Introduction

Grapevines can be affected by approximately 75 virus or virus-like diseases but their impact is not equivalent. Some of them are more important due to their wide geographical distribution and their economic losses. Grapevine FanLeaf Virus (GFLV) is the most important virus in vineyards worldwide (Andret-Link et al., 2004). GFLV is the main agent of grapevine fanleaf disease and it is specifically transmitted by the ectoparasite nematode Xiphinema index (Hewitt et al., 1958) but it is also propagated by plant material. In Europe, Arabis Mosaic Virus (ArMV) is the second most important nepovirus involved in grapevine fanleaf disease. Grapevine Leafroll Virus (GLRV) and rugose wood diseases also affect plant vigor and yield and lead to economic losses. Grapevines are also affected by “minor” virus diseases (i.e., fleck, vein mosaic, rupestris stem pitting, etc.), whose impact is still unclear (Mannini and Digiaro, 2017).

Since the 1990s, the development of serological and biomolecular virus detection tests allows to set up experiments based on the comparison between healthy and virus infected vines (Cretazzo et al., 2010). Several authors have shown the effect of GLRV on grapevine (Guidoni et al., 1997; Bertamini et al., 2004), there is less data on GFLV. The negative influence of GFLV on vine growth and grape yield as well as the variable influence on parameters of must quality potential such as color, sugar or acidity have been demonstrated. Crop losses caused by GFLV vary from moderate (30% of the crop) to high (80%) depending on the virulence of the virus isolate combined with the susceptibility of the varieties and the effects of environmental factors (Bovey et al., 1990; Martelli and Savino 1990; Legin et al., 1993). In a trial conducted by Martínez et al. (2016), yield decreased by nearly 40% due to both a significant reduction in cluster number and berry weight. With regard to grape composition variables, GFLV infection caused a significant increase in sugar contents, pH and color intensity or no difference.

Fanleaf degeneration can cause symptoms such as internode shortening, leaf asymmetry, fasciation of shoots, mosaic discoloration of leaves and lead to a decrease in grape quantity and quality through flower abortion and millerandage and finally to plant death (Laveau et al., 2013). The influence of virus strain is also acknowledged (Martelli and Savino, 1990; Bovey and Martelli, 1992; Walter and Martelli, 1996). The impact of virus on grapevine also depends on the environment and interaction with factors such as rootstock (Golino et al., 2003), cultivar (Credi and Babini, 1997; Legin et al., 1993), plant age, annual climatic conditions (Cretazzo et al., 2010), as well as training and pruning systems (Mannini et al., 2001; Clingeleffer and Krake, 2002).

Tomato Black Ring Virus (TBRV) is another possible agent of fanleaf disease. In France, TBRV was detected for the first time on grapevine in 2009. Infected plants showed typical symptoms of fanleaf disease on the bunches that were very small and drastically reduced vine productivity (Laveau et al., 2013).

The aim of this work is to evaluate the effect of TBRV in two grapevine varieties, evaluating the effects on grape yield and berry quality potential. Yield, berry weight and grape composition have been recorded over two vintages as well as the architecture and vigor of the vines. The strength of the study is that the incidence of the virus has been studied within a single plot, so with the same soil and climatic conditions, and that both varieties were grafted on the same rootstock.

Materials and methods

Results

1. Impact on yield

Yield decreases for both varieties (Figure 1D). The losses were greater for Merlot than for Cabernet franc because of the greater number of Merlot vines without bunches (approximately 25% of the vines).

Figure 1. Effect of Tomato Black Ring Virus (TBRV+: positive virus status) on yield parameters: bunch number (A), average bunch weight (B), average weight of 100 berries (C) and yield per vine (D).

Save View full size Expand inline Collapse inline

Error bars show standard deviation. Statistical analyses were carried out per year and per variety (CF: Cabernet franc, MN: Merlot noir and ***p< 0.001; **p< 0.01; *p< 0.05).

All yield components were affected by the presence of virus in the vine. There were fewer bunches with a lower weight and fewer berries/bunch on TBRV infected vines than on TBRV free vines in both years. The impact is more important on Merlot than on Cabernet franc except for the bunch number in 2011 (Figure 1A, B, C).

For bunch weight, infected Cabernet franc showed 39% and 37% decreases while infected Merlot had 60% and 58% losses in 2010 and 2011 respectively. The mean weight of 100 berries was significantly different for infected Merlot with 41% reduction in 2010 and 33% in 2011 whereas non-significant berry weight losses of only 7% and 20% were recorded on infected Cabernet franc. The final result was a decrease in yield of 52% and 61% on Cabernet franc in 2010 and 2011 respectively, and a decrease of 64% in 2010 and 66% in 2011 for Merlot (Figure 1).

