Detection and molecular characterisation of a group 16SrIX phytoplasma infecting citrus (Citrus sinensis and C. limon), coffee (Coffea arabica), periwinkle (Catharanthus roseus), and tabebuia (Tabebuia heterophylla) in Puerto Rico

Abstract

Few studies have determined the presence of phytoplasmas in important crops in Puerto Rico. Disease symptoms resembling those caused by phytoplasmas were observed in pigeon pea (Cajanus cajan), periwinkle (Catharanthus roseus), tabebuia (Tabebuia heterophylla), Spanish lime (Melicoccus bijugatus), ixora (Ixora coccinea), mango (Mangifera indica), cactus (Opuntia spp.), citrus trees (Citrus spp.), and coffee (Coffea arabica). Sixty-two samples from these species were tested using conventional PCR to amplify the 16S rRNA and ribosomal protein genes (rpIV- rpsC). Fifty-one percent of the tested samples (corresponding to periwinkle, pigeon pea, citrus, coffee and tabebuia) were positive for phytoplasmas, with amplicons of 0.8 (16S rRNA gene) and 1.2 kb (rpIV-rpsC genes), depending upon primers used in PCRs. For both genetic loci, DNA sequences showed 99 % identity with pigeon pea witches' broom phytoplasma (PPWB). Due to the lack of studies of potential insect vectors, common Auchenorrhyncha species were sweep-collected from pigeon pea and citrus and tested for phytoplasma. Of nine insect genera collected, Empoasca kraemeri (Cicadellidae), Melormenis antillarum (Flatidae), and Colpoptera maculifrons (Issidae) were positive for PPWB based on results from conventional PCR and DNA sequence analysis. The findings indicate that these insects fed upon the aforementioned plant species, ingesting contents of phloem, and may act as potential phytoplasma vectors in the field. These are first reports of PPWB phytoplasma infections in citrus species (C. sinensis and C. limon), coffee, periwinkle and tabebuia, and in insects (E. kraemeri, M. antillarum and C. maculifrons) for Puerto Rico.