First Report of Tomato Bushy Stunt Virus Isolated from Lettuce

In recent years a disease causing dieback and necrosis of Romaine and leaf lettuce has become increasingly important in California and incidence is becoming more widespread. This disease has been primarily found in areas where soil has been dredged from a river or in flooded land. Tomato bushy stunt virus (TBSV) isolates have been isolated from roots and leaves of symptomatic lettuce. The particles are isometric with a diameter of 30 nm. Double-stranded RNA (dsRNA) profiles are identical to the tomato and Prunus isolates of TBSV. However, spurs are formed in agar double diffusion tests when antisera to the tomato and Prunus isolates were used. A similar dieback disease of lettuce was observed in several counties of California during the mid-1980s. Symptoms of this disease are very similar to those described for the “brown blight” disease of lettuce reported in the 1920s (1), including severe stunting of plants and extensive chlorosis, mottling, and necrosis of older leaves. Plants infected early in their development may die. Although inoculation under greenhouse conditions has not reproduced the dieback disease in lettuce, TBSV has been consistently isolated from field-grown, symptomatic lettuce. The question of whether this new dieback disease of lettuce is caused only by lettuce isolates of TBSV or if some other viruses are also involved needs further studies. Reference: (1) I. C. Jagger. Phytopathology 30:53, 1940.