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Lettuce Ring Necrosis, a Viruslike Disease of Lettuce: Evidence for Transmission by Olpidium brassicae . R. N. Campbell, Department of Plant Pathology, University of California, Davis, CA 95616. H. Lot, INRA, Station de Pathologie Vegetale, B. P. 94, 84143 Montfavet Cedex, France. Plant Dis. 80:611. Accepted for publication 26 February 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0611.

Lettuce ring necrosis (LRN) caused severe symptoms on butterhead and crisphead types of lettuce but only mild symptoms on iceberg or cos types Single sporangial isolates of Olpidium brassicae were prepared from three sites in France to prove the vector role of the fungus and lo attempt the separation of the LRN agent (LRNA) and lettuce big vein virus (LBVV). A vector role for O. brassicae was demonstrated, but few isolates transmitted either agent, apparently because they were lost during one to two generation transfers of the fungus. Isolates transmitted LRNA and LBVV together or LBVV alone, but there was no clear evidence for transmission of LRNA alone. The LRNA was carried within the resting spores of the vector. Isolates of O. brassicae from two fields in the Salinas Valley of California carried LBVV and LRNA. This is the first report of LRNA in North America.