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The Congress, a triennial conference, attracted eighty attendees representing 26 countries. Over the week 58 oral presentations and 51 posters were presented. The meeting was opened with a plenary lecture of Professor Giovanni Martelli giving ‘A historical account with an eye to the studies of the last 60 years or so’. This very informative introduction retraced the historical discovery, the geographical origins and the main players involved in the identification of some of the 60+ viruses recorded in grapevine. Four viral diseases were predominant in the talks and posters reflecting their economic importance.
The nepoviruses, accountable for the oldest viral disease described in grapevine, are still an important threat for production, especially in some highly valuable wine regions in Europe. The virus is responsible for malformation of leaves, crop loss and plant death. It is transmitted by nematodes (Xiphinema sp) that remain infectious for several years, making a serious challenge for disease management. An original approach presented by the teams of Dr Olivier Lemaire and Dr Gerard Demangeat (INRA) was to use nanobodies to develop transgenics and for diagnostics.
Caroline Hemmer presented her data of resistance to the nepovirus Grapevine fanleaf virus (GFLV) by a transgenic Nicotiana benthamia expressing a nanobody specific to GFLV. Grapevine leafroll disease is the biggest viral disease in South Africa, USA and New Zealand. The causal agents are viruses belonging to the genus Ampelovirus with Grapevine leafroll-associated virus 3 (GLRaV-3) being the most frequent source. Dr Hano Maree from ARC Stellenbosch presented his work recently published on GLRaV-3 diversity, detection and quantification. He described another variant strain of GLRaV-3 (only 66% nt identity to closest relative) and the consequences it has on the detection methods (old primers do not detect the recently described strains). He proposed new taxonomic groups (Group I to VIII and supergroup A to D) for the various, highly diverse strains of GLRaV -3. Elize Jooste (ARC Pretoria) mentioned the results of a trial of transmission efficiency of four genetic variants of GLRaV-3 by mealybugs. Her preliminary results suggest that the mealybug Planococcus ficus is a better vector of GLRaV-3 group I and VI, explaining their prevalence. Another leafroll virus, GLRaV-1, was studied in Turkey (Dr Eminur ElçI, Niğde University) for its genetic diversity. During their study, the team at Nigde University have detected the virus in pomegranate (Punica granatum). If confirmed, this would be the first time a grapevine Ampelovirus has been detected in more than one natural host.
Red Blotch is a recently discovered disease reported in the USA. A virus member of the family Geminiviridae was reported as the causal agent, and this was brilliantly demonstrated by Dr Marc Fuchs (Cornell University). The virus named Grapevine red blotch associated virus (GRBaV) is considered to be responsible for leave reddening, declined yield, with similar if not greater impact than GLRaV-3. Dr Fuchs and co-workers completed Koch’s postulates by first cleaning an infected plant and showing that the reddening symptoms no longer express, and secondly re-infecting the plant with an infectious clone and showing that the symptoms caused by the infectious clone are similar to the ones observed in the original GRBaV-infected plant. Additional information gathered at the congress include the fact the virus is latent in rootstocks, and that the symptoms of GRBaV and GLRaV-3 are undistinguishable by the experts.
The only difference is that GRBaV tends to express symptoms at the base of the plant where the GLRaV-3 is systemic when the infection is older. Dr Maher Al Rwahnih (UC Davis) proved that the virus had been present in the US for a long time by detecting it in a herbarium sample collected in the 1940s. All that time (70 years) the virus has probably been misdiagnosed as GLRaV-3.
Grapevine pinot gris virus (GPGV) is also a recently discovered virus. It was described in Italy in 2011 and was since reported in most southern European countries. Dr Pasquale Saldarelli (NRC, Rome) described the difference of symptomatology of the virus (sometimes similar to symptoms caused by the nepoviruses) in different grapevine cultivars. He also described two distinct isolates of the virus, one symptomless and one symptomatic. He showed that the virus is now widespread in Italy, and it is transmitted by mites, although it was poorly transmitted under controlled conditions. An antiserum was raised against a recombinant protein, but it was not of sufficient quality for diagnostics. In addition to Dr Saldarelli’s presentation, Dr Elisa Angelini (CRA Conegliano) documented the speed of its spread by the low incidence of the virus in 10-year-old RNA (one positive in 75 samples) compared to the incidence in recent years (~ 78% of 250 samples). GPGV is an emerging virus with an alarming rate of spread, but with a variable impact (some strain are symptomless and some strains on susceptible cultivar can reduce the yield by up to 80%).
Interesting discussions were raised concerning the importance and sensitivity of NGS in today’s diagnostics. It has become evident that it is now only a question of time before NGS complements/ replaces biological indexing. Dr Maher Al Rwahnih presented a recent publication demonstrating that NGS was detecting all the viruses observed by biological indexing, but in addition it also detected new viruses.
Not all viruses are detrimental to their hosts, as shown by Dr Franco Mannini (CNR, Grugliasco), when he explained that blind testing of wine made from Grapevine virus B infected grapevine ranked better than wines made from virus-free plants. The yield was much reduced (-25%) but the higher level of flavonoids increased the body and the colour of the wine. In a different poster he also showed that Grapevine rupestris stem pitting virus improves tolerance to water stress.
This was a well-organised meeting with good-quality speakers. The atmosphere was great and the post-conference tour in Cappadocia was spectacular. There are so many cultural treasures in central Anatolia. Finally I would like to express my gratitude the BSPP for a travel grant that helped me to cross the world to attend this conference. My time in Turkey enabled me to present my own research on a novel approach for viral metagenomics studies and also allowed me to meet eminent scientists from around the world. See you in Chile in 2018 for the next meeting.
University of Auckland / Plant & Food Research, New Zealand