Leaf and Stem Spot Caused by Ramularia sphaeroidea on Purple and Lana Woollypod Vetch (Vicia spp.) Cover Crops in California
Authors: Koike S. T. , Smith R. F. , Crous P. W. , Groenewald J. Z. 
Published: May 2007

Vetches (Vicia spp.) are planted alone or in combination with other plants as cover crops in vegetable production areas of California. December 2001 through February 2003, purple (V. benghalensis) and lana woollypod (V. villosa subsp. varia) vetches in the Salinas Valley (Monterey County) developed a foliar disease. Symptoms were small (≤5 mm in diameter), circular to oblong, purple brown-to-red brown spots that were visible from the adaxial and abaxial leaf sides, and occurred lower in the plant canopy. White sporulation was visible in the spot centers. Stems were infected and had elongated, irregularly shaped, brown lesions that were <5 mm long and had white sporulation. When fungal masses or tissues from lesions were placed on acidified potato dextrose agar (LA-PDA), a fungus was consistently recovered. On LA-PDA, the isolates produced slow-growing (30 mm colony diameter in 45 days), irregularly raised, light pink and white colonies that produced dark exudates. The undersurfaces of cultures were gray black. The growth on lesions consisted of fascicles of conidiophores that were hyaline, smooth, flexuous, distinctly geniculate, and measured 20 to 120 × 2.5 to 6 µm. Conidia were hyaline, subglobose, smooth, aseptate, measured 9 to 15 × 8 to 13 µm, and formed singly. The internal transcribed spacer rDNA sequence of a representative strain (CBS 112891) was determined using standard protocols (GenBank Accession No. AY352584). A nucleotide BLAST search revealed a 94 to 97% similarity to other species of Ramularia (GenBank Accession Nos. AF222848, AF173310, AJ417496, AF362060, and AF297235). On the basis of these morphological and molecular data, the fungus was identified as Ramularia sphaeroidea Sacc. (= Ovularia sphaeroidea (Sacc.) Sacc.) (1). Pathogenicity of six isolates grown on LA-PDA was confirmed by spraying conidial suspensions (1.0 × 105 conidia per ml) onto direct-seeded, 8-week-old, potted purple and lana woollypod vetch (12 plants each). Plants were kept in a dew chamber for 48 h and maintained in a greenhouse (23 to 25°C). After 7 to 10 days, all plants developed the characteristic leaf spots and stem lesions, and R. sphaeroidea was reisolated from such symptoms. Plants treated with only water did not develop symptoms. However, because disease incidence on test plants was low, inoculum was also prepared in water amended with 1.0 ppm of Tween 20. Four pots each of purple and lana woollypod vetch were sprayed with amended or nonamended inocula, and plants were handled as described. After 10 days, plants inoculated with Tween 20 amended inoculum had significantly higher disease incidence and severity (purple = 83% of leaflets infected with a mean of 3.4 spots per leaflet; lana = 83% infected with a mean of 3.2 spots) than did plants inoculated with water-only conidial suspensions (purple = 27% and a mean of 0.4 spots; lana = 38% and a mean of 0.6 spots). Finally, two other vetches used in the Salinas Valley were inoculated with the two suspensions. After 2 weeks, common (V. sativa) and languedoc (V. sativa ‘Languedoc’) vetch showed no symptoms, and control plants of purple and lana vetch developed disease. All inoculation tests were repeated, and results were similar. To our knowledge, this is the first report of R. sphaeroidea as a pathogen of purple and lana woollypod vetches in California.

Reference: (1) U. Braun. A Monograph of Cercosporella, Ramularia, and Allied Genera (Phytopathogenic Hyphomycetes) Vol. 2. IHW-Verlag, Eching, Germany, 1998.