The pathogenicity of Gaeumannomyces incrustans on turfgrass Zoysia japonica

Abstract

The pathogenicity of the ectotrophic root-infecting fungus Gaeumannomyces incrustans on turfgrass Zoysia japonica 'Meyer 51' was examined in greenhouse, growth-chamber, and field assays. Symptoms of root infection (zoysia root rot) were observed in all three studies. In the greenhouse assay, the highest disease severity (percent root surface with lesions (mass necrosis), percent root surface with discoloration, and percent number of leaves with discoloration) was recorded after the longest incubation period (12 weeks). In growth-chamber assays, root-rot severity (percent root surface with lesions and percent root surface with discoloration) was the highest at 18 °C, while little or no injury was observed at 12 and 25 °C. In field assays, patch development was observed in only 3 of 20 inoculated field plots; however, 9 of the 20 plots had ectotrophic mycelium present, and G. incrustans was subsequently recovered from these plots. Gaeumannomyces incrustans is the causal agent of zoysia root rot, as Z. japonica enters and exits seasonal dormancy. Observations of radial expansion are also reported for naturally occurring patches, as well as disease severity ratings for selections of Zoysia spp. from entries in the National Turfgrass Evaluation Program inoculated with G. incrustans.