Eggplant Fruit Periderm Firmness Correlated with Resistance to Phytophthora nicotianae

Abstract

Worldwide, Phytophthora nicotianae and Pythium aphanidermatum are the Phytophthora and Pythium species most frequently reported on eggplant ( Solanum melongena). Both species were identified on the fruit of several eggplant cultivars grown in Charleston, South Carolina, in spring 2018. The objectives of this study were to determine whether seven cultivars, each representing a different fruit type, differed in susceptibility to Phytophthora nicotianae and whether periderm or flesh firmness or fruit density was associated with differences. Eggplant fruit were inoculated with colonized agar plugs and incubated for 4 days at high relative humidity. Japanese eggplant cultivar Millionaire had a greater incidence of fruit infection, wider lesion diameter, and greater percentage of lesion area with pathogen growth than the six other cultivars. Patio Baby, an Indian type, and Fairy Tale, a graffiti type, had the lowest incidence compared with 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) could also limit mycelial growth and sporangial production. Growers might need to apply oomycete-specific fungicides registered on eggplant more frequently to Japanese cultivars than to cultivars that produce graffiti- or Indian-type fruit.