A Recessive Gene Controlling Male Sterility Sensitive To Short Daylength/Low Temperature And Heterosis In A Novel Male Sterile Line 337S Of Wheat (Triticum Aestivum L.)

Wheat is one of the largest cultivated crops and plays an important role in the food safety. Since Sasakuma and Ohtsuka first reported wheat photoperiod sensitive cytoplasmic male sterility, a series of photoperiod-temperature sensitive male sterile wheat lines have been discovered. As wheat photoperiod-thermo sensitive male sterile line can conquer alloplasmic effects, lack of restorer source and restoring ability derived from cytoplasmic male sterile system, it will be valuable in the utilization of heterosis in wheat production.337S is the only male sterile wheat line sensitive to both long daylength/high temperature and short daylength/low temperature so far. In Hubei province, the development of spikelet of 337S can be put in a sterile environment if the sowing time is advanced or delayed, and the sterility maintains stable.337S returns to be fertile and the self setting rate amounts to over 50% under appropriate sowing date. In addition,337S has a good integrative agronomic character. The present study mainly aimed at analyzing its genetic mechanism, relationship between genetic distance and heterotic groups, and genetic characteristic of photosynthetic rate under short daylength/low temperature. In this study, the short daylength/low temperature male sterile gene was mapped, selection of the target gene was conducted, and the main results were as follows:1. Genetic character of 337S:337S was crossed as a female parent with five fertile parents to produce five F1s and 5 F2sto analyze the genetic mechanism. Under short daylength/low temperature,337S exhibited apparent differences in phenotype from others during anthesis, with the glume opening and the stigma exserting whereas F1 progenies from the five crosses showed the same phenotype of the corresponding male parental lines. Fertility analysis indicated 337S appeared completely sterile while the other five male parental lines and all F1s were highly fertile. Fertility segregation appeared and fitted a ratio of 3:1 with Chi-square test in all the F2 populations. The sterility in 337S was thus governed by a single recessive gene under short daylength and low temperature. We temporarily designated this gene wptms3.2. Mapping of wptms3:According to the genetic analysis, the male sterile gene of 337S was located under short daylength/low temperature using the combination of SSR and BSA analysis. Serious fertility screening and identification among the F2 (337S/ Huamai 8) mapping population was performed. Equal amounts of DNA from 12 fertile and 12 sterile individuals were mixed to construct fertile bulk (BF) and sterile bulk (BS), respectively. A total of 228 SSR primers distributing among the wheat genome were used to identify the target gene and the results indicated four SSR markers from chromosome 1B (Xgwm413, Xgwm273, Xgwm264 and Xgwml 1), one from chromosome 5D (Xgwm182) and the target gene (wptms3) construct a linkage map of 85.1 cM. The male sterile gene wptms3 was thus mapped in an interval between Xgwm413 and Xgwm182 at a genetic distance of 3.2 and 23.5 cM, respectively, on chromosome arm IBS. One-way variance analysis using marker genotypes as groups showed that the fertility difference or variation between the groups divided by Xgwm413 and Xgwm182 was highly significant. This again verified the linkage between markers and the target gene. The marker Xgwm182 was first mapped on chromosome 1B, and thus a new marker locus in the present study. Therefore, we can tentatively designate the new marker as Xgwml82-1B, distinguishing it from previous reports.3. Selection of the target gene via linked markers:When selection based on single marker Xgwm413 was performed, AMAS and EMAS was 82.84% and 86.85%, respectively, while they were 67.71% and 71.25% for Xgwm182. When the two bracketing markers were used to select male sterile plants in the F2 progeny, AMAS reached 90.10% in spite of the distance between the two markers extending to 26.7 cM. However, EMAS slightly declined.4. Relationship of genetic distance (GD) and hybrid performance derived from 337S: Forty SSR markers distributed over all 21 wheat chromosomes were used to analyze genetic divergence among 17 parental genotypes and estimate the GD. The results indicated the averaged GD among the 17 parental genotypes was 0.42, ranging from 0.26 to 0.57. The averaged GD between 337S and the 16 parental cultivars was 0.44. Correlation of GD between 337S and the other 16 parents with F1 performance, MPH and SCA displayed three agronomic characters positively correlated with GD were spikelets of main head, head number per plant and yield per plant while the other five characters were negatively correlated. However, grain weight per head is the only trait that showed significantly negative correlation with GD (r=-0.3695, p<0.05). No significant correlation of GD with MPH and SCA was detected. These results suggested that high heterotic effects might not be firmly obtained if parental genotypes with large GD between them are chosen. 5. Genetic character of photosynthetic rate of 337S:6 parental genotypes, and 2 F1 and 1 F2 derived from 337S as a female parent were used to conduct genetic analysis of photosynthetic rate of 337S. The result showed F1 exhibited mid-parent heterosis but obvious discrepancy existed among combinations. According to photosynthetic rate distribution in the F2 population, Chi-square test showed the genetic model of photosynthetic rate of 337S was a single major gene conditioning mechanism.