Evaluation of Resistance to Ergot, Caused by Claviceps purpurea, in Kentucky Bluegrass, Based on Incidence and Severity Estimates

Abstract

Ergot, caused by Claviceps purpurea, is an important disease of Kentucky bluegrass grown for seed. Resistance is a preferred means of disease control, although approaches to evaluating ergot resistance in Kentucky bluegrass are not well established. A large scale disease assessment trial was established to compare within-year and year-to-year variability among measures of ergot incidence or severity in Kentucky bluegrass and to determine the most efficient approaches for cultivar evaluation. The susceptibility of 104 Kentucky bluegrass cultivars (78 commercial and 26 experimental) to ergot was assessed, based on percentage of panicles with sclerotia (incidence), sclerotia per panicle (severity), percentage of seeds replaced by sclerotia, or percentage of sclerotia among seed by weight. Cultivar ranking for susceptibility within years was similar for all methods of ergot assessment. Yearly mean incidence of ergot among cultivars ranged from 1.0 to 97.5% for susceptible cv. HV102 to 0.0 to 2.5% for resistant cv. Huntsville, with remaining cultivars distributed between the extremes. Yearly mean values of ergot incidence and severity differed among years. Much of this variability was due to days with rain during the period from flower initiation to maturity (period of susceptibility). Disease incidence was correlated (P ≤ 0.05) with days with rain in 22 of the cultivars. Duration of flowering was correlated (P ≤ 0.05) with ergot incidence in 11 cultivars. Results from this study suggest that variability in host and environment would likely offset any gain in precision of severity data. In large trials in particular, collection of incidence data (percentage of panicles with ergot) would provide the most timely and efficient means for ergot assessment.