Genetic Analysis Of Six Early-maturing Varieties And Gene Mapping For The Earliness Trait Of Lexiang202 In Rice

Growth duration or heading date is one of the important agronomic traits in rice. Breeding for growth duration, especially for earliness, is very important to rice production.It is commonly suggested that the earliness (early maturity or early heading)is a recessive trait controlled by one or two major genes or a quantitative trait controlled by minor polygenes in rice. So far, there are only five earliness genes reported, in which thefe are four dominant genes and one recessive gene. In this study, six early-maturing varieties are carefully researched, the result is as follow:1. Under short day and long day, heading date of D64A/B, Lexiang101A/B, Lexiang 202A/B and Xianggai B were not photoperiod sensitivity but Zaoxian A/B and D63B weee photoperiod sensitivity.2. Six early-maturing varieties crossed with five various types of medium- or late-maturing varieties, such as Minghui63, 6078, Shuhui527, Duohuil and R368, the F1 progenies from some of these crosses had their heading date as early as or even earlier thai Lexiang202A/B and ZaoxianA/B. Meanwhile, the heading dates of F1 progenies were near closed to the mid-parent value for D64A/B and Lexiang101A/B which crossed with medium- or late-maturing varieties, but the F1 progenies from D63B and XianggaiB crossed with medium- or late-maturing varieties was near to late-parent value. These results suggested that earliness of Lexiang202A/B and ZaoxianA/B was mainly controlled by approximate dominate major genes and Lexiang101 A/B and D64A/B was a quantitative trait controlled by minor polygenes, but D63B and XianggaiB was a recessive trait.3. Significant segregation of heading date were observed in the F2 population from Lexiang202B crosses with the five medium- and late-maturing varieties. The segregation ratio of early to late heading plants in these population fitted the ratio of 3:1 and the segregation ratio in the crosses between ZaoxianB and the same medium- and late-maturing varieties is 9:7, but earliness of D64B is controlled by minor polygenes.4. To indentify the loci of the approximately dominate major gene in Lexiang202B, the near isogenic pools of earliness and lateness were constructed from the F2 population ofLexiang202B crossed with Shuhui527 and the polymorphisms existed in the two pools was screened by SSR markers. As a result, SSR marker RM154 and RM279 were found linked to the approximately dominate earliness gene in Lexiang202B, the gene was located on the short arm of the chromosome2 and their heredity distance to RM154 was 8.9cM and to RM279 was 13.5cM. The earliness gene was named as Ef-2(t).5. The combining ability of 9 indica type parents, including 4 early CMS lines and 5 medium- and late-maturing restorer lines, was analyzed in 8 economic traits. The results showed that Lexiang101A had the best general combining ability(gca) and specific combining ability(sca). Lexiang202A had the smallest gca values, but Lexiang202A had the biggest gca values in heading date, ZaoxianA was superior to D64A.In terms of the performances of heterosis in the above traits, we can coordinated the contradiction between earliness and high production existed in earliness hybrid riee by cloning and transferring the earliness of Lexiang202B to other hybrid parents. Therefore, the earliness gene has a splendid future in rice breeding.