Cassava frogskin disease (CFSD) is an economically important root disease of cassava (Manihot esculenta) in Colombia and other South American countries, including Brazil, Venezuela, Peru, Costa Rica, and Panama. The roots of severely affected plants are thin, making them unsuitable for consumption. In Colombia, phytoplasma infections were confirmed in 35 of 39 genotypes exhibiting mild or severe CFSD symptoms either by direct or nested polymerase chain reaction (PCR) assays employing ribosomal (r)RNA operon primer pairs. The CFSD-associated phytoplasmas were identified as group 16SrIII strains by restriction fragment length polymorphism (RFLP) and sequence analyses of amplified rDNA products, and results were corroborated by PCRs employing group 16SrIII-specific rRNA gene or ribosomal protein (rp) gene primers. Collectively, RFLP analyses indicated that CFSD strains differed from all phytoplasmas described previously in group 16SrIII and, on this basis, the strains were tentatively assigned to new ribosomal and ribosomal protein subgroups 16SrIII-L and rpIII-H, respectively. This is the first molecular identification of a phytoplasma associated with CFSD in cassava in Colombia.
Samples from plants of Cassia italica exhibiting typical witches'-broom symptoms (Cassia witches'-broom; CWB) were examined for the presence of plant pathogenic phytoplasmas by PCR amplification using universal phytoplasma primers. All affected plants yielded positive results. RFLP analyses of rRNA gene products indicated that the phytoplasmas detected were different from those described previously. Phylogenetic analysis of 16S rRNA gene sequences confirmed that CWB represents a distinct lineage and shares a common ancestor with 'Candidatus Phytoplasma phoenicium'. Molecular comparison revealed that the 16S rRNA gene sequences of the four CWB strains (IM-1, IM-2, IM-3 and IM-4) identified in symptomatic C. italica samples were nearly identical (99.6-100 % similarity). The closest relatives were members of the pigeon pea witches'-broom phytoplasma ribosomal group (16SrIX; 95-97 % sequence similarity). On the basis of unique 16S rRNA gene sequences and biological properties, the phytoplasma associated with witches
During a survey of large carrot fields in Serbia, plants showing leaf reddening and/or yellowing, adventitious shoot production and reduction in taproot size and quality were observed in a low percentage of plants. To verify phytoplasma association with the described symptoms and to carry out pathogen differentiation, PCR assays followed by restriction fragment length polymorphism (RFLP) analyses and/or sequencing of phytoplasma 16Sr DNA and ribosomal protein genes l22 and s3, tuf, putative aa kinase plus ribosomal recycling factor genes and DNA helicase gene were carried out. Phytoplasmas belonging to 16SrI-A and 16SrI-B ribosomal subgroups and to rpI-A and rpI-B ribosomal protein subgroups, respectively, were identified by RFLP analyses in 13 of 15 symptomatic plants tested. No amplification was obtained with non-symptomatic carrot samples. The identification was confirmed by sequence analyses of the phytoplasma genes studied. In two carrot samples, presence of interoperon sequence heterogeneity was detected and phytoplasma strains were identified as belonging to 16SrI group but were not assigned to any 16S rRNA or ribosomal protein subgroup. This research allowed the first molecular identification of phytoplasmas infecting carrot in Serbia using several molecular markers, and it indicates that under field conditions in non-epidemic outbreaks a certain amount of genetic mutation may occur in conserved genes of these prokaryotes.
BackgroundGeminiviruses infect a wide range of plant species including Jatropha and cassava both belonging to family Euphorbiaceae. Cassava is traditionally an important food crop in Sub - Saharan countries, while Jatropha is considered as valuable biofuel plant with great perspectives in the future.ResultsA total of 127 Jatropha samples from Ethiopia and Kenya and 124 cassava samples from Kenya were tested by Enzyme-Linked Immunosorbent Assay (ELISA) for RNA viruses and polymerase chain reaction for geminiviruses. Jatropha samples from 4 different districts in Kenya and Ethiopia (analyzed by ELISA) were negative for all three RNA viruses tested: Cassava brown streak virus (CBSV), Cassava common mosaic virus, Cucumber mosaic virus, Three cassava samples from Busia district (Kenya) contained CBSV. Efforts to develop diagnostic approaches allowing reliable pathogen detection in Jatropha, involved the amplification and sequencing of the entire DNA A molecules of 40 Kenyan isolates belonging to African cassava mosaic virus (ACMV) and East African cassava mosaic virus - Uganda. This information enabled the design of novel primers to address different questions: a) primers amplifying longer sequences led to a phylogenetic tree of isolates, allowing some predictions on the evolutionary aspects of Begomoviruses in Jatrophia; b) primers amplifying shorter sequences represent a reliable diagnostic tool. This is the first report of the two Begomoviruses in J. curcas. Two cassava samples were co - infected with cassava mosaic geminivirus and CBSV. A Defective DNA A of ACMV was found for the first time in Jatropha.ConclusionCassava geminiviruses occurring in Jatropha might be spread wider than anticipated. If not taken care of, this virus infection might negatively impact large scale plantations for biofuel production. Being hosts for similar pathogens, the planting vicinity of the two crop plants needs to be handled carefully.
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