First Report of Nigrospora sphaerica Causing Leaf Spots on Chinese Wisteria: A New Host of the Pathogen

Chinese wisteria, Wisteria sinensis (Sims) DC., is a woody, twining vine and is commonly cultivated as an ornamental for its foliage and striking, drooping racemes of white, pink, or lavender sweet pea-like flower. Distinct leaf spots were observed in several gardens, retail nurseries, and parks located in Hatay Province since May 2009. The primary infection zones are frequently observed on the leaf margins and apices, brown, up to 2 mm in diameter, and often surrounded by a yellow zone. Foliar symptoms are characterized by grayish, round, semicircular or irregular-shaped, numerous spots (up to 9 mm in diameter) with dark brown borders and the appearance of black, granular structure within the dead leaf tissues. A fungus was consistently isolated from symptomatic tissues on potato dextrose agar (PDA). Fungal colonies were initially white, becoming light to dark gray with the onset of sporulation with black, spherical to subspherical single-celled conidia (15 to 18 × 12 to 15 μm), which were borne on a hyaline vesicle at the tip of the conidiophore. These characteristics agree with published descriptions of Nigrospora sphaerica (Sacc.) E.W. Mason 1927 (1,3). To fulfill Koch's postulates, a conidial suspension (10⁶ conidia per ml) collected from PDA cultures was used to spray inoculate leaves of potted 3-year-old Chinese wisteria plants. Inoculated plants were kept for 48 h in polyethylene bags and maintained in a controlled environment chamber at 20°C with a 12-h photoperiod. The bags were removed after 3 days. In addition, five 3-year-old plants were sprayed with sterile water to serve as controls. After 14 to 20 days, inoculated leaves showed infection symptoms similar to those observed on naturally infected leaves with N. sphaerica. The pathogen was reisolated from the margins of necrotic tissues, but not from the controls. Although N. sphaerica is frequently encountered as a secondary invader or as a saprophyte on many plant species, this fungal agent is also known as a leaf pathogen on several hosts worldwide (2,4). To our knowledge, this is the first report of N. sphaerica as a leaf pathogen of Chinese wisteria in Turkey or worldwide. References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CMI, Kew, Surrey, UK, 1971. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory. Online publication. ARS, USDA. Retrieved 28 October from http://nt.ars-grin.gov/fungaldatabases/ , 2010. (3) P. M. Kirk. IMI Descr. Fungi Bact. 106:1056, 1991. (4) E. R. Wright et al. Plant Dis. 92:171, 2008.