Introduction

Grapevine trunk diseases including Eutypa dieback, Esca and Botryosphaeria dieback are among the most destructive diseases affecting established vineyards. They have been reported in most winegrowing regions over the world and are responsible for loss of productivity and vine death. Since 1990, the incidence of Esca has increased drastically affecting nearly 10% of French vineyards (Kobès et al., 2005; Bruez et al., 2013).

These diseases attack the vine wood: they cause death of spurs, arms, cordons and sometimes entire vines upon wood colonization by various pathogens (Larignon and Dubos, 1997; Mugnai et al., 1999; Surico et al., 2006; Van Niekerk et al., 2006; Lecomte et al., 2012). The development of necrosis inside the wood greatly hinders the sap flow and can induce a general weakening of the plant. The physiological balance of the plant seems affected when the critical volume of non-functional wood becomes too large (Lecomte et al., 2008; Luque et al., 2009; Maher et al., 2012). A high volume of inner necrosis may then seriously reduce water transport and may impact plant functioning, in particular in water stress conditions.

There are actually a large number of pathogens described associated with these diseases and increased knowledge about mechanisms of their development in vine wood (Bertsch et al., 2013). Furthermore, Esca is a complex syndrome (Mugnai et al., 1999; Graniti et al., 2000; Surico et al., 2006) and is still poorly understood unlike Eutypa dieback. The role of Botryosphaeria species in the development of the Esca syndrome is still a matter of debate (Mugnai et al., 1999; Lecomte et al., 2012). Both diseased and healthy adult plants show the same fungi species, suggesting they are normal mycota associated with adult vines (Hofstetter et al., 2012). These pathogens are latent and can become pathogenic under the influence of unidentified factors (Retief et al., 2006; Surico et al., 2004 and 2006).

There are no efficient methods for managing these diseases in the vineyard (Bertsch et al., 2009). Attempts to control these fungal diseases are currently based on the use of biological agents, natural molecules, chemical compounds and sanitation methods, alone or in combination (Darrieutort and Lecomte, 2007; Bertsch et al., 2013; Diaz and Latorre, 2013). Nevertheless, they are not yet completely effective and current research is focusing on the factors responsible for disease emergence (Lecomte et al., 2012).

Numerous factors are reportedly involved in the development of grapevine wood diseases (Lecomte et al., 2011; Hofstetter et al., 2012; Bruez et al., 2013). The quality of plant material and planting practices, vineyard management strategy and pruning systems are some factors that may influence the proportion of Esca symptoms in mature vineyards (Geoffrion and Renaudin, 2002; Lecomte et al., 2011 and 2012). It has been also shown for instance that young plants from nurseries already contain fungi associated with Esca and Botryosphaeria dieback (Larignon et al., 2007; Larignon et al., 2008; Aroca et al., 2010; Billones-Baaijens et al., 2013). Indeed, the quality of the initial plant material can promote the development of pathogens in grapevine wood. Graft quality is another important criterion for the global quality of plant. Grafted vines showed a higher percentage of symptomatic vines compared to own rooted vines (Andreini et al., 2014). Contrariwise, Fourie and Halleen (2006) showed that machine-grafted graft unions had lower pathogen incidences compared to hand-grafted graft unions in commercial nurseries. The authors explained these results by big grafting wounds created in hand grafting regime and by unsterile hands.

Plot age is also an important factor in the foliar development of Esca symptoms and has to be taken into account in comparative studies. Indeed, expression level is maximal between 15 and 35 years but high level of expression is now also found in several younger vineyards (Surico et al., 2006; Romanazzi et al., 2009). However, the National Grapevine Trunk Disease Survey conducted in France from 2003 to 2008 shows the incidence of Esca is maximal for vineyards aged between 15 and 25 years (Fussler et al., 2008; Grosman and Doublet, 2012).

