First Report of Clonostachys rhizophaga as a Pathogen of Dendrocalamus giganteus in Mozambique
Authors: Zazzerini A. , Quaglia M. , Davolio Marani O. 
Published: February 2010

Dendrocalamus giganteus Wall. ex Munro, a wild plant belonging to the family Poaceae, is widespread in Mozambique where it is used as a construction material. At the end of 2007, disease symptoms have been observed on D. giganteus plants growing in the neighborhood of Maputo. Diseased plants showed longitudinal dark streaks on the stem surface to which corresponded internal vascular browning and chlorosis in wide leaves that gradually developed into necrosis. At the final stage of the disease plants died. To isolate the pathogen, stem segments collected during September 2008 were surface sterilized with 1% HgCl2 for 30 s, rinsed with sterile deionized water for 30 s, and incubated on potato dextrose agar (PDA) medium at 22°C in the dark for 2 weeks. Monosporic cultures of the isolated fungus formed dimorphic Verticillium-like (primary) or penicillate (secondary) conidiophores and ovoidal to elongate, minutely curved, hyaline conidia, 5 to 9.5 × 2.5 to 4.5 μm, with laterally displaced hilum. These characteristics are typical of Clonostachys rhizophaga Schroers (3). Identification was confirmed by the Centraalbureau voor Schimmelcultures (Utrecht, the Netherlands) on the basis of the β-tubulin (tub2) gene sequence (3). For our isolate CBS 125416, the tub2 sequence was 100% similar to that of the C. rizhophaga strain CBS 124511 (GenBank Accession No. FJ 593883) (1). To verify the pathogenicity of the fungus, a 5-mm-diameter mycelial plug obtained from 2-week-old colonies grown on PDA was affixed to a portion of the stem of D. giganteus from which the superficial tissues had been removed and the inoculation site was covered with wet cotton and wrapped with Parafilm. Control plants were treated by the same method but using PDA plugs without mycelium. Twenty plants were used, ten of which were controls. They were grown in a controlled climatic chamber at 22°C with a photoperiod of 16 h at 40 μE·m–2·s–1. Two months after inoculation, all plants showed a dark area surrounded by an idropic halo on the stem surface and internal browning, whereas control plants remained healthy. C. rhizophaga was recovered from all infected plants. C. rhizophaga is apparently rare. The fungus (as Verticillium rhizophagum Tehon & Jacobs, nom. invalid.) has been previously reported from the United States, Chile, and Ecuador (4) and as a culture contaminant in Switzerland (3). More recently C. rhizophaga has been found to be associated with Pinus canariensis in Argentina (2) and it has been reported as a causal agent of chickpea wilt in Syria (1). To our knowledge, this is the first report of C. rhizophaga for subsaharian Africa. It may be under reported and more common than has been thought because of the difficulty in identifying Clonostachys species, but with the ability to identify species using tub2 (3), there can be no doubt of its identity.

References: (1) M. M. Abang et al. Plant Dis. 93:666, 2009. (2) L. Eduardo Piontelli and G. Giusiano. Bol. Micol. 18:89, 2003. (3) H. J. Schroers. Stud. Mycol. 46:85, 2001. (4) L. R. Tehon and H. L. Jacobs. Bull. Davey Tree Expert Company, Kent, OH. 6:3, 1936.