First Report of Tobacco Bushy Top Disease in China.

Abstract

In 1993, a severe epidemic of a new disease of flue-cured tobacco (Nicotiana tabacum) occurred in western Yunnan Province, People's Republic of China. Since then, over 40,000 ha of tobacco have been affected, with an average incidence of ≈15%. Infected plants were stunted, and leaves showed symptoms of vein distortion, vein clearing, mottling, and rounding. Axillary buds sprouted from the main stem of infected plants early and formed lateral shoots, on which other shoots were produced. As a result, the infected plants presented the characteristic "bushy" appearance. Aphid- (Myzus persicae (Sulzer)) and sap-transmission experiments were conducted. In aphid-transmission tests, after an acquisition feeding period of 24 h on diseased tobacco, the shortest test feeding that resulted in infection was 5 min. The causal agent(s) was readily sap-transmissible, but it could not be transmitted from sap-inoculated plants to healthy plants by aphids. Thirty-two species of plants in eleven families were tested by sap-inoculation for infectivity to alternative hosts by the casual agent(s). All the species of Nicotiana tested were infected. All the hosts were restricted to the solanaceae. The symptoms, transmission, and host range of this disease were identical to those of tobacco bushy top disease in Zimbabwe (1). Using umbravirus-specific primers (3), a 550-bp DNA fragment was amplified by reverse transcription-polymerase chain reaction (RT-PCR) from diseased tobacco, whose sequence (GenBank Accession No. AF402620) indicated the occurrence of an umbravirus. The results coincided with the taxonomic status of Tobacco bushy top virus, one of the causal agents of tobacco bushy top disease (1), a tentative species of the genus Umbravirus (2). To our knowledge, this is the first report of tobacco bushy top disease in China and the first report of a large outbreak of the disease outside sub-Saharan Africa.