Candidatus phytoplasma solani associated with papaya phytoplasma disease in Thailand

Abstract

Papaya disease caused by phytoplasma has been found severely epidemic in several countries for decades. The disease symptoms include yellows, dieback and mosaic types are similarly seen but has never been reported in Thailand. This is the first report of diseased papaya arisen by Candidatus Phytoplasma solani in Thailand. Detection of phytoplasma in symptomatic papayas by Nested Polymerase Chain Reaction (Nested PCR) using P1/P7 and R16F2n/R16R2 to amplify 16Sr RNA gene. Results showed positive in different six symptoms including; 1) yellow necrosis, 2) bunchy top-like, 3) yellow crinkle, 4) green vain, 5) yellow shoot, and 6) crinkle & mosaic/ mottle. The pleomorphic cells of phytoplasma in sieve cells of Nested PCR positive papaya samples were clearly visualized using transmission electron microscopy. Nucleotides of phytoplasma six isolates were sequenced and submitted as accession no. MT548611, MT548613, MT548614, MW464326, MW464330 and MW533147 in GenBank, NCBI database. Phylogenetic tree analysis of nucleotide sequences was analyzed to compared with 17 papaya phytoplasma sequences that found in foreign countries from GenBank database. Results showed that MT548614, MW464326 and MW464330 were clusterd in the same subgroup with Ca. Phytoplasma solani, of papaya in Taiwan due to their 100% similarity by pairwise distance analysis, while MT548611, MT548613 and MW533147 were clusterd in different subgroup. A close relation among these six isolates was also shown to be 99.86 – 100 % by similarity comparison.