A Critical-Point Yield Loss Model for Cylindrocladium Black Rot of Peanut

Groundnut yield losses due to C. crotalariae were estimated for 2 commercial cultivars and 2 advanced-generation breeding lines which were evaluated in 10 field trials in 4 N. Carol. counties in 1980, 1981 and 1982. Results from trials in stratified fields and established plots, and from C. black rot simulations, were similar for a highly susceptible commercial cultivar (Florigiant), a moderately resistant one (NC 8C) and a highly resistant breeding line (NC 18229). A critical-point model for predicting incidence of C. black rot c. 1 wk before digging explained disease incidence-yield relationships when yield was expressed as the percentage of the max. yield at a location. Critical-point models for Florigiant, NC 8C and NC 1229 were obtained. In trials where epidemics developed naturally, mean incidence 1 wk before digging were 0.21-0.74, 0.17-0.53 and 0.13-0.33 and mean predicted yield loss 15-53%, 13-40% and 9-22% for Florigiant, NC 8C and NC 18229, respectively. A single critical-point model was not applicable over locations for NC 18016, which appeared to be less agronomically stable than the other lines evaluated in this study