Regulation of leaf senescence, grain‐filling and yield of rice by kinetin and abscisic acid

Senescence of rice ( Oryza sativa L. cv. Jaya) leaves was regulated with kinetin and abscisic acid (ABA) sprays at the reproductive stage. The effect of such sprays on grain‐filling and yield was analyzed. Spraying 100‐day‐old plants with kinetin solution (100 μg ml ‐1 ) significantly delayed senescence as indicated by higher total chlorophyll and protein levels in the three uppermost leaves compared with the controls. In contrast, spraying with ABA (15 μg ml ‐1 ) significantly promoted foliar senescence. The number of spikelets per panicle, number of panicles, percentage filled grains, panicle weight and grain yield per plant and the mobilization and harvest indices were significantly increased by kinetin treatment, while ABA decreased most of them. The possibility of increased grain‐filling and thus, yield due to delayed foliar senescence by kinetin treatment and decreased grain‐filling due to hastening of senescence by ABA is discussed.