VIEW ARTICLE

Association of Beet Western Yellows and Lettuce Mosaic Viruses with Internal Rib Necrosis of Lettuce. F. W. Zink, Specialist in the Experiment Station, Department of Vegetable Crops, University of California, Davis 95616; James E. Duffus, Plant Pathologist, Plant Science Research Division, ARS, USDA, United States Agricultural Research Station, Salinas, California 93901. Phytopathology 62:1141-1144. Accepted for publication 12 April 1972. DOI: 10.1094/Phyto-62-1141.

The internal rib necrosis (IRN) disease of Lactuca sativa L. 'Climax' that caused considerable damage in the Imperial Valley of California in 1969 was associated with two viruses prevalent in the area. Both beet western yellows virus (BWYV) and lettuce mosaic virus (LMV) were recovered from Imperial Valley lettuce cultivar Climax severely affected with IRN. The disorder was not reproduced in IRN-susceptible cultivars Climax and Vanguard by infection with BWYV. Infection with LMV produced IRN symptoms in a relatively low percentage of Climax plants, but none in Vanguard. The incidence of IRN was higher in both Climax and Vanguard when infected with the combination BWYV + LMV. A synergistic effect on the growth of Climax and Vanguard was observed when both viruses were present. The IRN-resistant cultivars Great Lakes 118 and Calmar did not exhibit a synergistic response to the combination of the viruses. The genetic relationship of IRN-susceptible cultivars and the etiology of the disease on the basis of the combination of BWYV + LMV are discussed.