THE BEET LEAFHOPPER-TRANSMITTED VIRESCENCE AGENT CAUSES TOMATO BIG BUD DISEASE IN CALIFORNIA

Mycoplasmalike organisms (MLOs) are associated with big bud disease of tomatoes (Lycopersicon esculentum) in many parts of the world. In only a few cases, however, have the MLOs associated with the disease been characterized. We used biological and genetic data to establish that the causal agent of tomato big bud (TBB) disease in California is the beet leafhopper-transmitted virescence agent (BLTVA) MLO. Healthy Circulifer tenellus leafhoppers acquired the BLTVA MLO from field-collected, symptomatic tomato plants and transmitted it to healthy tomato plants, which developed typical big bud symptoms. Healthy tomatoes inoculated with the BLTVA type line (FC-83-13) also developed the floral gigantism and virescence characteristic of the disease. A California TBB MLO isolate caused symptoms typical of those caused by the BLTVA, including induction of premature flowering, on a standard plant host range. Southern blot analysis of DNA from field plants and from greenhouse tomato plants inoculated with a California TBB MLO isolate showed that all samples possessed plasmids that hybridized with a cloned BLTVA MLO plasmid. Macrosteles fascifrons did not transmit a virescence agent from symptomatic, field-collected tomatoes, and tomato plants infected with western aster yellows MLO failed to develop floral gigantism or virescence.