An Efficient Microinoculation Procedure to Study Plant Virus Multiplication at Predetermined Individual Infection Sites on the Leaves

The microinoculation procedure (inoculated are 0.02—0.05 mm² was carried out using the very thin tip of a stretched Pasteur pipette. It was dipped in a 500 μg/ml suspension of purified TMV, brought into contact with the upper epidermis of the leaf which had been dusted With an abrasive and rotated twice without actually pricking the leaf tissue. Five minutes later, the excess abrasive and virus were removed by rinsing the leaves under water. The procedure was applied to several tobacco-TMV combinations. It induced the formation of single local lesions with over 90% efficiency on hypersensitively reacting hosts. Comparable efficiencies were obtained with systemically reacting hosts, as evidenced by a radiochemical procedure coupled with indirect ELISA (KONATE and FRITIG 1983). It was found that residual virus originating from the inoculum was negligible and could casily be distinguished form newly synthesized virus, even shortly after the microinoculation. This makes it possible to measure the rates of virus cell-to-cell spread and of virus multiplication at various times after inoculation and at various distances form the points of virus entry. These approadies can be extended to the comparison between differently reacting hosts and to the study of interference between different viruses or different virus strains.     

Differentiation of Yam Virus Isolates Using Symptomatology, Western Blot Assay, and Monoclonal Antibodies

Monoclonal antibodies (mAbs) were prepared against a yam mosaic virus (YMV) isolate from the Côte d'Ivoire. Symptomatology, Western immunoblotting, and ELISA were used to discriminate 69 isolates of YMV originating from different Dioscorea species and from various yam producing areas. These isolates induced two types of symptoms, were of four different electrophoretic mobilities and formed two serogroups. These results suggest that at least six differetit groups of isolates exist, three of which infect the main cultivated species in various geographical areas while two others were from unusual samples in our collection. An isolate from 'Pilimpikou Yam' from Central Burkina Faso was serologically distinct. It is concluded that there is a significant variability among yam virus isolates which is unrelated to the origin of the isolate (geographic or host species). It is suggested that precautions should be taken in order to avoid international exchange of infected material.