Characterization and preliminary heterosis evaluation of novel wheat genetically divergent populations.

Heterosis is an important approach to improving wheat yield and quality. Previously, five recurrent selection populations were established to broaden genetic diversity via a recurrent selection strategy using French wheat, Spelt wheat, spike-branched wheat, Tibetan semi-wild wheat and common wheat as distinct germplasm donors. The present study aimed to characterize and preliminary heterosis evaluate of these wheat recurrent selection populations after 20 cycles of recurrent selection, providing a reference for long-term recurrent selection to enhance inter-population genetic differentiation and heterosis potential. In this paper, 94 materials including recurrent selection lines and their donors, together with 120 common wheat cultivars/lines, were phenotyped for agronomic traits and genotyped with the wheat 90K SNP array to assess genotypic variation and genetic distance. Furthermore, 23 elite lines derived from different recurrent selection populations were used as parents in an incomplete NCII (inter-population crosses) and a full NCI(intra-population crosses) design to evaluate their genetic distance and the heterotic performance. The main results showed that significant phenotypic variation existed within each population, and its magnitude varied with traits and populations. Plant height (PH) and 1000-grain weight (TGW) showed evidence of convergent selection during population improvement, whereas spike length (SL) and mean grains per spike (GSN) displayed divergent selection, particularly within the four male parent populations (Set B). The SNP-based genetic distance and population differentiation patterns were basically consistent with the classification of exotic germplasm resources. The genetic differences of inter-populations were generally greater than those within PopulationI(Domestic wheat population). The general combining ability (GCA) differed across traits, while special combining ability (SCA) showed a significant correlation with parental phenotypic values. The proportion of crosses with positive mid-parent heterosis (MPH) ranged from 45.24% to 98.41%, varying with traits. Meanwhile, the percentage of crosses showing positive commercial heterosis (CH) was 58.73%-99.21%, which also differed across traits. Among all measured traits, TGW had the highest proportion of crosses with positive heterosis. MPH values within PopulationIwere less than that between PopulationI and other populations (Set B) in five traits (except GSN). Seven superior TGW crosses were identified, with CH exceeding 15% and specific combining ability (SCA) ranging from 1.56 to 13.06. A two-year field trial revealed that two of these crosses showed plot yield CH values of 4.81% and 8.54%, respectively. This study provides a reference for broadening genetic diversity for hybrid parents by recurrent selection using exotic germplasm resources, and preliminarily screened promising combinations, which provide an important reference for further investigations.