| Days to heading (DTH, the number of days from sowing to emergence of the first panicle, also called heading date) is an important agronomic trait of rice because it is highly associated with the regional and seasonal adaptability of rice cultivars. Breeding for heading date, especially shortening heading date is of very important to rice production.In this study, a photoperiod insensitive and genie male-sterile, early maturing indica line 6442S-7 was used. It has been identified that 6442S-7 has two completely dominant earliness genes which are independent with each other. Under short day and long day, FI progenies from 6442S-7 crossed with four various types of medium-or late-maturing, such as Minghui63, Taiyinland ShuhuiSSl, shared the same heading date as 6442S-7. Significant segregation ratio of early to late heading plants in these populations fitted the ratio of 15:1. And the segregation ratio in their corresponding BiFi populations, which were from the crosses between the three late maturing parents and their FI plants, fitted the ratio of 3:1. These results proved that earliness of 6442S-7 is mainly controlled by two dominant major genes which have duplicate effect.The heading dates of FI progenies of 6442S-7 crossed respectively with four late maturing parents, such as 931K IR68> Xianguo and BG1639, approximate to the mean value of the two parents. The F2 progenies of 6442S-7 crossed with these four late maturing parents and the FI progenies of the three way crosses between 6442S-7 and the FI progenies of Minghui63 crossed with these four late maturing parents had significant segregation ratio which respectively agree with 3:1 and 15:49. Theseresults suggested that these four late maturing varieties each has one pair of allelic dominant genes which suppress the expression of earliness gene in 6442S-7.To determine the chromosomal location of the gene, we developed a three way cross population consisted of 313 plants from a cross between 6442S-7 and FI progenies of Minghui63 crossed with 9311 as the mapping population. 350 pairs of SSR primers were used to amplify the genomic DNA of the near isogenic pools of earliness and lateness, the parent plants and each plants of the mapping population. Linkage of two primers with the suppressing gene were detected in the mapping population. Then the local linkage map of the dominant suppressing gene was constructed with these vivo primers, RM152 and RM407 ,which are on the short arm of the rice chromosome 8. The genetic distance from the target gene to the two SSR primers are 29.3cM and 27.5 cM respectively. This major gene suppressing the dominant earliness in rice was identified for the first time, and is designated tentatively as Su-Ef-cd(t). This new mapped gene could be of great importance in cultivating different early and mid-early maturing varieties so as to adapt to different regions or seasons. In addition, the two primers used in the gene mapping can be used as selective markers for Su-Ef-cd(t) gene in marker-assisted selection. |
