Abstract: The change of catalase activity of leaves in various years and the change of the enzyme activity in the growing period for varieties of apple were studied. The results showed that there were significant differences both in the varieties and among years. The catalase activity was the highest in Starking Doyle, Grimes and Golden. At the first growing peak of shoots and fruits, the activity was the highest. Along with the decrease of the growing speed of shoots and fruits and the increase of leaf growing,the activity showed a dropping tendency, but the change of its activity related unsignificantly to the environment conditions (temperature and humidity).The change of the activity in the growing periods of these varieties was very identical. There was a significant negative correlation between catalase activity and the percentage of setting fruit before physiological fruit drop (r = - 0.8024). It was considered that the persentage of setting fruit in varieties or trees was related to the catalase activity.

Key words: Apple, Activity of catalase, Percentage of setting fruit