ASSESSMENT OF RESISTANCE TO RHIZOCTONIA-SOLANI IN TALL FESCUE BASED ON DISEASE PROGRESS AND CROP RECOVERY

Cultivars of turf-type tall fescue were assessed, in a controlled environment and in the field, for resistance to Rhizoctonia solani, the cause of brown patch or Rhizoctonia blight. Assessments were based on areas under disease progress curves (AUDPC) and AUDPC plus areas under crop recovery curves (AUCRC). Values of AUDPC were calculated from estimates of percent necrotic foliage during epidemics of brown patch with durations of 3-8 wk in the field or 8 days in a growth chamber. Values of AUCRC were calculated from postepidemic estimates of percent necrotic foliage over 4 wk in a greenhouse or 4-8 wk in the field. Thirty-five cultivars were separated into two groups (highly susceptible or moderately susceptible) on the basis of AUDPC values derived from epidemics of brown patch in the growth chamber. The ranking of cultivars according to AUDPC in the growth chamber was not significantly correlated with rankings in the field in 1990 (r = 0.31, P = 0.17) or 1991 (r = 0.58, P = 0.09). On the basis of relative susceptibility of cultivars to R. solani, however, correlation coefficients between results from the growth chamber vs. the field were r = 0.75, P = 0.001 and r = 0.62, P = 0.07 in 1990 and 1991, respectively. In all the studies, rankings of cultivars based on AUDPC were significantly (P less-than-or-equal-to 0.05) correlated with rankings based on AUDPC + AUCRC.