ABSTRACT
A previously uncharacterized virus with flexuous filamentous particles 660 nm in length was identified in the United States in florists' hydrangea (Hydrangea macrophylla), in which it caused chlorotic mottling, leaf deformation, and discoloration. The virus, tentatively named Hydrangea chlorotic mottle virus (HdCMV), was transmitted readily by mechanical inoculation and by Myzus persicae, but infected only H. macrophylla. The amino acid sequence of a 1.7-kb amplicon comprising the 3' terminus of the HdCMV genome contained one partial and three complete putative open reading frames (ORFs) most similar in size, arrangement, and sequence to the homologous regions of the genomes of known carlaviruses. Based on virion morphology, genome properties, and current criteria for species demarcation, it was concluded that HdCMV represented a new species in the genus Carlavirus. Hydrangea ringspot virus (HdRSV, genus Potexvirus) occurred in mixed infections with HdCMV, but the two viruses could be distinguished readily by serological tests.
ABSTRACT
A filamentous virus identified in coleus (Coleus × hybrida) in Minnesota and New York was found to cause veinal necrosis in coleus, although this symptom was observed only under certain conditions. The virus was transmitted readily by mechanical inoculation to coleus and Nicotiana spp. and was not transmitted by Myzus persicae. The particles of the coleus virus had a modal length of 640 nm and a single capsid protein with an estimated molecular mass of 34 kDa. The amino acid sequence of the coat protein region of the coleus virus genome had significant similarities only to the corresponding domain of carlaviruses. Based on virion morphology, capsid protein size, genome size and organization, amino acid sequence, and phylogenetic analyses, the coleus virus, which was named provisionally Coleus vein necrosis virus (CVNV), was concluded to be a new definitive member of the genus Carlavirus. A 2-kb fragment of the 3' terminus of the CVNV genome sequence is accessible under accession number DQ915963 in GenBank.
ABSTRACT
Ustilago maydis virus H1 (Umv-H1) is a mycovirus that infects Ustilago maydis, a fungal pathogen of maize. As Zea mays was domesticated, it carried with it many associated symbionts, such that the subsequent range expansion and cultivation of maize should have affected maize symbionts' evolutionary history dramatically. Because transmission of Umv-H1 takes place only through cytoplasmic fusion during mating of U. maydis individuals, the population dynamics of U. maydis and maize are expected to affect the population structure of the viral symbiont strongly. Here, the impact of changes in the evolutionary history of U. maydis on that of Umv-H1 was investigated. The high mutation rate of this virus allows inferences to be made about the evolution and divergence of Umv-H1 lineages as a result of the recent changes in U. maydis geographical and genetic structure. The phylogeographical history and genetic structure of Umv-H1 populations in the USA and Mexico were determined by using analyses of viral nucleotide sequence variation. Infection and recombination frequencies, genetic diversity and rates of neutral evolution were also assessed, to make inferences regarding evolutionary processes underlying the population genetic structure of ancestral and descendent populations. The results suggest that Mexico represents the ancestral population of Umv-H1, from which the virus has been carried with U. maydis populations into the USA. Thus, the population dynamics of one symbiont represent a major evolutionary force on the co-evolutionary dynamics of symbiotic partners.