Significant differences in Esca foliar symptom expression have been already recorded among grapevine cultivars, rootstocks, clones and pedo-climatic conditions (Surico et al., 2000; Marchi et al., 2006; Larignon et al., 2009; Kuntzmann et al., 2013; Travadon et al., 2013; Andreini et al., 2014; Murolo and Romanazzi, 2014). However, the incidence of Esca disease has highly increased over the past 25 years (Carbonneau et al., 2015). This period also corresponds to the generalization of the Omega grafting system. Grafting is an artificial multiplication technique which causes injuries and requires proper healing of plant tissue for good viability of future vines. Injuries or other wounds may favor the development of saprophytes or infections by trunk pathogens. Thus, another possible hypothesis is that the Omega grafting system might have promoted the development of Esca disease.

Omega grafting represents 95% of current grafting (http://www.vignevin-sudouest.com/publications/fiches-pratiques/production-plant-vigne-pepiniere.php). Grafting machines are used to cut and assemble the rootstock and the scion in a single manipulation. The mechanization of the grafting process is highly cost reducing. The Whip and Tongue grafting method is another grafting type examined in this study. The machine operates in two manipulations: double cutting in a Z shape followed by hand assembly (the traditional system with a low output per hour). For these last two graft types, grafting is performed in commercial nurseries according to standard practices. After matching the rootstock and the scion together, the newly grafted cuttings are packed in boxes and stacked in a humid, warm environment until the union has callused. This step seems to favor the transmission of fungi associated with Esca and Black dead arm (BDA) (Fourie and Halleen, 2006).

So far, little information exists on the role of the grafting method in the development of grapevine trunk diseases. Therefore, the purpose of our study was to investigate the putative influence of the grafting type on the foliar expression of Esca symptoms by comparing levels of Esca disease in different French vineyards where the three grafting systems described above were used to multiply the vines before planting.

Materials and methods

1. Grafting types

The study aimed at comparing the influence of one field grafting system, namely full cleft graft, and two table grafting systems, namely Omega graft and Whip and Tongue graft (Figure 1).

Figure 1. a) Full cleft graft, b) Whip and Tongue graft, c) Omega graft (Caroline Thienpont, 2013).

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Results

2. Grafting system effect on chronic form of Esca disease

Figure 2. Mean (±sd) percentage of Esca vines per year and per variety ("Total" is the mean of Cabernet-Sauvignon (CS) and Mourvèdre (M) plots).

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Analyses were carried out per year and per variety. Different letters above bars indicate significant differences between grafts (at P < 0.05).

For each test, all df=2, 3 different grafting types (FC = Full cleft graft; WT = Whip and Tongue graft; O = Omega graft). Grafting types are ranked (>: significant difference between grafts; ≥: value is higher but not significantly different).

Table 2. Results of GLM assessing effects of graft type on Esca percentage for the different years and varieties.

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Year	Variety	LR Chisq (df)	P
2013	Cabernet-Sauvignon	2.7 (2)	0.27	FC≤WT≤O
	Mourvèdre	16.9 (2)	0.0002	FC
	Total	18.2 (2)	0.0001	FC
2014	Cabernet-Sauvignon	4.6 (2)	0.1	FC
	Mourvèdre	14.7 (2)	0.0006	FC
	Total	19.1 (2)	< 0.0001	FC

For both years and both varieties, there was a significant effect of grafting type on the rate of chronic form of Esca (Figure 2). Full cleft grafted plots showed significantly lower percentages of Esca foliar symptoms than Omega or Whip and Tongue grafted plots (Figure 2). Thus, full cleft grafted plots showed percentages of Esca 6 to 15 times lower than the other two types of grafts for each year and grape variety considered.

On Cabernet-Sauvignon, for both years, full cleft grafted plots showed less vines with Esca symptoms than both other types of graft plots. In 2013 and 2014, on Mourvèdre, we found significantly lower percentages of Esca symptoms on full cleft grafted plots compared to Whip and Tongue grafted plots and Omega grafted plots (Table 2).

