SOME PROPERTIES OF BROAD‐BEAN MOTTLE VIRUS

Abstract

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 (NH 4 ) 2 SO 4 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 mμ in diameter. It is suggested that much of this nucleoprotein is non‐infective, but may otherwise resemble infective particles.