Arkoola nigra gen. et sp.nov. (Venturiaceae) causing black leaf blight of soybean in Australia.

Arkoola nigra gen. et sp.nov. (Venturiaceae) is described, causing black leaf blight of soybean in New South Wales. It forms a superficial black mycelial web on infected plants and penetrates the host from large appressoria, causing severe spotting and blighting of leaves, stems and pods. Ascocarps develop on dead fallen leaves and on detached leaves inoculated in culture. They are black, setose and contain large cylindrical bitunicate asci with pale greenish two-celled ascospores and abundant pseudoparaphyses. The connexion between ascosporic and mycelial states has been proved by pure culture studies, and plant inoculations reproduce the disease symptoms. It is transmitted to a limited extent with seed. A range of native legumes were infected in artificial inoculation tests. The relationship of A. nigra to other genera of Venturiaceae, its possible origin, host range and associated matters are discussed.