First Report of Guignardia psidii, an Ascigerous State of Phyllosticta psidiicola, Causing Fruit Rot on Guava in Venezuela

During August 2003, guava fruit (Psidium guajava L.) cv. Red Dominicana from Cojedes state in Venezuela showed circular, purple-to-brown lesions (0.5 to 1.0 cm) that spread over all surfaces and became black and shrunken on severely affected fruit. Symptomatic tissues were plated aseptically on potato dextrose agar (PDA). Colonies that were initially gray and turned black with age were consistently isolated. The fungus was characterized by dense, submerged, brown-to-black mycelium with septate hyphae. Ascocarps were perithecial, abundant, granulose, subglobose to cylindric obpyriform, solitary or aggregated, mostly unilocular with prominent long necks; ascocarp walls were stromatic, composed of several layers of cells, thick walled, and deeply pigmented on the outside. Asci were subclavate to cylindrical, stipitate, 44 to 84 × 7 to 9 μm, and eight-spored; asci walls were thick and bitunicate. Ascospores were unicellular, hyaline, guttulate, fusiform ellipsoid, widest in the mid-region with rounded ends and gelatinous plugs, and 12 to 17 × 4.5 μm. Conidiomata were pycnidial, intermixed among ascocarps, variable in shape, dark brown, solitary or aggregated, ostiolate, and with long necks up to 1 mm. Pycnidial walls were pseudoparenchymatic, multicellular, and composed of many layers of brown compressed cells. Conidiogenous cells were hyaline, subglobose to cylindrical, and smooth, and holoblastic. Conidia were hyaline, unicellular, obovate, 6 to 12 (7.5) × 5 to 8 μm, slightly truncate at the bases, rounded at apices, guttulate, and provided a gelatinous envelope and apical appendage. Appendages were hyaline, tubular, smooth, and 3.0 to 4.5 × 0.5 μm. The fungus is homothallic because single ascospores and single conidia developed ascigerous states. The ascigerous state was identified as Guignardia psidii (1) and the anamorph as Phyllosticta psidiicola (1,2). Pathogenicity tests were conducted on detached fruits inoculated with monosporic cultures. Pathogenesis and symptom development only occurred when a mixture of mycelium, ascospores, and conidia was used as inoculum. The fungus was reisolated from symptomatic fruit tissues. To our knowledge, this is the first report of Guignardia psidii, an ascigerous state of Phyllosticta psidiicola from guava fruits in Venezuela. References: (1) B. A. Ullasa and R. D. Rawal. Curr. Sci. 53:435, 1984. (2) H. A. van der Aa. Page 95 in: No. 5, Stud. Mycol., 1973.

Dothistroma Needle Blight, Caused by Dothistroma septospora, of Pinus spp. in Vermont

Dothistroma needle blight, caused by Dothistroma septospora (teleo-morph Mycosphaerella pini), is a serious foliage disease of pine species throughout the world. In the northeastern United States, the fungus has been reported from Pennsylvania, but not New York, New Jersey, or any of the New England states. It has been reported from the eastern provinces of Canada (Newfoundland, Quebec). During 1994 to 1998, stromatic conidomata consistent with descriptions of D. septospora were associated with needle blight symptoms on mature landscape pines at four locations (Jericho, Montpelier, Williamstown, Williston) and one Christmas tree farm (Barre) in Vermont. Pinus nigra was affected at four locations; P. mugo and P. ponderosa were affected at one location each. Severe foliar blight and defoliation occurred during successive years on P. nigra and P. mugo. Collections from each location and host were examined microscopically. Mean lengths and widths of 20 or more conidia from each of three collections of P. nigra (Barre, Montpelier, and Williston) were 2.3 × 25, 2.7 × 20, and 2.6 × 24 μm, respectively. Corresponding values for collections from P. mugo and P. ponderosa were 2.4 × 26 and 3.6 × 31 μm, respectively. All collections conformed to descriptions and illustrations of D. septospora (1). No ascigerous state was observed from 1994 to 1998. This is the first report of D. septospora in New England. Reference: (1) H. C. Evans. 1984. The Genus Mycosphaerella and Its Anamorphs Cercoseptoria, Dothistroma and Lecanosticta on Pines. Commonwealth Mycological Institute, Kew, England.