Cross protection and mutual exclusion by three strains of barley yellow dwarf virus in Avena sativa L

Abstract

Avena sativa L. var. Clintland 64 inoculated in the early one-leaf stage with a mild barley yellow dwarf virus strain was protected against subsequent invasion by either of two severe strains of the virus under field conditions. The protection was indicated by the failure of the second-introduced virus to induce characteristic symptoms and the failure to recover the second virus by specific vectors. When the oat seedlings were simultaneously inoculated with the three strains in the early one-leaf stage, mutual exclusion was observed; the plants showed mild symptoms soon after inoculation, but complete recovery followed and no virus could be recovered from the healthy appearing plants. The same phenomenon did not occur, however, when the plants were inoculated at a more advanced stage of growth: after later inoculation the infection induced a severe acute disease, typified by necrosis, from which the plants never recovered. These phenomena and other strain interactions were further substantiated by highly significant quantitative differences among plant characters that reflected the behavior of the virus strains within the host. It is suggested that the three strains of BYDV be regarded as closely related.