Widespread distribution and a new recombinant species of Brazilian virus associated with cotton blue disease.

BACKGROUND: Cotton blue disease (CBD), an important global cotton crop pathology responsible for major economic losses, is prevalent in the major cotton-producing states of Brazil. Typical CBD symptoms include stunting due to internodal shortening, leaf rolling, intense green foliage, and yellowing veins. Atypical CBD symptoms, including reddish and withered leaves, were also observed in Brazilian cotton fields in 2007. Recently, a Polerovirus named Cotton leafroll dwarf virus (CLRDV) was shown to be associated with CBD. RESULTS: To understand the distribution and genetic diversity of CLRDV in Brazil, we analyzed 23 CBD-symptomatic plants from susceptible cotton varieties originating from five of the six most important cotton-growing states, from 2004-2007. Here, we report on CLRDV diversity in plants with typical or atypical CBD symptoms by comparing viral coat protein, RNA polymerase (RdRp), and intergenic region genomic sequences. CONCLUSION: The virus had a widespread distribution with a low genetic diversity; however, three divergent isolates were associated with atypical CBD symptoms. These divergent isolates had a CLRDV-related coat protein but a distinct RdRp sequence, and probably arose from recombination events. Based on the taxonomic rules for the family Luteoviridae, we propose that these three isolates represent isolates of a new species in the genus Polerovirus.

Molecular characterization of a virus from the family Luteoviridae associated with cotton blue disease.

Cotton blue disease is an aphid-transmitted cotton disease described in Brazil in 1962 as Vein Mosaic "var. Ribeirão Bonito". At present it causes economically important losses in cotton crops if control measures are not implemented. The observed symptoms and mode of transmission have prompted researchers to speculate that cotton blue disease could be attributed to a member of the family Luteoviridae, but there was no molecular evidence supporting this hypothesis. We have amplified part of the genome of a virus associated with this disease using degenerate primers for members of the family Luteoviridae. Sequence analysis of the entire capsid and a partial RdRp revealed a virus probably belonging to the genus Polerovirus. Based on our results we propose that cotton blue disease is associated with a virus with the putative name Cotton leafroll dwarf virus (CLRDV).

Co-suppression mediated virus resistance in transgenic tobacco plants harboring the 3'-untranslated region of Andean potato mottle virus.

Nicotiana tabacum plants were transformed with the 3'-untranslated region of the Andean Potato Mottle Virus (APMoV) genome RNA-2. Three strategies were used: the introduction of this region in sense and in antisense orientation and of a fragment comprising the entire 3'-untranslated region from RNA-2 and part of the CP22 coat protein sequence. The transgenic lines were inoculated with the virus and different responses were observed, ranging from susceptibility to APMoV to complete immunity to virus infection, in which neither the virion nor viral RNA was detected in the inoculated leaf and leaves that emerged after inoculation. The R1 progeny from different R0 lines also showed an array of virus resistance phenotypes, which was not correlated with the zygotic state of the transgene. Resistance was positively correlated with low levels of transgene mRNA accumulation, indicating a co-suppression-mediated mechanism towards the transgenic transcripts and APMoV viral RNA.