Linkage Analysis Detects the Eyespot Resistance Gene Pch2 On Cappelle Desprez Chromosome 7A.

Recombinant substitution lines, derived from the cross Chinese Spring (CS) by Cappelle Desprez chromosome 7A substitution line (CS/CD7A), were evaluated for response to infection with β-glucuronidase (GUS)-transformed Oculimacula acuformis and O. yallundae. Seedlings were inoculated at the two-leaf stage with conidia (1X10⁵ conidia per ml) and evaluated for disease severity 8 weeks later. Using GUS expression as a measure of fungal colonization of the plants, we found evidence of a QTL for resistance to O. acuformis in two separate experiments (LOD = 2.7 and 6.7 at 305 and 289 cM, respectively), which was equivalent in location to that for resistance to O. yallundae (LOD = 13.2 and 11.4 at 289 and 304 cM, respectively).  Using a visual disease scoring system, peak LOD scores were 4.3 at 292 cM and 6.0 at 307 cM for O. acuformis and 3.8 at 304 cM for O. yallundae. Nearest-marker variation accounted for 10.8% to 38.9% of phenotypic variation. Phenotypic variation was also accounted for by pathogen species (p <0.0001), experiment-within-species (p <0.0001) and line by experiment-within-species interaction (p =0.002 for the GUS assay and p <0.0001for the visual scores). These results suggest that Pch2 confers some level of resistance at the seedling stage against both eyespot pathogens.