Phaeotheca dimorphospora sp.nov.: description et caractéristiques culturales

Abstract

An unknown fungus isolated from an elm branch and inhibitory against Ophiostoma ulmi in vitro is described as Phaeotheca dimorphospora sp.nov. This dematiaceous deuteromycete propagates by endoconidia released after exfoliation of chlamydospore outer wall, as in mother cells of the type species Phaeotheca fissurella. However, P. dimorphospora differs from the type species by producing hyaline secondary ameroconidia between the endoconidial masses. Other ameroconidia, similar to the secondary ameroconidia, are produced through the chlamydospore outer wall. The optimal growth temperature of P. dimorphospora is 23 °C, whereas it is 15.5 °C for the type species. On media containing a high dextrose concentration (30 g ∙ L−1), colonies of P. dimorphospora are gray and crustose and grow slowly, at least initially. Conversely, on media with a low dextrose concentration (5 or 10 g ∙ L−1) colonies have a faster growth rate and appear whitish or ivory and fluffy. Key words: Phaeotheca dimorphospora, diagnosis, inhibition, Ophiostoma ulmi, Dutch elm disease.