Combining high grain number and weight through a DH-population to improve grain yield potential of wheat in high-yielding environments
a b s t r a c t Previous yield gains in wheat have been achieved through increased expression of grain number per unit area, while fruiting efficiency has also been shown to explain improved grain number. However, com- bining a high grain number and weight in the same genotype is a difficult task in practical breeding. This study evaluated the progeny of a cross between two elite parents that contrast in grain number and grain weight, as a way to better understand how the two desired traits might be combined to achieve a signifi- cant boost in yield. The two parents are both high biomass elite spring wheat lines that achieve high yield through contrasting strategies: Bacanora achieves high grain number with a high density of relatively small spikes. Weebil has a lower density of larger spikes in which larger grain size is expressed. The spe- cific objectives of this research were: (i) to evaluate grain yield performance of DH lines and parents over two seasons, (ii) to identify promising physiological traits explaining high yield performance and (iii) to determine whether these traits are also expressed at the low plant densities. Two experiments were car- ried out under field conditions in southern Chile where the highest yield potential of wheat has ever been recorded. In Exp. 1 the performance of the 105 spring wheat DH lines, their parents and a Chilean spring cultivar (Pandora-INIA) with similar phenology were assessed together. Results showed that it is possi- ble to increase yield potential by combining high grain number and grain weight, thereby reducing the trade-off between both components. 42 and 50% of the DH lines showed transgressive segregation in S1 and S2, respectively. 3 and 4% of the DH lines yielded between 15,000 and 16,000 kg ha −1 . Grain yield was highly correlated with above-ground biomass (R 2 = 0.78, p < 0.0001 in S1 and R 2 = 0.77, p < 0.0001 in S2) and grain number (R2 = 0.69, p < 0.0001 in S1 and R2 = 0.71, p < 0.0001 in S2), whereas no correlation was found with either harvest index or grain weight. In Exp. 2, the high-yielding DH lines selected from Exp. 1 showed on average 45% higher grain yield (p < 0.01) than the Chilean checks. Differences in yield between the DH lines and the checks were explained by grain number m −2 , which was closely related to grain number spike−1 and fruiting efficiency. The latter trait was in line with faster post-anthesis spike dry matter accumulation, explaining in turn the higher radiation use efficiency of the selected DH lines recorded during this period. When comparing yield and its components at different plant densities, grain yield and both main yield components showed strong correlations between environments as a result of increased expression of grains spike −1 (p < 0.001) under low plant density that was able to offset the reduction in spike number m−2 (p < 0.001).