Figure 3. Percentage of Esca symptoms of plots according to date of planting.

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Triangles represent full cleft grafted plots, open dots represent Whip and Tongue grafted plots and closed dots represent Omega grafted plots).

Figure 3 represents the percentage of Esca symptoms as a function of planting year and highlights the age difference among plots. Omega grafted plots were younger than the two others, whereas the years of planting of the full cleft grafted plots and Whip and Tongue grafted plots spread out over the same period. Therefore, it appears that only the comparison between full cleft grafted plots and Whip and Tongue grafted plots is rationally possible. On the other hand, the comparison between these two graft types and Omega grafted plots was biased because of the younger age of the latter plots. However, the rates of Esca of Omega grafted plots appear to reach the same orders of magnitude as the rates of Whip and Tongue grafted plots and are higher to the rates of full cleft grafted plots.

3. Grafting system effect on apoplectic form of Esca disease

Figure 4. Mean (±SE) percentage of apoplectic vines per year and per variety ("Total" is the mean of Cabernet-Sauvignon (CS) and Mourvèdre (M) plots).

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Analyses were carried out per year and per variety. Different letters above bars indicate significant differences between grafts (at P < 0.05).

For each test, all df=2, for 3 different grafting types (FC = Full cleft graft; WT = Whip and Tongue graft; O = Omega graft). Grafting types are ranked (>: significant difference between grafts; ≥: value is higher but not significantly different).

Table 3. Results of GLM assessing effects of graft type on apoplectic percentage for the different years and varieties. "Total" corresponds to the analyses of the mean of Cabernet-Sauvignon and Mourvèdre plots.

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Apoplectic	Variety	LR Chisq (df)	P
2013	Cabernet-Sauvignon	3.9 (2)	0.14	O≤FC≤WT FC=O=WT
	Mourvèdre	9.0 (2)	0.01 *	FC FC=O=WT but FC
	Total	9.8 (2)	0.007 **	FC=O=WT but FC
2014	Cabernet-Sauvignon	6.1 (2)	0.05 *	FC=O=WT
	Mourvèdre	9.6 (2)	0.008 **	FC
	Total	12.1 (2)	0.002 **	FC

For both years and both varieties, a significant effect of the grafting type was found, with a lower percentage of apoplectic vines for full cleft grafted plots compared to both Omega and Whip and Tongue grafted plots. The percentages of apoplectic vines in Omega grafted plots were higher than those observed in full cleft grafted plots but lower than those observed in Whip and Tongue grafted plots. A similar pattern was observed in both years but the difference was significant only in 2014 (Figure 4).

When the two varieties were analyzed separately (and associated climatic regions), results were quite similar. On Cabernet-Sauvignon, no significant difference was found between grafting types in 2013 and in 2014, but Whip and Tongue grafted plots showed a higher rate of apoplectic vines compared to the other two graft types and for both years (Table 3). On Mourvèdre, in 2013 and 2014, full cleft grafted plots showed a lower rate of apoplectic vines than Whip and Tongue grafted plots (Table 3). A significant difference was found between full cleft grafted plots and Omega grafted plots in 2014. The same trend was observed in 2013 (although not statistically significant), with less apoplectic vines for full cleft field grafted plots (Table 3).

Discussion

The mean percentages of vines showing apoplectic or chronic forms of Esca, whatever the grafting type, were consistent with those observed by the French National Grapevine Trunk Disease Survey (Fussler et al., 2008; Bruez et al., 2013). Furthermore, our survey, conducted in two representative French winegrowing regions, showed a weak variation of foliar expression between years. In both regions, high differences have been observed between plots (0% to 43% of vines with Esca foliar symptoms), particularly on Omega (0% to 39.9%) and Whip and Tongue grafted plots (0% to 43.4%). This observation suggests there is a difference in Esca foliar expression due to the quality of the batches of plants. As shown in Tuscany, when there is a substantial increase in the demand for propagating material, and hence in the production of grafted rooted cuttings, there is probably a decrease in plant quality (Surico et al., 2004). The authors highlighted the possibility that nurseries were forced to produce as much plant material as they could, of whatever type, including almost certainly shoots from Esca-infected vines. Several studies showed canes of rootstock mother were still infected by Phaeomoniella chlamydospora (Retief et al., 2006).

