Sanjiv Gupta

The development of array-based high-throughput genotyping methods created significant opportunities to increase the number of genetic populations for linkage analysis. In the present study, a strategy was proposed for mapping QTLs (quantitative trait loci) based on DArT (diversity arrays technology) genotyping system. A consensus linkage map was constructed with both DArT and SSR markers by utilizing a subgroup DH population, and a second linkage map was constructed with SSR markers alone and a more extensive full DH population. Resistance to barley net-type net blotch disease was analyzed using the subpopulation data with the high-density consensus linkage map and the full-population data with the low-density SSR linkage map, respectively. Two interactive QTLs were detected either by the sub- or full population. Simulation studies were conducted to validate the strategy presented in this chapter. In addition, a computer program written in C++ is freely available on the web to deal with the data files. Based on both real data analysis and simulation studies, we concluded that high-density molecular markers, small population size, and precise phenotyping can improve the precision of mapping major-effect QTL and the efficiency of conducting QTL mapping experiment.

Race-specific resistance genes (Rph) for leaf rust (Puccinia hordei) are often overcome by new pathotypes with matching virulence. Adult plant resistance (APR) is considered potentially more durable for controlling barley leaf rust. Previous studies established that the cultivar Pompadour carried APR to leaf rust. A doubled haploid population (DH) of 200 lines developed from a cross Pompadour/Stirling, and the parents were phenotyped for leaf rust resistance at five field experimental sites in three agricultural zones in Australia. Using a linkage map of SSR and DArT molecular markers, a major QTL associated with the leaf rust resistance was identified on the short arm of chromosome 5H. This QTL explained between 31% and 86% of the phenotypic variation for the APR at different sites. A PCR-based molecular marker was developed and mapped at 1.6 cM to the APR gene. The present study provides new genetic material and a molecular tool for breeding new varieties with adult plant leaf rust resistance using marker-assisted selection.