| Dollar spot caused by Sclerotinia homoeocarpa F. T. Bennett is the most economically important turf disease on golf courses in North America. Dollar spot resistance in creeping bentgrass (Agrostis stolonifera L., 2n=4x=28) cultivars would greatly reduce the costs and environmental impacts of fungicide application. Host resistance is an alternate disease management strategy, but not much work has been done to understand dollar spot resistance. Therefore, in this study, quantitative trait locus (QTL) analysis was used to determine the location, number and effects of genomic regions associated with field resistance to dollar spot in creeping bentgrass. At first, greenhouse pathogenicity experiments were performed, and a significant difference in response of bentgrass clones and cultivars to S. homoeocarpa isolates was detected at the species, cultivar, and clone levels. The isolates showed significant differences in levels of aggressiveness, but a lack of isolate by cultivar interaction was also noted. The next step towards QTL mapping was to develop a genetic mapping population having the F1 full-sib structure from the cross between the heterozygous creeping bentgrass clones '372' and '549'. Later, this '549x372' population was used for constructing a genetic linkage map consisting of 14 linkage groups, and also for dollar spot evaluations conducted in the field over two years using a single S. homoeocarpa isolate. Dollar spot resistance seemed to be inherited quantitatively with broad sense heritability estimated at 0.86. Using the field data, we detected one QTL with large effect on linkage group 7.1, with LOD values ranging from 3.4 to 8.6 and explaining 14% to 36% of the phenotypic variance. Several QTLs specific to rating dates, locations and years were also detected. The high significance of the QTL on LG 7.1 at a sample size of 697 (P < 0.0001), along with its consistency across locations, years and rating dates, indicated that it is stable over environments. RAPD marker 3.AW 10.650 was tightly linked to this QTL, and it was converted to a robust PCR-based sequence characterized amplified region (SCAR) marker. The SCAR marker associated with dollar spot resistance in creeping bentgrass will facilitate selecting resistant genotypes via marker assisted selection. |
