CUCUMBER NECROSIS VIRUS

Abstract

Cucumber necrosis virus (CNV) has been isolated several times during the last 7 years from cucumbers grown under glass in southwestern Ontario. Cucumber is the only host known to be systemically infected by the virus. Although CNV exhibits many properties of viruses included in the tobacco necrosis (TNV) group, it is considered to be sufficiently different to warrant the above distinctive designation.CNV possesses a small thermal coefficient, a thermal inactivation point between 75 and 80 °C, and a dilution end point between 10⁻⁴ and 10⁻⁵.During the short-day season of greenhouse production of cucumbers the virus causes severe foliar symptoms. Serious stunting of growth occurs and infected plants usually die 6 weeks to 2 months after the virus becomes systemic. In natural infections CNV enters by way of the roots, and subsequently may invade the aerial organs. Wide variability in the upward movement of the virus from inoculated cotyledons and roots of cucumber plants of the same age is noted.In inoculated unifoliate leaves of cowpea and French bean CNV displays a lower invasive capacity than TNV. With serial transfers of juice from cowpea leaves, inoculated initially with both viruses, TNV soon predominates.