Male sterility of wheat-breeding line 337S (Triticum aestivum L.) is sensitive to both short day-length/low temperature and long day-length/high temperature. 337S was crossed with the common wheat variety, Huamai No. 8 and the F1 was highly fertile. The F2 population segregated in a 15:1 ratio for fertility/sterility in 243 individuals under long day-length/high-temperature. The two thermophotoperiod-responsive male sterile genes were mapped to chromosomes 5B and 2B using Simple Sequence Repeat (SSR) markers and bulked segregant analysis. Partial linkage maps around the sterility loci of chromosomes 2B and 5B were constructed using the 243 individuals in the F2 population. One gene (wptms1) for male sterility was flanked by the SSR markers Xgwm335 and Xgwm371 at a genetic distance in chromosome 5B of 4.1 and 24.4 cM, respectively. The second gene (wptms2) was mapped between markers Xgwm374 and Xgwm120 at a genetic distance of 6.6 and 20.9 cM, respectively. The closest linked markers Xgwm335 (wptms1) and Xgwm374 (wptms2) explained 53 and 38% of phenotypic variation for the fertility. The SSR markers provide a useful tool to transfer the male sterile genes into elite wheat germplasm.

The fertility of a wheat male sterile line 337S was investigated in 4 consecutive years with 18 different sowing dates. Line 337S showed high sterility under both short daylength/low temperature and long daylength/high temperature during ear development. It has 2 time windows to be used as a male sterile line for hybrid seed production. Its fertility rate can be >50% with suitable sowing time; thus, it can be self-maintained as a male sterile line. Line 337S was reciprocally crossed with 7 common wheat varieties and the fertility of their F1, F2, and BC1 hybrids was investigated at different sowing dates. The results showed that recessive nuclear genes controlled male sterility in 337S and no cytoplasmic effect was observed. All common wheat varieties were able to restore its fertility. The male sterility was controlled by a pair of recessive genes under short daylength/low temperature, but was governed by 2 pairs of recessive genes under long daylength/high temperature. This novel male sterile line provides a new tool for using heterosis in wheat.

Utilization of a two-line breeding system via photoperiod-thermo sensitive male sterility has a great potential for hybrid production in wheat (Triticum aestivum L.). 337S is a novel wheat male sterile line sensitive to both short daylength/low temperature and long daylength/high temperature. Five F(2) populations derived from the crosses between 337S and five common wheat varieties were developed for genetic analysis. All F(1)'s were highly fertile while segregation occurred in the F(2) populations with a ratio of 3 fertile:1 sterile under short daylength/low temperature. It is shown that male sterility in 337S was controlled by a single recessive gene, temporarily designated as wptms3. Bulked segregant analysis (BSA) coupled with simple sequence repeat (SSR) markers was applied to map the sterile gene using one mapping population. The wptms3 gene was mapped to chromosome arm 1BS and flanked by Xgwm413 and Xgwm182 at a genetic distance of 3.2 and 23.5 cM, respectively. The accuracy and efficiency of marker-assisted selection were evaluated and proved essential for identifying homozygous recessive male sterile genotypes of the wptms3 gene in F(2) generation.

Heterosis has been exploited in many crops and made a significant contribution to the world food supply. Genetic distance (GD) is one of valuable criteria for selecting parents in hybrid breeding. The objectives of this study were to estimate GD between a novel photoperiod-thermo sensitive male sterile wheat line 337S and several common cultivars using simple sequence repeat (SSR) markers, and to evaluate the relationship of GD and heterosis. The line 337S, as a maternal parent, was crossed with 16 common wheat varieties to produce 16 hybrids. Eight agronomic traits were investigated for the parents and F1 hybrids. Mid-parent heterosis (MPH) and specific combining ability (SCA) were calculated. GD and cluster analysis were performed among the 17 parents. The correlations of GD with F1 performance, MPH and SCA were analyzed. The results showed that GD estimates among the 17 parents averaged 0.42 with a range from 0.26 to 0.57, and the averaged GD between 337S and the 16 parental cultivars was 0.44. Cluster analysis separated the 17 parents into three main groups. SSR markers were useful in analyzing genetic divergences among the 17 parental lines. However, GD based on SSR markers poorly correlated with F1 performance, MPH and SCA. Thus, GD revealed by SSR markers can not provide a reliable prediction in practical wheat hybrid breeding.