Molecular Identification of ' Phytoplasma malaysianum'-Related Strains Associated with Palm Yellow Leaf Disease and Phylogenetic Diversity of the Phytoplasmas Within the 16SrXXXII Group.

palm is an important cash plant in Hainan Island of China and also in the tropical regions of the world. palm yellow leaf (AcYL) disease caused by phytoplasmas is a devastating disease for plant production. In the study, the phytoplasmas associated with the AcYL disease were identified and characterized based on their conserved genes, and genetic variation and phylogenetic relationship of the phytoplasma strains in the 16SrXXXII group were demonstrated. The results indicated that palm plants showing yellow leaf symptoms were infected by ' Phytoplasma malaysianum'-related strains belonging to the 16SrXXXII-D subgroup. BLAST and multiple sequence alignment analysis based on 16S rRNA and genes showed that the AcYL phytoplasmas shared 100% sequence identity and 100% homology with the '. P. malaysianum'-related strains. Phylogenetic analysis indicated that the AcYL phytoplasmas and ' P. malaysianum'-related strains belonging to the 16SrXXXII group clustered into one clade with a 100% bootstrap value. Based on computer-simulated digestions, six kinds of restriction fragment length polymorphism patterns within the 16SrXXXII group were obtained, and a novel subgroup in the 16Sr group was recommended to propose and describe the relevant strains in this 16Sr subgroup. To our knowledge, this is the first study to report that palm showing yellow leaf symptoms was infected by '. P. malaysianum'-related strains belonging to the 16SrXXXII group. A novel 16Sr subgroup, 16SrXXXII-F, was proposed based on the systematical analysis of genetic variation of all phytoplasmas within the 16SrXXXII group. The findings of this study will support references for monitoring the epidemiology and developing effective prevention strategies for AcYL disease.