High diversity, expanding populations and purifying selection in phytoplasmas causing coconut lethal yellowing in Mozambique

In this study, the putative phytoplasma species causing coconut lethal yellowing disease in Mozambique and Tanzania were characterized. The 16S rRNA and secA genes were sequenced. Phylogenetic analysis revealed that Mozambican coconut phytoplasmas belong to three different types: 'Candidatus Phytoplasma palmicola' 16SrXXII-A, a second strain that was previously isolated in Tanzania and Kenya (16SrIV-C), and a third strain that was different from all known lethal yellowing phytoplasma species. The third strain potentially represents a novel species and is closely related to pine phytoplasma. Co-infection with 'Ca. Phytoplasma pini'-related and 'Ca. Phytoplasma palmicola' 16SrXXII-A strains was observed. Furthermore, sequence variation in 'Ca. Phytoplasma palmicola' at the population level was consistent with purifying selection and population expansion.