Wheat yield improvements in China: Past trends and future directions

Wheat has been cultivated in China for at least 4000 years, but it took until 1914 in Nanjing before crossbreeding programs commenced. Wheat breeding has made substantial contribution to China's wheat production capacity over the years. Data on more than 1850 Chinese wheat varieties from the 1920s to 2014 (categorized into north winter wheat, south winter wheat and spring wheat varieties) were collected in order to (1) better understand progress in agronomic performance, (2) analyze the evolution of yield-related traits, and (3) formulate strategies for future breeding.Since the 1920s, average grain yield has increased annually by 1.29% for north winter wheat, 1.5% for south winter wheat and 0.52% for spring wheat. For north and south winter wheat, kernel number per spike and 1000-kernel weight (TKW) have increased significantly, with no change to spike number per unit area. Spike number per m2 has not changed significantly in any of the three major agro-ecological production zones. Average plant height of north winter wheat declined from the 1950s to 2000s to stabilize at 80cm; south winter wheat declined from the 1930s to 1990s to stabilize at 86cm; and spring wheat decreased from the 1960s to 1990s to stabilize at 89cm. Seedling density in both north and south winter wheat has significantly reduced, with no significant changes for spring wheat. Variability of varieties in yield and agronomic traits has declined since the 2000s.Breeding programs for wheat varieties have contributed to food security in China. Yields for north and south winter wheat have steadily increased since the 1920s, following the rule of thumb to increase TKW and kernel number per spike without changing spike number per unit area. For spring wheat, average grain yield has increased annually significantly since the 1920s, and reached its peak in the 1980s but has since decreased. Future increase in yield may be achieved through improvement in kernel size and kernel number per spike. This paper comprehensively evaluates the historical development of wheat varieties in three main agro-ecological regions of China, and will act as a guide for future wheat breeding and production technology.