Genetic Diversity of Sclerotinia Homoeocarpa Delineated by AFLP and Vegetative Compatibility

Sclerotinia homoeocarpa F.T. Bennett is the causal agent of dollar spot disease that infects turfgrasses of golf courses in Tennessee as well as around the world. Dollar spot taints the uniformity and aesthetic value of putting greens, therefore causing a serious problem on golf courses. Isolates were collected from across Tennessee and northern Mississippi and tested for fungicide resistance by Pamela Baird. Genetic diversity between the isolates was investigated by vegetative compatibility, conserved gene sequences, and AFLP (amplified fragment length polymorphism) to reveal associations with fungicide resistance. Vegetative compatibility tests were completed by pairing six tester strains with Tennessee and northern Mississippi isolates on potato dextrose agar. Additionally, isolates from all locations were paired against each other. After observations of the mycelial interaction zone, isolates were generally compatible within a location and incompatible between locations. Some isolates were delineated into vegetative compatibility groups (A, B, and D), and fungicide resistance could not be associated with a particular vegetative compatibility group. Genetic similarities of isolates at the vegetative compatibility level could be attributed to founder effects. Conserved gene sequences of the CPS region of CAD, EF1-α, β-tubulin, and ITS indicated 100% homology between isolates. The ITS region of Sclerotinia spp., Rutstroemia sp., and Lanzia sp. were compared using parsimony analysis to reveal S. homoeocarpa could be more genetically related to Rutstroemia spp. than Sclerotiniaspp. AFLPs were detected by capillary gel electrophoresis, and calculated similarity indices indicated 86-100% similarity between the 60 isolates. Pairwise differences ranged 0-14 implying some isolates were completely identical at all loci. Isolates did not cluster according to fungicide resistance during UPGMA analysis, but did appear to cluster according to vegetative compatibility group and location. Although associations could not be made between molecular markers and fungicide resistance, links between vegetative compatibility and AFLP markers provide a foundation from which other studies could be performed.