Richa Rai

Development of an immunocapture–reverse transcription–polymerase chain reaction (IC-RT-PCR) using modified viral RNA release protocol for the detection of Grapevine leafroll-associated virus 3 (GLRaV-3)

Grapevine leafroll-associated virus 3(GLRaV-3) is the most destructive virus causing leaf roll disease in grapevine. ELISA has been widely used to screen the propagating materials for indexing of this virus at nursery stage. But the uneven distribution of GLRaV-3 in vines, its confinement to phloem tissues and impact of seasonal influences on its concentration limit the scope of ELISA. RT-PCR (reverse transcription-polymerase chain reaction), is a more sensitive technique, but not feasible for large scale screening purpose because of the tedious process of RNA isolation. Furthermore, location of virus particles and the presence of inhibitory compounds in the woody tissues of grapevine make RNA isolation problematic. Immunocapture-RT-PCR (IC-RT-PCR), more sensitive than ELISA and RT-PCR alone, is a technique where the virus can be detected without isolating the RNA. In this study, IC-RT-PCR was performed using different combinations of three virus extraction buffers and two virus nucleic acid releasing buffers along with one virus RNA releasing condition for the detection of GLRaV-3. The modified extraction and RNA release protocol developed in this study was validated for specific detection of the virus in the vines of five infected grapevine cultivars. This protocol can help in complementing the GLRaV-3 specific certification program of the country.

Development of immunodiagnostics for the detection of Grapevine leafroll - associated virus 3 (GLRaV-3) in grapevine using in vitro expression and purification of its coat protein gene

A previously cloned coat protein (CP) gene of Grapevine leafroll-associated virus 3 (GLRaV-3) from cultivar Cabernet Souvignon was over-expressed in Escherichia coli strain BL21 expression system as ~xa043xa0kDa fusion protein containing polyhistidine tag (6His) at its N terminal. The protein was purified from insoluble fraction and reacted positively in western blotting with commercial anti GLRaV-3 polyclonal antiserum (Bioreba, Switzerland) and hence, used as immunogen for the production of polyclonal antisera in New Zealand white rabbits. Polyclonal antiserum specific to GLRaV-3 detected the virus by double antibody sandwich enzyme linked immunosorbent assay using commercial alkaline phosphatase (ALP) conjugated globulin fraction (Bioreba, Switzerland) in GLRaV-3 positive grapevine samples. The immunoreactivity of the antiserum was confirmed through western blotting. The purified antiserum was conjugated with ALP. The primary antiserum along with ALP conjugate successfully detected the GLRaV-3 from the infected sample at 1:8000 and 1:10,000 dilutions, respectively. To the best of our knowledge, it is the first global study wherein the CP of GLRaV-3 was cloned in pET28a(+) expression vector having many advantages over the earlier used expression vectors. The cloned CP gene was expressed, purified and subjected to the production of immunoreagents. The developed immunoreagents will be useful for certification programmes as well as for large scale virus screening to produce GLRaV-3 free grapevines. The indigenously developed immunereagents will provide a cost-effective way of managing grapevine leafroll disease in Indian sub-continent.

Ampeloviruses Associated with Grapevine Leafroll Disease: A New Group of Viruses in India

Ampeloviruses (family Closteroviridae) are filamentous monopartite, single-stranded, positive-sense RNA genome. They are transmitted by mealybugs in semi-persistent manner and vegetative propagating material remains the major route of spread. Ampeloviruses are recent addition to the plant viruses in India. Grapevine leafroll-associated virus 3 (GLRaV-3) was first ampelovirus to be recorded from India in the year 2012. Of the nine distinct species of the genus Ampelovirus, only three, Grapevine leafroll-associated virus 1 (GLRaV-1), GLRaV-3, GLRaV-4 infecting grapevine have been reported from India. The isolates of GLRaV-3 and GLRaV-4 are diverse, a few being the recombinant ones. This chapter describes the grapevine leafroll disease caused by different ampeloviruses, their geographical distribution, characterization, diversity, management strategies and also discusses about the future course of works to be taken.