Occurrence of Grovesinia pyramidalis on Soursop and Avocado in Bahia, Brazil

The discomycete Grovesinia pyramidalis M.N. Cline, J.L. Crane & S.D. Cline (Leotiomycetes, Helotiales, Sclerotiniaceae; anamorphs Sclerotium cinnamomi Sawada and Hinomyces moricola (I. Hino) Narumi-Saito et Y. Harada, comb. nov.(synonyms Cristulariella pyramidalis Waterman & R.P.Marshall and C. moricola (Hino) Redhead [Cline et al., 2007; Tomoko, et al., 2006]) causes leaf spots on many woody plants (Sinclair et al., 1993). In 1999, 2002, 2005 and 2006, in southern Bahia it was commonly observed on soursop (Annona muricata L.), sometimes causing serious defoliation, and was less commonly observed on avocado (Persea americana Mill.). Lesions on soursop leaves were up to 1 cm broad, round to irregular, grayish brown with dark margins (Fig. 1). They were similar on avocado leaves, but smaller, less than 1 cm broad.

Conical white structures protruded from tissue that had lesions (Fig. 2). Slides of the structures stained in cotton blue showed the arbuscular propagules producing phialide-like cells, but no conidia were observed (Fig. 3). Propagules measured up to 500 µm long and 120 µm wide, at the base. They are thought to function as infective multicelled spores, dispersed by splashing water (Sinclair et al., 1993). A fungus was isolated from lesions onto PDA plates where, in two weeks, it formed whitish, cottony, 1 to 2 cm wide mycelial colonies with concentric zones; eight-sided crystals were observed embedded in agar in older cultures. The teleomorph stage was not seen.

Discs cut from 20 days old colonies growing on PDA were placed on freshly cut soursop leaves in moist chamber and incubated at 25 ± 2ºC for 15 days. Spots developed on the inoculated leaves that were similar to those observed in the field and the organism was re-isolated from these lesions. A similar test was performed in the field using ten healthy young leaves of a mature soursop plant inoculated in the same way and bagged in transparent polyethylene. After fifteen days the same type of symptoms were observed. Inoculation experiments were not done with avocado leaves since diseased material was scarce and isolates were not available.

Annona muricata is reported as a new host of G. pyramidalis. This pathogen is also reported for first time on Persea americana in Brazil. Specimens of G. pyramidalis on these hosts have been deposited at CEPEC Herbarium (mycological collection), Cacao Research Centre, CEPLAC/CEPEC, Ilhéus, Bahia, Brazil (Accession numbers 158, 168, 223, 378, 468 469 and 470).

Acknowledgments

This research was supported in part by CNPq and Fapesb. We thank Dr.Nina Shishkoff for her revision and comments on the manuscript.