Evaluation of cross protection by an attenuated strain of Chinese yam necrotic mosaic virus in Chinese yam

We evaluated the cross protection effectiveness of an attenuated strain of the Chinese yam necrotic mosaic virus (CYNMV), KM3, in the field. Chinese yam (Dioscorea opposita) cv. Nagaimo plants infected with KM3 were protected from subsequent CYNMV infections in the field for 5 years, whereas non-inoculated plants were easily infected with CYNMV. Furthermore, KM3 infection did not induce the deterioration of the internal quality of the tubers. Total tuber and grade A tuber yields of KM3-infected plants were 25 and 57 % higher, respectively, than those of the non-inoculated plants after 5 years of cultivation. Additionally, grade A tuber yield of KM3-infected plants was 31 % higher than that of the non-inoculated plants grown from virus-free seed tuber. The results of this study indicate that KM3 is an effective agent for controlling necrotic mosaic disease in cv. Nagaimo.