Encapsidated and unencapsidated double-stranded RNAs in flax rust, Melampsora lini

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Abstract
Double-stranded (ds) RNA molecules in different strains of Melampsora lini have been assigned to three transmission groups. (L, A, and B) on the basis of sexual, asexual, and infectious transmission studies. This paper correlates different transmission with different cellular locations. The L transmission unit, comprising a single dsRNA of 4200 base pairs (bp) is present in isometric virus particles of 40 nm diameter, with a major capsid protein of 75 kDa. These properties suggest that the virus should be classified in the A group of Mycoviruses and the designation MeliV is proposed for this virus. The A and B transmission units, each composed of several discrete dsRNA molecules in the size range 1200-2800 bp, are not packaged in virus capsids but are found in some as yet undefined RNas resistant complex. The two units have different banding patterns in Cs2SO4 buoyant density gradients suggesting they are present in complexes of different composition correlating with the different transmission characteristics of the two units.