Report

on the

12th Meeting of the International Council for

the Study of Viruses and Virus-like Diseases of the

Grapevine {ICVG)

2

The virus diseases which affect Australian grapevines have been imported from

overseas together with their host plant. Whilst the effect of viral diseases varies

depending on conditions, the Australian viticultural industry can benefit from knowledge

of research done in other viticultural areas of the world. The forum of the ICVG was

founded for the purpose of communicating achievements in the study of viruses and

virus-like diseases of the grapevine and gives the opportunity for participants to discuss

these findings.

The 12th meeting of the ICVG was held in Lisbon, Portugal, during the period 28th

September to 2nd October, 1997. The excellent conference facilities were located w ithin

the Calouste Gulbenkian Foundation Complex.

The meeting was regarded as the largest held to date, with 143 registered part icipants

from countries including Italy (31) , Portugal (26), France (18), USA (11), Australia (8),

Spain (7), Germany (5), South Africa (5), Slovenia (5), Switzerland (4), Hungary (4),

Canada (3), Israel (3) , Austria (3) , Greece (2), Chile (2) , Croatia (1), Cyprus (1 ), Japan

(1), Tunisia (1) , Turkey (1) , and Uruguay (1).

There were 45 oral presentations and 52 posters spanning the following topics: studies

on known viruses, diseases of unclear aetiology, grapevine viroids, phytoplasmas and

phytoplasma diseases, advances in diagnosis, epidemiology, new strategies fo r

introducing resistance to viruses, selection, control , performance of virus-tested clones,

health preservation and economic importance.

An analysis of the topics presented, shows that viruses associated with leafroll

disease were the subject of 23% of the presentations, followed by phytoplasmas ( 19%),

fanleaf virus (15%), rugose wood associated viruses (14%) , molecular stratagies fo r

induced resistance to viruses (12%), sanitary procedures and certification (8%), fleck

virus (3%), enation disease (2%), viroids (2%), and shiraz disease from South Af ri ca

(1%) .

3

The highlights of grapevine virology during the period 1994-97 were reviewed by the

President of the ICVG Scientific Committee (Prof. G. P.Martelli). It was claimed that

approximately 400 papers had been published on various aspects of grapevine virology

since the 11th Meeting of the ICVG. It was shown that to date, some 44 different viruses

have been detected in grapevines (Table 1).

Table 1. Viruses isolated from grapevine and their vectors

Virus species Known vectors

Nepoviruses (Nematode-transmitted viruses)

Artichoke Italian latent Arabis mosaic Blueberry leaf mottle Bulgarian latent Grapevine chrome mosaic Grapevine fanleaf Grapevine Tunisian ringspot Raspberry ringspot Tobacco ringspot Tomato ringspot

X. diversicaudatum

Xiphinema index, X. italiae

Paralongidorus maximus X. americanum X. californicum, X. rivesi Longidorus attenuatus Tomato black ring

Strawberry latent ringspot Peach rosette mosaic X. americanum, X. rivesi, L. diadecturus

Viruses (closteroviruses) associated with the leafroll disease complex

Grapevine leafroll-associated virus 1 Grapevine leafroll-associated virus 2 Grapevine leafroll-associated virus 3 Grapevine leafroll-associated virus 4 Grapevine leafroll-associated virus 5 Grapevine leafroll-associated virus 6 Grapevine leafroll-associated virus 7

Scale (2 spp.) Mealy bug (2 spp.) Mealy bug (4 spp.), Scale (1 sp.)

Viruses (Vitiviruses) associated with the rugose wood complex

Grapevine A Grapevine B Grapevine C Grapevine D

Mealy bug (4 spp.), Scale (1 sp) Mealy bug (3 spp.)

