Radiation interception and use efficiency as affected by breeding in Mediterranean wheat

Past breeding achievements in grain yield were mainly related to increases in harvest index (HI) without major changes in biomass production. As modern cultivars have already high HI, future breeding to improve grain yield will necessarily focus on increased biomass. Improved biomass would depend on our capacity to improve the amount of photosynthetically active radiation intercepted by the crop (IPAR%) or the efficiency with which the canopy converts that radiation into new biomass (radiation use efficiency, RUE). Four field experiments with a set of wheat cultivars selected, bred and introduced in the Mediterranean area of Spain and that represent important steps in wheat breeding in Spain were conducted in order to identify whether and how wheat breeding in this area affected the amount of IPAR% and RUE both before and after anthesis. Although there was genotypic variability, cultivars did not show any consistent trend with the year of release of the cultivars for their biomass, pre and post-anthesis IPAR%, Crop growth rate (CGR) or RUE but, the post-anthesis CGR and RUE of the two oldest genotypes were lower than that of the other cultivars. As the oldest genotypes have lower number of grains per m2 than their modern counterparts, it is suggested that post-anthesis RUE in these cultivars was reduced by lack of sinks and therefore further increases in grains per unit area in modern cultivars could permit to improve biomass via increases in post-anthesis RUE.