Venturia orni sp nov., a species distinct from Venturia fraxini, living in the leaves of Fraxinus ornus

Venturia fraxini Aderh. s.l. is an endophytic fungus in the leaves of different ash species like Fraxinus excelsior and F. ornus. This study shows that the Venturia species on F. ornus is not conspecific with V. fraxini s.s., but is a closely related species which is described as a new species: Venturia orni sp. nov. The two species distinctly differ morphologically and genetically. In contrast to V. fraxini, V. orni constantly lacks setae lining the ostiolum of the pseudothecia. In addition, the two species differ significantly and constantly in the sequences of the internal transcribed spacer (ITS) region and the genes coding for calmodulin, elongation factor EF-1 alpha, and beta-tubulin. Using the same molecular markers, another unknown endophytic Venturia species was discovered on F. ornus. However, this species never sporulated and, thus, a description of its morphology was not possible. Venturia fraxini and V. orni are host-specific and infect only F. excelsior and F. ornus, respectively, although the two hosts are sympatric at all examined sites. Venturia orni is abundant and exhibits high genetic and morphological variability, also in F. ornus planted as ornamentals outside its native range. This study indicates that Fraxinus spp. host an undiscovered wealth of fungal diversity.