-

Table 1. (cont.) Viruses isolated from grapevine

Virus species Known vectors

Viruses isolated, which directly cause a grapevine disease

Grapevine fleck Grapevine asteroid mosaic Grapevine ajinashika Grapevine stunt Grapevine berry inner necrosis ( Trichovirus) Alfalfa mosaic (Aifamovirus) Grapevine line pattern (1/arvirus)

Other viruses isolated from grapevines

Cucumber mosaic (Cucumovirus) ? Tomato spotted wilt (Tospovirus) Broadbean wilt (Fabavirus) Petunia asteroid mosaic (Tombusvirus) Grapevine Algerian latent (Tombusvirus) Carnation mottle ( Carmovirus) Tobacco necrosis 0 (Necrovirus) Sowbane mosaic ( Sobemovirus) Potato X (Potexvirus) Tobacco mosaic (Tobamovirus) Tomato mosaic (Tobamovirus) Grapevine labile rod-shaped Un-named virus (?Capillovirus)

4

The un-named capillo-like virus (particles 600-?00nm long) was observed in vines

affected by Rupestris stem pitting (RSP) and LN33 stem grooving diseases, from Canada.

The relationship of this virus to the previously named diseases remains unknown. This

virus was serologically unrelated to a number of filamentous viruses.

Leafroll disease complex

It was widely recognised that leafroll-affected vines are commonly infected with

variable mixtures of different viruses, and the vines are seldom infected with one virus.

Currently, there are seven distinct long filamentous viruses (closteroviruses) recognized

to be associated with leafroll disease, and there was informal talk of the possibility of an

5

eighth type. It was suggested that at least three different closteroviruses (GLRaV-1,

GLRaV-3, and GLRaV-7) are genuine causal agents of leafroll disease.

The GLRaV-7 was first found in an Albanian grapevine accession, but recently found in

grapevines from several countries including Italy, Greece, Turkey, Palestine and Armenia.

Some renaming of disease-associated viruses has occurred . The virus known

previously as corky bark-associated virus was shown to be the same as the French

source of GLRaV-2, which has been designated as the authentic reference species.

This source has been mechanically-transmitted to a herbaceous plant (Nicotiana

benthamiana) in two different laboratories, and shown to possess two biological

variants which induce different symptoms in the inoculated herbaceous host. The source

of GLRaV-2 has also been implicated in the cause of a graft-incompatibily which occurs

with the Kober 588 rootstock. In 1995, it was suggested that the virus previously known

as GLRaV-IIa should be renamed as GLRaV-6. This proposal had been accepted .

Information was provided on the molecular characterization of GLRaV-1 (Australia),

GLRaV-2 (Italy, and USA), and GLRaV-3 (USA). The genome organization of these

viruses have largely been determined, and all have been shown to be typical

closteroviruses.

Further information was provided on advances in the diagnosis of leafroll-associated

viruses, using tests including enzyme-linked immunosorbent assays (ELISA) and the

polymerase chain reaction (PCR). Details on the relative merits and limitations of these

techniques were provided. Generally, the PCR techniques were reported to detect a

given virus earlier than ELISA-based techniques, while both techniques had their

advantages, neither were 100% reliable for all situations. It was generally agreed that

basal leaf petioles sampled from the flowering period to autumn, and one year old bark

were regarded the best sources of tissues for detection of viruses by ELISA. The young

leaves gave erratic results.

6

Several papers have been previously published on the spread of leafroll disease in the

field. These reports have come from Yugoslavia {1973), South Africa (1985, 1990),

Mexico (1989), Italy (1993) , Cyprus (1993), New Zealand (1993), Australia (1993) , and

France (1997) .

Experimental transmission of GLRaV-3 from grapevine to grapevine had been

demonstrated for scale insects (Pu/vinaria vitis L.) in Italy, and by at least the first instars

of mealybug (Pseudococcus /ongispinus, Ps. ca/ceolariae) in New Zealand, by Ps. citri

in Spain, and by Pseudococcus affinis and Ps. /ongispinus in the USA Also, a low rate

of transmission of GLRaV-2 was also obtained with mealybug (Pseudococcus

longispinus, and Ps. affinis) in the USA

Previous published reports from Spain and Italy, indicated the probablity of a virul iferous

mealybug transmitting the virus to another grapevine was in the order of 1-11%. The

interval between mealybug-mediated viral transmission and detection of the viral infection

by ELISA, was influenced by the number of viruliferous mealybugs. When the population

of viruliferous mealybug was reduced to 5, the interval between feeding and detection of

the virus in the grapevine was 13 months. If the population of viruliferous mealybugs was

increased to 20-30 and 50, the period between feeding and detection of the virus was 13

and 8 months respectively.

