The effect of temperature on symptom expression and detection of banana streak badnavirus (BSV) by immunosorbent electronmicroscopy (ISEM) and enzyme-linked immunosorbent assay of 12 in vitro-propagated plantain hybrids (genome AAB x AA), 3 ABB cooking banana, and 3 AAB plantain landraces was studied. Experiments were done for 2 years under two temperature regimes, 28 to 35 degrees C in a screenhouse and 22 degrees C in a temperature-controlled room. Most BSV-infected plants of plantain hybrids expressed symptoms under both conditions. Symptom expression was enhanced when plants were continuously grown at 22 degrees C, but later became indiscernible when plants were continuously grown at 28 to 35 degrees C. Plants grown at 22 degrees C and showing severe symptoms contained significantly higher virus titer than plants grown at 28 to 35 degrees C. When asymptomatic plants with very low virus titer at 28 to 35 degrees C were transferred back to 22 degrees C, there was a significant increase in both symptom severity and concentration of virus (greater than 3 to 5 times) in leaf tissues after 9 months. In contrast, the concentration of virus and symptom severity decreased in plants after transfer from 22 degrees C to 28 to 35 degrees C. Micropropagated plants of AAB plantain landrace cv. Mimi Abue and ABB cooking bananas (cvs. Bluggoe, Cardaba, and Pelipita) did not express visible symptoms under either temperature regime, but BSV was detected by ISEM in 23% of the plants. After 2 years at 22 degrees C, virus was detected in 64% of the plants, but the concentration of virus remained low. Implications of these results on quarantine screening of in vitro plants and virus diagnosis are discussed.
