The underestimated diversity of phytoplasmas in Latin America

Abstract

Phytoplasmas ('Candidatus Phytoplasma') are insect-transmitted, cell-wall-less, plant-pathogenic bacteria that cause economically important crop diseases. Because phytoplasmas are difficult or impossible to culture in vitro, they are classified taxonomically according to the convention used for unculturable micro-organisms. The first coherent scheme of classification of phytoplasmas, based on the RFLP pattern of the 16S rRNA-encoding gene generated with 17 restriction endonucleases, was updated several times until the development of the iPhyClassifier. iPhyClassifier is an interactive online tool capable of determining the species, group and subgroup of 'Candidatus Phytoplasma' of unknown samples using the 16S F2nR2 sequence. Latin America, an important geographical area in relation to food production, has a high incidence of plant diseases caused by phytoplasmas. However, many phytoplasmas associated with these diseases have not been properly classified. An extensive literature review and the use of iPhyClassifier allowed us to identify two new tentative groups (16SrXXXIII-A and 16SrXXXIV-A) and the following tentative new subgroups among Latin American strains that were either previously unclassified or misclassified: six in 16SrI, six in 16SrII, one in 16SrIII, one in 16SrVII, one in 16SrIX, one in 16SrXII and two in 16SrXIII.