In this meeting of the ICVG, information from Cyprus showed the relationship between

spread of leafroll disease in Cyprus, the incidence of GLRaV-3 and the occurrence of

mealybugs (Pianococcus ficus and P. citn) in the field. The natural spread of GLRaV-3

was monitored on four sites including the old and new propagation station. The first

indication of natural spread of leafroll was observed in the late 1980's, when previously

clean stocks introduced from California or those selected locally, started to become

infected. The monitoring results showed significant differences among the sites. The

highest rate of spread increased from 20% in 1991 to 70% in 1996. By contrast, the virus

incidence at another site has remained at about 5% since 1991. The incidence of GLRaV-

7

3 was not found at the new station until 1996, when the incidence was found to be 1%,

contrasting with the incidence of GLRaV-3 at the old station , which increased from 44%

in 1991 to 70% in 1996. The viral incidence varied between Vitis vinifera cultivars (73-

94%) and V. rupestris (7%) rootstocks. Results also indicated the importance of micro­

climate in the development of mealybug infestation and its subsequent spreading of the

virus. Transmission tests were done with both field-collected and laboratory-reared

mealybugs. It was found that 75 larvae of Planococcus ficus gave 100% transmission of

GLRaV-3 to Cabernet Franc plants, whereas the same number of insects of P. citri

larvae gave only a 45% transmission rate.

Research in Italy provided new information on the field spread of leafroll disease

caused by GLRaV-1, and on its transmission in Italian vineyards by scale insects

(Partheno/ecanium corni and by Neopulvinaria innumerabilis, when mixed with the

GVA virus).

A survey of viruses associated with leafroll in Gamay and Pinot Noir vines in the

different localities within France was reported. The results showed the variable

incidence of GLRaV-1 and GLRaV-3 in these cultivars. The incidence of GLRaV-1 ranged

from 3-17% in Gamay vines in the Beaujolais region and 1-30% in the Bourgogne region,

while the incidence of GLRaV-3 ranged from 0-80% in Pinot Noir vines in the Beaujolais

region and 0.5-11% in the Bourgogne region.

A poster was displayed giving further information on the graft-transmissible vein

yellowing leafroll symptoms from France, which was described in 1983. Previously it

was noted that the symptoms were similar to leafroll disease, appeared two years after

planting, and appeared to spread quickly through the vineyard . New information was

provided showing that the disease did not spread. The apparent spread was due to the

milder expression of symptoms in young vines, which were not observed in the previous

year. The disease was thought to be contributed by the rootstock used, and the affected

plants were found infected with NY-1 strain of closterovirus (?GLRaV-3). In addition,

8

other closterovirus-like particles were observed in symptomatic tissues. It is not known

whether the symptoms are caused by a new virus or due to synergy between d ifferent

viruses.

Table 2. Relative percentage of Closteroviruses found in samples of grapevine

Country Cultivar GLRaV-1 GLRaV-2 GLRaV-3 GLRaV-7

New Zealand V. vinifera 3.5% 97%

France Gamay 3-17% 0-80%

France Pi not Noir 1-30% 1-11%

South Africa Table cvs. 10% 73% 70%

Palestine V. vinifera 46% 8% 22% 0.2%

Palestine Rootstocks 0% 1% 10% 0%

Turkey V. vinifera 0-100% 0-50% 0-25%

Spain (Guadiana) V. vinifera 2-12% 14-37%

Spain (NW) V. vinifera 40%

Greece V. vinifera 42% 48%

Southern Italy Table cv 0% 0-76% 0-55%

Italy (Sardinia) V. vinifera 33% 16% 83%

Slovenia Refosk 5% 10%

Slovenia Laski rizling 76%

Portugal V. vinifera 45%

Australia V. vinifera 27% 8% 10%

9

Several papers were presented on the effects of GLRaV-3 on the performance of

grapevines. A Spanish group compared the field measurements for net photosynthesis

on diseased and healthy vines. The leaves from GLRaV-3 infected vines when showing

the leaf roll ing symptoms gave significant lower rates of photosynthesis than similar aged

leaves on healthy plants. The net photosynthesis of symptom-free leaves of infected

plants were also lower than similar leaves on healthy plants, but the difference was only

statistically significant in one out of three tests. These findings indicate the reduced

photosynthetic rate of symptomatic leaves is one of the factors contributing to the

differences between healthy and GLRaV-3 diseased plants. It seems likely that this

deleterious affect would be greater in cultivars in which the leafroll symptoms develop

earlier.

