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

Chemical Budbreak Induction Methods to Increase Blackberry Yields under Inadequate Chilling Conditions

“…In the untreated plants, the final percentage of budbreak recorded in late March ranged from 26.6% to 31.6% (Lin and Agehara 2020b;Lin and Agehara 2021a). Urea and zinc sulfate treatments increased budbreak up to 63.2% and 53.8%, respectively (data not shown), and increased yield by up to 87% and 34%, respectively, compared with the untreated control (Figure 1).…”

“…In Florida, however, inadequate winter chill limits blackberry production by causing poor and erratic budbreak. To compensate for lack of winter chill, we developed chemical budbreak induction methods based on field trial data collected over three growing seasons (Lin and Agehara 2020b;Lin and Agehara 2021a). This article is intended to provide Florida growers with guidelines on how to improve budbreak of current major blackberry cultivars, with the aim of supporting the development of subtropical blackberry production.…”

Budbreak patterns and phytohormone dynamics reveal different modes of action between hydrogen cyanamide- and defoliant-induced flower budbreak in blueberry under inadequate chilling conditions

“…In blackberry, we examined the budbreak induction effects of lime sulfur over two growing seasons under climate conditions similar to this study. The final percentage of budbreak was 76.8% in the first season with 194 pretreatment chilling hours, but it was only 42.6% in the second season with 101 pre-treatment chilling hours [ 37 ].…”

“…All data were analyzed by the generalized linear mixed model procedure (PROC GLIMMIX) in SAS statistical software (SAS 9.4; SAS Institute Inc., Cary, NC, United States). Continuous data (yield and berry fresh weight), count data (berry number), and repeated measures (defoliation, budbreak, and phytohormone) were analyzed as described in Lin and Agehara [ 37 ]. Five different covariance structures, including compound symmetry (TYPE = CS), spatial Gaussian [(TYPE = SP(GAU)], spatial power [(TYPE = SP(POW)], spatial spherical [(TYPE = SP(SPH)], and unstructured covariance (TYPE = UN), were compared using maximum likelihood estimation with Laplace approximation (METHOD = LAPLACE) and default bias-corrected sandwich estimators (EMPIRICAL = MBN).…”