Complete genome sequence analysis of a genetic variant of grapevine virus L from the grapevine cultivar Blanc du Bois.

The complete genome sequences of two grapevine virus L (GVL) isolates collected from the wine grape cultivar Blanc du Bois (Vitis spp.: 'Florida D 6-148'×'Cardinal') in Texas were determined. The two genome sequences (excluding the polyA tail) were each 7594 nucleotide long and 99.7% identical to each other, but they shared only ~74% identity with those of previously published GVL isolates. Further analysis showed that the two Texas GVL isolates also diverged significantly from previously published isolates of the virus in each of the five ORFs at both the nucleotide and amino acid level, indicating that they represent a new phylogroup of this virus.

Grapevine virus M, a novel vitivirus discovered in the American hybrid bunch grape cultivar Blanc du Bois in Texas.

A novel ssRNA (+) virus with molecular properties typical of members of the genus Vitivirus (family Betaflexiviridae; subfamily Trivirinae) was discovered by high-throughput sequencing in samples of the American hybrid bunch grape cultivar Blanc du Bois in Texas. The results were independently confirmed by Sanger sequencing of the virus isolate, whose genome length is 7,387 nt, excluding the polyA tail. The genome sequence contains five ORFs that are homologous and phylogenetically related to ORFs of grapevine-infecting vitiviruses. The name "grapevine virus M" is proposed for this new virus, whose sequence divergence exceeds the current ICTV species demarcation threshold for the genus Vitivirus.

Xylella fastidiosa: a model for analyzing agricultural biosecurity.

The threat to national security posed by the hostile release of human pathogens has been extensively documented. However, conclusions regarding the menace that plant pests and pathogens pose to the national economy and food supply are less developed. Here we present a risk analysis for the arrival and spread of foreign plant pathogens into the U.S. agricultural system. Xylella fastidiosa Citrus Variegated Chlorosis strain, an exotic plant pathogenic bacterium listed as a regulated biological agent under the Agricultural Bioterrorism Protection Act of 2002, serves as a model to evaluate the threat that plant diseases pose to crops and agriculture-dependent industries. We assess the nation's capacity to detect, contain, and manage newly introduced plant pathogens, exposing areas that need improvement and limitations of the system. This analysis provides a framework for understanding the risk that exotic plant diseases pose to U.S. agricultural biosecurity and a reference to continue preparing for the possible arrival of these threats.

Genomic and biological analysis of phage Xfas53 and related prophages of Xylella fastidiosa.

We report the plaque propagation and genomic analysis of Xfas53, a temperate phage of Xylella fastidiosa. Xfas53 was isolated from supernatants of X. fastidiosa strain 53 and forms plaques on the sequenced strain Temecula. Xfas53 forms short-tailed virions, morphologically similar to podophage P22. The 36.7-kb genome is predicted to encode 45 proteins. The Xfas53 terminase and structural genes are related at a protein and gene order level to P22. The left arm of the Xfas53 genome has over 90% nucleotide identity to multiple prophage elements of the sequenced X. fastidiosa strains. This arm encodes proteins involved in DNA metabolism, integration, and lysogenic control. In contrast to Xfas53, each of these prophages encodes head and DNA packaging proteins related to the siphophage lambda and tail morphogenesis proteins related to those of myophage P2. Therefore, it appears that Xfas53 was formed by recombination between a widespread family of X. fastidiosa P2-related prophage elements and a podophage distantly related to phage P22. The lysis cassette of Xfas53 is predicted to encode a pinholin, a signal anchor and release (SAR) endolysin, and Rz and Rz1 equivalents. The holin gene encodes a pinholin and appears to be subject to an unprecedented degree of negative regulation at both the level of expression, with rho-independent transcriptional termination and RNA structure-dependent translational repression, and the level of holin function, with two upstream translational starts predicted to encode antiholin products. A notable feature of Xfas53 and related prophages is the presence of 220- to 390-nucleotide degenerate tandem direct repeats encoding putative DNA binding proteins. Additionally, each phage encodes at least two BroN domain-containing proteins possibly involved in lysogenic control. Xfas53 exhibits unusually slow adsorption kinetics, possibly an adaptation to the confined niche of its slow-growing host.

The origin of Ceratocystis fagacearum, the oak wilt fungus.

The oak wilt pathogen, Ceratocystis fagacearum, may be another example of a damaging, exotic species in forest ecosystems in the United States. Though C. fagacearum has received much research attention, the origin of the fungus is unknown. The pathogen may have been endemic at a low incidence until increased disturbances, changes in land use, and forest management created conditions favorable for disease epidemics. The host genus Quercus contains some relatively resistant species native to the United States, further supporting the hypothesis that the pathogen is native in origin. However, there are also many common, highly susceptible Quercus species--a characteristic typical of introduced pathogens. Most convincingly, studies have shown that the known populations of C. fagacearum have experienced a severe genetic bottleneck that can only be explained by a single introduction. The weight of evidence indicates that C. fagacearum is an introduced pathogen, with possible origins in Central or South America, or Mexico.