It should be recognized that other viruses and combinations of viruses can induce

earlier leafroll symptoms than GLRaV-3 in the same cultivar. These mixtures of viruses

may also induce a lower photosynthetic rate in leaves of diseased vines.

Another paper was presented showing the effects of a combined GLRaV-3 and GVA

infection in Nebbiolo (clone 415) grapevines in north-east Italy. In this case, the Nebbiolo

clone was compared before and after heat-therapy. The vines derived from the heat­

therapy treatment were free of the two viruses. Leaf measurements showed a reduction

in the rate of photosynthesis of leaves from diseased plants compared with the healthy

vines. The healthy vines produced a larger and greener canopy which resulted in better

grape maturity. No significant differences in the yield per vine were obtained between the

diseased and healthy vines. The heat-treated vines produced a signifiantly higher level of

prunings (1058g verses 905g), larger bunches (212g verses 199g), more soluble solids

(21.3° Brix verses 20.8°), essentially the same pH (3.01 verses 3.00), lower malic acid

(3.3g/l verses 3.55g/l), essentially the same tartaric acid (7.08g/l verses 6.91 g/1) and

potassium content (1.35% verses 1.36%).

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In Portugal, the occurrence of leafroll disease was common in many different cultivars,

with GLRaV-3 the predominant virus. The incidence of GLRaV-3 was very high in some

cultivars, 90% infection in the cultivar Tinta Francisca, 93% infection in Alvarinho, and

98% infection in Esgana Cao. Studies have evaluated the effect of GLRaV-3 on yield of

27 Portugese cultivars. The yield influenced by this virus was reported to range from

-17% to +14%, with a mean of about -5%.

In the Apulia region of Italy, studies were reported on the effect of filamentous viruses

on the performance of Red Globe and King's Ruby table grape cultivars. Leafroll

symptoms were common in these cultivars and affected vines had delayed bud-burst by

a couple of weeks and the vines exhibited extensive bud-break fai lure. Four different

viruses were found in these cultivars. A survey of Red Globe vines showed that 85% of

the vines showed leafroll symptoms. Of these, 76% were infected with GLRaV-2, 54%

infected with GLRaV-3, 51% infected with GVA, and 10% infected with fleck virus.

These vines yielded a mean of 19 kg per vine compared with 24 kg from symptomless

vines, produced a mean of 23 bunches compared with 30 bunches on symptomless

vines, and developed 9% sugar concentration compared with 14% sugar in the

symptomless vines. In addition, the fruit from the vines showing leafroll symptoms had

pale coloured berries, and many of the bunches were unmarketable. Decline and death of

symptomatic Red Globe vines was not uncommon, for it was recorded that 28% of

affected vines died. None of the symptomless vines died, but they were not virus-free.

It was found that 12% of them were infected with GLRaV-2, while 2% was additionally

infected with fleck virus. It seems possible that GVA may also be involved in the decline

of Red Globe, because this virus was present with closteroviruses in 51% of the

symptomatic vines and was detected in more than 67% of those which died.

Symptomless and leafroll-infected vines of the King's Ruby cultivar were also compared.

The results showed that 78% of the vines surveyed had leafroll symptoms, of these,

24% were infected with GLRaV-2, 55% infected with GLRaV-3, 24% infected with GVA,

11

and 53% infected with fleck virus. Some virus infections were found in the symptomless

vines, these included 5% infection with GLRaV-3, 11% infection rate of GVA, and 53%

infection with fleck virus. The lower infection rate of GLRaV-3 and GVA in symptomless

vines may indicate natural spread of viruses to previously healthy vines. The origin of the

heavy viral inoculum was thought to have come from budwood and/or rootstocks, rather

than from viruliferous mealybugs.

