Microfungi associated with dying quiver trees (Aloidendron dichotomum) in South Africa

Quiver trees (Aloidendron dichotomum) are large iconic succulent plants found in arid areas of southern Africa. These trees have been observed suffering from die-back symptoms for many years. Various environmental and abiotic factors have been investigated as possible causes of the symptoms. However, biotic causes, especially microfungi that commonly cause die-backs in trees, have never been considered. During a routine disease survey, symptomatic stems and roots of the dying trees were collected in the Cape Province, South Africa. Isolations were made from tissues at the leading edges of the lesions on symptomatic stems and roots, and the resulting fungi were identified using morphological characteristics and DNA sequence data of four loci (LSU, SSU, ITS and β-tubulin). Five species were identified: Paecilomyces formosus , Phaeoacremonium ( Pm. ) parasiticum , Pm. luteum , Xylogone sphaerospora , and the newly described Coniophoma aloidendri gen. et sp. nov . Three species, Pm. parasiticum and C. aloidendri from this study and Alanphillipsia ( Ala. ) aloes were tested for their pathogenicity on A. dichotomum plants in a greenhouse trial. All three species gave rise to lesions significantly different in size from the controls. The Pm. parasiticum strains showed larger necrotic lesions than C. aloidendri and Ala. aloes . However, none of the isolated fungi were aggressive or are known as primary pathogens, and the cause of the die-back on symptomatic trees remains to be determined.