Although good progress has been made internationally to understand tan spot (TS) (syn. yellow spot), caused by Pyrenophora tritici repentis, resistance in wheat, relatively few resistance genes have been identified in Australian germplasm. Under a current national project, major effort was made to identify novel resistance genes and develop a series of fixed lines, each carrying genes from 2 or 3 resistance sources in elite Australian backgrounds that can be used as parents in resistance breeding.
Two doubled haploid (DH) mapping populations Calingiri/Wyalkatchem (C/W) (247 DH lines) fixed for the ToxA-insensitivity allele tsn1 and IGW2574/Annuello (I/W) (97 DH lines) fixed for the ToxA-sensitivity allele Tsn1 were used in this study. The populations were screened for TS resistance at various growth stages, environments and national sites. Frequency distributions for TS severity traits were continuous. Major quantitative trait loci (QTL) were detected on chromosomes 2A and 1A. Each QTL had effects at various growth stages and in experiments conducted at various locations in Australia. QTL on 2A explained up to 29.2% of the genotypic variation in C/W (resistance contributed by Wyalkatchem). QTL on 1A explained up to 28.1% of the genotypic variation in I/A (resistance contributed by Annuello). These resistance loci were stacked along with tsn1 using single seed descent and marker assisted selection. Thirty two F5 lines were developed which are triple homozygotes at the three TS resistance loci and are also fixed for the vrn-1 locus.
Sixteen of these F5 lines were screened for TS resistance at various growth stages and environments in Western Australia. Lines expressed significantly higher resistance than parents and grandparents at both seedling and adult plant stages that was effective in various environments. These lines are important resources that can be used by breeders for rapid development of varieties with high levels of resistance.