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

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Abstract
Three approaches were used to estimate peanut yield loss due to Cylindrocladium black rot [C. crotalariae] for 2 commercial cultivars and 2 advanced-generation breeding lines which were evaluated in 10 field trials in 4 North Carolina [USA] counties in 1980, 1981 and 1982. Results from trials in stratified fields and established plots, and from Cylindrocladium black rot simulations, were similar for a highly susceptible commercial cultivar (Florigiant), a moderately resistant commercial cultivar (NC 8C), and a highly resistant breeding line (NC 18229). A critical-point model for predicting incidence of Cylindrocladium black rot approximately 1 wk before digging explained disease incidence-yield relationships when yield was expressed as the percentage of the maximum yield at a location. Critical-point models for ''Florigiant'', ''NC 8C'' and ''NC 18229'' were: Y = 98.8-72.7 X(r2 = 0.84); Y = 100.2-74.5 X(r2 = 0.79); and Y = 98.3-66.6 X(r2 = 0.57), respectively, in which Y = predicted percentage maximum yield and X = incidence at the critical rating date. In trials where epidemics developed naturally, mean incidence 1 wk before digging ranged from 0.21-0.74, 0.17-0.53 and 0.13-0.33 and mean predicted yield loss ranged from 15-53%, 13-40% and 9-22% for ''Florigiant'', ''NC 8C'' and ''NC 18229'', respectively. A single critical-point model was not a applicable over locations for ''NC 18016'', which appeared to be less agronomically stable than the other lines evaluated in this study.