Virgaviridae: A new family of rod-shaped plant viruses.

The new plant virus family Virgaviridae is described. The family is named because its members have rod-shaped virions (from the Latin virga = rod), and it includes the genera Furovirus, Hordeivirus, Pecluvirus, Pomovirus, Tobamovirus and Tobravirus. The chief characteristics of members of the family are presented with phylogenetic analyses of selected genes to support the creation of the family. Species demarcation criteria within the genera are examined and discussed

Identification of Gaeumannomyces-Graminis var. tritici and G-graminis var avenae using a DNA probe and nonmolecular methods

Fungi in the Gaeumannomyces-Phialophora complex were compared using a DNA probe and by pathogenicity and other biological tests. Isolates from cereal and grass hosts which were pathogenic on cereals were differentiated as G. graminis var. tritici or G. graminis var. avenae on the basis of pathogenicity tests on wheat and oat seedlings, ascospore measurements and comparison of growth rates on oat-leaf agar. DNA was extracted from pure cultures of these isolates and also from non-pathogenic isolates of Phialophora spp. from cereals, grasses and sedges, and from fungi of other genera. The samples were digested with restriction enzymes, separated by electrophoresis on agarose gels and hybridized with a radio-labelled DNA probe (pMSU315) known to have homology almost exclusively with DNA from fungi within the complex. Thirty-three isolates of G. graminis var. tritici and 20 of G. graminis var. avenae, previously identified by the much slower non-molecular methods, produced distinctive restriction fragment length polymorphisms after digestion with BamHI. In particular, a prominent band of a 2.9 kb fragment occurred in all isolates and was diagnostic for these two take-all pathogens. The same result was obtained using a non-radioactive method for labelling the probe. The possible value of using pMSU315 in this way as a diagnostic test for the take-all pathogens is discussed.Peer reviewe

Comparison of three pathogenesis-related proteins from plants of two cultivars of tobacco infected with TMV

A procedure is described for purifying the b1, b2 and b3 proteins from leaves of Nicotiana tabacum cv. Xanthi-nc, a cultivar reacting hypersensitively to tobacco mosaic virus (TMV). All three proteins consist of a single polypeptide, have similar mol. wt. of about 14200 but differ in charge. In contrast, the b4 protein differs from b1 to b3 in both charge and size. The same procedure purifies the proteins IV, III and II from TMV-infected leaves of N. tabacum cv. Samsun NN. The Samsun NN proteins IV to II resemble the b1 to b3 proteins from Xanthi-nc in electrophoretic mobility in polyacrylamide gels and in mol. wt.; b1, IV and III have similar amino acid compositions. It is suggested that these proteins be called pathogenesis-related proteins (PRs) and a unified system of nomenclature is proposed which groups similar proteins

Development and uptake of a scheme for predicting risk of severe light leaf spot on oilseed rape

To reduce reliance on fungicides for disease control on oilseed rape, Decision Support Systems (DSS) are being developed to guide fungicide applications as part of an integrated pest and disease management strategy. This paper reports the development and uptake of an empirical model for prediction of risk of severe light leaf spot using disease survey and meteorological data to produce autumn regional and crop-specific prediction of epidemic risk for the following spring. Following initial delivery of the light leaf spot forecast via the farming press, an Internet-based interactive website was developed to provide crop-specific predictions. Uptake by growers, advisors and other members of the arable industry has been encouraging. There is evidence to suggest that growers and their advisors visit the website for an up-to-date prediction at the time when they are making fungicide application decisions.Peer reviewe