Whatever the grape variety, results showed a lower percentage of apoplexy on full cleft grafted plots compared to Whip and Tongue and Omega grafted plots. Whip and Tongue grafted plots showed the highest rates of apoplectic plants. Omega grafted plots exhibited intermediate rates of apoplectics with no significant difference with Whip and Tongue grafted plots.

The percentage of vines showing a chronic form of Esca was not significantly different between Whip and Tongue grafted plots and Omega grafted plots (6.70% and 8.93%, respectively, in 2013 and 8.65% and 11%, respectively, in 2014). However, in this survey, these two grafting systems showed significantly higher rates of chronic form of Esca compared to full cleft grafted plots realized on field. Indeed, the rate of Esca foliar symptoms on this grafting system was below 1% in both 2013 and 2014. However, in the Bordeaux region and Cabernet-Sauvignon variety, we did not notice strong and significant differences between graft types because of high variation in the percentages of Esca affected vines between plots. But the trend remains the same as Mourvèdre with a lower rate of Esca on full cleft grafted plots and a higher rate on Omega grafted plots.

Due to the recent development of this industrial technology, the Omega grafted plots were younger than the other two types of graft plots. Indeed, Omega graft was invented in the 1980s' and this graft type is related to vine age. The age of the full cleft grafted plots and Whip and Tongue grafted plots was comparable, with mean age (year ± SE) of 47.1 ± 6.7 and 41.3 ± 10.7, respectively. Omega plots were younger (22.4 ± 4.5). This age difference between Omega grafted plots and the two others may induce a bias in the expression of Esca rates. Indeed, expression of Esca foliar symptoms varies with the plot age. In this survey, Omega grafted plots were slightly younger than the maximal period of Esca expression (Surico et al., 2006) and in the maximal period shown in the National Grapevine Trunk Disease Survey (Fussler et al., 2008). Thus, the rates on these plots may decrease as plots become older. Further studies may focus on older Omega grafted plots to allow a better comparison of this more recent technology.

However, other factors could be involved such as the quality of material or plantation. Environmental and plant material factors have been much studied in the last ten years. Impacts of rootstock, climate and training system on Esca foliar symptoms were established (Surico et al., 2000; Marchi et al., 2006; Boso et al., 2008; Larignon et al., 2009; Van Niekerk et al., 2011; Andreini et al., 2014; Murolo and Romanazzi, 2014; Spagnolo et al., 2014). Impacts of planting conditions need to be taken into account. In Mediterranean conditions, spring is warmer than in oceanic conditions. Vine growers usually plant their vines earlier in the season than those from oceanic conditions where spring is usually wetter. These differences in planting conditions could affect vine development and sensitivity to Esca foliar symptoms. To take account of a maximum of factors, further studies may also carry out a trial with all grafting systems on the same plot, in the same planting conditions.

Significant differences in the percentage of Esca symptoms were revealed in this survey between the other two graft types: full cleft field grafted plots showed fewer foliar symptoms than Whip and Tongue grafted plots. Several studies showed a high rate of fungi contamination occurring along the propagation process in nurseries (hydration, disbudding, callusing and rooting, etc.) (Fourie and Halleen, 2006; Larignon et al., 2009; Aroca et al., 2010; Gramaje and Armengol, 2011; Agusti-Brisach et al., 2013; Billones-Baaijens et al., 2013). Full cleft grafted vines are not subject to these operations. Manual grafting in the field avoiding the nursery environment reduces potential contacts with fungi and finally shows lower rates of Esca foliar symptoms. Furthermore, the summer period is less favorable to spore dissemination of Phaeomoniella chlamydospora, which is considered as a pioneer fungus (Larignon et al., 2009; Bertsch et al., 2013).

