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Viruses from Rusts and Mildews. C. E. Yarwood, Professor, Department of Plant Pathology, University of California, Berkeley 94720; Eva Hecht-Poinar, Assistant Specialist, Department of Plant Pathology, University of California, Berkeley 94720. Phytopathology 63:1111-1115. Accepted for publication 5 March 1973. DOI: 10.1094/Phyto-63-1111.

Particles resembling tobacco mosaic virus (TMV) were found in dip preparations of five species of rusts (Uredinales) and in two species of powdery mildews (Erysiphaceae), but were not found in seven other rusts and five other mildews. For three of these five rusts, similar rods were found associated with germinating uredospores in vitro. Virus-like infections were transmitted to, and recovered from, Chenopodium quinoa by 13 rusts and three mildews. Of the positive cases for TMV rods and transmission to C. quinoa, the most consistent and most studied were Uromyces phaseoli on Phaseolus vulgaris cultivar ‘Pinto’ (bean rust) for the rusts, and Erysiphe graminis on Hordeum vulgare cultivar ‘Mariot’ (barley mildew) for the mildews. Electron microscopy was reasonably consistent for different independent collections and observations, and the number of rods per unit of rusted bean tissue was about one four-thousandth of the number in systemically infected tobacco. Most attempts to produce virus-like infections by inoculation with spores, or with juice preparations of rusted or mildewed tissues were unsuccessful, even for bean rust and barley mildew. The TMV-like infections usually had a wide host range but, with two exceptions, were less virulent on tobacco than ordinary TMV. Most isolates became systemic in C. quinoa, whereas ordinary TMV did not. One nonTMV-like infection was recovered from Uromyces polygoni on Polygonum aviculare (knotweed rust). This virus was transmitted only to C. quinoa and had a half-life of only 7 sec at 55 C.