Abstract1. A mosaic virus disease of papaya (Carica papaya) causing yellow mottling, slight wrinkleness of the leaves, and oily spots on the stem but no extreme distortion and deformation of the leaves has been observed in the northwestern part of Puerto Rico near the town of Isabela. 2. The physical properties of the virus are: Thermal inactivation point, 60° C; dilution end-point, 1-100; and it is inactivated in about 72 hours at laboratory temperature (around 74° F.). The virus is not seed- nor soil-transmitted. 3. The virus has been transmitted mechanically thus far only to members of the family Cucurbitaceae belonging to the following genera: Cucumis, Luffa, Citrullus, Lagenaria and Melothria. It has not been possible to transmit mit the virus to plants of the following families: Solanaceae, Amaranthaceae, Phytolacaceae, Malvaceae, Balsaminaceae, Leguminoseae, Scrophulariaceae, Mimosaceae, and Cesalpinaceae. 4 Cross-protection tests have demonstrated that the Isabela mosaic and the Puerto Rican southern coast papaya mosaic viruses are related. 5. Preliminary experiments indicate that the Isabela mosaic virus may be transmitted by the nematode Trichodorus christiei. 6. The results of extensive inoculation trials have shown that Carica candamarcensis Hook, is resistant to the Isabela mosaic virus.
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