Another study of the effect of viruses on the performance of grapevines was reported

in Sardinia. A survey of clones of cultivars Cannonau, Malvasia di Bosa, Pascale di

Cagliari, Vermintino, and Vernaccia, showed that some clones of most cultivars were

free of GLRaV-1, -2, -3, GVA and fleck virus. The exception was Malvasia di Bosa,

which was totally infected with either GLRaV-2 plus fleck or GLRaV-3 and fleck.

Following the survey, 25 virus tested-free clones of four cultivars (Cannonau, Pascale di

Cagliari, Vermentino and Vernaccia) and 56 virus-infected clones of the same cultivars

plus Malvasia di Bosa, were observed for 9 years. Results showed that the presence of

viruses did not significantly reduce the yield of most cultivars, except for Cannonau,

where an average reduction of 25% in the yield was recorded. Likewise, the viruses _did

not seem to affect the sugar concentration and titratable acidity of the juice.

Phytoplasmas

Several papers were presented on methods for detecting and identifying the associated

phytoplasma organisms, phytoplasma-vector relationships, and epidemiology of recent

outbreaks of phytoplasma diseases.

In Europe, flavescence dore~e disease is known to be transmitted from infected vine to

vine by the leafhopper Scaphoideus titanus. The disease is known to occur in France

and northern Italy. The causal agent is widely believed to be a phytoplasma organism

classified as a member of the elm yellows group. The disease can be graft-transmitted

provided that the budwood has been taken from shoots that are symptomatic for the

disease.

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Also in Europe, other yellows diseases are recognised that are not vectored by

Scaphoideus titanus but are vectored by another leafhopper, Hyalesthes obsoletus. This

type of yellows disease is known as Bois Noir in France, Vergibungskrankheit in

Germany, and also known as Mediterranean grapevine yellows. It is generally agreed

that the causal agent of the regionally-named diseases are the same and are caused by

a phytoplasma classified as a member of stolbur group of phytoplasmas. The principal

mode of infection in the vineyard is believed to be from weeds via the leafhopper to

grapevine, and not from grapevine to grapevine. Experimental graft-transmission has

been achieved using newly-infected shoots. The subject of one presentation at the

conference was on the transmission of Bois Noir by bench grafting. The results

presented indicated that the rate of disease transmission by bench grafting was low, and

was in the range of0.1-0.14% probability.

In Spain, the incidence of Bois Noir infection in vineyards during 1994 was 3%,

increasing to 7% in 1995, and to 14% in 1996. The survey showed that the incidence of

the disease increased along the rows, spanning 1-25 vines.

A survey of Vergilbungskrankheit-infected vineyards in Germany showed that the

infected vines increased from 18% in 1990 to 26% in 1995. The disease incidence varied

between individual vineyards from 5-65%. It has increased in 7 of 12 vineyards and

decreased in 3 vineyards. The increase in symptomatic vines was the highest in young

plantings which often provide favorable conditions for the phytoplasma vector

Hyalesthes obsoletus and its weed host known as bindweed (Convolvulus arvensis).

Clusters of infected vines were frequently found associated with clumps of bindweed. It

was found that the incidence of Vergilbungskrankheit depended on the interactions

between new infections and recovery from the disease. Another group of vines seemed

to recover, but symptoms re-occurred after one or two years. Although some of the

vines may have been re-infected, it was concluded that some vines remained latently

infected. Almost 1/3 of the infected vines recovered from the disease and stayed free

13

from symptoms for at least two years, even in vineyards where the disease incidence

was increasing. The recovery may have resulted from pruning. In one vineyard where

the symptomatic shoots were removed during two years, consequently 61 % of the

symptomatic vines recovered.