The effect of TBRV on grape yield was greater on Merlot compared to Cabernet franc. Differences in grape shatter have been observed between varieties. Grape shatter was scored for each vine from 0 to 4 according to importance with a score of 4 representing vine with no berries. On average Merlot score was 50% higher compared to Cabernet franc (Table 2).

Table 2. Average score of grape shatter (from 0 to 4) according to year, variety (CF: Cabernet franc, MN: Merlot noir) and sanitary status (Tomato Black Ring Virus).

View popup Expand inline Collapse inline

Year	Status	Variety	Average score
2010	TBRV -	CF	0.70
2010	TBRV +	CF	1.81
2010	TBRV -	MN	1.13
2010	TBRV +	MN	2.66
2011	TBRV -	CF	1.10
2011	TBRV +	CF	1.81
2011	TBRV -	MN	1.40
2011	TBRV +	MN	2.56

2. Impact on must quality

The effect of TBRV on grape sugar content, juice titratable acidity and pH, malic acid content, richness in polyphenolic compounds (tannins and anthocyanins) and yeast assimilable nitrogen is shown in Figures 2 and 3. Sugar content was higher on TBRV+ vines for both varieties and years, but the difference was statistically significant only for MN in 2010 (Figure 2A).

Figure 2. Effect of Tomato Black Ring Virus (TBRV) on grape composition: sugar content (A), titratable acidity (B) and malic acid (C).

Save View full size Expand inline Collapse inline

Error bars show standard deviation. Statistical analyses were carried out per year and per variety (CF: Cabernet franc, MN: Merlot noir and ***p< 0.001; **p< 0.01; *p< 0.05).

Titratable acidity (Figure 2B) and pH (data not shown) showed no uniform trends and were not significantly different between TBRV+ and TBRV- vines. There was more malic acid in the berries of infected vines in Merlot in 2011 and in Cabernet franc in both years; differences found in CF were significant (Figure 2C).

Figure 3. Effect of Tomato Black Ring Virus (TBRV) on grape composition: total polyphenols (A), yeast available nitrogen (B), anthocyanins (C) and extractable anthocyanins (D).

Save View full size Expand inline Collapse inline

Error bars show standard deviation. Statistical analyses were carried out per year and per variety (CF: Cabernet franc, MN: Merlot noir and ***p< 0.001;**p< 0.01; *p< 0.05).

Significantly higher total polyphenol content was observed on TBRV+ vines of Merlot in both years and in Cabernet franc in 2010 (Figure 3A). There were also more total and extractable anthocyanins in TBRV+ vines in Merlot in 2011 (Figure 3D).

A significant increase for yeast assimilable nitrogen was found in the juice of TBRV+ vines of Merlot in 2010. There was more yeast available nitrogen in the juice of TBRV+ vines in 2010, but the difference was significant only for Merlot (Figure 3B).

3. Impact on vigor

A reduction in pruning weight was observed for TBRV+ vines of the two varieties in both years (Figure 4A). This reduction was significant for MN in 2010 and for CF in both years. Concerning vegetative expression, CF was more impacted than MN with 31% and 26% decrease of pruning weight in 2010 and 2011 respectively, while this reduction was 19% and 13% for MN.

Pruning weight was lower on positive vines than on negative ones but a greater development of the lateral shoots was observed on TBRV+ vines (Figure 4B). The average length of lateral shoots of TBRV infected vines was greater than those of the negative vines for both MN and CF but differences were not significant.

This increased growth of lateral shoots leads to a two-fold increase in terms of pruning weight relative to primary shoots (Figure 4C). No significant difference between Merlot and Cabernet franc on vine growth was observed in terms of average length of lateral shoots.

The Ravaz index was significantly different between TBRV- and TBRV+ Merlot vines both years. In this case, the value of the Ravaz index was almost halved (Figure 4D).

Figure 4. Effect of Tomato Black Ring Virus (TBRV) on vine vigor: total pruning weight (A), average lateral shoot length (B), ratio between lateral and primary shoot weight (C) and Ravaz index (D).

Save View full size Expand inline Collapse inline

Error bars correspond to standard deviation. Statistical analyses were carried out per year and per variety (CF: Cabernet franc, MN: Merlot noir and ***p< 0.001; **p< 0.01; *p< 0.05).

Discussion and conclusion

Investigations on the sanitary status of V. vinifera cv. Merlot and cv. Cabernet franc of a same plot confirmed the presence of TBRV by ELISA tests. The results showed the impact of this virus on vine development, yield and grape composition. A very significant impact on the vegetative growth and fruit production of vines infected by TBRV was found.

