Evidence that Beet Necrotic Yellow Vein Virus RNA-4 Is Essential for Efficient Transmission by the Fungus Polymyxa betae

Publisher Website
Google Scholar
Abstract
The efficiency of transmission by Polymyxa betae of beef necrotic yellow vein virus (BNYVV) isolates containing different RNA components was compared using sugar-beet seedlings as test plants. Isolate S-4, containing RNA-1 + 2 + 4, was transmitted by P. betae about 100 times more efficiently than isolate S-3 (RNA-1 + 2 + 3) and about 1000 times more efficiently than isolate S-0 (RNA-1 + 2). Isolate S-34 (RNA-1 + 2 + 3 + 4) was transmitted even more efficiently than isolate S-4. Each isolate retained its characteristic RNA composition after transmistion of P. betae. The virus content, measured by ELISA, of infected rootlets was S-34 > S-3 > S-4 > S-0. In inoculated leaves of Tetragonia expansa and Beta macrocarpa, isolates S-3 and S-34 multiplied more extensively than did S-4 and S-0. The inefficient transmission of isolate S-3 by P. betae, as compared with S-4, cannot be attributed to a poorer ability to spread in root tissue, but the difference in transmissibility of S-3 and S-0 may be explained in this way. These results show that RNA-4 of BNYVV is essential for efficient transmission by P. betae, and suggest that RNA-3 may influence the ability of the virus to spread to root tissue. RNA-4 and RNA-3 therefore seem to play important, but different, roles in virus survival and spread in nature.