WEEDS AS RESERVOIR HOSTS OF THE LETTUCE BIG-VEIN VIRUS

Abstract

The lettuce big-vein virus (BVV) was recovered from 2 of 23 lettuce plants (Lactuca sativa L.) and 2 of 24 sow thistle (Sonchus oleraceus L.) plants sampled in 1962 and 1963 in areas of the lower Sacramento Valley where lettuce had not previously been grown. BVV is considered to be an indigenous virus of plant species in the Compositae family; these apparently are symptomless hosts and the presence of BVV is noted only when lettuce is planted under favorable environmental conditions. A BVV-Olpidium isolate from sow thistle was shown to be a physiological strain differing from the lettuce isolate in transmitting BVV to sow thistle and multiplying well in sow thistle roots. In addition, the susceptibility of Lactuca spp., Cichorium spp., and Taraxacum officinale to BVV-lettuce Olpidium was tested; only Laciuca serriola, Lactuca saligna, Cichorium sp., and a sow thistle from Japan showed good symptoms, Lactuca gracoglossum and Lactuca virosa showed symptoms poorly. Of the symptomless species, Olpidium and BVV were recovered from Lactuca muralis, T. officinale, and chicory (cv. asparagus) but not from endive (cv. No. 5) or chicory (cv. Large rooted). Sow thistle yellow-vein virus produces symptoms suggestive of big vein in sow thistle but its identity as a distinct virus transmitted by Nasonovia lactucae (L.) was confirmed.