Dischloridium gloeosporioides on Annona muricata: a new pathogen in Brazil

Soursop (Annona muricata), a plant member of the Annonaceae, is a fruit tree indigenous to central and northern South America. In Brazil, it is commonly cultivated in the north and northeastern states for commercial exploitation of fruits and pulp. Over five million fruits are harvested each year in Brazil. During a survey of plant diseases in October 2007 in Pacaraima (RoraimaState), trees of A. muricata were observed exhibiting necrotic dark brown circular leaf spots, 0.7-3.0 cm wide, frequently with concentric circles (Fig. 1). All plants surveyed presented symptoms in high severity. Microscopic examination revealed an association with a fungus that displayed amphigenous fructification, predominantly on the abaxial leaf surface, and stromata 21-83 μm in diameter. Conidia were solitary, short subcylindrical to ellipsoid, 10-21 x 2.6-5.2 μm, base rounded to subtruncate, hyaline, smooth, and non-septate (Fig. 2). Conidiophores in fascicles were erect, 63-101 x 2.6-5.2 μm, brown, smooth, 1-5 septate, and unbranched. Conidiogenous cells were monophialidic and inconspicuous, 7.8-34 x 2.6 μm (Fig. 3-4). Based on these features, the lesion-associated fungus was identified as Dischloridium gloeosporioides (Schubert & Braun, 2005). A specimen was deposited at the herbarium of the Universidade Federal de Viçosa (VIC 30548).

To perform Koch’s postulates, 30-day-old soursop plants cultivated in the greenhouse were sprayed with a conidial suspension (10³ conidia per ml) until runoff. After inoculation, plants were covered with plastic bags for 48 hours to simulate a dew chamber and kept in a greenhouse. Control plants were sprayed only with water. Two weeks after inoculation, leaf lesions developed only on the inoculated plants from which the pathogen was re-isolated.

Previously denominated Cladosporium gloeosporioides, D. gloeosporioides has a known restricted distribution being reported only in the United States and associated with plants belonging to the genus Hypericum (Saccardo & Sydow, 1899; Schubert & Braun, 2005).It is reported to cause lesions on leaves and stems of H. stans (= Ascyrum stans), H. mutilum and H. virginicum. Therefore, this is the first report of D. gloeosporioides in Brazil.