Genetic improvement of important agronomic traits in Chinese wheat breeding over the past 70 years

Abstract Background Understanding the genetic improvement patterns of agronomic traits in Chinese wheat (Triticum aestivum L.) breeding is essential for devising future breeding strategies. However, a systematic analysis of the genetic improvement of important traits in Chinese wheat is lacking. This study aimed to provide insights into the improvement progress of yield-related traits in the Chinese wheat breeding process and clarify the selection pressure on important agronomic traits in different agroecological zones. Phenotypic evaluations of 481 wheat accessions including 157 Chinese landraces (CLs) and 324 modern Chinese cultivars (MCCs), were carried out in multiple locations and years. Results The population structure analyses showed that all accessions could be basically divided into CLs and MCCs subpopulations. Pearson correlation analysis revealed that the negative correlation between grain number per spike and thousand-grain weight gradually decreased while thousand-grain weight, grain number per spike, and effective tiller number exhibited synergistic improvements during the modern breeding process. Phenotypic differences among MCCs released from the 1950s to the 2000s indicated that grain number per spike and grain weight-related traits increased linearly, whereas plant height and effective tiller number decreased significantly. Furthermore, since the 1950s, the heading date, flowering date, and maturity date have become earlier, while the spike length and spikelet number per spike have not changed significantly with the advancement of breeding years. The annual genetic gain analysis of agronomic traits showed that plant height had the greatest increase (‒0.96%), followed by thousand-grain weight (0.38%), while the lowest for grain number per spike (0.13%). Phenotypic difference analysis of CLs and MCCs with different geographical origins further revealed that heading date, flowering date, plant height, thousand-grain weight, grain width, and grain thickness experienced strong selection with the same trend in seven agroecological zones. Among zones, the northern winter wheat zone experienced the strongest selection pressure, and plant height and thousand-grain weight were strongly selected in all zones. Conclusions This study reveals that CLs and MCCs in China with obvious phenotypic differences, plant height and thousand-grain weight were strongly selected during wheat breeding, and further improvement of wheat in China will inevitably involve a continuous increase in grain number per spike.