Squash Mosaic Virus Isolated from Melon (Cucumis melo L.) in Hokkaido

Abstract

Squash mosaic virus (SMV) was isolated from a melon (Cucumis melo L. var. reticulatus) showing mosaic symptoms in Yuhbari, Hokkaido. The host range was limited to Cucurbitaceae, except for Pisum sativum and Lathyrus odoratus, among 41 plant species belonging to 10 families tested. The virus was not transmitted by the aphids, Myzus persicae and Aphis gossypii, but transmitted by the chrysomelid beetles, Aulacophora femoralis and Atranchya menetriesi, and coccinelled beetles, Epilachna admirabilis and E. sparsaorientalis. When the insects, A. femoralis and E. sparsaorientalis, were transferred daily to healthy melon plants, they remained infective for 16 days and 4 days, respectively. The percentage of transmission through seeds of melons, cv. Yuhbari King, Earl's Favourite, Honeydew, Spicy, and Prince, and pumpkin (Cucurbita maxima), were 13.5%, 0.5%, 1.0%, 15.3%, 10.7%, and 2.0%, respectively. No seed transmission occurred in pumpkin (Cucurbita moschata), cucumber, and watermelon. Infectivity of crude sap from infected melons was lost by heating at 65-70C for 10minutes, by diluting 2×10-5-10-5, and by aging at 20 C for 12 days. The virus was isometric particles of 25 to 30nm in diameter. In ultrathin sections of the virus-infected melon leaves, the virus particles were observed in the vacuoles of spongy parenchyma cells and palisade parenchyma cells. The tubular structures were observed in the cytoplasm of spongy parenchyma cells and palisade parenchyma cells. The titer of antiserum to the virus was 1: 1600 in the ring interface tests. The antiserum reacted with four isolates of SMV from Hokkaido and an isolate from Okayama, but not with cucumber mosaic virus (CMV) and muskmelon necrotic spot virus (MNSV) in gel diffusion test. From the results, the virus was identified as a strain that belongs to group I of squash mosaic virus. Within 72 samples of diseased melons showing mosaic symptoms, collected in the fields of Hokkaido from 1970 to 1975, 6 different viruses were recovered. They are 47 of CMV, 11 of watermelon mosaic virus, 5 of SMV, 3 of cucumber green mottle mosaic virus, 5 of MNSV, and 1 of tomato ringspot virus.