Phytopathogenic Mollicutes

Cassava witches’ broom CWB disease is associated with the presence of phytoplasmas. Typical symptoms include witches’ broom, shoot proliferation, short internodes and stunting. Severely infected plants decline, resulting in yield losses of up to 80%. CWB has been reported in several cassava growing regions in Thailand. In total, 25 CWB symptomatic cassava plant samples were collected from 9 plots in Kanchanaburi Province in November 2023. Detection of CWB phytoplasma was carried out using nested PCR assay to amplify the 16S rRNA gene using primers P1/P7, followed by R16F2n/R16R2. A target DNA fragment of approximately 1,800 bp was obtained by PCR in 15 samples, and a 1,200 bp fragment from nested PCR was obtained in 24 samples. Sample KRI-M-4 (GenBank accession number PQ333137) was used for molecular identification. It showed 98.65% identity with the reference strain ‘Candidatus Phytoplasma solani’ (GenBank accession number AF248959). BLAST analysis in the GenBank, NCBI database showed 99.07% similarity to a ‘Ca. P. solani’ strain from Japan (GenBank accession number LC460259). The partial stamp gene of KRI-M-4 strain was cloned, sequenced, and analyzed in the GenBank, NCBI database showing 100% identity to a ‘Ca. P. solani’ strain from Thailand (GenBank accession number MW464308). Phylogenetic tree analysis and a heatmap of pairwise distance analysis of the 16S rDNA sequences and partial stamp gene sequences confirmed that the KRI-M-4 strain clustered with phytoplasmas in the 16SrXII group. This is the first report of the presence of a ‘Ca. P. solani’ strain associated with CWB disease, in plants exhibiting witches’ broom, yellow leaf, and short internode symptoms in Thailand.