Development of a greenhouse method to evaluate peanut resistance to Athelia rolfsii

Peanut stem rot (also known as white mold), caused by the fungus Athelia rolfsii, is one of the most damaging soilborne pathogens for U.S. peanut production. The disease is mainly controlled by fungicides and by adopting cultivars with moderate resistance. Field evaluation is the main approach for evaluating plant resistance, but it is costly and labor-intensive. Reliable methods for in vitro or greenhouse evaluations are desirable. Greenhouse, growth chamber, and in vitro methods have been tried to assess resistance, but they generally do not correlate well with field results. In this study, we developed a reliable method to assess resistance to stem rot on peanut under greenhouse conditions: stem cuttings were taken from 60-day-old plants and placed into a cup filled with potting mix. Cuttings were inoculated with active A. rolfsii mycelial plugs above the soil line, with mycelium directly contacting the stem. Inoculated cuttings were put in a mist chamber to keep humidity high. Highly significant differences of disease resistance among genotypes were found at seven days after inoculation (P< 0.05). Moreover, evaluations done at 3, 5, 7, and 9 days after inoculation and AUDPC were significantly correlated with field evaluations of the same genotypes. This greenhouse assay is a step forward to more efficiently screen peanut germplasm for stem rot resistance.