Heterothallism in Scedosporium apiospermum and description of its teleomorph Pseudallescheria apiosperma sp. nov.

Scedosporium apiospermum has traditionally been thought of as the anamorph of Pseudallescheria boydii (Microascaceae, Ascomycota), but recent molecular studies has demonstrated that they are different species. Since a teleomorph was not observed among isolates recently identified as S. apiospermum, we investigated whether this species could be heterothallic. In this study, 15 isolates of S. apiospermum were paired in all possible combinations, including self-pairings. Several combinations produced fertile ascomata typical of the genus Pseudallescheria, while all isolates were self-sterile. The isolates were grouped into two different mating types. Crosses among F1 progeny ascospores demonstrated a bi-allelic heterothallic mating system. The new species Pseudallescheria apiosperma, teleomorph of S. apiospermum, is proposed and described.