The major impact of the presence of TBRV in vines was the very significant yield decrease of infected vines compared to virus free vines. The losses were over 50% for Cabernet franc and up to 66% for Merlot. The real effect of the virus was even greater, considering the fact that the virus free vines had been thinned to a maximum of eight bunches per vine, which is the standard practice of the estate where this study was carried out. TBRV+ vines rarely reached eight bunches or more per vine and were almost not thinned. The effect of grape shatter was stronger for the Merlot vines. All yield parameters were affected by the presence of the virus. Bunch number, average bunch weight and average berry weight were decreased on TBRV+ vines compared to TBRV free vines. This impact of viruses of infectious degeneration is well known. Andret-Link et al. (2004) evaluate crop losses caused by GFLV between 30% when the impact is moderate and up to 80% in highly impacted vines. This study shows that TBRV had a high impact on yield for both varieties considered, and that this impact was greater for Merlot than for Cabernet franc.

The effect on grape composition has also been recorded. The impact on grape quality potential was quite moderate. The results of this study showed no significant differences between healthy vines and infected vines in terms of titratable acidity and only slight differences in sugar content, malic acid content and yeast available nitrogen, depending on the variety and the year. However, on infected vines, grape sugar content, malic acid, available nitrogen, polyphenols and anthocyanins showed a tendency to increase in both varieties and years. The increase of total polyphenols was greater on Merlot than on Cabernet franc for both years and this was the major effect on the quality potential of the grape must. There was also an increase of anthocyanins and especially for those extracted at pH3.2, representing the extractable anthocyanins during vinification. Hence, the wines made with grapes of infected vines could potentially have more color. In the literature, however, the viruses of infectious degenerations are often described as affecting the quality potential of grapes especially through decreases in sugar and total acidity. Cretazzo et al. (2010) demonstrated that GFLV infection may lead to a decrease of anthocyanins in berries despite the decrease of berry size and yield. There is probably an interaction between the infection by the virus and the variety. In this study, as the berries were much smaller on infected vines, the increase of quality potential can be a consequence of yield reduction rather than a direct effect of the infection. It is possible that berry size reduction results in a concentration of compounds. It would be interesting to compare the composition of grapes from infected vines versus that of non-infected vines with different yield levels, in order to measure the real impact caused by the infection on grape quality potential.

The third impact observed in this study was the reduction of vegetative expression. Several measurements have been implemented to characterize the vegetative development of the studied vines. The infected vines were visually bushy with anarchic development of shoots. The total pruning weights were measured with a focus on lateral shoots. Number, length, and weight of the laterals were measured. Total pruning weight of infected vines was lower than that of healthy vines. The reduction of vegetative expression reached 30% in Cabernet franc, while it reached only 19% in Merlot. Despite the reduction of vegetative expression, there were more and longer lateral shoots on infected vines. Hence, the ratio of lateral shoot weight to primary shoot weight was much greater for TBRV infected vines. This result is important in terms of vineyard management. In particular, in cool to moderately cool climates, laterals in the fruit zone need to be removed. Hence, production cost can be assumed higher in TBRV+ vines. In addition, the pruning will be more difficult to implement because of a lack of well-developed primary shoots. From a qualitative point of view, the development of lateral shoots is often considered to have a negative impact on the quality potential of the grapes. However, this study showed an increase in most quality-related parameters of the grapes in the infected vines while these vines showed an increased growth of the lateral shoots. The negative effect of laterals is supposed to be due to competition for nutrients between clusters and secondary shoots which may still be growing after veraison. In the context of this study that involved a soil with low water holding capacity and two dry vintages, the secondary shoots stopped their growth early in the season, which may have reduced the negative impact of laterals on fruit quality potential. Finally, the infected vines were vigorous compared to the fruit weight they carry. Indeed, yield was highly impacted by grape shatter. Hence, source sink ratio was high in TBRV+ vines considering regular leaf functioning in infected vines.

The very low Ravaz index calculated for the TBRV+ vines reflects this particular development of the virus infected vines.

This study demonstrates the importance of TBRV whose impact on yield is at least as important as that of GFLV. The slight positive effect observed on grape quality potential in infected vines is not sufficient to counterbalance the strong negative impact on yield. To date, this virus has been detected in several plots of the French vineyard and is not eliminated during the sanitary selection of vines in nurseries. Given the results of this study, further research on the impact of this virus is needed, as well as potential transmission in vineyards and nurseries.

Acknowledgements

Authors thank the staff of the estate where the study was carried out for assistance and financial support.

