Group 16SrVI Research Articles

Differential amplification of sequence heterogeneous ribosomal RNA genes and classification of the ‘ Fragaria multicipita’ phytoplasma

Ribosomal (r) RNA interoperon sequence heterogeneity in the 'Fragaria multicipita' phytoplasma, a member of group 16SrVI, was initially observed in RFLP patterns of rDNA amplified in the polymerase chain reaction (PCR), and was confirmed through sequence analysis of cloned rDNA. Sequences from operons rrnA and rrnB were amplified in PCR primed by primer pair P1/P7 but from only rrnA in PCR primed by primer pair R16mF2/R16mR1. Preferential amplification of DNA from operon rrnA was explained by base mismatches between the R16mF2/R16mR1 primers and primer annealing sites in rrnB. The results revealed potential for classification of a phytoplasma into two different subgroups within a 16S rRNA group, if the phytoplasma's 16S rRNA gene sequences are independently characterized. It is suggested that the rRNA operon containing species-specific signature sequence(s) should be specified, and where possible sequences from both 16S rRNA genes should be included, in descriptions of new 'Candidatus Phytoplasma species'.

The Association of Clover Proliferation Phytoplasma with Stolbur Disease of Pepper in Spain

A phytoplasma disease, `stolbur', affects pepper (Capsicum annuum) in Spain. Affected plants have short internodes, green flowers buds and other symptoms that are characteristic of phytoplasma‐induced diseases. Herein the detection and classification of the phytoplasma that may cause the disease is reported. DNA amplification by polymerase chain reaction, sequencing and phylogenetic analysis indicate that this phytoplasma should be classified in the clover proliferation group 16SrVI, a group that is clearly distinct from the stolbur group 16SrXII.

First Report of Alfalfa Witches Broom Disease in Oman Caused by a Phytoplasma of the 16Sr II Group.

Alfalfa (Medicago sativa L.) is a primary forage crop in the Sultanate of Oman. A new disease of alfalfa in Oman is characterized by proliferation of shoots and yellowing of leaves in 1- to 2-year-old plants and tillering of stems in 4- to 5-year-old plants. Annual losses due to this disease are estimated at more than US$ 23 million. Samples of healthy and infected alfalfa plants were collected from different regions. Total DNA was extracted according to Khadhair et al. (1), with minor modifications. Amplification of 16S rDNA was done using a nested polymerase chain reaction (PCR) approach with primers P1/P7 and R16F2n/R16R2. DNA from healthy leaves and sterile water was used as a negative control, while DNA from periwinkle infected with faba bean phyllody (16SrII-C), aster yellows (16SrI), tomato big bud (16SrII-D), sweet potato little leaf (16SrII-D), catharanthus phyllody (16SrVI), and sesame phyllody (16SrII-A) were used as positive controls and for restriction fragment length polymorphism (RFLP) comparisons. Nested 1.25-kb PCR products from infected plant samples were subjected to RFLP analysis with restriction endonucleases RsaI, AluI, HaeIII, HhaI, EcoRI, TaqI, Tru9I, and Sau3AI. The analysis showed that the alfalfa witches' broom phytoplasma (AWBP) belonged to the 16SrII group (peanut witches' broom) and that the AWBP was most similar to sweet potato little leaf (16SrII-D) but distinct from "Candidatus Phytoplasma aurantifolia," the cause of lime witches' broom in Oman. Other phytoplasmas infecting alfalfa have been reported from Europe and North America (1,3), but they belong to the 16SrVI (clover phyllody) and 16SrI (aster yellows) groups. An alfalfa witches' broom reported from Italy (2) forms a separate grouping (4). To our knowledge, this is the first report of a phytoplasma from the peanut witches' broom group infecting alfalfa in the Sultanate of Oman.