Physiological processes associated with wheat yield progress in the UK

Knowledge of the changes in physiological traits associated with genetic gains in yield potential is essential to improve understanding of yield-limiting factors and to inform future breeding strategies. Our objective was to identify physiological traits associated with genetic gains in grain yield of winter wheat (Triticum aestivum L.) in the UK. The growth and development of eight representative cultivars introduced from 1972 to 1995 (one tall rht-D1b cultivar and seven Rht-D1b, formerly Rht2, semidwarf cultivars) was examined in field experiments at Sutton Bonington in 1996-1997,1997-1998, and 1998-1999. A linear genetic gain in grain yield of 0.12 Mg ha(-1) yr(-1) (1.2% yr-1) was positively correlated with both harvest index (HI) and aboveground biomass; a quadratic function fitted to the data showed that progress in HI was most apparent during the earlier phase of the 23-yr period, whereas biomass contributed most since about 1983. There was a linear increase across time of 217 grains m(-2) yr(-1), but no change in grain weight. Significant genetic changes across time and correlations with grain yield were also found for preanthesis radiation-use efficiency (RUE, 0.012 g MJ(-1) yr(-1)) and water soluble carbohydrate (WSC) content of stems and leaf sheaths at anthesis (4.6 g m(-2) yr(-1)). Our results suggest that recent genetic gains in grain yield have been based on a combination of improved growth rate in the preanthesis period, which has driven increases in number of grains per square meter, and a larger source for grain filling through increases in stem soluble carbohydrate reserves.