Genetic improvement of wheat yield potential in North China.

During 2001–03 seasons, three trials including 11 varieties from Hebei Province, 15 varieties from Shandong Province, and 11 varieties from Henan Province were sown in Shijiazhuang, Jinan, and Zhengzhou, respectively. All tested genotypes are the major varieties from 1970s to present. A randomized block design with three replicates was employed. Measurements consisted of heading date, plant height, spike number m-2, thousand kernel weight, kernel number and kernel weight per spike, yield, biomass, and harvest index. In addition, SDS-PAGE and SSR markers were used to detect the presence of 1B/1R translocation, and distribution of dwarfing genes, respectively. Results indicate that annual genetic gain in yield potential is 0.54% (35.4 kg ha-1 year-1, P<0.05), 0.48% (32.0 kg ha-1year-1, P<0.01), and 1.05% (72.1 kg ha-1 year-1, P <0.01), in Hebei, Shandong, and Henan, respectively. In all three trials, yield is positively and significantly associated with kernel weight per spike (r=0.77, 0.73, and 0.75, in Shijiazhuang, Jinan, and Zhengzhou, respectively, the same order below, P<0.05), biomass (r=0.72, 0.70, 0.80, P<0.05) and harvest index (r=0.86, 0.67, 0.76, P<0.05). Significant and negative association is also observed between yield and plant height in Shijiazhuang and Zhengzhou, but not in Jinan. However, positive and significant association between yield and kernel number per spike is presented in Shijiazhuang and Jinan, but not in Zhengzhou. Use of dwarfing genes and 1B/1R translocation are the major factors for yield improvement. Frequencies of Rht-D1b, Rht-B1b, and Rht8c are 67.6%, 16.2%, and 43.2%, respectively