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Abstract
Cassia yellow blotch virus (CYBV) is a previously undescribed bromovirus infecting the Australian indigenous legume, Cassia pleurocarpa, in western Queensland. Although CYBV infected test plants in several families, symptoms were usually restricted to local lesions on the inoculated leaves. Systemic infection occurred in only eight leguminous species and in the non-legume, Nicotiana clevelandii. Chenopodium amaranticolor was a suitable host for local lesion assays and CYBV was readily purified from N. clevelandii. Purified CYBV preparations, when negatively stained, contained isometric particles 25 to 27 nm in diameter with a penetrated central core of approx. 10 nm. The virions sedimented as a single component with a sedimentation coefficient (s 20,w) of 85S and had an isoelectric point of 3.6. At pH 7.0, the virions sedimented more slowly than at pH 5.0 and 6.5 probably because they swelled. Purified virions contained a single coat protein species with a molecular weight of 20800 comprising 196 amino acid residues as estimated by FITMOL analysis of the amino acid composition. The virion genome consisted of four single-stranded RNA molecules of which only the three largest were required for infectivity. CYBV appeared to be serologically unrelated to three other bromoviruses and this lack of relationship correlated with differences in their coat protein amino acid compositions.
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