Distinction of strains of bean common mosaic virus and blackeye cowpea mosaic virus using antibodies to N- and C- or N-terminal peptide domains of coat proteins

Earlier attempts to discriminate serologically strains NL1, NL3 and NY15 of bean common mosaic virus (BCMV) and strain W of blackeye cowpea mosaic virus (B1CMV) had been unsuccessful. Antibodies directed towards N- and C-, or N-terminal peptide regions of the coat proteins of the above strains enabled the distinction between B1CMV-W, BCMV-NY15 and BCMV-NL3 in electroblot immunoassay and in ELISA. The distinction was better with antibodies directed towards N-termini than with those to N- and C-termini. Strain NL1 of BCMV cross-reacted with both B1CMV-W and BCMV-NY15, but not with BCMV-NL3. Taxonomic implications of these findings are discussed.     

Field resistance of transgenic burley tobacco lines and hybrids expressing the tobacco vein mottling virus coat protein gene

Fifty transgenic lines expressing the tobacco vein mottling virus (TVMV) coat protein (CP) gene in five genetic backgrounds were evaluated under field conditions for response to mechanic inoculation with TVMV, tobacco etch virus (TEV) and potato virus Y (PVY). TVMV CP transgenic lines conferred resistance to TVMV, TEV and PVY under field conditions. Combining two strategies, coat protein-mediated resistance (CPMR) coupled with an endogenous resistance gene (Virgin A Mutant, VAM) significantly extended the range and magnitude of virus resistance and provided a potential valuable new source of protection against potyviruses. CP transgenic lines lacking the VAM gene had high resistance to TEV, medium resistance to PVY, and a recovery phenotype to TVMV. A series of hybrids involving transgenic lines were generated and tested under field conditions for response to virus inoculation. One copy of TVMV-CP gene presented in lines homozygous for the VAM gene provided effective resistance to all three potyviruses. These studies also suggested that selection of a suitable recipient genotype was critical and that field evaluation was necessary in order to select elite resistant transgenic lines. Engineering viral CP genes into genotypes possessing some level of virus resistance could be critical to achieve an effective level of resistance.     

Biological properties of necrotic and non-necrotic strains of bean yellow mosaic virus in cool season grain legumes

A collection of 51 bean yellow mosaic virus (BYMV) isolates was transmitted from infected Trifolium subterraneum (subterranean clover) to Lupinus angustifolius (narrow‐leafed lupin) by Myzus persicae (green peach aphid). Depending on isolate and L. angiistifolius genotype used, two distinct responses developed in L. angustifolius plants, either systemic necrosis and plant death or non‐necrotic reactions of varying severity. Ten isolates caused necrosis and plant death in cv. Danja. However, when nine of these were inoculated to breeding line 90L423‐07‐13, seven induced non‐necrotic reactions, while two caused necrosis and plant death. Thirty seven isolates always produced non‐necrotic reactions regardless of genotype of L. angustifolius inoculated. Non‐necrotic and necrotic isolates originally came both from lupins and other species, and the non‐necrotic isolates were no less efficiently transmitted by M. persicae than the necrotic ones. When one isolate of each type was inoculated together to T. subterraneum and nine months later this culture was used as an acquisition source for aphid transmission to L. angustifolius, only the necrotic type was detected. Previous infection of L. angustifolius plants with a non necrolic isolate prevented subsequent infection by a necrotic one. All necrotic and non‐necrotic isolates reacted with BYMV antiserum in ELISA but only two cross‐reacted with antiserum to clover yellow vein virus (CYVV). When selected necrotic and non‐necrotic isolates were inoculated to differential hosts, all behaved like BYMV and not CYVV. When three isolates of each type were transmitted to 11 other cool season grain legume species, except in Cicer arietinum (chickpea), there were no necrotic reactions, but symptom severity varied with the isolate and species inoculated. The two isolates that caused necrosis in C. arietinum did not do so in L. angustifolius. The six isolates from Vicia faba (faba bean) all caused non‐necrotic reactions in L. angustifolius cv. Danja and 90L423‐07‐13. These and two necrotic isolates readily infected five genotypes of V. faba always causing severe symptoms. However, three non‐necrotic isolates from L. angustifolius and a further necrotic isolate were poorly infectious on V. faba in which they generally induced mild symptoms. These results show that at least three strain groups of BYMV can be distinguished by their reactions in different L. angustifolius genotypes, one causing necrosis and death in cv. Danja and 90L423‐07‐13, one causing necrosis and death in Danja but not 90L423‐07‐13, and one causing non‐nccrotic reactions in both. These strain groups could not be distinguished when representative necrotic and non‐necrotic isolates were inoculated to other grain legume species. However, inoculation to V. faba distinguished two other BYMV strain groupings differing in severity of symptoms and ability to infect this species.     

Antibody-mediated improved resistance to ClYVV and PVY infections in transgenic tobacco plants expressing a single-chain variable region antibody

Transgenic Nicotiana tabacum plants expressing a single-chain variable region antibody fragment derived from a broad-spectrum monoclonal antibody 3-17 showed suppression of virus infection following challenge by two distinct potyviruses: potato virus Y strain D, and clover yellow vein virus strain 300. Monoclonal antibody 3-17, which was raised against the potyvirus Johnsongrass mosaic virus, was shown to react strongly with 14 potyvirus species. Two different single-chain antibody constructs were used to produce chimeric genes encoding recombinant proteins designed to be targeted either to the apoplasm or to the cytoplasm. Transgenic plant lines showed reduced numbers of local lesions and systemic symptoms when challenged with potato virus Y, strain D and reduced local lesions following challenge with clover yellow vein virus, strain 300. The level of suppression conferred by the transgene when plants were challenged under laboratory conditions with high concentrations of virus, together with the ability of the transgene to partially protect plants against distinct viruses suggest that one single-chain gene construct might be used to protect plants from distinct potyviruses.     

Endophytic colonisation of squash by the fungal entomopathogen Beauveria bassiana (Ascomycota: Hypocreales) for managing Zucchini yellow mosaic virus in cucurbits

We investigated the potential of endophytic Beauveria bassiana to provide protection against Zucchini yellow mosaic virus (ZYMV), one of the most economically important viral diseases in cucurbits. Four selected B. bassiana strains were able to successfully colonise squash plants following foliar inoculation with the conidial suspension of each respective strain. However, no significant difference in percentage colonisation was observed among the tested B. bassiana strains. Disease incidence (percentage of plants showing ZYMV symptoms) and severity (rating based on a 5-point scale), sampled weekly for four weeks following the challenge inoculation of plants with ZYMV, were significantly lower in B. bassiana-inoculated plants as compared to control plants, regardless of the inoculated strain. This is, to our knowledge, the first report on the potential of endophytic B. bassiana to confer protection against plant viruses. Further studies should be conducted to determine whether such endophytic B. bassiana-mediated protection against ZYMV in squash extends to other cucurbits.