Chemical thinning of 'Forelle' pear with S-abscisic acid and 1-aminocyclopropane-1-carboxylic acid
'Forelle' is the second most planted pear cultivar in South Africa. The average fruit size is relatively small, therefore early fruitlet thinning is important. Earlier research with 6-benzyladenine (6-BA) proved to be ineffective as thinner, but recently metamitron was registered as a chemical thinner for 'Forelle' in South Africa. The search for further chemical thinning agents was expanded to S-abscisic acid (S-ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC). During the 2015/16 season S-ABA and ACC were evaluated in two production regions, viz., Warm Bokkeveld (33°18'00.9S; 19°21'13.8E) and Elgin (34°10'25.8S; 10°03'40.3E), and in the 2016/17 season research was concentrated on the more promising S-ABA, again in the same two regions. S-ABA was evaluated at 100 to 600 mg L-1 and ACC at 75-300 mL L-1 applied at 8-10 mm fruitlet diameter. During the 2015/16 season, ACC significantly reduced fruit set at the Elgin site and improved fruit size when applied at 225-300 mL L-1, but not at the Koue Bokkeveld site. S-ABA significantly thinned 'Forelle' pear fruitlets at both sites and improved fruit size when applied at 200-300 mg L-1. During the 2016/17 season, a linear decrease in fruit set occurred with increasing S-ABA rate at the Warm Bokkeveld site. This resulted in a decrease in yield at the highest S-ABA rate (600 mg L-1). All S-ABA rates increased fruit weight at harvest except the 100 mg L-1 application. At the Elgin site, no significant effect was obtained in fruit set or thinning efficacy, but the two highest rates of S-ABA (400 and 600 mg L-1) increased average fruit weight at harvest. S-ABA at 300 mg L-1 therefore appears to be a promising chemical thinner for 'Forelle' pears, but further research is required to verify this rate.
Theron, K.I., Lötze, G.F.A. and Reynolds, J.S. (2018). Chemical thinning of 'Forelle' pear with S-abscisic acid and 1-aminocyclopropane-1-carboxylic acid. Acta Hortic. 1206, 13-20
Pyrus communis L., 6-benzyladenine, naphthalene acetic acid, fruit quality, fruit size