Molecular characterization identifies 16SrXI-B group phytoplasma (‘Candidatus Phytoplasma oryzae’-related strain) associated with root wilt disease of coconut in India

Abstract

The root wilt disease of coconut is a major threat to coconut cultivation in southern India. Here we report the species assignment and 16Sr sub group classification of phytoplasma associated with coconut root wilt disease. Leaf samples were collected from root wilt symptomatic palms in Kayankulam district of Kerala. The phytoplasma 16S rRNA gene was amplified using three sets of primers namely, 1F7/7R3-1F7/7R2, 3Fwd/3Rev-3Fwd/5Rev, and P1/P7-R16F2n/R16R2 producing amplicons of 490, 1300, and 1250bp respectively. Partial secA gene sequence of 480bp from root wilt disease phytoplasma was amplified using primers cocsf/cocsr. Sequence characterization and phylogenetic analysis of 16S rRNA and secA genes of root wilt disease phytoplasma grouped it with the rice yellow dwarf group phytoplasmas and identified coconut RWD phytoplasma as ‘Candidatus Phytoplasma oryzae’ related strain. Further, in silico restriction digestion study of phytoplasmal 16S rRNA gene region between primers R16F2n/R16R2 was performed for 16Sr group/sub group classification. The root wilt disease phytoplasma grouped with the 16SrXI group members. In the sub group classification it produced identical restriction profile as the sugarcane white leaf phytoplasma and arecanut yellow leaf disease phytoplasma, and hence, it was placed in the 16SrXI-B sub group.