Crown rot, caused by Fusarium pseudograminearum, is an important disease of wheat in Australia and elsewhere. In order to identify molecular markers associated with partial seedling resistance to this disease, bulked segregant analysis and QTL mapping approaches were undertaken using a population of 145 doubled haploid lines constructed from '2-49' (partially resistant) x 'Janz' (susceptible) parents. Phenotypic data indicated that the trait is quantitatively inherited. The largest QTLs were located on chromosomes 1D and 1A, and explained 21% and 9% of the phenotypic variance, respectively. Using the best markers associated with five QTLs identified by 1

Abstract. We have tested the efficacy of putative microsatellite single sequence repeat (SSR) markers, previously identified in a 2-49 (Gluyas Early/Gala) × Janz doubled haploid wheat (Triticum aestivum) population, as being linked to partial seedling resistance to crown rot disease caused by Fusarium pseudograminearum. The quantitative trait loci (QTLs) delineated by these markers have been tested for linkage to resistance in an independent Gluyas Early × Janz doubled haploid population. The presence of a major QTL on chromosome 1DL (QCr.usq-1D1) and a minor QTL on chromosome 2BS (QCr.usq-2B1) was confirmed. However, a putative minor QTL on chromosome 2A was not confirmed. The QTL on 1D was inherited from Gluyas Early, a direct parent of 2-49, whereas the 2B QTL was inherited from Janz. Three other putative QTLs identified in 2-49 × Janz (on 1AL, 4BL, and 7BS) were inherited by 2-49 from Gala and were not able to be confirmed in this study. The screening of SSR markers on a small sample of elite wheat genotypes indicated that not all of the most tightly linked SSR markers flanking the major QTLs on 1D and 1A were polymorphic in all backgrounds, indicating the need for additional flanking markers when backcrossing into some elite pedigrees. Comparison of SSR haplotypes with those of other genotypes exhibiting partial crown rot resistance suggests that additional, novel sources of crown rot resistance are available.

The segregation of both high and low molecular weight glutenin subunits across 7 F1 wheat (Triticum aestivum L.) × maize (Zea mays L.) derived doubled haploid populations was examined. The F1 wheats used in each population were produced from parents of interest to Australian wheat breeding programs. The parents varied by up to 5 glutenin subunit loci. Examination of subunits individually within each population using a chi-square analysis revealed that all but 2 of the 26 pairs of alleles analysed fitted the expected 1 : 1 segregation ratio. Glutenin profiles were examined for each cross individually and all but one (Sonalika/Hartog) fitted the expected Mendelian segregation pattern. The analysis of allele distribution of the 6 glutenin loci across all 7 crosses showed all falling well within expected segregation ratios. Closer examination of parental lines and populations revealed irregularities which conflict with original assumptions and provide a valid explanation for the few segregation distortions observed. It is concluded that wheat × maize-derived doubled haploid populations represent a unbiased assortment of parental gametes on both arms of Group 1 chromosomes.