Microfungi associated with dying Euphorbia mauritanica in South Africa and their relative pathogenicity

Abstract

Euphorbia mauritanica is a succulent shrub that is indigenous to South Africa and widely distributed throughout the country. Dying plants have been observed in their natural habitat in the Northern and Western Cape Provinces of South Africa in recent years. Stems displaying lesions were collected and the emerging cultures were identified based on ITS, LSU, ACT, RPB2, TEF1 and/or TUB2 sequence data. Four filamentous fungi were consistently observed and isolated. One was identified as Alanphillipsia (Ala.) aloes, and the other three were new to science and are described here as Cytospora euphorbiicola sp. nov., Nothomicrosphaeropsis namakwaensis sp. nov. and Austrophoma (Aus.) euphorbiae gen. et sp. nov. These new species and Ala. aloes were the most commonly encountered, and their pathogenicity was tested on E. mauritanica plants in a greenhouse trial. All four species gave rise to lesions that were significantly larger than those associated with the controls, but they were not significantly different to each other. Although the lesions associated with the inoculations were well-developed, they did not give rise to plant death, suggesting that they are not responsible for the large-scale die-off of E. mauritanica in the field. The primary cause of the death of E. mauritanica in the studied area remains unknown and could be due to environmental factors such as has been found with the die-off of Euphorbia ingens in South Africa.