Yellow Dwarf of Pea and Broadbean Caused by Milk-Vetch Dwarf Virus

Abstract

The occurrence of yellow dwarf disease of pea and broadbean was noticed in Wakayama, Aichi, and Okayama Prefectures since 1963. In general, the outbreak was sporadic, but was observed to be epidemic in occasional fields.The virus causes yellowing, leaf-curling or rolling, and dwarfing in various leguminous plants, such as pea, broadbean, bean, azuki-bean, soybean, milk-vetch, crimson clover, and subterranean clover, and also in Datura stramonium. In tobacco (Samsun and White Burley), N. glutinosa, N. rustica, and spinach leaf-curling and stunting are observed as well, although the virus is not yet recovered. The causal virus is not transmitted by plant juice. It is transmitted by Aphis craccivora, but not by Myzus persicae, Acrythosiphon pisum, and Megoura viciae japonica. In the dip-preparation from diseased plants, no elongated virus particles are detected under the electron microscope. No inclusion body is demonstrated in epidermal cells of infected pea and broadbean. Aphis craccivora could acquire the virus in as short time as 5 minutes. Efficiency of transmission, however, increased with more time than 4 hours on the source plants. The aphids which had received sufficient acquiring feed, transmitted the virus to about 7 per-cent of plants if fed for inoculation for 5 minutes on test plants, but infection increased to above 30 percent when aphids fed for 4hr. or more. Latent period invector aphid was found to be at least 36 hours at alternating temperatures of 24°C (day) and 18°C (night). As a result of daily serial transfers, individual aphids seemed to transmit the virus as long as they lived, although not every plant in a series was infected. In one case, a single aphid was able to infect all the test plants during a period of successive 15 days. Thus, the virus can be considered a persistent virus. By reference to the literature, the virus in the present work is apparently distinct in symptoms and agents of transmission from such persistent aphid-borne viruses as pea ena-tion mosaic virus, pea leaf roll virus, groundnut rosette virus and subterranean clover stunt virus, but identical with milk-vetch dwarf virus (MDV) which was described in Japan by Matsuura in 1953 and by Hino et al. in 1967.