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Detection and classification of Candidatus Phytopalsma associated with cassava witches’ broom disease in Thailand

Phanuwat Moonjuntha: Tokyo university of Agriculture

<div>Cassava witches’ broom (CWB) diseases have been reported in Viet Nam since 2013 with phytoplasma in 16SrI and 16SrII groups and in Thailand since 2017 in 16SrI group. The CWB shows symptoms such as small and yellowing leaves, leaf proliferation and stem necrosis. In Thailand CWB like symptoms are observed in many cassava planted area. To detect phytoplasma associated with CWB in Thailand, 65 CWB samples were collected from 156 fields in 11 provinces in Thailand during year 2015 – 2016. Nested PCR by two sets of primer pairs (SN910610 and SN011119 followed by R16F2n and R16R2), RFLP, phylogenetic analysis and observation by transmission electron microscope (TEM) were conducted to detect possible <em>Ca</em>. Phytoplasma. Fifty one samples were positive by nested PCR. Nucleotide sequence showed 99% similarity to <em>Ca</em>. Phytoplasma accession no. KM280680 from CWB in Viet Nam. Phyologenetic analysis from nucleotide sequence of 16S rDNA classified Thai isolates into 16SrII group. By PCR-RFLP using <em>Hae</em>III, nucleotides of Thai CWB and Sugarcane white leaf phytoplasma were separated. TEM micrographs of CWB leaves showed phytoplasma like cells with the approximate size of 740 – 920 nm. The detection of other genes and pathogenicity test will be useful to confirm this possible pathogen</div>

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