References

• Andret-Link P., Laporte C., Valat L., Ritzenthaler C., Demangeat G., Vigne E., Laval V., Pfeiffer P., Stussi-Garaud C. and Fuchs M., 2004. Grapevine fanleaf virus: still a major threat to the grapevine industry. Journal of Plant Pathology 86(3), 183-195. http://www.sipav.org/main/jpp/volumes/0304/030401.pdf
• Bertamini M., Muthuchelian K. and Nedunchezhian N., 2004. Effect of grapevine leafroll on the photosynthesis of field grown grapevine plants (Vitis vinifera L. cv. Lagrein). Journal of Phytopathology 152(3), 145-152. doi:10.1111/j.1439-0434.2004.00815.x
• Bovey R. and Martelli G.P., 1992. Directory of Major Virus and Virus-Like Diseases of Grapevines. Mediterranean Fruit Crop Improvement Council (MFCIC)/International Council for the Study of Virus and Virus Diseases of Grapevine (ICVG).
• Bovey R., Gärtel W., Hewitt W.B., Martelli G.P. and Vuittenez A., 1990. Soil-borne viruses transmitted by nematodes. In: Bovey R., Gärtel W., Hewitt W.B., Martelli G.P., Vuittenez A. (eds.). Virus and Virus-Like Diseases of Grapevines, 46-50. Editions Payot, Lausanne, Switzerland.
• Clingeleffer P.R. and Krake L.R., 2002. Light (minimal) pruning enhances expression of higher yield from clones of Vitis vinifera L. cv. Sultana following thermotherapy for virus attenuation. Australian Journal of Grape and Wine Research 8(2), 95-100. doi:10.1111/j.1755-0238.2002.tb00217.x
• Credi R. and Babini A.R., 1997. Effects of virus and virus-like infections on growth, yield, and fruit quality of Albana and Trebbiano Romagnolo grapevines. American Journal of Enology and Viticulture 48(1), 7-12.
• Cretazzo E., Padilla C., Carambula C., Hita I., Salmerón E. and Cifre J., 2010. Comparison of the effects of different virus infections on performance of three Majorcan grapevine cultivars in field conditions. Annals of Applied Biology 156(1), 1-12. doi:10.1111/j.1744-7348.2009.00355.x
• Golino D.A., Sim S. and Rowhani A., 2003. The role of rootstock genotype in the effects of single and mixed infections of grapevine viruses. Proceedings of the 14th ICVG Conference, Locorotondo, Italia, 246-247.
• Guidoni S., Mannini F., Ferrandino A., Argamante N. and Di Stefano R., 1997. The effect of grapevine leafroll and rugose wood sanitation on agronomic performance and berry and leaf phenolic content of a Nebbiolo clone (Vitis vinifera L.). American Journal of Enology and Viticulture 48(4), 438-442.
• Hewitt W.B., Raski D.J. and Goheen A.C., 1958. Nematode vector of soil-borne fanleaf virus of grapevines. Phytopathology 48, 586-595.
• Laveau C., van Helden M., Darrieutort G., Esmenjaud D. and Demangeat G., 2013. First detection of Tomato black ring virus (TBRV) in a French vineyard. OENO One 47(3), 191-194. doi:10.20870/oeno-one.2013.47.3.1549
• Legin R., Bass P., Etienne L. and Fuchs M., 1993. Selection of mild virus strains of fanleaf degeneration by comparative field performance of infected grapevines. Vitis 32(2), 103-110. https://ojs.openagrar.de/index.php/VITIS/article/view/5186
• Mannini F. and Digiaro M., 2017. The effects of viruses and viral diseases on grapes and wine. In: Meng B., Martelli G., Golino D., Fuchs M. (eds.). Grapevine Viruses: Molecular Biology, Diagnostics and Management. Cham: Springer, 453-482. doi:10.1007/978-3-319-57706-7_23
• Mannini F., Argamante N., Gerbi V. and Ferrandino A., 2001. Interazione tra gestione del vigneto e malattie virali. Quaderni di Viticoltura ed Enologia. Universita di Torino 25, 51-65.
• Martelli G.P. and Savino V., 1990. Fanleaf degeneration. In: Person RC., Goheen A. (eds.). Compendium of Grape Diseases, 48-49. APS Press, Saint Paul, USA.
• Martínez L., Miranda C., Royo J.B., Urrestarazu J., Martínez de Toda F., Balda P. and Santesteban L.G., 2016. Direct and indirect effects of three virus infections on yield and berry composition in grapevine (Vitis vinifera L.) cv. ‘Tempranillo’. Scientia Horticulturae 212, 20-28. doi:10.1016/j.scienta.2016.09.023
• Vasconcelos M.C. and Castagnoli S., 2000. Leaf canopy structure and vine performance. American Journal of Enology and Viticulture 51(4), 390-396. https://www.ajevonline.org/content/ajev/51/4/390.full.pdf
• Walter B. and Martelli G.P., 1996. Sélection clonale de la vigne : sélection sanitaire et sélection pomologique. Influence des viroses et qualité. 1ère partie : effets des viroses sur la culture de la vigne et ses produits. Bulletin de l’OIV 69, 945-971.