Pseudocercospora opuntiae sp. nov., the causal organism of cactus leaf spot in Mexico.

Pseudocercospora opuntiae is newly described from Opuntia spp. from Mexico, where it causes a serious disease of this host. Although P. opuntiae is morphologically similar to other members of the genus with pigmented conidia and conidiophores, and unthickened, not darkened conidiogenous scars, DNA sequence data of the ITS region revealed that it clusters distant from other species of Pseudocercospora within Mycosphaerella. These data support the assumption that Pseudocereospora is paraphyletic within Mycosphaerella