Genotype-Isolate Interaction for Dollar Spot Resistance in Seashore Paspalum.

Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is a major fungal disease that affects seashore paspalum (Paspalum vaginatum Swartz) and other turfgrass species.  Current management of this disease relies heavily on frequent fungicide applications, which has led to cases of fungicide resistance.  An alternate management strategy is host plant resistance, but more needs to be known about the pathogen and host interaction to incorporate this resistance into elite genotypes.  Five genotypes of seashore paspalum with dollar spot resistance differences were artificially inoculated with five isolates of S. homoeocarpa from three warm-season and one cool-season turfgrass species, and visually evaluated for disease expression (0-100%).  Significant differences among isolate treatments were found indicating varying levels of isolate virulence, irrespective of seashore paspalum genotype.  The general paspalum isolate (P1) was the most virulent isolate used in this study based on area under the disease progress curve (AUDPC) values.  A lack of race-specific interactions was indicated by no significance (p=0.3042) in genotype by isolate treatments.  Using this information, breeders should be able to use one or a few highly virulent dollar spot isolates to select for host plant resistance in seashore paspalum.