Association of beet necrotic yellow vein virus with isolates of Polymyxa betae Keskin.

Abstract

Seven isolates of Polymyxa betae with a different host range were compared with respect to their association with beet necrotic yellow vein virus (BNYVV). When 14 species of plants were inoculated with the fungus isolates under greenhouse conditions, transmission of BNYVV was related to the fungal isolates from sugar beet, spinach and Chenopodium murale which were infective to sugar beet. But the isolates from C. album, Amaranthus retroflexus and Portulaca oleracea which were not infective to sugar beet did not carry the virus. Viruliferous sugar beet isolates became virus-free after being propagated in the roots of C. ficifolium. When these virus-free resting spores were propagated in the roots of sugar beet infected with BNYVV by manual inoculation, the fungus again acquired and transmitted the virus to healthy plants. Infectivity of BNYVV was maintained together with the survival of P. betae in air-dry and moist soil for fifteen years. The virus infectivity was also retained in zoospores of P. betae treated with BNYVV antiserum and resting spores treated with virus antiserum, HCl or NaOH. In ultrathin sections of sugar beet rootlets infected with the viruliferous sugar beet isolate of P. betae, the virus particles were usually encountered in the cytoplasm in contact with the outer plasmodial wall of the infected cells, and were also present in the vacuoles and the protoplasm of immature zoospores of the fungus. No virus particles were observed in resting spores. The virus, however, was detected by ELISA in the extracts of viruliferous resting spore clusters isolated from root tissues. From these results, it is concluded that BNYVV transmission is depending on strains of P. betae and the plant species which the fungus proliferates. It is suggested that BNYVV remains in P. betae for a long period of time but does not multiply in the fungus.