Studies on the nature of relationships between grain size, spikelet number, grain yield and spikelet filling in late duration varieties of rice (Oryza sativa L.)

Studies on the nature of relationship between grain size (in terms of thousand grain weight), grain number, rate of filling and yield have been worked out with late duration (140–150 days) rice varieties. Grain number per m2, grains per panicle and yield showed a negative relationship with grain size. There was no compensatory balance between grain size and grain number within a range of thousand grain weight of 15 to 30 g. Based on the peaks in grain filling activity, the varieties were classified into four groups. There was no relationship between grain size and rate of grain filling thereby suggesting that grain filling is determined by inherent endogenous factors.