Observations on a Virus Disease of Certain Crucifers in Trinidad

Abstract

A virus disease ofBrassica juncea Coss., B. Mnensis L. and Raphanus sativus L. var.hortensis Backer occurs in Trinidad, but is not serious. Rape (Brassica napus L.), turnip(B. rapa L.) and Lepidium virginicum L. are susceptible, but cabbage, cauliflower, kohlrabi and the European radish seem to be immune. Zinnia elegans Jacq. and tobacco (Nicotiana tabacum L.) are also susceptible, but no infections were obtained on six other Nicotiana species, beetroot, Swiss chard and cowpea. Tobacco gives only necrotic local lesions, whereas the other hosts give no local lesions, but a systemic mottling, usually accompanied in crucifers by leaf deformation and stunting of the plant.The virus is transmitted by Rhopalosiphum pseudobrassicae (Davis), which is probably responsible for spread in the field. Its thermal inactivaticm‐point is 58d̀ C, dilution end‐point 1:1000, and longevity in vitro 4 days at 16–18d̀ C. and 3 days at 24–30d̀ C. The properties and host range of this virus are compared with those of others affecting the Cruciferae. It has affinities with some of them, but is considered to be distinct.