Abstract
Effect of two kinds of Apple plus (No.4 and No.6), reagents developed for overcoming apple self-incompatibility by inactivating stylar S-RNase, on fruit set was tested in the Japanese pear ‘Kousui’. First, the inhibitory action of Apple plus on the RNase activity of proteins prepared from ‘Kousui’ style was monitored. Both reagents reduced the RNase activity dose-dependently; Apple plus No.4 and No.6 lowered the activity to about half of the control at 0.1 and 1%, respectively. Next, the promotive effect of Apple plus was tested on fruit set in self-pollinated ‘Kousui’ flower. When the trees were sprayed 0, 1, or 2 days before anthesis at 0.1 or 0.5%, all treatments caused 10-40% fruit set and treatment with 0.5% Apple plus No.4 one day before anthesis was most effective, with 40% fruit set 4 weeks after pollination. However, Apple plus at a concentration higher than 1% caused injuries to flowers and young leaves, and did not show sufficient fruit setting. The number of intact seeds at harvest was 0 to 3 in fruit induced by Apple plus, in contrast to 2 to 7 in cross-pollinated fruit. Apple plus also produced fruit in non-pollinated flowers, indicating that the reagent induces not only partial breakdown of self-incompatibility but also parthenocarpy in ‘Kousui’ pear. The fruit induced showed considerably inferior growth; fruit weight was about 70% of the fruit obtained by cross-pollination at harvest. It is concluded that overcoming self-incompatibility by Apple plus is insufficient and the reagent, at least in the present form, will not be useful in practical culture of the pear.
