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ISHS Acta Horticulturae 1138: EUFRIN Thinning Working Group Symposia

The efficacy of chemical and mechanical thinning strategies for 'African Roseż' Japanese plum (Prunus salacina Lindl.)

Authors:   K.I. Theron, H. Steenkamp, G.F.A. Lötze, W.J. Steyn
Keywords:   1-aminocyclopropane-1-carboxylic acid (ACC), 6-benzyladenine (6-BA), thinning, yield, fruit quality
DOI:   10.17660/ActaHortic.2016.1138.8
Japanese plum production is a significant component of the South African deciduous fruit industry. Thinning is an important practice in plum production and there is a huge need for new thinning strategies. The purpose of this study was to evaluate new chemical thinning strategies on 'African Rose™'. The chemicals evaluated were 1-aminocyclopropane-1-carboxylic acid (ACC) at 150, 300 and 500 µL L-1 in the 1st season and 400, 600 and 800 µL L-1 in the 2nd season, and 6-benzyladenine (6-BA) at 100 or 300 µL L-1 in the 1st season and 100 µL L-1 in the 2nd season. 6-BA was included to prevent ACC-induced leaf drop. ACC was also combined with mechanical thinning utilizing the Darwin 300™ and hand thinning during bloom included as treatment.All the foliar applications were made when the average fruitlet size was 8-10 mm. ACC consistently reduced the commercial hand thinning requirement in both seasons. In the second season, there was a linear decrease in yield efficiency as the ACC rate increased, while a quadratic response was seen in fruit size with the two higher rates inducing larger but similar fruit size. The combination treatment of ACC (600 and 800 µL L-1) and the Darwin 300™ thinned more aggressively, improved fruit size and shifted harvest distribution earlier without decreasing the yield efficiency compared to the control. The recommended ACC rate for 'African Rose™' would be 600 µL L-1. No leaf drop/phytotoxicity or broken stones were recorded.

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