<;P>;PROBLEM TO BE SOLVED: To provide a breeding method for isolating and identifying a new gene associated with the increase of a grain shape (including a floret, a fruit, a seed or the like) of a plant, consequently a thousand-kernel weight, and enlarging the size of a grain (including a fruit and a seed) of the plant by utilizing the gene. <;P>;SOLUTION: The isolation and identification of a tgw6 gene associated with the increase of the length of the grain (including the floret, the fruit and the seed) of the plant, the thousand-kernel weight and consequently the yield are achieved by linkage analysis. It is also cleared from the base sequence of the tgw6 that a termination codon is present in a Kasalath-type allele to prevent a mature protein from being formed. It is also cleared that only the Kasalath type increases the grain length and the thousand-kernel weight by the analysis of the functions of the TGW6 proteins in a Nihonbare type and the Kasalath type. <;P>;COPYRIGHT: (C)2010,JPO&INPIT