WITHIN-PANICLE VARIABILITY OF GRAIN FILLING IN RICE CULTIVARS WITH DIFFERENT MATURITIES

Rice (Oryza sativa L.) milling quality is a complex trait and influenc ed by many factors including the uniformity of grain filling and other grain characteristics. Although much is known concerning genotypic di fferences in rate and duration of grain filling, quantitative informat ion on uniformity or non-uniformity of grain filling and kernel charac teristics on the panicle is lacking. This study investigated and compa red the degree of non-uniformity of grain filling among 6 rice cultiva rs of different grain types, maturities, and the plant characteristics that may influence the uniformity of grain filling. Models of grain g rowth and rate of growth were developed for grains on the upper, middl e and lower parts of the panicle. Non-uniformity of grain filling para meters (duration and rate of grain filling, maximum grain weight) were estimated and compared among cultivars of different grain types and m aturities. Results showed that, in general, grain size and rate of fil ling decrease from upper part to the lower part of the panicle. The ra nges among grain growth curves from the upper, middle and lower parts of the panicle of the very early, and early maturing cultivars were gr eater than those of intermediate and late maturing cultivars. However, non-uniformity of grain filling is not necessarily a function of matu rity. Plant and grain characteristics such as even distribution of gra in size, high grain filling rate between 10-15 days after heading, and optimum weight ratio of panicle to above-ground leaf and stem matter may be selected for by breeders to improve the uniformity of grain fil ling, independent of maturity.