Host Range and Some Properties of Iris Severe Mosaic Virus found in Japan

Abstract

Pronounced mosaic symptoms are commonly observed in many cultivars of bulbous iris in Japan. The causal virus was transmitted readily by aphids (Aphis gossypii and Myzus persicae) in the non-persistent manner. It was also transmitted by sap-inoculation to 6 of 44 plant species in 13 families. Bulbous iris (Dutch iris) was infected systemically and exhibited pronounced mosaic symptoms. Local lesions were produced on Chenopodium amaranticolor, C. quinoa, Tetragonia expansa, Gomphrena globosa and Nicotiana clevelandii, but G. globosa was infected with difficulty while N. clevelandii was infected without visible symptoms. The presence of the virus in these plants was confirmed by immuno-electron microscopy with antiserum against iris severe mosaic virus (ISMV). Sap from the diseased T. expansa was infective after 10min at 60C but not 65C, after dilution to 10^-3 but not 10^-4, or 3-4days at 20C. The virus particles were filamentous, about 750×13nm. In ultrathin sections of diseased plant leaf tissue, pinwheel and laminated aggregate inclusions were observed in the cytoplasm in the cells. The inclusions found in negatively stained dip-preparations exhibited fine striations with a periodicity of 5.3nm. In immuno-electron microscopy, the virus particles reacted with ISMV antiserum, but not with iris mild mosaic virus antiserum. The virus did not react with antisera against turnip mosaic virus, potato virus Y and bean yellow mosaic virus, in micro-precipitin test. Based on the result mentioned above, the virus was identified as iris severe mosaic virus.