Abstract:
Isometric virus particles measuring 35-40 nm in diameter with double stranded RNA genomes of molecular weight (1.48 - 6.1) x 106 dalton was detected in the field isolates of the wheat take all fungus Gaeurnarmornyces graminis var. tritici. Out of three isolates of Ggt four different viruses based on particle size, size of RNA and molecular weight of coat protein belonging to three groups of mycoviruses were detected.
Introduction
Lapierre et aL, (1970) discovered the first isometric virus particles in two weakly pathogenic isolates of Gaeurnannomyces graminis var. tritici (Sacc) Arx. olio, (Ggt) the cause of take all disease of wheat. Previous work has established four ,groups of Ggt viruses based on physical and serological properties and on their double stranded RNA (dsRNA) and capsid polypeptide mol. wt. (Buck et al., 1981; Buck, 1984). The size distribution of these viruses within four group were: group I and II virus particles 35 nm, group III particles 40 nm and group IV particles 29 nm in diameter. These viruses are unusual in that they are transmitted only intracellularly, during growth in asexual and sometimes in sexual spores and via heterokaryosis. Pryor et al., (1.988) have isolated a dsRNA mycovirus from maize rust fungus Puccinia sorghi. Presence of isometric virus particles in germinated uredospores of the fungus has presented the evidence of intracel¬lular horizontal transmission of virus. Association of these virus particles with patho genecity of the fungi has not been established, although it is becoming increasingly clear that dsRNA can affect a fungus phenotype in other ways. For example, protein toxin secreted by Killer strains of Saccharomycescere visiae and of Ustilago inavdis are encoded by specific dsRNA molecule (Bostian et al., 1980, Koltin & Kendel, 1978). Similarly Rogers et al., (1986) reported a clear association between specific segments of dsRNA and a cytoplasmically transmitted disease in the aggressive strain. Yeast Killer viruses, has been reported to be transmitted only by cytoplasmic mixing during division, mating or other induced forms of cell fusion. El-Sherbeni & Bostian (1.987) have demonstrated the extracellular transmission of these virus particles. The present report describes the isolation and characterization of some viruses associated with Gaeumannomyces graininis var. tritici, the cause of take all disease of wheat.
