Properties of a previously undescribed supercoiled filamentous virus infecting papaya in Venezuela.

Supercoiled filamentous virus particles with lengths of 400 to 700 nm and 3 nm wide were isolated from leaves of Carica papaya L. plants showing a mild yellowing between the veins. The morphological properties of this virus resemble those of tenuiviruses. However, it was serologically unrelated to three of the five definitive members of this group of plant viruses and had biochemical features quite different from tenuiviruses. Therefore, the virus described here is possible an unreported new virus infecting papaya for which the name of papaya mild yellow leaf virus (PMYLV) is proposed. PMYLV was mechanically transmitted to papaya and to several Cucurbitaceae species. Virus particles sedimented as one component in sucrose density gradients, containing one molecule of ssRNA with an apparent size of 6400 nucleotides which constitutes 5% of the particle weight. The buoyant density of PMYLV was 1.26 g/cm3 in cesium chloride equilibrium gradients, and the virus coat protein consisted of a single polypeptide with mol. wt. of c. 39 kDa. Estimated virus yield in purified preparations was 2.6 g/kg leaf tissues. An antiserum was produced with a titer of 1:1500. Ultrastructural observations of PMYLV-infected leaf tissues showed crystalline aggregates of virus particles, closely associated with electron dense amorphous inclusion bodies only within xylem cells.