Abstract
Response to oxalic acid was evaluated as an assay for screening peanut breeding lines for resistance to Sclerotinia blight caused by Sclerotinia minor. Detached stems of six runner- and seven Spanish-type peanut genotypes, varying in resistance to Sclerotinia blight, were placed in 0, 20, and 50 mM oxalic acid. Wilt severity and length of stem discoloration were rated 12, 18, and 24 hrs after immersion. Wilt and stem discoloration were not observed on stems placed in water (0 mM), but differences among entries were observed for some time intervals when placed in the 20 and 50 mM oxalic acid solutions. Susceptible runner cultivars exhibited the most severe wilt symptoms, but few differences in wilting were found among the Spanish genotypes. More differences in stem discoloration were observed among the Spanish peanuts than the runner entries, but length of discoloration did not appear to be correlated with field resistance. Oxalic acid appears to have some potential as a resistance assay for Sclerotinia blight in runner peanuts, but may have limited use for screening Spanish peanuts. Rapid and accurate methods for screening peanut breeding lines for resistance to Sclerotinia blight would accelerate progress in breeding for disease-resistant peanuts.