Detection and identification of ‘Candidatus Phytoplasma asteris’-related phytoplasmas associated with a witches’ broom disease of cassava in Vietnam

Cassava witches’ broom (CWB) is an important disease of Manihot esculenta Crantz that is widely cultivated across South East Asia. In 2010, more than 60,000 ha were affected in Vietnam with crop losses as high as 80%, and reductions in yield and starch content reached 30%. The disease was observed in Quang Ngai, Dong Nai and Yen Bai provinces of Vietnam, also affecting the availability of clean planting material. Studies were then carried out on the etiology of this disease to acquire information about its management. Aster yellows phytoplasmas were detected and restriction fragment length polymorphism analyses of nested PCRamplified fragments from Vietnamese CWB phytoplasmas indicated the presence of differentiable strains all related to the 16SrI group. Sequence analyses of partial 16S rDNA fragments showed that Vietnamese CWB phytoplasmas have 99% similarity with ‘Candidatus Phytoplasma asteris’. To our knowledge, this is the first report of cassava infection with phytoplasmas related to the 16SrI group in Vietnam.