Parasitism and measurement of damage to Fusarium oxysporum by species of Melanospora, Sphaerodes, and Persiciospora

Five pyrenomycete isolates found in association with different form species of Fusarium oxysporum were evaluated for their in vitro ability to parasitize the watermelon wilt pathogen (IF. oxysporum f. sp. niveum). Several assays were also developed that attempted to measure damage to the wilt pathogen directly in culture. The pyrenomycetes used for pathogenicity and parasitism tests included three isolates of Sphaerodes retispora var. retispora, and one each of Melanospora zamiae and Persiciospora moreaui. A collection of 24 different isolates of F. oxysporum was employed to define a parasitic host range for this group of pyrenomycetes within the species oxysporum. The ability to sporulate on the Fusarium hosts was the primary criterion used for establishing host ranges. Results indicated that all five isolates were capable of parasitizing the wilt pathogen, but P. moreaui was the only one that caused no detectable damage in both the aerial hyphal reduction and growth inhibition assays. Melanospora induced significant damage with the growth inhibition assay only. Significant differences were observed among and between the pyrenomycetes and the different form species in terms of ability to parasitize and reproduce.