Studies on Resistance to Biotic and Abiotic Stresses in Wheat

This investigation was focused on the assessment of genetic diversity for resistance to stem rust and stripe rust in an international wheat nursery, genetic characterisation of adult plant stripe rust resistance in Australian wheat cultivar Sentinel, understanding of genetic relationship between two stem rust resistance genes (Sr36 and Sr39) located on chromosome 2B and assessment of genetic diversity for physiological traits among a set of wheat landraces. Ten seedling stem rust resistance genes (Sr8a, Sr8b, Sr9b, Sr12, Sr17, Sr23, Sr24, Sr30, Sr31 and Sr38) and seven stripe rust resistance genes (Yr3, Yr4, Yr6, Yr9, Yr17, Yr27 and Yr34) were postulated either singly or in combinations in an international wheat nursery. Genotypes carrying uncharacterised resistance for stem rust and stripe rust against the Australian rust flora were identified for genetic analysis. Three consistent QTL (QYr.sun-1BL, QYr.sun-2AS and QYr.sun-3BS) were demonstrated to condition high level of adult plant stripe rust resistance in Sentinel. QYr.sun-1BL, QYr.sun-2AS and QYr.sun-3BS explained on an average 18.0%, 15.6% and 10.6% variation in stripe rust response, respectively. Additive nature of three QTL to condition high level of stripe rust resistance was demonstrated through comparison of recombinant inbred lines (RILs) carrying these QTL in all different combinations. Detailed characterisation of these loci will be performed. Stem rust tests on F3 populations involving Sr39 on a large and a shortened Aegilops speltoides translocation with Sr36 on a Triticum timopheevi segment showed complete repulsion linkage. The molecular cytogenetic analysis however indicated that these can be recombined using large F2 population. Significant variation for water-use efficiency related physiological traits was observed among wheat landraces. Genotypes with low and high mesophyll conductance, stomatal conductance and other physiological attributes will be useful in designing crosses to achieve high water-use efficiency in future wheat cultivars