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Exogenous Gibberellic Acid Advances Reproductive Phenology and Increases Early-Season Yield in Subtropical Blackberry Production

Lin, Syuan-You, Agehara, Shinsuke
Agronomy 2020 v.10 no.9
Rubus, blackberries, budbreak, climatic factors, crop production, cultivars, dormancy breaking, flowering, fruit growing, fruit quality, fruits, gibberellic acid, growing season, phenology, ripening, subtropics, total soluble solids, winter
Inadequate winter chill causes poor and erratic budbreak in blackberry (Rubus L. subgenus Rubus Watson), limiting the commercial production in subtropical climates. We examined the effects of exogenous gibberellic acid (GA₃) 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 GA₃ at 0 or 49 g·ha⁻¹ was performed when plants were dormant in late December to late January. Exogenous GA₃ 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 GA₃ 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 GA₃, 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 GA₃ is an effective bud dormancy breaking compound for blackberry, and it could be an important adaptation tool for subtropical blackberry production.