EFFECT OF SPIKELET REMOVAL ON THE WHOLE PLANT SENESCENCE OF RICE

The rice (Oryza sativa L.) cultivar IET 1444 showed a nonsequential mode of senescence as evident from the decline in chlorophyll and protein of the flag and second leaves at the senescent stage. Removal of 50, 75 and 100 % spikelets from the panicle of rice plant or emasculation of the panicle by hot water treatment induced the development of secondary branch from the axil of second leaf but 25 % removal had no effect. Similarly, removal of 75 and 100 per cent spikelets from the panicle of secondary branch induced tertiary branch development, while 25 and 50 per cent removal had no such effect. Similar treatments on tertiary branch had no effect on further branch production. The pattern of leaf senescence of the untreated (control) main tiller, secondary and tertiary branches was identical, i.e. nonsequential, which could be changed into the sequential type only by the development of additional sinks (i.e. side branch). The leaf area and the seed number of secondary and tertiary branches were gradually reduced and reached a critical value in the tertiary branch. The removal of spikelets or emasculation delayed leaf senescence of the main tiller and the secondary and tertiary branches. Also the longevity of the whole plant could be increased by 40 d i.e., up to the senescence of the tertiary branch. Both leaves and reproductive parts control side branch production, which, in turn, controls the longevity of the whole rice plant.