Comparative Analysis of Cylindrocladium Black Rot Resistance in Peanut: Greenhouse, Microplot, and Field Testing Procedures

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Abstract
Two promising advanced generation Virginia-type peanut breeding lines, NC 18016 and NC 18229, and 2 commerical Virginia-type cultivars, NC 8C and Florigiant, were evaluated for Cylindrocladium black rot (CBR) resistance in greenhouse, microplot and field trials. NC 18016 was slightly more resistant than NC 18229; NC 8C was intermediate in resistance between the highly susceptible cultivar, Florigiant, and the resistant breeding lines, NC 18229 and NC 18016. Interpretations of results were slightly different when greenhouse, microplot and field testing procedures were compared. In greenhouse and microplot evaluations, substantial differences in CBR resistance among cultivars Florigiant and NC 8C, and the 2 breeding lines were apparent, but the more subtle difference between NC 18016 and NC 18229 was not detected. In field evaluations, NC 18016 was more resistant than NC 18229 when the data were categorized by inoculum density. Results from field trials suggested that much of the variation in field evaluations of CBR resistance is due to the clustered spatial distribution of microsclerotia of Cylindrocladium crotalariae in naturally infested soils. Evaluations of microsclerotial production in roots of infected plants were highly variable. In general, numbers of microsclerotia per gram of root increased with root rot rating; however, reduced microsclerotia production apparently would be an extremely difficult trait for which to select in a breeding program.