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.
The Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia.
Hamid
H
Shirdelmoghanloo
School of Agriculture Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia.
Julian D
JD
Taylor
The Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia.
Iman
I
Lohraseb
Phenomics and Bioinformatics Research Centre, University of South Australia, GPO Box 2471, Adelaide, SA, 5001, Australia.|Present address: Mathematics Department, Bethlehem University, PO Box 11407, Rue des Freres, Bethlehem, 92248, Jerusalem, Palestine.
Huwaida
H
Rabie
Phenomics and Bioinformatics Research Centre, University of South Australia, GPO Box 2471, Adelaide, SA, 5001, Australia.|The Plant Accelerator, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia.
Chris
C
Brien
The Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia.
Andy
A
Timmins
EH Graham Centre for Agricultural Innovation, Pine Gully Road, Wagga Wagga, NSW, 2650, Australia.
Peter
P
Martin
School of Agriculture Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia.
Diane E
DE
Mather
EH Graham Centre for Agricultural Innovation, Pine Gully Road, Wagga Wagga, NSW, 2650, Australia.
Livinus
L
Emebiri
The Australian Centre for Plant Functional Genomics, School of Agriculture Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5064, Australia. nick.collins@acpfg.com.au.
Nicholas C
NC
Collins
D000222:Adaptation, Physiological / Q000235:genetics; D001315:Australia; D002734:Chlorophyll / Q000378:metabolism; D002874:Chromosome Mapping; D032461:Chromosomes, Plant / Q000235:genetics*; D003433:Crosses, Genetic; D002523:Edible Grain / Q000235:genetics* / Q000254:growth & development; D017343:Genes, Plant / Q000235:genetics*; D005838:Genotype; D006238:Haploidy; D018869:Heat-Shock Response / Q000235:genetics; D006358:Hot Temperature; D010641:Phenotype; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci / Q000235:genetics*; D012621:Seasons; D014908:Triticum / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism
D002734:Chlorophyll
Grain filling; Grain size; Heat tolerance; QTL; Quantitative trait loci; Senescence; Stay-green; Triticum aestivum; Wheat