Grain filling duration, a crucial determinant of genotypic variation of grain yield in field-grown tropical irrigated rice

Grain filling, a crucial determinant of grain yield in cereal crops, is characterized by duration and rate of grain filling. This study aimed to (1) seek genotypic variations in grain filling duration and rate on area basis, (2) compare the contribution of grain filling duration and rate to grain yield and (3) examine the influence of temperature and solar radiation on grain filling duration and rate for effective grain filling period in the field-grown tropical irrigated rice. Six tropical genotypes were used in the 2004 dry season and wet season at the International Rice Research Institute (IRRI), Laguna, Philippines.Grain filling rate and duration exhibited highly significant genotypic variations in each crop season. Grain weight on area basis was positively associated with grain filling duration, irrespective of crop seasons, but negatively or not significantly associated with grain filling rate. Grain filling rate and duration were negatively correlated with each other. Final grain weight linearly increased with the rise in cumulative mean temperature and cumulative solar radiation. Longer grain filling duration resulted in higher cumulative mean temperature and cumulative solar radiation for effective grain filling. Higher daily mean temperature and radiation did not accelerate daily grain filling rates of different rice genotypes.It was concluded that longer grain filling duration, which provided rice plants with more cumulative mean temperature and cumulative solar radiation for effective grain filling period, was the main factor that determined grain yield on unit area basis in the field-grown tropical irrigated rice genotypes.