Knowledge of changes associated with advances in crop productivity is essential for understanding yield limiting factors and developing strategies for future genetic improvement. The objectives of this study are to understand genetic gain for grain yield and associated traits in the Northern China Winter Wheat Region (NCWWR). Four trials, comprised of 47 leading common wheat (Triticum aestivum L.) cultivars from the NCWWR from 1960 to 2000, were conducted during 2001 to 2003 using a completely randomized block design of three replicates under controlled field environments. Molecular markers were used to detect the presence of dwarfing genes and the 1B/1R translocation. Results showed that average annual genetic gain in grain yield ranged from 32.07 to 72.11 kg ha−1yr−1 or from 0.48 to 1.23% annually in different provinces. The most significant increase in grain yield occurred in the early 1980s, largely because of the successful utilization of dwarfing genes and the 1B/1R translocation. There was no common trend across trials in terms of changes in spikes m−2, kernels per spike, 1000‐kernel weight (TKW), or biomass. The genetic improvement in grain yield was primarily attributed to increased grain weight per spike, reduced plant height, and increased harvest index (HI). The dwarfing allele Rht‐D1b was the most frequent (68.0%) among the cultivars, followed by Rht 8 (42.0%) and Rht‐B1b (16.0%). The frequency of 1B/1R translocation cultivars was 42.6%. The future challenge of wheat breeding in this region is to maintain the genetic gain in grain yield and to improve grain quality, without increasing inputs for the wheat‐maize double cropping system.

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Glutenin, one of major factors effecting bread-making quality, is comprised of a mixture of polymers, viz. high-molecular-weight glutenin subunits (HMW-GSs) and low-molecular-weight glutenin subunits (LMW-GSs). Understanding variation among these glutenin subunits can help breeders determine allelic effects on specific quality traits and to use them as genetic markers. The HMW-GS and LMW-GS compositions of 390 landraces and 225 released varieties were analyzed by SDS-PAGE, and some quality traits, including Zeleny sedimentation volume, dough development time, stability time and strengths, were evaluated. The results indicated that 17 and 13 HMW-GSs were present in landraces and released varieties, respectively. For LMW-GS (Glu-A3 and Glu-B3 loci), 12 alleles were found in both landraces and released varieties. Total allelic richness at glutenin loci in landraces was higher, but the genetic dispersion index was lower than in released varieties. Two new subunit combinations 6 ? 16 and 7 ? 22, and some rare subunits 6 ? 9*, 23 ? 22, 6* ? 8, 7 and 8, were identified in landraces and released varieties. The Glu-D1 and Glu-B3 loci had significantly positive effects. Based on the comparison of the effect of each subunit on quality, it was concluded that subunits 1 at Glu-A1, 13 ? 16, 17 ? 18 and 6 ? 16 at Glu-B1, 5 ? 10 at Glu-D1, Glu-A3b at Glu-A3 and Glu-B3d at Glu-B3 contributed larger positive effects on bread-making quality than alternative alleles. From this study, genetic materials with strong gluten and good quality were identified in landraces that did not carry the 1BL.1RS translocation.

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