Another explanation could be that greater surface area of cambium contact between rootstock and scion would assure a better graft quality. In order for the grafting operation to be successful, the vascular cambiums responsible for cell division of the two grafting partners must be in contact with each other so that they can build a connection between their separate vascular systems for water and nutrient supply (Keller, 2010). At each cut edge of the two cambiums, the callus, a mass of undifferentiated cells, grows and finally the scion becomes a part of the whole plant vascular system. Traditionally, grafting was carried out by hand and on one- or two-year-old rootstocks. This manual on-field grafting (or full cleft graft) promotes greater surface contact between cambium compared to mechanical on-table grafting (Omega graft and Whip and Tongue graft).

Moreover, when the rootstock is rooted, the plant focuses all resources on development of continuity between the two plant vascular systems. Plants grafted in field already have an established root system and consequently are more resistant and allocate more resources to callus production. Table grafted plants have to allocate some resources to root production and therefore fewer resources to establish the callus and the relation between the two vascular systems of rootstock and scion. Fourie and Halleen (2006) found more pathogens on machine-grafted graft unions compared to hand-grafted graft unions. These results are not contradictory because more pathogens are not always associated with greater incidence of Esca disease. Hofstetter et al. (2012) indeed showed that healthy asymptomatic vines carried the same fungi as diseased vines (Hofstetter.

Conclusion

As a conclusion, in this study, Whip and Tongue grafted plots show higher percentages of apoplexy and chronic form of Esca compared to full cleft field grafted plots. Several hypotheses can explain these results. First, the nurseries are a high source of fungi contamination. Then, the contact surface between cambiums may be different according to graft type. Finally, vines grafted manually on field are already rooted, which means that they could allocate more resources to callus production.

Acknowledgments : This research was partly supported by Worldwide Vineyards. We thank Caroline Thienpont and Guillaume Darrieutort for technical assistance.

