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

Abstract

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.

Emerging pests and diseases of South‐east Asian cassava: a comprehensive evaluation of geographic priorities, management options and research needs

“…The systemic cassava witches' broom (CWB) is thought to be associated with Candidatus Phytoplasma belonging to 16SrI, 16SrII and 16SIII groups . The disease causes symptoms such as dwarfism, leaf proliferation, shortened internodes and, at times, smaller roots .…”

“…CWB is widely distributed in the Americas and SE Asia, and cassava plants with CWB‐like symptoms were recently reported from Uganda . In SE Asia, CWB was first reported in eastern Thailand in the 1990s, and subsequent reports were made in several other Asian countries . CWB can cause yield reductions of up to 90%, and is equally thought to affect starch content and quality .…”

“…In SE Asia, CWB was first reported in eastern Thailand in the 1990s, and subsequent reports were made in several other Asian countries . CWB can cause yield reductions of up to 90%, and is equally thought to affect starch content and quality . While region‐wide spread of CWB is facilitated through human‐mediated distribution of infected planting material, the pathogen is likely to be transmitted by one or more insect vectors .…”

“…In stark contrast to the wealth of scientific information on CBB, little is known about CWB. While the disease is assumed to be caused by different phytoplasma strains, and vectored by one or more insect species, key aspects of disease etiology, epidemiology and control remain to be investigated. Once the identity and ecology of CWB vectors have been elucidated, vector management could constitute an effective way of managing this disease and slowing its within‐field spread .…”

“…However, over the past decade, several non‐native pests have made their arrival, and a number of long‐time invaders or endemic pests are increasingly reported at outbreak levels. The invasive cassava mealybug Phenacoccus manihoti Matile‐Ferrero (Hemiptera: Pseudococcidae) and the phytoplasma disease cassava witches' broom are among the emergent phytosanitary problems of local cassava crops . Several of these pest invaders have readily established, spread fast through natural and anthropogenic means, and have progressively widened the yield gap.…”