Properties of a filamentous virus isolated from grapevines affected by corky bark

Abstract

A virus with highly flexuous filamentous particles c. 800 nm long, showing distinct transverse striations was isolated with high frequency (60%) by inoculation of Nicotiana occidentalis with sap from grapevine accessions indexing positive for corky bark. The virus, for which the name grapevine virus B (GVB) is proposed, has an ssRNA genome with mol. wt. of c. 2.5 x 10(6) Da (c. 7600 nt) and coat protein subunits with mol. wt. of c 23,000 Da. GVB has a very restricted herbaceous host range and was experimentally transmitted by the mealybug Pseudococcus ficus. The physicochemical and ultrastructural properties of GVB resemble those of closteroviruses. However, it is serologically unrelated to other grapevine closteroviruses including grapevine virus A, with which it shares some biological and physicochemical properties.

Detecção de um isolado de Grapevine virus A e caracterização do gene da proteína capsidial

“…A massa molecular da proteína capsidial do GVA-RS, estimada em 21,6 kDa, é praticamente idêntica àquela calculada por com base na sequência de aminoácidos deduzidos do gene da proteína capsidial, e muito próxima àquela de 22,5 kDa determinada pela mobilidade eletroforética de preparações virais purificadas (Boscia et al, 1993). Rubinson et al (1997) concluem que embora menos sensíveis do que a PCR, os métodos sorológicos, como o ELISA, são mais adequados para procedimentos rotineiros de detecção de vírus, incluindo-se o GVA, assim como na indexagem viral em grande escala, pois tais métodos se utilizam de extratos brutos da planta.…”

“…Embora se constate homologias de 56-57% entre as proteínas capsidiais de isolados de GVA e GVB, e de cerca de 75% entre GVA e GVD, neste trabalho e em outros Nickel et al, 2002), estas similaridades não se refletem nas propriedades sorológicas e moleculares desses vírus, cujos anti-soros e sondas moleculares não apresentam reações cruzadas ou, se presentes, são fracas (Boscia et al, 1993;Martelli et al, 1997). Entretanto, reações heterólogas ocorrem em procedimentos desnaturantes, que expoem e tornam acessíveis os poucos determinantes antigênicos compartilhados por estes vírus (Goszczynski et al, 1996).…”

Production of polyclonal antisera using recombinant coat proteins of Grapevine leafroll-associated virus 2 and Grapevine virus B

“…Elimination of GVB had also a benefi cial impact, with an increase in vigor (35%) and production (16%) (Komar et al, 2007). There is experimental proof of controled transmission of GVB by several species of pseudococcid mealybugs (Boscia et al, 1993).…”

“…Corky bark, a component of grapevine rugose wood complex, is caused by Grapevine virus B (GVB; genus Vitivirus, family Flexiviridae) (Martelli et al, 2007), which possesses a positive single-stranded RNA genome of 7,599 nucleotides, with fi ve ORFs, of which ORF 4 encodes the coat protein (23 kDa) (Boscia et al, 1993;Minafra et al, 1994;Saldarelli et al, 1996). GVB has been reported earlier in Brazil (Kuniyuki & Costa, 1982;Kuhn, 1992;Nickel et al, 2002).…”

“…However, the production of high-quality virus-specifi c antisera to GLRaV-2 and GVB, suitable for their large scale detection and based on virus purifi cation procedures, faces substantial drawbacks, including complex virus infections, low yields of virus particles, presence of inhibitory compounds -such as polyphenols, tannins and polysaccharides -, narrow range and poor mechanical transmission to herbaceous hosts, contamination of antigens with host proteins (Uyemoto et al, 1997;Xu et al, 2006;Beuve et al, 2007;Fajardo et al, 2007;Ling et al, 2007), and, especially in the case of GVB, low immunogenicity (Boscia et al, 1993).…”