The Association of Brome Mosaic Virus and Wheat Rusts: I. Transmission of BMV by Uredospores of Wheat Stem and Leaf Rust

Both the stem and leaf rust fungi of wheat (Puccinia graminis f. sp. tritici, P. recondita f. sp. tritici) were investigated as potential vectors of brome mosaic virus (BMV), a pathogen of Gramineae. They were found to transmit BMV to healthy plants through uredospore transfer from hosts infected with both the viral and fungal pathogens. Virus was transmitted even to rust-resistant and non-susceptible hosts. Rust-transmitted virus produced atypical symptoms on plants, could not be extracted by normal low pH methods, and multiplied only to low levels in leaf tissue. Extracted virus was shown to be similar to BMV-type strain (ATC) by serology, density gradient centrifugation and immunospecific electron microscopy. The importance of the association of BMV with the rust fungus in natural infections is discussed.