Leaf photosynthesis traits and associations with biomass and drought tolerance in amphidiploid and ancestral wheat genotypes

Future progress in wheat grain yield will depend on increasing photosynthesis capacity and biomass. Wheat wild relatives represent sources of novel genetic variation for photosynthesis traits. Our objective was to quantify variation in leaf photosynthesis traits, biomass and grain yield in a panel of diverse germplasm comprising: i) elite winter bread wheat (Triticum aestivum L.) lines, ii) wheat amphidiploid lines and iii) accessions of two wheat wild relatives Thinopyrum bessarabicum and Aegilops speltoides under well watered and drought conditions. A field experiment was carried out in one season examining 94 bread winter wheat Savannah x Rialto (S x R) doubled -haploid (DH) lines under irrigated and unirrigated conditions; and two glasshouse experiments were carried out examining: i) six bread wheat S x R DH lines, ii) seven amphidiploid lines (durum wheat (Triticum turgidum subsp. Durum) x Thinopyrum bessarabicum crosses) and iii) three accessions each of Th. bessarabicum and Aegilops speltoides under well-watered and drought conditions. In the field experiment, drought reduced grain yield by 22% (P < 0.001). Flag-leaf photosynthetic rate (Amax), stomatal conductance (gs) and grain Delta 13 C were each positively associated with grain yield in the unirrigated treatment (P < 0.05). In the glasshouse experiments, biomass plant-1 was higher in Ae. speltoides accessions (54.7 g plant-1) and the amphidiploid lines (50.8 g plant-1) than the bread wheat S x R lines (40.9 g plant-1) (P < 0.001) under drought. Flag-leaf Amax was higher in the Th. bessarabicum accessions and the amphidiploid lines than the bread wheat S x R lines under both irrigation and drought conditions (P < 0.05). There was a positive association between flag-leaf specific weight (FLSW) and flag-leaf Amax across the 19 genotypes in both irrigated and unirrigated conditions; there was no association between flag-leaf area and flag-leaf specific weight. Our results indicated that Th. bessarabicum ac-cessions and amphidiploid lines (durum wheat x Th. bessarabicum) offer novel variation for high expression of leaf photosynthesis rate for introgression into bread wheat genotypes to support genetic gains in biomass.