FRUITS THINNING ON PLUM TREES USING POTASSIUM SALT OF NAA

Seven-year old Stanley plum trees were sprayed with potassium salt of alpha-naphthylacetic acid towards the end of the blooming period and about 10 days later. In the first year of the experiment the applied concentrations were 30 and 40 mg NAA/L. In the second year the doses of 30, 40, and 50 mg NAA potassium salt/L were used in the period of falling of corolla petals; 10 days later the applied doses were 20, 40, and 80 mg potassium salt/l. Both in the first and in the second year the spraying of trees reduced the number of fruits in comparison with the control. In the two years the highest mass of fruit was noted on trees sprayed with NAA potassium salt at the concentration of 40 mg. In the treatments with the tested preparation a distinct increase in ethylene evolution by young plum fruits was observed. Microscopic observations of fruit sets showed the destructive effect of NAA potassium salt on the development of plum embryos. The first cytological changes were already observed on the fourth day after spraying.