Interrelations between leaf senescence, cytokinin and resistance to green rice leafhopper in rice.

Interrelations between leaf senescence, cytokinin and resistance to the green rice leafhopper (Nephotettix cincticeps UHLER) were examined. Cut leaves were prepared by cutting the base of the leaf sheath of the seedlings. The resistance level of the cut leaves which was considerably lower than that of intact seedlings became even lower with the progression of senescence. However the resistance of the cut leaves was as strong as that of intact seedlings when the cut leaves were cultured in solutions containing cytokinin which prevents leaf senescence. Hence it was concluded that senescence is responsible for the breakdown of the resistance of the cut leaves and that the cytokinin which prevents leaf senescence is involved in the resistance mechanism.