Foliar application of defoliants after winter chill accumulation changes phytohormone dynamics and improves budbreak in blackberry under subtropical climatic conditions

Abstract Inadequate winter chill causes poor budbreak in blackberry ( Rubus L. subgenus Watson), limiting the commercial production subtropics. In ‘Natchez’ blackberry, our previous study found that, under inadequate chilling conditions, urea and lime sulfur (LS) applied as defoliants before accumulation advanced but did not improve final budbreak. this study, we two at end of examined their effectiveness breaking dormancy, with a hypothesis that it can be enhanced increased exposure to chilling. Field experiments were conducted over growing seasons subtropical climatic conditions. was sprayed or LS 10%. Both effective both advancing maximizing Final reached 42.6% 76.8% defoliant treatments, compared 27.1% 31.6% control. Advanced by early season yield 35% 88%. Although statistically significant, total-season 19% 56%, Phytohormone profiling revealed no changes abscisic acid gibberellic 4, increasing trends jasmonic indole-3-acetic (IAA) during The treatment IAA up 377% These results suggest are highly dormancy-breaking agents for when after accumulation. could an important adaptation tool production. Furthermore, appears be, least part, mode action LS-induced