Use of Gene Sequencing, Soil Chemical Properties and Microbial Analysis to Confirm the Nature of the Sugarcane Disease Phytoplasmas in Thailand

Phytoplasmas are a group of plant pathogens that reduce yield in various plants including many crops, shrubs, and tree species. They have been classified into various 16Sr groups or ‘ Candidatus Phytoplasma species’ based primarily on the sequences of their 16S rRNA genes. However, other non-ribosomal sequences are often used to fine-tune their classifications. This research aimed to clarify the categorization of the sugarcane phytoplasma s that cause sugarcane white leaf and sugarcane grassy shoot symptoms in Thailand and determine whether they are different strains, based on non-16S ribosomal genes. Forty samples from plants exhibiting both sugarcane symptoms and from symptomless sugarcane were collected and PCR amplifications were done with primers for the 50S rRNA Ser and SecA genes moreover soil samples from non-symptom and symptom fields were collected for soil chemical properties and rhizospheric microorganism analysis. The phylogenetic tree results revealed that isolates displaying both symptom types grouped together based on all three sets of primers, including with isolates from other countries. Additionally, soil chemical properties and rhizospheric microorganism analysis results showed that soil chemical factors and rhizospheric microorganisms did not appear to correlate with the differences in symptoms. It is concluded that the two sugarcane symptoms are caused by the same Phytoplasma strain and that other, as yet unidentified factors, are responsible for this Phytoplasma giving different symptoms in different situations. This is the first evidence of soil chemical properties and rhizospheric microorganism not correlating with the diverse symptoms. As for further study, unidentified factors will be studied including quarantine methods to control the symptoms.