Thesis Presentation on Molecular Mapping and Genetic Characterisation of Rust Resistance in Wheat

mamtaThis Friday on 27/11/2015 at 10 am at the RDC Yusipang Conference Hall there will be a Thesis Presentation by Mamta Chhetri on Molecular Mapping and Genetic Characterisation of Rust Resistance in Wheat.

Abstract: The first aspect of this investigation covers QTL analysis of triple rust resistance segregating among W195/BT-Schomburgk Selection (BTSS) recombinant inbred line (RIL) population. Three QTL each for stripe rust (QYr.sun-3BS; QYr.sun-4DL; QYr.sun-7AS), leaf rust (QLr.sun-2BS; QLr.sun-3BS; QLr.sun-4DL) and stem rust (QSr.sun-2BL; QSr.sun-4DL; QSr.sun-6AS) resistance were identified. QYr.sun-3BS, QYr.sun-4DL, QLr.sun-4DL and QSr.sun-4DL were contributed by W195, whereas other QTL were contributed by the alternate parent BTSS.

QTL analysis was followed by detailed characterization of the resistance loci. QYr.sun-3BS explained 34-59% phenotypic variation and was chosen for characterisation at different growth stages and temperature regimes. It expressed well at the 4th leaf stage at a higher than normal temperature (21±2 ºC) for stripe rust growth. This locus was formally named Yr58. The co-located QTL for stripe rust, leaf rust and stem rust resistance in chromosome 4DL was demonstrated to correspond to the pleiotropic adult plant resistance (APR) locus Yr46/Lr67/Sr55 through linked marker genotyping. Yr58 produced infection type 23C when present singly and in the presence of Yr46 it produced infection type; 1N.These results demonstrated the interaction of APR gene Yr46in improving expression of the middle stage resistance gene Yr58. QLr.sun-2BS and QSr.sun-6AS were confirmed to be Lr23 and Sr8a, respectively, through seedling tests using relevant pathotypes. QYr.sun-7AS, QLr.sun-3BS, QSr.sun-2BL appear to be unique APR loci and need to be characterised in detail.

Microsatellite markers sun474 and sun476 designed from genomic survey sequences (GSSs) co-mapped 2.4cM proximal to Yr58. These markers produced 210 and 208 bp fragments when genomic DNA of W195 was used. Both produced 200 bp products in BTSS. The absence of Yr58-linked alleles sun474210bp  and sun476208bp in a set of 17 Australian common wheat and two durum wheat cultivars demonstrated their usefulness in marker assisted selection of Yr58 in breeding programs.

A  GSS derived SSR marker sun471 co-segregated with Lr23 in W195/BTSS RIL population. This marker was genotyped on a Tamaroi/Bansi durum wheat RIL population and was mapped 0.6 cM distal to Lr23. Marker sun471 identified the presence and absence of Lr23correctlyamong a set of durum and common wheat genotype

Genetic analysis of stripe rust resistance in two landraces AUS27506 and AUS27894 from France and Spain, respectively, indicated the monogenic inheritance of stripe rust resistance. Considering similar seedling responses and linkage of same markers in bulked segregant analysis of both populations, AUS27506 and AUS27894 were crossed. Absence of stripe rust segregation among F3 families indicated presence of the same gene in AUS27506 and AUS27894 and the resistance locus was temporarily named YrAW4. A DArT-derived STS marker sun481 and a SNP marker IWB12294 flanked YrAW4 1.7cM proximally and 1.2 cM distally. None of 19modern cultivars amplified the YrAW4-linked alleles at these marker loci indicating their usefulness for marker assisted selection. Comparison of gene-marker associations of resistance genes previously located in chromosome 2BL, YrAW4 appears to be a new locus and a case for its formal naming has been submitted.

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