The influence of AB genome variation on the high-temperature tolerance of wheat

Heat stress is a major constraint to wheat yield in many wheat growing regions including Australia. This study examined potential new genetic diversity for heat tolerance from emmer wheat introgressed into hexaploid bread wheat. A total of 554 genotypes (537 emmer based hexaploid lines and 17 commercial cultivars and/or parents) were evaluated at two times of sowing in 2014, 2015 and 2016. Many of the field selected emmer derived lines had stable yield across environments. The impact of high temperature was greatest at anthesis and grain yield was reduced by between 4 and 7% with every 1oC rise in maximum temperature above the optimum of 25°C under field conditions. A contrasting pair of emmer derived lines, with equivalent yield under optimal conditions and a divergent yield under high temperature was chosen for more intensive study using in-field controlled temperature chambers and the glasshouse. The heat tolerant line expressed better photosynthetic capacity and a faster rate of grain fill. All material was genotyped using a 90K SNP platform. A genome wide association analysis was then performed to identify possible marker trait associations based on the multi-year, multi-environment data. A number of marker trait associations (MTAs) were detected for yield and associated traits under heat stress. Thus the probable genetic control of heat tolerance was identified; however these MTAs must be confirmed in unrelated germplasm. The combination of phenotyping methods was effective in identifying heat tolerant germplasm. A heat tolerant wheat ideotype for north-western NSW was constructed on the basis of the observed trait responses and their association with grain yield under heat stress. The new genetic variability identified in this study, the probable genetic control of heat tolerance and the three-tiered screening methodology can be used to improve the heat tolerance of wheat

Genetic Contribution of Emmer Wheat (Triticum dicoccon Schrank) to Heat Tolerance of Bread Wheat

Rising global temperatures cause substantial yield losses in many wheat growing environments. Emmer wheat (Triticum dicoccon Schrank), one of the first wheat species domesticated, carries significant variation for tolerance to abiotic stresses. This study identified new genetic variability for high-temperature tolerance in hexaploid progeny derived from crosses with emmer wheat. Eight hexaploid and 11 tetraploid parents were recombined in 43 backcross combinations using the hexaploid as the recurrent parent. A total of 537 emmer-based hexaploid lines were developed by producing approximately 10 doubled haploids on hexaploid like BC1F1 progeny and subsequent selection for hexaploid morphology. These materials and 17 commercial cultivars and hexaploid recurrent parents were evaluated under two times of sowing in the field, in 2014–2016. The materials were genotyped using a 90K SNP platform and these data were used to estimate the contribution of emmer wheat to the progeny. Significant phenotypic and genetic variation for key agronomical traits including grain yield, TKW and screenings was observed. Many of the emmer derived lines showed improved performance under heat stress (delayed sowing) compared with parents and commercial cultivars. Emmer derived lines were the highest yielding material in both sowing dates. The emmer wheat parent contributed between 1 and 44% of the genome of the derived lines. Emmer derived lines with superior kernel weight and yield generally had a greater genetic contribution from the emmer parent compared to those with lower trait values. The study showed that new genetic variation for key traits such as yield, kernel weight and screenings can be introduced to hexaploid wheat from emmer wheat. These genetic resources should be explored more systematically to stabilize grain yield and quality in a changing climate

Morpho-physiological responses of diverse emmer wheat genotypes to terminal water stress

Emmer wheat (Triticum dicoccon Schrank) is the allo-tetraploid progenitor of the modern wheat and holds genetic variation for tolerance to drought. Water use efficient emmer wheat genotypes are considered better maintainers of yield under water limited environments. However, existing genetic variation for water use efficiency (WUE) in emmer germplasm has not been fully explored nor are the underlying mechanisms of this trait properly understood. Three field selected, contrasting emmer wheat genotypes were assessed at 90% and 50% pot soil water capacity (PSWC) in quadruplicated design for water use response under glasshouse conditions. Significant differences were observed between water treatments and among genotypes for various traits including carbon isotope discrimination (CID) and the grain yield. Water stress had significant negative impact on grain yield but less so in genotypes superior in water use efficiency. The relationship between grain yield and WUE was positive both at 90% and 50% PSWC. Genotypes with lower CID scores had higher WUE and grain yield under water stress. The genetic variation for WUE observed in emmer wheat is a potential resource to improve drought tolerance in hexaploid wheat