GENOME-BASED STRATEGIES FOR DETECTION AND IDENTIFICATION OF PLANT PATHOGENIC PHYTOPLASMAS AND SPIROPLASMAS
Title: 'Candidatus Phytoplasma sudamericanum' a novel taxon from diseased passion fruit (Passiflora edulis f. flavicarpa Deg.)
Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2011
Publication Date: April 1, 2012
Citation: Davis, R.E., Zhao, Y., Dally, E.L., Jomantiene, R., Lee, I., Wei, W., Kitajima, E. 2012. 'Candidatus Phytoplasma sudamericanum' a novel taxon from diseased passion fruit (Passiflora edulis f. flavicarpa Deg.). International Journal of Systematic and Evolutionary Microbiology. 62:984-989.
Interpretive Summary: Phytoplasmas are very small bacteria that are responsible for hundreds of diseases affecting agriculturally important plants around the world. There is need to improve methods and tools for detecting and identifying phytoplasmas in order to aid efforts to curb the spread of diseases caused by phytoplasmas and to prevent the introduction of foreign phytoplasmas into U.S. agriculture. The present work was initiated to expand knowledge concerning phytoplasmas that infect edible fruit-bearing plants. The work focused on disease of passion fruit in Brazil, where passion fruit is widely grown commercially, is valued as a nutritious source of vitamins, and is used in producing fruit juices. Using DNA-based molecular methods for detection and identification, we discovered that diseased plants of passion fruit were infected by two different phytoplasmas. We found that one is a previously unknown phytoplasma that is related to the phytoplasma that causes X-disease of stone fruit trees, such as peach trees, in the U.S. and Europe. We found that the second represents a previously unknown phytoplasma species. We report DNA markers for both phytoplasmas, and we describe molecular features of the new phytoplasma species, for which we propose the name ‘Candidatus Phytoplasma sudamericanum’. The results of our study provide new information about, and provide new molecular markers for, detection and identification of the two previously unknown phytoplasmas. This advance is significant in part because the complete plant host ranges of the two phytoplasmas are not yet known, and because the phytoplasmas might have potential to invade passion fruit and other agricultural crops in the U.S. This work will interest scientists and students studying plant diseases, diagnostics companies and centers involved in pathogen detection, companies producing disease-free fruit trees, fruit growers and juice producers, and government agencies that implement plant quarantine regulations to prevent the introduction of foreign pests and diseases into U.S. agriculture.
Symptoms of abnormal proliferation of shoots resulting in formation of witches’ broom growths were observed in diseased plants of passion fruit (Passiflora edulis f. flavicarpa Deg.) in Brazil. RFLP analysis of 16S rRNA gene sequences amplified in polymerase chain reactions containing template DNAs extracted from diseased plants collected in Bonita, PE, and Vicosa, MG, Brazil, indicated that such symptoms were associated with infections by two mutually distinct phytoplasmas. One phytoplasma, PassWB-Br4 from Bonita, represents a new subgroup, 16SrIII-U, in the X-disease phytoplasma group (‘Candidatus Phytoplasma pruni’-related strains). The second phytoplasma, PassWB-Br3 from Vicosa, represents a previously undescribed subgroup in group 16SrVI. Phylogenetic analyses of 16S rRNA gene sequences were consistent with the hypothesis that strain PassWB-Br3 is distinct from previously described ‘Ca. Phytoplasma’ species. Nucleotide sequence alignments revealed that strain PassWB-Br3 shared less than 97.5 % similarity of 16S rDNA with previously described ‘Candidatus Phytoplasma’ species. The unique properties of DNA, in addition to natural host and geographical occurrence, support the recognition of strain PassWB-Br3 as a representative of a novel taxon, ‘Candidatus Phytoplasma sudamericanum’.