Polymyxa graminison NewSorghumSpecies in Africa

Abstract

THOUVENEL. J. C., and C. FAUQUET. 1980. Polymyxa graminis on new Sorghum species in Africa. Plant Disease 64:957-958. PoIymyxa graminis (Plasmodiophoraceae), a fungus parasitic on the roots of a few species of Gramineae. was found in the roots of great millet (Sorghum anurdinaceum) in Upper Volta. This is the first report of this fungus in Africa. In inoculated pot tests. six Sorghum spp. became infected @ with P. graminu in addition to the previouslyestablished hosts. wheat ( 7kiticwn aestivum). barley (Hordetun vulgare). and oats ( A WM sotiw). Polymyxa graminis Ledingh. is an intracellular root fungus that parasitizes Gramineae and does not produce any external symptom in the host. It may tiansmit soilborne wheat mosaic (2), oat mOsaic (7), and barley yellow mosaic (8). P. graminis has been observed inCanada, the United States, New Zealand (9). Japan (g), Italy (4). England and Wales (1 I), and Brazil (IS). Peanut clump virus is a soilborne pathogen-found on peanut (Arachis hypog6eadL.) (14) and great, millet (Sorghum arundinaceum (Desv.) Stapf) (6) in Upper Volta and Senegal. During experimental tests for transmission of peanut clump virus in Upper Volta, resting spores similar to those of P. graminis were observed in the roots of S. arundinaceum. Because P. graminis has not been described on Sorghum spp. nor reported in Africa, we investigated its importance in Africa. MATERIALS AND METHODS A great millet plant and its roots were Sollected from a field near Saria in Upper Xolta. Soil samples were collected from the same area, around peanut seedlings with symptoms of peanut clump virus infection (14). Soil samples were placed in window boxes and seeded to 12 graminaceous species. Seedlings were grown in a greenhouse at 23-30 C. In some xperiments, plants were grown in an artificial medium, vermiculite with KNOP solution (12.5 g each of KN03.MgSO4.7H20,and KHzPO4,and 50.0 g of Ca(N03)~ per liter of solution; diluted 60 times), so that the entire root system could be sampled easily. Roots of S. arundinuceum infected with P. graminis were u,sed for inoculum and incorporated into the soil or vermiculite. To stain resting spores, infected roots were boiled for 1 min in lactophenol containing I mg/rnl of acid fuchsin and then destained and mounted in clear a1 91-291 7/8o/l0095702/$03.00/0 a1.980 American Phytopathological Society