Genetic analysis and physical mapping of Lk-4(t), a major gene controlling grain length in rice, with a BC2F2 population.

Grain size and shape are important factors affecting grain quality and yield in rice. Mapping, tagging and identification of their related genes can lead us to understand their expression pattern and mechanism network, which is to their control. In this study we mapped a grain length controlling gene named Lk-4(t) with SSR and CAPs markers by screening 800 recessive plants in a BC2F2 population derived from a cross of Shuhui527xXiaoli and backcrossed with Xiaoli as the donor parent. The distribution of grain shape parameters and thousand grain weight in F2 and BC2F2 population showed that backcross can diminish most unnecessary variations to identify the target gene more clearly. There were only two grain length phenotypes found among the 3 209 BC2F2 plants, long and short, indicating it is a qualitative trait. The frequency distribution for the grain length showed a typical segregation ratio of 3:1, suggesting that only one allele was responsible for the variation. By screening the recessive long grain plants with three CAPs markers, P1-EcoRV, P2-Sac I and P3-Mbo I, we tagged the locus on the arm of chromosome 3 near the centromere. Lk-4(t) was located between P1- EcoRV and P2-Sac I, with genetic distance of 0.90 cM and 0.50 cM from the two markers respectively. Mapping of the gene is a foundation for its final identification and function analysis.