growth and enhance drought stress tolerance of several vegetable species, including pepper, tomato, melon and artichoke. Our current work is targeted to optimizing methods of foliar spray application to control growth of ‘mature’ vegetable transplants in the greenhouse. The objective of this experiment was to determine the effects of rates and frequency of ABA application on growth and overall transplant quality of watermelon and pepper exposed to ABA concentrations up to 2000 mg/L applied weekly up to 3 weeks after transplant maturity. Growth responses to ABA were species-dependant. In triploid watermelon cv. Majestic, ABA reduced shoot dry matter, but increased dry matter partitioning to roots compared to the untreated control. Temporal chlorosis/phytotoxicity was observed for the highest ABA rates (>1000 mg/L) in diploid watermelon cv. Summer Flavor 800; however, those rates delayed the onset of flowering compared to control transplants when remained in trays in the greenhouse. In bell pepper cv. Aristotle, ABA decreased leaf abscission rates after 3 weeks in the greenhouse and there was a trend for ABA to improve survival under stressful field conditions in south Texas. Understanding seedling morphological and physiological responses prior to and after field establishment under extreme temperature and drought environments is crucial to developing seedling conditioning treatments to mitigate those stresses.