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Wheat is sensitive to heat stress, particularly during grain filling, and this reduces grain yield. Ancestral wheat species, such as emmer wheat (Triticum dicoccon Schrank), represent potential sources of new genetic diversity for traits that may impact wheat responses to heat stress. However, the diversity available in emmer wheat has only been explored superficially. Recently developed emmer derived hexaploid wheat genotypes were evaluated for physiological, phenological and agronomic traits in a multi-environment, multi-season strategy. The emmer-based hexaploid lines were developed from crosses and backcrosses to 9 hexaploid recurrent parents and these genotypes and 7 commercial cultivars were evaluated under two times of sowing (E1 and E2) in the field for three consecutive years (2014-2016). The materials were genotyped using a 90 K SNP platform and these data used to estimate the contribution of emmer wheat to the progeny. Significant phenotypic and genetic variation for traits were observed. Higher temperature during reproductive development and grain filling reduced trait expression. Emmer progeny with greater trait values than their recurrent parents and commercial cultivars in both environments were found. Derivatives with higher physiological trait values yielded well in both environments; as indicated by the clustering of genotypes. The emmer wheat parent contributed between 1 and 43 % of the genome of the emmer-based hexaploid progeny, and progeny with greater emmer contribution had superior trait values in both environments. These results showed a positive effect of direct emmer introgression on wheat performance under heat stress. Mitigation of high temperature stress through the introgression of favorable alleles from wheat close relatives into modern wheat cultivars is possible.

High temperature has a negative impact on wheat grain quality and reduces market value. Emmer wheat (Triticum dicoccon Schrank), one of the earliest domesticated wheat species, is a source of genetic diversity for the improvement of heat and drought tolerance in modern wheat. However, the potential of emmer wheat for the improvement of grain physical quality under high temperature stress is little studied. A diverse set of 184 emmer-based hexaploid lines was developed by crossing emmer wheat with hexaploid wheat and backcrossing once to hexaploid wheat. These materials, seven hexaploid recurrent parents and seven commercial cultivars, were evaluated at two times of sowing (E1 and E2) in the field, in 2015–2016. The materials were genotyped using a 90 K SNP platform and these data were used to estimate the contribution of emmer wheat to the progeny. Significant phenotypic and genetic variation for grain physical quality traits including protein content and test weight was observed. High temperature significantly increased protein content and decreased test weight. Large scale field phenotyping identified emmer progenies with improved grain characteristic compared to their respective parents and commercial cultivars in both environments. A few families consistently produced higher trait means across environments compared to their recurrent parents. The emmer wheat parent contributed between 1 and 37% of the genome in emmer-based genotypes. Selected emmer derived lines with superior protein content and test weight, tended to have a greater genetic contribution from the emmer parent, ranging from 12 to 37% and 7–37% in E1 and E2, respectively. It was concluded that new genetic variation for seed traits, such as protein content and test weight, can be introduced to hexaploid wheat from emmer wheat. The newly developed emmer derivatives identified with enhanced grain quality under high temperature stress can potentially be used to improve grain quality through breeding.

Increases in atmospheric carbon dioxide concentration ([CO2]) and temperature associated with future climates are expected to affect wheat growth and grain yield. The ability of wheat to adapt to these changes is close related to the response of the root system. The effect of elevated CO2, high temperature and the interaction elevated CO2 × high temperature (3 °C above the ambient temperature) on the growth and proliferation of the root system of two spring wheat genotypes differing in vigorous growth was evaluated. The breeding line Vigor 18 selected for vigorous shoot and root growth and the commercial cultivar Janz were grown in rhizo-boxes inside specially designed tunnel houses under ambient (390–400 μL L−1) and elevated CO2 (700 μL L−1), and ambient and 3 °C above the ambient temperature. Growth and proliferation of the root system was monitored through root mapping. Elevated CO2 enhanced root and shoot biomass, but this positive effect was reduced when plants were grown under high temperature. Total root length was also increased by elevated CO2, but only when plants were grown under ambient rather than under high temperature. Root growth response to elevated CO2 differed between genotypes; elevated CO2 stimulated root growth in the non-vigorous cultivar Janz, but not in vigorous liner Vigor 18. High temperature reduces the positive effect that elevated CO2 has on root growth and proliferation.

Wheat grown in the Mediterranean-type environments of southern Australia is often exposed to end-of-season drought (terminal drought). During the development of terminal drought, soil dries from the top of the profile exposing the upper part of the root system to water stress while deeper roots may still be able to access deeper soil water for grain filling. It is hypothesised that the part of the root system exposed to drying soil signals abscisic acid (ABA) production and the corresponding rise in ABA concentration in leaves causes partial stomatal closure, regulating the extraction of available water at depth. In the first step to test this hypothesis, a glasshouse experiment was conducted to identify contrasting stomatal response to terminal drought and production of ABA using four wheat genotypes adapted to different soil moisture environments. Terminal drought was induced by withholding water from anthesis in one half (WD) or both halves (DD) of the root system using split pots. Stomatal conductance decreased in all four genotypes in WD plants, but leaf ABA concentration and leaf water status differed. The cultivar Drysdale had higher leaf ABA concentrations and lower stomatal conductance, but leaf water status decreased. Leaf ABA concentration did not increase in WD plants of the breeding line IGW-3262, but stomatal conductance decreased and leaf water status was unchanged. All the genotypes behaved similarly under DD conditions, with increased leaf ABA concentration, lower stomatal conductance and severely dehydrated leaves. The possible causes of the above differences in leaf ABA concentration despite similar stomatal behaviour in wheat genotypes are discussed.