Use of digital image analysis to identify Rhizoctonia solani and Rhizoctonia zeae resistance in Festuca arundinacea plant introductions
Brown patch, caused by Rhizoctonia solani Kuhn, is an important disease on tall fescue (TF, Festuca arundinacea Schreb, synonym Schedonorus phoenix (Scop.) Holub). Rhizoctonia zeae Voorhees, a related pathogen, causes similar symptoms. Confusion over which Rhizoctonia species is causing symptoms and subjective visual evaluations of disease severity may contribute to variability in observed BP resistance of TF cultivars at multiple locations. The objectives of this study were to develop an objective digital image analysis (DIA) method for evaluating disease and to use DIA to screen tall fescue plant introductions (PIs) for resistance to R. solani and R. zeae. There was a strong correlation (r2 = 0.97) between actual disease severity, measured by applying lesioned tissue of a known area to healthy leaves, and DIA calculated disease severity using scanned images of individual leaves (DIA-IL). The accuracy and precision of visual evaluations and DIA evaluations of entire plants (DIA-WP) were evaluated using DIA-IL as a standard of accuracy. Accuracy of DIA-WP was not significantly different from visual evaluation accuracy. Precision was significantly higher for DIA-WP. Evaluation of PIs and putatively BP resistant TF cultivars for resistance to R. solani and R. zeae using DIA-WP identified clones within each PI that ranked high for resistance to R. solani or R. zeae. No clones were identified with high resistance to both R. solani and R. zeae. Improved precision of DIA evaluation methods and inclusion of R. zeae in BP resistance breeding may decrease variability of TF cultivar performance across locations.