A QTL on the short arm of wheat (Triticum aestivum L.) chromosome 3B affects the stability of grain weight in plants exposed to a brief heat shock early in grain filling

Background: Molecular markers and knowledge of traits associated with heat tolerance are likely to provide breeders with a more efficient means of selecting wheat varieties able to maintain grain size after heat waves during early grain filling. Results: A population of 144 doubled haploids derived from a cross between the Australian wheat varieties Drysdale and Waagan was mapped using the wheat Illumina iSelect 9,000 feature single nucleotide polymorphism marker array and used to detect quantitative trait loci for heat tolerance of final single grain weight and related traits. Plants were subjected to a 3 d heat treatment (37 °C/27 °C day/night) in a growth chamber at 10 d after anthesis and trait responses calculated by comparison to untreated control plants. A locus for single grain weight stability was detected on the short arm of chromosome 3B in both winter- and autumn-sown experiments, determining up to 2.5 mg difference in heat-induced single grain weight loss. In one of the experiments, a locus with a weaker effect on grain weight stability was detected on chromosome 6B. Among the traits measured, the rate of flag leaf chlorophyll loss over the course of the heat treatment and reduction in shoot weight due to heat were indicators of loci with significant grain weight tolerance effects, with alleles for grain weight stability also conferring stability of chlorophyll ('stay-green') and shoot weight. Chlorophyll loss during the treatment, requiring only two non-destructive readings to be taken, directly before and after a heat event, may prove convenient for identifying heat tolerant germplasm. These results were consistent with grain filling being limited by assimilate supply from the heat-damaged photosynthetic apparatus, or alternatively, accelerated maturation in the grains that was correlated with leaf senescence responses merely due to common genetic control of senescence responses in the two organs. There was no evidence for a role of mobilized stem reserves (water soluble carbohydrates) in determining grain weight responses. Conclusions: Molecular markers for the 3B or 6B loci, or the facile measurement of chlorophyll loss over the heat treatment, could be used to assist identification of heat tolerant genotypes for breeding.Hamid Shirdelmoghanloo, Julian D. Taylor, Iman Lohraseb, Huwaida Rabie, Chris Brien, Andy Timmins, Peter Martin, Diane E. Mather, Livinus Emebiri and Nicholas C. Collin

Genome-wide association analysis identifies a major gene for late maturity alpha-amylase (LMA) activity in synthetic hexaploid wheat

L.C. Emebiri, J.R. Oliver, K. Mrva and D. Mare

Genetic control of grain protein, dough rheology traits and loaf traits in a bread wheat population grown in three environments

Abstract not available.Lancelot Maphosa, Peter Langridge, Helen Taylor, Livinus C. Emebiri, Diane E. Mathe

Effects of heat exposure from late sowing on the agronomic and technological quality of tetraploid wheat

Background and objectives: Heat stress is a major limiting factor to wheat yield that also impacts on grain quality, and its incidence is likely to increase. Thirty-seven durum wheats were grown in irrigated replicated field trials over two seasons in Australia, normal sown (NS) or a 2-month late sown (LS). Agronomic and technological quality traits were examined. Findings: Later sowing exposed the crop to more days at temperatures of 30°C and above indicating more heat stress while the irrigation ensured no drought stress. Relative to NS, LS reduced yield, grain weight, test weight, and milling yield but grain vitreousness and hardness either increased or decreased depending on the trial. However, LS had positive effects on increasing protein content, dough quality indicators, and increased the proportion of high molecular weight gluten polymer. LS also enhanced pasta end-use traits, increasing pasta yellowness and firmness and decreasing cooking loss. Genotypes that showed relatively stable yield and grain characteristics under LS were identified (Caparoi, Jandaroi, Kalka, Kronos, Saintly, and WID802). Conclusions: These findings suggest that the heat stress experienced enhanced dough and pasta quality, despite having a negative impact on yield and physical grain characteristics. Genotypes were identified that represent potential sources of heat tolerance that could be useful in breeding to help limit the undesirable effects of heat stress on durum production. Significance and novelty: Late sowing of wheat is a good strategy to obtain exposure to heat stress in the Australian environment and can be used to select genotypes with better yield and quality stability.Mike Sissons, Denise Pleming, Julian D. Taylor, Livinus Emebiri, Nicholas C. Collin

Boron toxicity tolerance in wheat and barley: Australian perspectives

Boron (B) toxicity is a significant constraint to cereal production in regions worldwide, including parts of southern Australia. In recent years, much progress has been made by research groups investigating the molecular and physiological mechanisms involved in B toxicity tolerance in both barley (Hordeum vulgare L.) and wheat (Triticum sp. L.). In barley, genes have been identified controlling B tolerance at two of the four known B toxicity tolerance loci, both of which encode B transporters. Progress has also been made towards the identification of genes involved in B toxicity tolerance in wheat. Here we describe the current status of this work, in the context of B toxicity tolerance research in Australia and internationally. We also summarize prospects for breeding new cereal varieties with B toxicity tolerance in the future.Thorsten Schnurbusch, Julie Hayes and Tim Sutto

Identification of QTLs associated with variations in grain protein concentration in two-row barley

Grain protein concentration (GPC) is arguably the most important factor when marketing malting barleys. Excessively high and excessively low GPC are both undesirable for malting and brewing. GPC variation is influenced to a high degree by the environment and exhibits relatively large genotype × environment interaction. Identification of molecular markers linked to genes influencing GPC would allow barley breeders to select for GPC independent of environmental effects. A genetic linkage map with 270 markers was constructed to identify the genetic basis for variation in GPC, using 180 doubled haploid lines from a cross of VB9524 and ND1 1231*12. The parental genotypes were chosen on the basis of their known low GPC phenotype and their lack of common ancestry. A combination of composite interval and multiple-trait quantitative trait locus (QTL) mapping approach allowed the identification bfQTLs with specific impact on GPC, and those likely to depend on or be influenced by variations in grain yield and heading date. The study identified a major QTL with a 'stable' and specific effect on GPC and located near the centromeric region of chromosome 5H. The QTL accounted for ~21% of the phenotypic variation in this trait. The allele for reduced GPC at this region was inherited from the ND11231*12 parent, with additive effect of ~1% in GPC. Additional QTLs with minor effects (5-10% explained variation) were also detected on chromosome 2H, 4H, and 7H. The parent VB9524 was the source of the low GPC alleles at these regions