| Abstract: | Four indica rice varieties belonging to two maturity groupswere cultivated in medium irrigated land during the wet seasonof 1989. In all varieties, the primary branches of the panicledeveloped basipetally. Poor development of spikelets on thebasal branches resulted in a high percentage (50–60%)of degeneration and sterility and, consequently, grain yieldwas poor. Application of gibberellic acid (GA3) and kinetin(6-furfuryl amino purine) improved development and grain yieldon all branches. The treatments were more effective on the proximalbranches and reduced the existing gradient in growth, developmentand yield between the distal and proximal branches. In contrastto this, 3-indole acetic acid (IAA) treatment increased spikeletgrowth and development in the distal branches, but suppressedthem in the proximal branches thus increasing the heterogeneityin primary branch growth and development. The soluble carbohydrateand amino acid content per unit dry weight of the primary branchesincreased at the time of anthesis following the applicationof growth regulators. The assimilate level declined rapidlyat the post-anthesis stage. Associated with the depressed growthand development in the lower branches of the panicle by IAAtreatment, was a significantly higher level of assimilates inthese branches in the post-anthesis period. The physiologicalmechanism of spikelet growth regulation is discussed. Key words: Rice, assimilates, development, spikelets, fertility, hormones |
