Abscisic Acid and Kaolin for Heat Stress Mitigation during Strawberry Plug Transplant Establishment

Although Florida is the leading producer of winter strawberries (Fragaria ×ananassa Duch.) in the United States, in recent years the Florida strawberry industry has faced increasing competition for the winter market from Mexico and California. Shifting strawberry production in Florida to earlier in the season has been suggested as a means of increasing profits in a challenging market. However, earlier planting would expose transplants to higher soil and air temperatures and heat tolerant cultivars are not currently available. The objective of the present research was to evaluate the effects of s-abscisic acid (s-ABA) and kaolin on the mitigation of heat stress during early-season establishment of ‘Florida Radiance’ strawberry plug transplants. The s-ABA was applied at 250, 500, 750, 1000 mg/L as a five second root dip just prior to transplanting. Kaolin (56 kg/ha) was applied as either a single spray application shortly after transplanting or as two sequential spray applications of 56 kg/ha each: the first at the time of the single spray application and the second at 7 days after planting. Nontreated plants were included as a control. Plant vigor, plant survival, chlorophyll content, leaf number, leaf area, crown size, days to first flower, shoot and root dry weights, and fruit yield were assessed. Rates of s-ABA higher than 250 mg/L had pronounced adverse effects on vegetative parameters, delayed flowering and fruiting, and decreased fruit yield. Although a single application of kaolin significantly increased yield compared to the control, the highest strawberry yield was obtained with the double application of kaolin. The lowest s-ABA rate and the double application of kaolin appear to have the best potential for mitigating heat stress during strawberry plug transplant establishment.