Unraveling the Etiology of North American Grapevine Yellows (NAGY): Novel NAGY Phytoplasma Sequevars Related to 'Candidates Phytoplasma pruni'

摘要

North American grapevine yellows (NAGY) disease has sometimes been attributed to infection of Vitis vinifera L. by Primus X-disease phytoplasma ('Candidatus Phytoplasma pruni') but this attribution may not be fully adequate. In this study, phytoplasmastrains related to 'Ca. Phytoplasma pruni' were found in NAGY-diseased grapevines in Maryland, Pennsylvania, Virginia, Ohio, Missouri, and New York State. Based on restriction fragment length polymorphism analysis of 16S ribosomal RNA gene (16S rDNA) sequences, the strains (termed NAGYII1 strains) were classified in group 16SrIII (X-disease group) but they contained a recognition site for the restriction endonuclease Msel that is not present in the 16S rDNA of 'Ca. Phytoplasma pruni'. The 16S rDNA of the strains differed by three or four nucleotides from that of 'Ca. Phytoplasma pruni', indicating that they belonged to two novel 16S rDNA sequevars, designated NAGYIIIa and NAGYIIip. Both sequevars differed from 'Ca. Phytoplasma pruni' by a single basein each of three regions corresponding to species-unique (signature) sequences described for 'Ca. Phytoplasma pruni'. Phylogenetic analyses of 16S rRNA genes and SecY proteins, and single-nucleotide polymorphism analyses of secY and ribosomal protein genes, further distinguished the two grapevine sequevar lineages from one another and from 'Ca. Phytoplasma pruni'. The NAGYIIIa and NAGYIII3 sequevars also differed from 'Ca. Phytoplasma pruni' in regions of the folded SecY protein that are predicted to benear or exposed at the outer surface of the phytoplasma membrane. No evidence indicated that diseased grapevines contained any phytoplasma strain conforming to 'Ca. Phytoplasma pruni' sensu stricto. Because the NAGYIII sequevars have not been reported in X-disease, a question is raised as to whether NAGYIII and Primus X-disease are caused by different phytoplasma genotypes.