| Summary: | Heat stress adversely affects wheat production in many regions of the world and is
particularly detrimental during reproductive development. The objective of this study
was to identify quantitative trait loci (QTL) associated with improved heat tolerance in
hexaploid bread wheat (Triticum aestivum). To accomplish this objective, an analysis of
both the phenotypic and genetic responses of two recombinant inbred line (RIL)
populations was conducted. RIL populations Halberd x Cutter and Halberd x Karl 92
(H/K) both derive heat tolerance from Halberd and segregate in their response to heat
stress. A heat susceptibility index (HSI) was calculated from the reduction of three yield
components; kernel number, kernel weight, and single kernel weight, following a three-day
38 degrees C heat stress treatment during early grain-filling. The HSI, as well as
temperature depression of the main spike and flag leaf were used as measurements of
heat tolerance. Genetic linkage maps were constructed for both populations and were
used in combination with phenotypic data and statistical software to detect QTL for heat
tolerance.
In a comparison across the two across populations, seven common QTL regions were
identified for HSI, located on chromosomes 1B, 3B, 4A, 5A, 5B, and 6D. Subsequent
analysis of temperature depression in the H/K population identified seven QTL that co-localized
for both cooler organ temperature and improved HSI. Four of the beneficial
alleles at these loci were contributed Halberd. The genetic effect of combining QTL,
including QHkw.tam-1B, QHkwm.tam-5A.1, and QHskm.tam-6D showed the potential
benefit of selection for multiple heat tolerant alleles simultaneously. Analysis of the
H/K population in the field under abiotic stress detected QTL on chromosome 3B and
5A, which were in agreement with results from the greenhouse study. The locus
QYld.tam-3B was pleiotropic for both temperature depression and HSI in both
experiments and was associated with higher biomass and yield under field conditions.
The results presented here represent a comprehensive analysis of both the phenotypic
response of wheat to high temperature stress and the genetic loci associated with
improved heat tolerance and will be valuable for future understanding and improvement
of heat stress tolerance in wheat.
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