Electro-blot radioimmunoassay of virus-infected plant sap - a powerful new technique for detecting plant viruses.

A new technique for detecting viruses in plant sap is described. It consists of sodium dodecyl sulphate-polyacrylamide gel electrophoresis of the infected plant sap, electrophoretic transfer of protein bands to activated paper by the Electro-Blot technique, the subsequent probing of the viral coat protein band by specific antiserum (prepared against intact virus), and detection of immune complex with 125 I-labelled protein A. The technique successfully detected tobacco mosaic virus at a sap dilution of 1 : 10,000, four strains of sugarcane mosaic virus (a potyvirus) in their perennial hosts infected for about 4 years, and five different isolated of potato leaf roll virus (a luteovirus). The latter virus occurs in extremely low concentration and is difficult to detect by the other known methods.