ADVANCES IN RESEARCH OF LONGAN WITCHES' BROOM DISEASE

This paper reports recent advances in the research of longan witches' broom disease (LWBD), a wide-spread and important disease in China. In the studies to identify the causal organism a filamentous virus, the particles of which were mostly 700-1300nm in length, was purified from infected trees. The virus was not found in healthy plants. Rabbit antiserum against the virus (longan witches' broom disease virus, LWBDV) was prepared and used to trap the virus from infected leaves by the SP-ISEM (staphylococcin protein A-immune serum electron microscope) technique. Transmission tests showed that the seeds and budwoods of longan, dodder (Cuscuta campestris), litchi stink bug (Tessaratoma papillosa) and longan psylla (Cornegenapsylla sinica) transmitted this virus, whereas transmission via pollen requires further research. However, the possibility of transmission by sap smearing was excluded. Based on pathology and transmission, integrated management was proposed incorporating: strict quarantine inspection, selection and use of disease-resistant varieties, such as ‘Lidongben’ and ‘Shuinan No. 1’, establishment of virus-free nurseries, timely control of insect vectors, removal of infected branches, inflorescences and infected seedlings from the nursery, and improvement of tree vigor by judicious fertilization, irrigation and soil management.