The epidemiology of a grapevine die-back disease in the Liguria region of northern Italy

was also presented. It was shown that the disease spread rapidly from 1992-1995,

causing dramatic losses. The vineyards, which were most affected were located higher

on the hill-side, had inter-row crops of vegatables, and the vineyards were surrounded

by shrub species of the Linaria sp., Plantago media, Prunus spinosa, Rubus fruticosus

and Spartium junceum. These shrubs were all infected with a phytoplasma of the aster

yellows group. Several leafhopper species were found including the known vector of

aster yellows phytoplasma. Samples of symptomatic vine material were also found to be

infected with aster yellows phytoplasma. The recommendations given to reduce the

incidence of the disease included keeping the vineyard and surrounding fields free from

weeds and shrubs during the vegatative season, the removal and destruction of all

pruning cuttings, to avoid growing a mixture with herbaceous plants among the vines,

monitor the leafhopper population and spray to control the leafhopper infestation.

A new type of yellows disease was reported in the cultivar Scheurebe growing in the

Palatine area of Germany. The disease closely resembled flavescence doree, but was

shown not to be identical. The vector of flavescence doree has not been found in

Germany. The plants grown around the affected vineyards were alder, blackberry and

almond. Phytoplasma organisms related to the elm yellows phytoplasmas were found in

the symptomatic vine tissues and also from tissues of most alder plants. Phyllid insects

were found feeding on the alder leaves, and a considerable proportion of Psylla alni

insects were found carrying the same phytoplasma organism as found in the alders and

affected vines. Transmission experiments with Psylla alni and the phytoplasma-infected

plants are in progress.

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Further information was given supporting a previous published result that an organism

associated with Australian grapevine yellows was a member a different subgroup of the

stolbur group and thus a different organism to those phytoplasmas associated with

yellows diseases in Europe.

Nepoviruses

Presentations were centered on interactions between nepoviruses and their nematode

vectors, methods to study the molecular determinants of vector specificity, and surveys

for fanleaf virus in Palestine (1% incidence), Turkey (0-35% incidence), Azorean Islands

(high incidence) and Spain (7% incidence).

Rugose wood complex

This complex consists of the stem-pitting , stem-grooving and corky-bark disorders. They

are widely regarded as important graft-transmitted diseases of the grapevine. The ICVG

currently recognises four distinct diseases (corky-bark, LN33 stem grooving, Rupestris

stem pitting, and Kober stem grooving) within the complex. These diseases commonly

occur in mixtures, in different combinations and commonly occur with leafroll disease. To

date, the causal viruses of the rugose wood diseases are unknown, but the vitiviruses

(GV A, GVB, GVC, GVD) are commonly found in diseased vines.

In Hungary, the percentage of European vines affected with rugose wood diseases

was moderately high: the frequency of Rupestris stem-pitting was found to be 22%,

Kober stem-grooving was 20%, and LN33 stem-grooving disease was 13%. Samples of

566 European vines growing in Palestine showed a 66% infection with GVA and a 4%

infection with GVB, whereas 69 samples of rootstock vines showed only a 6% infection

with GVA.

Data was presented suggesting that GVA may be the causal agent of the Kober stem

grooving disease. This conclusion was based on the common association of GVA

occurring with diseased vines. No direct proof has been obtained. In Italy, another study

showed the association of GVA with Kober stem grooving to be only 62%, also no

15

relationship was found between GVA and Rupestris stem pitting and no relationship of

GVA with either corky-bark or LN33 stem grooving diseases.

The GVA and GVB viruses have been shown to be transmitted by mealybugs

(Pseudococcus spp. and Planococcus spp.) and GVA was additionally reported to be

transmitted by the scale insect, Neopulvinaria innumerabilis.

The genome of both GVA and GVB have been completely sequenced and GVD is

partially completed. This information has allowed the development of molecular detection

tests.

New stratagies for introducing resistance to viruses

Research groups in France, USA, Italy, Switzerland, Israel and Austria are attempting to

genetically engineer grapevines to produce resistance to some of the common viruses.

The general approach used is based on the reported viral resistance resulting from the

insertion of either a viral gene or part of a viral gene into the genome of plants. Some

rootstocks and V. vinifera cultivars which have been transformed with the viral genes

from fanleaf virus, arabis mosaic and grapevine chrome yellow mosaic virus, are

currently being evaluated.

Most of the research groups have used the strategy of testing their gene inserts in

tobacco plants before attempting to transform grapevines. Some of these gene inserts

have delayed the replication of viruses in the experimental inoculated tobacco plants.

