| Summary: | Inadequate winter chill causes poor and erratic budbreak in blackberry (<i>Rubus</i> L. subgenus <i>Rubus</i> Watson), limiting the commercial production in subtropical climates. We examined the effects of exogenous gibberellic acid (GA<sub>3</sub>) on the reproductive phenology, fruit number, yield, and fruit quality of three blackberry cultivars (‘Natchez’, ‘Navaho’, and ‘Ouachita’) grown under subtropical climatic conditions in two consecutive growing seasons. A single spray application of GA<sub>3</sub> at 0 or 49 g·ha<sup>−1</sup> was performed when plants were dormant in late December to late January. Exogenous GA<sub>3</sub> advanced the onset of budbreak by 12 to 82 days, flowering by four to 20 days, and fruit ripening by 0 to 15 days. When pooling across the cultivars, it also increased early-season yield by 83% to 276% in two consecutive growing seasons and total-season yield by 60% in the second growing season. Among the cultivars, the yield responses to GA<sub>3</sub> were most consistent in ‘Ouachita’, with early-season yield increasing by up to 499%. The average berry weight and soluble solids concentration were slightly reduced by GA<sub>3</sub>, but these reductions were not consistent in the two growing seasons and the impact on overall fruit marketability was small. These results suggest that exogenous GA<sub>3</sub> is an effective bud dormancy breaking compound for blackberry, and it could be an important adaptation tool for subtropical blackberry production.
|
|---|
