FRUIT THINNING OF SATSUMA 'OKITSU' MANDARIN

The plant growth regulator naphthalene acetic acid (NAA) is used as a fruit thinning agent before the physiological drop stage of citrus fruit. Chemical and manual fruit thinning of ‘Satsuma Okitsu’ mandarin (Citrus unshui Marc.) was studied in an experiment carried out at Concordia, Entre Ríos, Argentina. In the spring of 2010 and 2011, fourteen-year-old mandarin trees grafted on Poncirus trifoliate rootstock were sprayed with NAA (at 0, 200, 300 mg L^-1) 40 days after full bloom (DAFB). Manual thinning was done at 80 DAFB. Treatments were: control (0 NAA), manual thinning (MT), 200 mg L^-1 NAA, 200 mg L^-1 NAA with MT, 300 mg L^-1 NAA and 300 mg L^-1 NAA with MT. Fruit number, cross sectional shoot area, and fruit diameters were measured at 40, 70, 120 and 170 DAFB in two shoots per tree. Yield per tree was recorded at commercial harvest time in three trees per treatment. Physiological fruit drop at 70 DAFB was 20-26% and with NAA fruit drop was 30-48%. In the first year, there was no significant effect in yield per tree or diameter of fruit at harvest, although NAA increased the number of fruits with larger diameters. Chemical thinning might be a useful tool to improve commercial harvests in ‘Satsuma Okitsu’ mandarin.