Genetic variation and recombination of RdRp and HSP 70h genes of Citrus tristeza virus isolates from orange trees showing symptoms of citrus sudden death disease

<p>Abstract</p> <p>Background</p> <p>Citrus sudden death (CSD), a disease that rapidly kills orange trees, is an emerging threat to the Brazilian citrus industry. Although the causal agent of CSD has not been definitively determined, based on the disease's distribution and symptomatology it is suspected that the agent may be a new strain of <it>Citrus tristeza virus </it>(CTV). CTV genetic variation was therefore assessed in two Brazilian orange trees displaying CSD symptoms and a third with more conventional CTV symptoms.</p> <p>Results</p> <p>A total of 286 RNA-dependent-RNA polymerase (RdRp) and 284 heat shock protein 70 homolog (HSP70h) gene fragments were determined for CTV variants infecting the three trees. It was discovered that, despite differences in symptomatology, the trees were all apparently coinfected with similar populations of divergent CTV variants. While mixed CTV infections are common, the genetic distance between the most divergent population members observed (24.1% for RdRp and 11.0% for HSP70h) was far greater than that in previously described mixed infections. Recombinants of five distinct RdRp lineages and three distinct HSP70h lineages were easily detectable but respectively accounted for only 5.9 and 11.9% of the RdRp and HSP70h gene fragments analysed and there was no evidence of an association between particular recombinant mosaics and CSD. Also, comparisons of CTV population structures indicated that the two most similar CTV populations were those of one of the trees with CSD and the tree without CSD.</p> <p>Conclusion</p> <p>We suggest that if CTV is the causal agent of CSD, it is most likely a subtle feature of population structures within mixed infections and not merely the presence (or absence) of a single CTV variant within these populations that triggers the disease.</p

The Genetics and Genomics of Virus Resistance in Maize

Viruses cause significant diseases on maize worldwide. Intensive agronomic practices, changes in vector distribution, and the introduction of vectors and viruses into new areas can result in emerging disease problems. Because deployment of resistant hybrids and cultivars is considered to be both economically viable and environmentally sustainable, genes and quantitative trait loci for most economically important virus diseases have been identified. Examination of multiple studies indicates the importance of regions of maize chromosomes 2, 3, 6, and 10 in virus resistance. An understanding of the molecular basis of virus resistance in maize is beginning to emerge, and two genes conferring resistance to sugarcane mosaic virus, Scmv1 and Scmv2, have been cloned and characterized. Recent studies provide hints of other pathways and genes critical to virus resistance in maize, but further work is required to determine the roles of these in virus susceptibility and resistance. This research will be facilitated by rapidly advancing technologies for functional analysis of genes in maize

A strain of soybean mosaic virus infecting Passiflora spp. in Colombia

Viruses causing severe mosaic, epinasty, defoliation, and premature death of Passiflora spp. were isolated from west central Colombia. Western blot analyses indicated the presence of potyviruses. Two Colombian isolates (COL-22 and -GR) were compared to known potyviruses as to host range, symptomatology, serological activity, amino acid and nucleotide sequence similarity in the coat protein and 3' noncoding region (3'NCR), and reactivity in dot-blot hybridization. Host range and symptomatology of COL-22 and -GR indicated they are similar to soybean mosaic virus (SMV). Also, both isolates reacted strongly with SMV antisera in immunodiffusion plates. Aphid transmission by Aphis gossypii and Toxoptera citricida was confirmed, but seed transmission was not demonstrated. In addition to COL-22 and -GR, five other Colombian isolates were cloned and sequenced. The deduced coat protein amino acid sequences for all of the Colombian isolates were virtually identical and shared a 98% similarity with SMV. Dot-blot hybridization experiments, using DNA complementary to the 3'NCR of the virus as a probe, further confirmed that the potyvirus infecting Passiflora spp. in Colombia is a strain of SMV. To our knowledge, infection of Passiflora spp. by a strain of SMV has not been previously reported