Studies on melon necrotic spot virus disease of cucumber and on the control of the fungus vector (<i>Olpidium radicale</i>)

Abstract

SUMMARY Melon necrotic leaf spot virus (MNSV) caused a major outbreak of a leaf necrosis disease of hydroponically‐grown cucumber plants at Humberside in 1983. The virus had c . 33 nm diam. particles which reacted serologically with MNSV antiserum of Dutch or American origin. Virus particles, which contained a single polypeptide (mol. wt 45 × 10 3 ) and a presumed RNA species (mol. wt 1.5 × 10 6 ), had a sedimentation coefficient ( s 20.w ) of 134 S and a buoyant density in caesium chloride of 1.35 g/cm 3 . The virus was mechanically transmissible, confined to species of Cucurbitaceae , transmitted by zoospores of Olpidium radicale and retained in the resting spores of the fungus. MNSV is thus both water‐borne and soil‐borne. O. radicale zoospores were killed in &lt;5 min in suspensions containing 20 μg/ml of the surfactant Agral (alkyl phenol ethylene oxide). The disease did not reappear in 1984 when the cucumber crops were fed with nutrients containing 20μg/ml Agral.