Field Studies on Cross-protection against Japanese yam mosaic virus in Chinese yam (Dioscorea opposita) with an Attenuated Strain of the Virus

An attenuated strain of Japanese yam mosaic virus (JYMV), designated T-3, was evaluated for its crossprotection efficacy against virulent (native) strains of JYMV in Chinese yam (Dioscorea opposita) grown in farmers fields in Japan. Native strains of JYMV were detected by a polymerase chain reaction-based assay in all the Chinese yam plants grown from virus-free tubers in the first growing season in the fields. In contrast, the virus was detected in only one of fifty plants grown from tubers preinoculated with T-3 during the experiments for 6 years, suggesting that T-3 consistently cross-protected against native JYMV in Chinese yam in the field. Chinese yam plants preinoculated with T-3 produced significantly greater yield of tubers per plant compared with non-inoculated plants