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Further Evidence for the Association of Polymyxa graminis with the Transmission of Wheat Spindle Streak Mosaic Virus. B. L. Nolt, Graduate research assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; C. P. Romaine(2), S. H. Smith(3), and H. Cole, Jr.(4). (2)(3)(4)Assistant professor, professor and head, and professor, respectively, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 71:1269-1272. Accepted for publication 20 March 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1269.

Wheat spindle streak mosaic (WSSM), which is caused by wheat spindle streak mosaic virus (WSSMV), was detected in 36 of 76 Pennsylvania wheat fields surveyed in the spring of 1977 and 1978. The disease was identified by symptomatology, the temperature requirement for symptom development, and by an association with virus particles. Long, flexuous, rod-shaped virus particles measuring 14 nm wide and 600 to 925 nm long were detected in leaf dip preparations from plants that had developed characteristic WSSM symptoms at 515 C. Three zoosporic fungi, Polymyxa graminis, Olpidium brassicae, and Lagena radicicola were most commonly observed in the roots of both symptomatic and asymptomatic plants. The occurrence of WSSM in the field was correlated with the presence of P. graminis, but not O. brassicae or L. radicicola, suggesting that P. graminis plays a major role in the natural spread of WSSMV. The incidence of WSSM was not correlated, however, with the extent of root colonization by P. graminis WSSMV transmission occurred when test plants were inoculated with root washings and root pieces containing P. graminis from WSSMV-infected plants.