Identification of Resistance in Festuca arundinacea Schreb Lines to Both Rhizoctonia solani Kuhn and Rhizoctonia zeae Voorhees Using Digital Image Analysis.

Brown patch, caused by the fungus Rhizoctonia solani Kuhn, is a major disease affecting tall fescue. Rhizoctonia zeae Voorhees, a related pathogen, presents similar symptoms, but is typically not included in the screening process when developing brown patch resistant cultivars. This, along with the subjectivity of visual disease severity evaluation methods, may contribute to the variability in brown patch resistance observed among available cultivars. The development and quantification of a digital image analysis (DIA) method were performed prior to this study. The objective of this study was to use DIA to evaluate tall fescue plant introductions (PIs) for resistance to both R. solani and R. zeae. This study included 15 PIs selected from the USDA germplasm database and 3 commercial cultivars with varying brown patch resistance. PIs were initially screened using conetainers containing 4 plants from each PI or variety. These were placed in a randomized complete block design, inoculated with either R. solani or R. zeae, and maintained within a closed chamber for 12 days at temperature and humidity ideal for pathogen development. PIs were screened twice per pathogen with each run containing 4 reps of each PI. Disease severity was measured using DIA and compared using ANOVA. Mean disease severity was not significantly different from the commercial cultivars for PIs 578712, 600801, 561430, 578715, 469244, and 598945 in the R. solani screen, and for PIs 561431, 561430, 578715, 598891, 469244, and W620487 in the R. zeae screen. The commercial cultivars had the lowest mean disease severity in each experiment. Mean disease severity ranged from 59-93% across R. solani runs and from 32-64% across R. zeae runs. Current work involves screening the PIs identified, using 20 seeds sampled from each PI, to evaluate the diversity of resistance to both R. solani and R. zeae that may be present in each PI.