Some properties of broad-bean mottle virus

A severe disease affecting many plants in a crop of broad beans was found to be caused by a previously undescribed virus, provisionally named broad-bean mottle virus. The distribution of diseased plants suggested spread by a vector, but none of the six insects tested transmitted it. The virus was transmitted to several species of leguminous plants by mechanical inoculation of sap; infectivity for some hosts seemed to be increased by propagation in these hosts. The virus has an unusual combination of properties. Its thermal inactivation point is about 95°C., whereas sap becomes non-infective within 3 weeks at room temperature. The infection end-point of broad-bean sap is 1/1000, only a little higher than the precipitation titre with specific antiserum. Precipitation with antiserum occurs over a smaller range of antigen/antibody ratios than with other viruses previously studied, possibly because of its greater solubility; it is not precipitated with (NH4)2SO4 until the salt concentration exceeds 75% saturation. A specific nucleoprotein, containing nucleic acid of the ribose type, can be isolated from infective broad-bean sap in yields up to 2 g./l. Purified preparations, made by salt precipitation and ultracentrifugation, contain uniform spherical particles approximately 17 m? in diameter. It is suggested that much of this nucleoprotein is non-infective, but may otherwise resemble infective particles.