Eggplant Fruit Periderm Firmness Correlated with Resistance to Phytophthora nicotianae

Based on worldwide reports, Phytophthora nicotianae and Pythium aphanidermatum are the Phytophthora and Pythium species most frequently reported on eggplant (Solanum melongena). Both species were identified on fruit of several eggplant cultivars grown in Charleston, SC, in spring 2018. The objective of this study was to determine if seven cultivars, each representing a different fruit type, differed in susceptibility to Phytophthora nicotianae and if periderm or flesh firmness or fruit density was associated with differences. Eggplant fruit were inoculated with colonized agar plugs and incubated 4 days at high relative humidity. Japanese eggplant cv. Millionaire had a greater incidence of fruit infection, wider lesion diameter, and a greater percentage of lesion area with pathogen growth than six other cultivars. Patio Baby, an Indian type, and Fairy Tale, a graffiti type, had the lowest incidence compared to the other five cultivars and no pathogen growth in lesions. Periderm firmness was negatively correlated with incidence, lesion diameter, and diameter of pathogen growth within lesions (P ≤ 0.01). The significant correlations of lesion size with the size of pathogen growth suggest that the same characteristics that limit lesion expansion, e. g., some aspect of periderm firmness, also may limit mycelial growth and sporangial production. Growers may need to apply oomycete-specific fungicides registered on eggplant more frequently to Japanese cultivars than to cultivars that produce graffiti or Indian type fruit.