Double-stranded RNA in banana plants with bunchy top disease

Double-stranded RNA (dsRNA) has been isolated from bananas infected with banana bunchy top disease (BBTD) but not from healthy bananas of the same cultivar. Four major dsRNA species were present in seven different extracts and these had molecular weights of 4.40 x 10 6, 1.35 x 10 6, 0"50 × 106 and 0.48 x 106. This pattern of dsRNA species is similar to that in extracts from plants infected with barley yellow dwarf virus or beet western yellows virus strain ST9. The amount of extractable BBTD-specific dsRNA was affected by the temperature at which the infected plants were incubated and the interval between infection and harvest. The maximum amount of dsRNA was obtained from plants incubated at 30 °C and harvested 23 days after inoculation. Banana bunchy top disease (BBTD) is a severe disease of banana plants in many countries of the Asian-Pacific Basin as well as North Africa and India. In Australia, BBTD virtually destroyed the banana industry in the late 1920s and the industry now exists because of a vigorous but expensive inspection and eradication scheme. The cause of BBTD is thought o be a virus, probably a luteovirus (Matthews, 1982) because it is persistently transmitted by the banan