The French group has been testing the usefulness of viral coat protein-mediated

protection against fan leaf virus in the rootstock varieties, 110 Richter and V. rupestris.

Several transformants were obtained exhibiting a significant level of coat protein

production. The protection tests against fanleaf virus included green-graft inoculation of

transformants, micro-graft inoculation of the in vitro plantlets, and transmission tests

using fanleaf-viruliferous nematodes. All green-graft inoculated transformants became

infected after I month. The micro-graft inoculated plants also became infected, although 2

plants showed apparent recovery. None of the plants exposed to the viruliferous

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nematodes were immune to fanleaf virus infection. Several alternative versions of viral

gene constructs have been made with the view of further testing pathogen-derived

resistance in the 11 OR rootstock.

The Americans have produced several putative transformed lines of Riparia Gloire,

3309 C, 110 Richter, and MGT 101-14 containing a range of molecular constructions

derived from genes of fanleaf virus, GLRaV-2, and GLRaV-3. The process of

characterizing the plants is in progress and there are plans to test resistance to fanleaf

virus infection by approach-grafting to infected Chenopodium quinoa, micro-grafting onto

infected vines, green-graft inoculation of plants.

In Austria, attempts are being made to transform V. vinifera cv. Russalka and 110

Richter with gene inserts based on the coat protein gene from fanleaf virus, arabis

mosaic virus and GVA and GVB.

In Italy and Israel, the transformation of grapevines has been attempted with gene

inserts based on the coat protein. Also in Italy, gene inserts based on the putative

movement protein genes from GVA and GVB are being used.

In Switzerland, the rootstocks V. rupestris du Lot and 3309 Couderc have been

transformed with the coat protein genes of fanleaf virus and arabis mosaic virus The

plants tranformed with the fanleaf virus coat protein gene were challenge-inoculated

using micro-graft and green-graft inoculation techniques, but all were found to be

susceptible to infection with the fanleaf virus. Infection tests with viruliferous nematodes

have been initiated.

Selection and certification of grapevines

Recently an expert group of the O.I.V. in France discussed clonal selection of the

grapevine. The issue of virus infection was considered as well as the recommended

tests which should be done to achieve sanitary certification. It was agreed that there

was plenty of evidence showing that fanleaf, leafroll , rugose wood, and other viruses

can be very detrimental to grapevines, and to their products. It was suggested that vines

17

that underwent field selection, prior to planting in performance plots for clonal evaluation,

should be hot-water treated to eliminate phytoplasmas, and must be checked for disease

freedom with the following tests:

• indexing for leafroll (Pi not Noir or Cabernet Franc)

• indexing on V. rupestris (for fanleaf, stem-pitting, fleck)

• indexing on Kober 588 (stem-grooving, graft-incompatibility)

• indexing on LN33 (corky-bark, stem-grooving)

• ELISA for nepoviruses which may occur in the grapevine source region

• ELISA for mealybug-transmitted closteroviruses

• ELISA for mealybug-transmitted vitiviruses

Foundation blocks for the production of basic and certified material must be kept under

continuous surveillance, especially for contamination by vector-transmitted viruses and

phytoplasmas.

Concluding comments

It should be recognized that the effect of viruses on the performance of the grapevine

is not only influenced by cultivar and environmental conditions but also by the vine

management. Generally, a lower fruiting demand on the vine results in a smaller

difference between the normal and virus-infected vines. As the fruiting potential is

increased, the difference between normal and virus-infected vines become greater.

The threat to the viticultural industry from viral diseases is real and on-going. The

interest in importing new clones and cultivars into Australia from overseas carries both

benefits and the risk of introducing new diseases.

The common practice of top-working unpopular varieties to premium cultivars needed

today, gives further opportunity to create new combinations of viruses in the premium

vine material. Today's relatively harmless virus may be tomorrows viticultural problem,

when combined with other harmless viruses or other unknown disease agents.

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I wish to thank the Dried Fruits Research and Development Council and the Grape and

Wine Research and Development Corporation for some financial support, to attend the

12'h Meeting of the International Council for the study of virus and virus-like diseases of

the grapevine.