Improvement effect of agronomic traits in the second backcrossing generation of dryland and irrigated wheat varieties

The winter wheat growing season in the Huang-Huai-Hai area of China is often exposed to drought stress posing a serious threat to the safety of food production. The molecular design breeding by using backcross selection and molecular marker-assisted selection to improve breeding of drought resistant and high water use efficiency varieties become a new direction of future wheat breeding. A total of 200 BC₂ (the second backcrossing generation) plants were obtained from the hybridization between dryland variety 'Chang 6878' as donor parent and irrigated variety 'Jimai 22' as recurrent parent. Ten agronomic traits, including plant height, spike length, internode length under spike, tiller number, spikelet number, grains per spike, biomass per plant, grain weight per plant, 1000-grain weight, economic index, were investigated to analyze the hybridization and backcross effect by the analysis of correlation, cluster and principal component. The results showed that the plant height, spike length, internode length under spike and tiller number of BC₂ plants were biased in favor of the recurrent parent 'Jimai22', while the spike number, grain number per spike, biomass per plant, grain weight per plant, 1000-grain weight, economic index showed super-parents effect. The correlation analysis showed that grain weight per plant was extremely significantly correlated with plant height, spike length, tiller number, spikelet number, grains per spike, biomass per plant, 1000-grain weight. And grain weight per plant was significantly and positively correlated with economic index. The cluster analysis showed that BC₂ population was divided into 4 groups at the Euclidean distance 40. The Class Ⅱ including 'Jimai 22' accounted for 30.5% of the total BC₂ generations, while 'Chang 6878' was divided into Class Ⅳ separately. Class Ⅰ (58% of the total number of BC₂) and Class Ⅱ were merged into a new group at the Euclidean distance 45, therefore 88.5% of BC₂ individuals and 'Jimai 22' were classified into the same cluster. The principal component analysis obtained five principal components, which contributed over 85.51% of variance, and ten BC₂ strains with high comprehensive score were screened as the key choice in the future. These results implied positively direction of genetic improvement in the BC₂ generation, which provided theoretical basis and technical support for the water use efficiency and drought-resistance breeding by wheat backcross.