QTL Mapping For Terminal Heat Stress Tolerance In Synthetic Hexaploid Wheat Derived Population
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Date
2020
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Punjab Agricultural University, Ludhiana-
Abstract
Common bread wheat (2n=AABBDD) ranks among the primary cereal crop throughout the world and
is an allohexaploid evolved from two spontaneous hybridization events followed by spontaneous
chromosome doubling. The D-genome of this polyploidy is the least diverse among the three
constituting wheat genomes and is unarguably less diverse than that of diploid progenitor Aegilops
tauschii (2n=DD). Due to this considerable similarity, Ae. tauschii is extensively used in wheat
improvement programs introducing new genetic diversity for various biotic and abiotic traits. A large
number for Ae. tauschii accessions are available at Punjab Agricultural University, Ludhiana. Seven of
these accessions were used to generate wheat synthetics targeting heat stress tolerance. All of these
SHWs performed better than elite cultivars under terminal heat tolerance. Two of these synthetics,
Syn14128 and Syn14170 selected on the basis of their better and stable performance under heat stress.
These two synthetic wheat were crossed with stripe rust resistant version of two elite wheat varieties
PBW343 and HD2967 to generate four nested population of chromosomal segmental substitution lines
(CSSLs). CSSLs thus generated, were evaluated for terminal heat tolerance and yield associated traits
under timely and late sown conditions. A majority of CSSLs out-performed the checks for different
traits like number of effective tillers, ear length, TGW and harvest index, as compared to checks and
recurrent parents used in the study. The genotypic performance evaluated using Heat Susceptibility
Index (HSI) further suggested that almost 50 percent CSSLs from each set were either highly heat
tolerant or moderately heat tolerant. Further, to assess the extent of alien introgressions these lines,
genotype-by-sequencing was outsourced and unique SNP from SHW and derived populations were
identified. A total of 724 synthetic wheat specific SNPs found in syn14170xHD2967 derived CSSLs
while 1546 synthetic specific SNPs were identified in syn14128xPBW343 derived CSSLs. The
graphical genotype of SNPs derived from syn14170xHD2967, identified four potential introgressions
on chr 2A, 3D, 6D and 7A. Based on yield per plot, harvest index and TGW, 18 out-performing lines
had one or more of these introgressions. In CSSLs derived from syn14170xPBW343, two potential
introgressions on chr 1B and 5B were found. Based on yield per plot, harvest index and TGW, 15 outperforming
lines had introgressions either on chr 1B or 5B. Further to explore the seedling stage heat
tolerance in the selected SHW lines, a 35°C heat shock for 12- and 20-hr was given to 4 day old
seedlings. A significant variation was observed in the content of MDA, DPPH, total phenols and total
flavanols, total sugars and amylase activity along with antioxidant scavenging activities and synthetics
better activities of most of these parameters compared to elite and durum wheats. One of the synthetic,
Syn14128 had higher amylase activity and better recovery even after a heat shock of 20hrs which was
confirmed by the gene expression analysis of α-amylase gene. A better performance of synthetics under
both seedling stage and terminal stage heat stress makes them the potential source for the improvement
of heat tolerance in the present day wheat cultivars. However, a deep exploration the exotic
introgressions in the synthetic derived lines will also help to refine useful exotic chromosome segments
for improving various traits and increasing D-genome diversity among cultivated varieties.
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Citation
Amandeep Kaur (2020). QTL Mapping For Terminal Heat Stress Tolerance In Synthetic Hexaploid Wheat Derived Population (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.