Quantification of Large Patch Disease Caused by Rhizoctonia Solani (Kühn) On Zoysiagrass in Controlled Environmental Conditions Using Visual Rating, Dry Tissue Weight and Digital Image Analysis.

 

The fungal pathogen Rhizoctonia solani (Kühn), anastomosis group (AG) 2-2- LP, is the causal agent of the disease large patch.  Symptoms of large patch manifest as distinct water-soaked orange/brown lesions on the leaf sheath, which pulls off easily from the crown; little to no foliar blighting or lesions have been observed in case of large patch. The objective of this study is to accurately assess the pathogenicity of seven fungal isolates belonging to AG 2-2-LP on seven different Zoysiagrass (Zoysia japonica Steud.) cultivars.  In a preliminary work, plugs of cv. El Toro were vegetatively divided into three replicates (50mm² polygon) and maintained in the greenhouse for two-months prior to inoculation. Each replication was separately challenged with all seven fungal isolate in controlled environmental conditions maintained at near 100% humidity, 21-23°C temperature, and lighting at ca. 113 µmols^-1m^-2. Tissue dry weights and digital pictures were taken pre vs. post inoculation for each plug, including the non-inoculated control. Digital pictures were scanned using Assess 2.0 Image Analysis Software for Disease Quantification^®. Visual turfgrass quality ratings (1-9 best) and a “pull-test” to determine percentage of diseased sheaths per plug were preformed 14- days post inoculation. Dunnett’s one-tailed t- test was preformed on the data collected for various parameters to determine significant differences between inoculated and non-inoculated control.  Pearson correlation coefficient was preformed using SAS^® proc corr statement, showing a positive  linear relationship between tissue dry weights and digital imagery scanning (r=.90; p=.0001); tissue dry weights and visual quality rating  (r=.81; p=.0001); and digital imagery scanning and visual quality rating (r=.82; p=.0001).  Data showing disease assessment for six additional zoysiagrass cultivars will also be presented.