The contribution of green parts of the ear to grain filling in old and modern cultivars of bread wheat (Triticum aestivum L.): Evidence for genetic gains over the past century

Abstract

Green parts of the ear (e.g., bracts, awns) are sources of photosynthates in C3 cereals. However, the contribution of ear photosynthesis to grain filling in bread wheat (Triticum aestivum L.) is less known compared with other sources of assimilates (e.g., flag leaf photosynthesis, C stem retranslocation). The main objectives of this work were: (i) to analyze if empirical breeding has changed the contribution of ear photosynthesis to grain filling through a retrospective study of cultivars of bread wheat released in Argentina between 1920 and 2008 and (ii) to study if the introgression of dwarfism alleles has changed the contribution of ear photosynthesis to grain filling using near-isogenic lines of a cultivar of bread wheat differing in absence/presence in Rht alleles. In both experiments we covered ears with aluminum foil to reduce photosynthesis, in intact and defoliated plants. Grain weight per ear was measured and the ear contribution to grain filling was calculated as: [(GWear of non shaded ear - GWear of shaded ear)* 100 / GWear of non shaded ear], where GWear is total grain weight per ear. The contribution of ear photosynthesis increased in modern cultivars, more in defoliated than intact plants. Ear contribution was negatively correlated with plant height (r2= 0.62 and 0.71 in intact and defoliated plants, respectively) and especially with stem dry weight (r2= 0.75 and 0.80 in intact and defoliated plants respectively). Dry matter translocation efficiency (DMTe) did not change consistently with year of release of the cultivars. The contribution of preanthesis stem assimilates to grain yield (CPA, i.e. the ratio of stem mobilized reserves to GWear) clearly decreased in more modern cultivars. The correlation of ear contribution with awn size was rather low in this retrospective study. In near-isogenic lines differing in Rht alleles, the contribution of the ear was higher when dwarfism alleles were present, mainly in non-defoliated plants. However, there was no consistent relationship between stem weight of the near-isogenic lines and their respective contributions of ear photosynthesis, suggesting that other factors (beyond the Rht alleles) are involved in the increase of ear contribution in the retrospective study.