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

• Main Authors: Syuan-You Lin, Shinsuke Agehara
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Agronomy
• Subjects: budbreak; caneberry; chilling requirement; dormancy; plant growth regulator; <i>Rubus</i>
• Online Access: https://www.mdpi.com/2073-4395/10/9/1317

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 (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.