Ethephon and Methyl Jasmonate Affect Fruit Detachment in Rabbiteye and Southern Highbush Blueberry

Two abscission agents, ethephon and methyl jasmonate, were investigated in five studies to determine their potential for increasing fruit detachment during harvest in rabbiteye (Vaccinium ashei Reade) and southern highbush (hybrids based largely on Vaccinium corymbosum L. and Vaccinium darrowi Camp.) blueberry. In the first study with a rabbiteye blueberry genotype, T-451, ethephon applications up to 1000 mg.L-1 did not affect fruit drop but reduced fruit detachment force (FDF) by up to 21%. In the second study with two southern highbush blueberry genotypes, ethephon (up to 1500 mg.L-1) and methyl jasmonate (MeJa; up to 10 mM) applications resulted in significant fruit drop in 'Star' but neither of the growth regulators affected the fruit detachment characteristics of 'Farthing'. In a third study with rabbiteye blueberry genotypes, MeJa applications of 10, 20, and 30 mm displayed an increasing linear trend in fruit drop in 'Climax' and linear and quadratic trends in fruit drop in 'Powderblue'. In a fourth study with 'Powderblue', MeJa (20 mm) and ethephon (1000 mg.L-1) applications resulted in rapid and significant fruit drop. The fruit drop induced by MeJa in this study was attenuated by the coapplication of aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor, suggesting that MeJa induced fruit detachment partly through its effects on ethylene biosynthesis. In another study with the southern highbush blueberry genotype, O'Neal, MeJa applications (20 mm) induced significant fruit drop but ethephon (1000 mg.L-1) applications did not affect fruit detachment. Overall, MeJa applications (20 mm or greater) generally induced rapid and extensive fruit abscission, often within 1 day after treatment. Applications of MeJa resulted in leaf yellowing and necrosis of leaf tips and margins, especially at high rates of application (20 Mal or greater). Ethephon applications resulted in the abscission of mature and immature berries. Both ethephon and MeJa applications resulted in the detachment of the pedicel along with the fruit. Together, these data suggest that although ethephon and MeJa have the potential to be used as harvest aids in blueberry, the rates of application require further optimization to minimize potential phytotoxicity. Additionally, effective de-stemming of the berries may be essential if these compounds are to be used as harvest aids.