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Title: Transfer of quantitative trait loci for heat tolerance from Triticum durum – Aegilops speltoides introgression lines to bread wheat (Triticum aestivum L.) using marker assisted selection and QTL mapping for disease resistance
Authors: Dhillon, Guriqbal Singh
Supervisor: Das, Niranjan
Chhuneja, Parveen
Keywords: Wheat;Heat tolerance;QTL;Ae. speltoides;Disease resistance;QTL mapping
Issue Date: 12-Apr-2022
Abstract: Wheat is one of the major food crops providing 21% of calories and proteins to the world population. Wheat yields are being hampered by losses induced by numerous biotic and abiotic stresses. The majority of modern-day spring wheat cultivars developed in India are vulnerable to severe temperature stress, particularly during reproductive phases. The most likely option for mitigating the impacts of global warming on wheat yield is to breed for heat-tolerant genotypes. Using marker assisted selection, seven heat tolerance QTLs were transferred to three distinct hexaploid backgrounds using Triticum durum–Aegilops speltoides backcross introgression lines (DS-BILs). A total of 164 BC2F3 progenies with various QTL combinations were developed, and 40 of these progenies were tested in replicated trials over the course of two years in both normal (OE) and heat stress conditions (HSE). Phenotypic evaluation and heat tolerance index (HTI) analysis over two environments showed that grain filling duration, spikelets/spike, tiller number, thousand grain weight, and yield were enhanced due to the introgression of heat stress tolerance QTLs. Progenies pauHTIL_10, 11, 12, 33, and 34 have shown higher yield than tested cultivars under OE with pauHTIL_10, 11, and 12 showed yields higher than 2.0 kgs/plot under OE and pauHTIL_14 showed the highest yield of 1.6kg/plot under HSE. The progenies developed during this study can further be used for developing heat-tolerant wheat varieties. Likewise, biotic stressors produced by diseases such as rusts and powdery mildew have a substantial economic impact on production. Because the causative organisms are always evolving, the search for novel genes/quantitative trait loci (QTLs) for resistance to regulate the impact is never-ending. At both the seedling and adult plant stages, DS-BILs were screened for stripe rust and powdery mildew. At the adult plant stage, DS-BILs demonstrated full to moderate resistance, with variable resistance and susceptibility at the seedling stage. For QTL mapping, 1095 single-nucleotide polymorphisms (SNPs) were identified on 14 chromosomes of T. durum utilising genotyping by sequencing. Using a stepwise regression-based likelihood ratio test for additive effect of markers and single-marker analysis, eleven unique QTLs for resistance were identified across six chromosomes (chr1B, chr2A, chr2B, chr3B, chr6B, and chr7B), four QTLs for field mixture of stripe rust pathotypes, two QTLs for stripe rust pathotype 78S84, and five QTLs for field mixture of powdery mildew pathotypes Eleven DS-BILs carrying multiple QTLs have been identified, which will be useful in transferring resistance to susceptible cultivars in order to develop all-stage resistant elite cultivars where QTL for stripe rust resistance QYrAs.pau-2A.1 (LOD 3.8, PVE 24.51 linked to SNP S2A_16016633) and QTL for powdery mildew resistance QPmAs.pau-6B (LOD 3.2, PVE 17.75 linked to SNP S6B_26793381) are major targets of the transfer. Also, putative candidate genes liked to the SNPs of the mapped QTLs were identified which would help in studying the function pathways or modes of action of the associated genes.
Description: PhD thesis on plant biotechnology
Appears in Collections:Doctoral Theses@DBT

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