Selection and discrimination of an attenuated strain of Chinese yam necrotic mosaic virus for cross-protection

An attenuated strain of Chinese yam necrotic mosaic virus (CYNMV), designated KM3, was selected from among CYNMV field isolates. KM3 causes a mild mosaic on leaves of Chinese yam (Dioscorea opposita) cv. Nagaimo during the early stages of growth, and the severity of the symptoms is reduced with growth of the plants. In cross-protection tests using aphids to transmit the virus, Nagaimo plants that had been infected with KM3 were protected from infection with CYNMV severe strains YS117 and IW5. A reverse transcription-polymerase chain reaction-restriction fragment length polymorphism (RT-PCR-RFLP) method was developed to discriminate KM3 from other isolates in the field. © 2007 The Phytopathological Society of Japan and Springer-Verlag.