1989年,神奈川県でエキザカム(Exacum affine)に激しい萎縮と葉巻き症状が発生した。C. amaranticolorあるいはC. quinoaに接種して得たウイルスにより宿主を調べたところ,9科21種に感染し,エキザカムでは萎縮症状が再現され,C. amaranticolorやC. quinoaでは接種葉に灰白色斑点を生じた後に全身感染し,ソラマメでは頂葉の枯死が観察された他, 各種のタバコ類にも感染した。電子顕微鏡観察では直径約27nmの小球型ウイルス粒子が観察された。また,モモアカアブラムシ(Myzus persicae)で非永続的に伝搬された。粗汁液中の安定性は,耐熱性が60-65℃(10分),耐保存性が4日であった。ウイルス粒子はソラマメウイルトウイルス(BBWV)に対する抗血清を用いた免疫電子顕微鏡法で捕捉・修飾され,パチョリ微斑モザイクウイルス(PaMMV)に対する抗血清を用いたELISA法でも検出された。ウェスタンブロット法では2種のウイルス外被タンパク質が検出され,その分子量は約42,000と約26,000であった。本ウイルスを部分純化したところその収量は感染C. quinoa葉50gあたり3.6mgであった。部分純化標品をウサギに免疫し,抗血清の作製を行ったところ,ELISA法やウェスタンブロット法に利用可能であった。以上より,本ウイルスをBBWVの1系統と同定し,BBWVによるエキザカムの病害は未報告のため,病名を萎縮病,英名をdwarfとすることを提案した。

Exacum (Exacum affine) is an ornamental plant, which is popular as a pot flower in summer in Japan. In several glasshouses of growers in Kanagawa prefecture in 1989, high incidence of symptoms such as severe dwarf, upward rolling of leaves, and reduced number and size of flowers was observed. Host range of the pathogen was tested with the inocula obtained by manual inoculation from diseased exacum to Chenopodium amaranticolor and C. quinoa. Plants of 21 species in 9 families including exacum were infected. Inoculated exacum showed systemic dwarf symptom, sometimes with ring spots, about 3 weeks after inoculation. C. amaranticolor showed chlorotic local lesions followed by systemic downward leaf curling and chlorosis. C. quinoa showed chlorotic local lesions followed by severe systemic chlorosis. Broad bean showed apical necrosis. N. tabacum cv. Samsun and N. occidentalis were also infected. Electron microscopic observation of leaf dips of infected plants stained with 2% phosphotungstic acid (PTA, pH 6.0) revealed isometric particles with a diameter of approximately 27nm. Myzus persicae transmitted the pathogen from systemicaly infected C. amaranticolor to healthy C. amaranticolor after 1hr starving, 10min of acquision period and 3hr of inoculation period. Thermal inactivation point was between 60 and 65℃ and longevity in vitro was up to 4 days. Virus particles were trapped and decorated by Immuno-sorbent electron microscopy with antiserum to Broad bean wilt virus (BBWV)-serotype I (gift from Dr. V. Lisa). Cucumber mosaic virus was not detected by ELISA. Molecular weights of the coat proteins were estimated by Western blotting with antiserum to patchouli mild mosaic virus which is closely related to broad bean wilt virus. Two coat protein bands with molecular weights of approximately 42,000 and 26,000 were observed. The virus was partially purified by the modified method described by Xu et al. (1988) and the yield was 3.6mg/50g of fresh infected C. quinoa. With partially purified virus, antiserum (As-BBWV-E) to the virus was produced by a series of immunization to rabbits. As-BBWV-E could detect the virus by ELISA and Western blotting. Based upon the results, the virus, which caused severe dwarf in exacum was identified as a strain of Broad bean wilt virus (BBWV). Though patchouli mild mosaic virus (PaMMV) shares similar characters with BBWV and is serologically related to BBWV, PaMMV has narrower host range with mild symptoms on some plants. Since BBWV has two serotypes, analysis of the serotype of the virus isolated from exacum is necessary. The disease of exacum caused by BBWV has not been reported in Japan and it was named as dwarf (Ishuku byo).

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