Selection of an attenuated isolate of Bean yellow mosaic virus for protection of dwarf gentian plants from viral infection in the field

Abstract

An attenuated isolate of Bean yellow mosaic virus (BYMV), designated B-33, that caused barely any mottling on the leaves of gentian plants (Gentiana scabra) was isolated from dwarf gentian plants. Infection with this isolate did not cause severe symptoms in several leguminous plants or in prairie gentian (Eustoma grandiflorum) plants. Dwarf gentian plants that had been infected with an inoculum of partially purified B-33 were propagated vegetatively from cuttings without difficulty. The B-33 isolate could be distinguished from other, more virulent, isolates by comparing symptoms on prairie gentian plants and by examining restriction fragment length polymorphism after reverse transcription and amplification by the polymerase chain reaction. In cross-protection tests, dwarf gentian plants that had been infected with B-33 were protected from infection with the virulent BYMV isolate 35-1. Potted plants that had been inoculated with B-33 grew larger and produced more flowers than unprotected plants. Thus, B-33 is an effective agent for controling mosaic and atrophic diseases caused by BYMV in clonal dwarf gentian plants.