Increasing demand on cereal grains to meet the population growth requires more production of rice as well as other cereals, which is supposed to rise up to 40% until 2030. Grain size and shape are critical factors determining grain yield. Several genes on grain shape and size have been reported, and of them, seven cloned genes were chosen for haplotype analysis, such as GS3, GW2, qSW5, GS6, GW8, GS5, and TGW6. We genotyped 218 rice varieties which had diverse grain size and shape originating from 25 countries. As for GS3 and qSW5, PCR markers were developed for point mutation and deletion, respectively. For the other five genes in which functional SNPs were reported, we designed primer sets to distinguish a fuctional allele for each gene. GW2 and TGW6 had two alleles, while the other five genes displayed three alleles which were evenly distributed throughout the population. Analysis on the relationship between haplotype of the genes and grain phenotype is in progress. We expect that desirable allelic combination of genes would assure the optimal grain size and shape for higher grain yield and market quality. This work was supported by a grant from the Next-Generation BioGreen 21 Program (Plant Molecular Breeding Center No.PJ009076), Rural Development Administration, Republic of Korea.

Hybrid sterility is a critical barrier of inter-subspecific crosses in rice. However, hybrid sterility can be overcome by wide compatibility variety. The HWC-line of rice had slender grain shape, tall culm length, wide compatibility with both indica and japonica cultivars. For QTL analysis of HWC-line, two F2 populations were derived from the crosses between the HWC-line and each of two Korean variety, Dasan (Korean Tongil-type cultivar) and Hwacheong (temperate japonica cultivar). In the cross between HWC-line/Dasan (HD), 93 STS markers and 13 SSR markers were mapped on 12 chromosomes. In the population from HWC-line/Hwacheong (HH) cross, 28 STS markers, 29 SSR markers and 1 FNP marker were mapped on 11 chromosomes. Eight agronomic characters were evaluated for QTL analysis in two F2 populations and parents. The F2 population from HD cross revealed 21 M-QTLs and 3 E-QTL for culm length, spikelet per panicle, spikelet fertility, grain length, grain width, grain shape and 100 grains weight. 8 QTLs of culm length, grain length, grain width and grain shape were newly detected in this study. In the F2 population from HH cross, 17 M-QTLs were detected for culm length, panicle length, spikelet fertility, grain length, grain width, grain shape and 100 grains weight. 6 QTLs of culm length, grain length, grain width and grain shape were newly found in this study. These QTLs will be able to provide basic information on putative functional genes related with agronomic characters and promote breeding new rice cultivar. HWC-line could be used as bridge for inter-subspecies crosses and in hybrid breeding.