Twelve peanut (Arachis hypogaea L.) genotypes of the Spanish botanical type and two of the Valencia botanical type were compared for reaction to the soil-borne pathogen, Cylindrocladium crotalariae (Loos) Bell & Sobers, that causes Cylindrocladium black rot (CBR) in peanuts. In Virginia, experiments were conducted in three fields (two in 1974 and one in 1975) with a history of severe CBR in previous peanut crops. The Spanish genotypes included all current cultivars grown commercially in the United States. Valencia genotypes (PI 355982 and 355987) were included as reference standards because of their known susceptibility to CBR.

Differences among genotypes were significant on the bases of percent diseased plants and visual scores of root and pod damage at each field and combined across fields. Differences also were significant among fields for percent diseased plants and pod damage score and for the genotype by field interaction for percent diseased plants. All Spanish genotypes were significantly lower in percent diseased plants than the Valencia checks. Pod and root damage scores indicated that different genetic mechanisms might control pod and root resistance to CBR. A high degree of resistance is available in Spanish genotypes, but critical progeny selection for both pod and root resistance might be necessary for transfer of resistance in successive generations of a breeding program.