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Twenty-four M4 mutants derived from japonica rice cultivar Wuyujing3 were used to investigate the variation in occurrence of white-belly rice kernel (WBRK) and white-core rice kernel (WCRK) among different positions within panicle.These mutants were of four panicle types,namely the compact,intermediate,loose,and chicken toe panicle.Considerable differences in morphological characters exist among the four types of panicle especially in the panicle length,secondary branch number,and ratio of grain number to total branch length.Marked differences were found in WBRK and WCRK among different positions within a panicle for all types of panicle.In general,grains located on primary and top rachis branches had higher WBRK and WCRK percentage than those on secondary and bottom rachis branches.WCRK exhibited larger variation among different grain positions than that of WBRK.Moreover,there were significant differences in WCRK/WBRK among grain positions within a panicle,with primary and top rachis branches having higher values than the secondary and bottom.In addition,panicle type showed no significant effect on the pattern of WBRK and WCRK occurrence within panicle.The results indicate different mechanism between WBRK and WCRK formation with regard to position variation within panicle and are of value for breeding and agronomic practices aimed at lowering chalky grain rate.