| Abstract: | Two high yielding semi-dwarf rice varieties namely IR-36 andJava, and one traditional tall indica rice variety, Akul, werecultivated in the dry and wet seasons, respectively, in 1987under irrigated field conditions. A few days after visible panicleinitiation, the panicle on the main shoot was dissected outto measure development, growth, soluble carbohydrates, aminoacid and phosphate contents of individual primary branches.Primary branch developmnent was quantified by noting the averagetime to anthesis of spikelets on the branch. The pattern ofdevelopment was hierarchical with each successive branch dominatingthe one immediately below it and hence, the measure of developmentincreased in an acropetal fashion from the bottom to the topin all varieties. However, in comparison to the developmentallyadvanced distal branches, the branches at the proximal regionhad the potential to generate larger numbers of spikelets, althoughactual potential to produce grains in them was quite poor. Almost2 weeks prior to mean anthesis, the gradient in assimilate concentrationof the primary branches was found to increase acropetally frombottom to top and correlated negatively with the developmentalscore (high score indicates less development and vice versa).During the following week, the situation reversed and a higherconcentration of assimilates was found in the lower branchesthan in the upper. Subsequent observations taken before meananthesis showed assimilate contents to be correlated positivelywith the developmental score. The role of assimilates in spikeletdevelopment on the primary branches has been discussed and itis concluded that there is no clear causative relationship betweenassimilate concentration and spikelet development. In the postanthesis period, little difference in assimilate concentrationof the branches was observed. The presence of a higher concentrationof assimilates did not help spikelet survival on the proximalbranches any more than that on the distal. Key words: Rice, spikelet, primary branch, anthesis, assimilates |
