Heat stress mitigation effects of kaolin and s-abscisic acid during the establishment of strawberry plug transplants

Abstract

In Florida, early planting to take advantage of higher prices for early fruit has been proposed for the strawberry (Fragaria ×ananassa Duch.) industry, but it can expose strawberry transplants to heat stress which is common in sub-tropical conditions. Additionally, strawberry plug transplants are of interest for addressing the high sprinkler irrigation requirement for bare-root transplant establishment. The objective of this study was to examine the effectiveness of antitranspirants, s-abscisic acid (s-ABA) and kaolin, in heat stress mitigation for strawberry plug transplants. Trials were conducted in Citra, Florida during three seasons (2015–2016, 2016–2017, and 2017–2018). The s-ABA was applied as a root dip just prior to transplanting. In 2015–2016, s-ABA was applied at 250, 500, 750, and 1000 mg L−1. Lower rates of 50–250 mg L−1 were used during the subsequent years. Kaolin was applied at 56 kg·ha−1 as either a single foliar spray immediately after transplanting or as two consecutive sprays seven days apart. Transient stomatal closure with ≤ 100 mg L−1 of s-ABA provided protection from heat stress with little or no negative side effects and resulted in higher early and total season yields than the untreated control. Both the single and double applications of kaolin consistently protected strawberry transplants from heat stress, enhancing photosynthesis as well as early and total marketable fruit weight. Since the double application of kaolin provided higher early marketable fruit weight than the single kaolin application, the double applications of kaolin appear to have better potential than the single application for mitigating heat stress in sub-tropical conditions during strawberry plug transplant establishment.