Effects of BA and NAA on thinning and fruit quality of apple cultivars 'Golden Delicious' and 'Red Delicious'

Abstract

'Golden Delicious' and spur types 'Red Delicious' apples cultivars are considered difficult to thin. 'Golden Delicious' is prone to alternate bearing if crop load is not annually regulated, while 'Red Delicious' sets 'pygmy fruits' when treated with NAA. The effects of different rates of BA (6-benzyladenine) and combined spray of BA and NAA (α-naphtaleneacetic acid) on fruit thinning of apple cultivars 'Golden Delicious' and spur type 'Red Delicious' (Camspur and Superchief Sandidge strains) were investigated during a two-year period. The number of fruits per cluster and fruits per tree were counted at harvest, and fruit quality and yield were evaluated. In 'Golden Delicious', BA + NAA combination had good thinning efficiency, the same as the higher rate of BA alone, with the highest average fruit weight. In the trial where different BA rates were applied, the best thinning effect was obtained with 7.5 ml/L BA treatment, which also had the highest yield per tree. 12.5 ml/L BA resulted in over thinning. BA-treated fruits had higher L/D ratio, firmness, starch index, soluble solids content and total acidity than control fruits. Thinning 'Golden Delicious' with BA increased the number of seeds. BA successfully thinned 'Red Delicious' in both years. 7.5 ml/L BA + 0.1 ml/L NAA treatment gave the best thinning results without causing 'pygmy fruits'. BA treatments led to fruit elongation, decreased fruit firmness and starch index, increased soluble solids content and did not affect acidity. In Camspur strain, the treatments decreased the number of seeds in the fruits. BA's thinning efficiency and its positive impact on fruit quality in both cultivars is confirmed. BA + NAA treatments can be used on 'Golden Delicious' for best thinning results without a risk of over thinning, as well as on 'Delicious' with lower NAA rates. ACKNOWLEDGEMENTS This work has been funded by Ministry of Science of Republic of Serbia through project No. 20134, Modern technologies and innovations in fruit growing and viticulture.