References

• Agusti-Brisach C., Gramaje D., García-Jiménez J. and Armengol J., 2013. Detection of black-foot and Petri disease pathogens in soils of grapevine nurseries and vineyards using bait plants. Plant Soil, 364, 5-13. doi:10.1007/s11104-012-1333-1
• Andreini L., Cardelli R., Bartolini S., Scalabrelli G. and Viti R., 2014. Esca symptoms appearance in Vitis vinifera L.: influence of climate, pedo-climatic conditions and rootstock/cultivar combination. Vitis, 53, 33-38.
• Aroca A., Gramaje D., Armengol J., García-Jiménez J. and Raposo R., 2010. Evaluation of the grapevine nursery propagation process as a source of Phaeoacremonium spp. and Phaeomoniella chlamydospora and occurrence of trunk disease pathogens in rootstock mother vines in Spain. Eur. J. Plant Pathol., 126, 165-174. doi:10.1007/s10658-009-9530-3
• Bertsch C., Larignon P., Farine S., Clément C. and Fontaine F., 2009. The spread of grapevine trunk disease. Science, 324, 721. doi :10.1126/science.324_721a
• Bertsch C., Ramirez-Suero M., Magnin-Robert M., Larignon P., Chong J., Abou-Mansour E., Spagnolo A., Clement C. and Fontaine F., 2013. Grapevine trunk diseases: complex and still poorly understood. Plant Pathol., 62, 243-265. doi:10.1111/j.1365-3059.2012.02674.x
• Billones-Baaijens R., Ridgway H.J., Jones E.E., Cruickshank R.H. and Jaspers M.V., 2013. Prevalence and distribution of Botryosphaeriaceae species in New Zealand grapevine nurseries. Eur. J. Plant Pathol., 135, 175-185. doi :10.1007/s10658-012-0076-4
• Boso S., Santiago J.L. and Martínez M.C., 2008. The influence of 110-Ritcher and SO4 rootstocks on the performance of scions of Vitis vinifera L. cv. Albariño clones. Span. J. Agric. Res., 6, 96-104. doi:10.5424/sjar/2008061-297
• Bruez E., Lecomte P., Grosman J., Doublet B., Bertsch C., Fontaine F., Ugaglia A., Teissedre P.L., da Costa J.P., Guerin-Dubrana L. and Rey P., 2013. Overview of grapevine trunk diseases in France in the 2000s. Phytopathol. Mediterr., 52, 262-275.
• Carbonneau A., Deloire A., Torregrosa L., Jaillard B., Pellegrino A., Métay A., Ojeda H., Lebon E. and Abbal P., 2015. Traité de la vigne. 2nd edition. Pratiques Vitivinicoles, Dunod.
• Darrieutort G. and Lecomte P., 2007. Evaluation of a trunk injection technique to control grapevine wood diseases. Phytopathol. Mediterr., 46, 50-57.
• Diaz G.A. and Latorre B.A., 2013. Efficacy of paste and liquid fungicide formulations to protect pruning wounds against pathogens associated with grapevine trunk diseases in Chile. Crop Prot., 46, 106-112. doi:10.1016/j.cropro.2013.01.001
• Fourie P.H. and Halleen F., 2006. Chemical and biological protection of grapevine propagation material from trunk disease pathogens. Eur. J. Plant Pathol., 116, 255-265. doi:10.1007/s10658-006-9057-9
• Fussler L., Kobes N., Bertrand F., Maumy M., Grosman J. and Savary S., 2008. A characterization of grapevine trunk diseases in France from data generated by the National Grapevine Wood Diseases Survey. Phytopathology, 98, 571-579. doi:10.1094/PHYTO-98-5-0571
• Geoffrion R. and Renaudin I., 2002. Tailler contre l’esca de la vigne. Une mesure utile face à la menace de recrudescence de cette ancienne maladie du bois. Phytoma, 554, 23-27.
• Gramaje D. and Armengol J., 2011. Fungal trunk pathogens in the grapevine propagation process: potential inoculum sources, detection, identification, and management strategies. Plant Dis., 95, 1040-1055. doi:10.1094/PDIS-01-11-0025
• Graniti A., Surico G. and Mugnai L., 2000. Esca of grapevine: a disease complex or a complex of diseases? Phytopathol. Mediterr., 39, 16-20.
• Grosman J. and Doublet B., 2012. Synthèse des dispositifs d’observation au vignoble, de l’observatoire 2003-2008 au réseau d’épidémiosurveillance actuel. Phytoma, 651, 31-35.
• Hofstetter V., Buyck B., Croll D., Viret O., Couloux A. and Gindro K., 2012. What if Esca disease of grapevine were not a fungal disease? Fungal Divers., 54, 51-67. doi:10.1007/s13225-012-0171-z
• Keller M., 2010. The science of grapevines. Anatomy and physiology. Elsevier Academic Press.
• Kobès N., Grosman J. and Decoin M., 2005. Grapevine trunk diseases, results from the French National Observatory. Phytoma, 589, 52-54.
• Kuntzmann P., Barbe J., Maumy-Bertrand M. and Bertrand F., 2013. Late harvest as factor affecting Esca and Botryosphaeria dieback prevalence of vineyards in the Alsace region of France. Vitis, 52, 197-204.
• Larignon P. and Dubos B., 1997. Fungi associated with Esca disease in grapevine. Eur. J. Plant Pathol., 103, 147-157. doi:10.1023/A:1008638409410
• Larignon P., Berud F., Girardon K. and Jacquet O., 2007. Premiers résultats sur le cycle biologique des champignons associés aux maladies du bois de la vigne en pépinière. Rhône VO., 2, 16-23.
• Larignon P., Giansetto K., Salancon E., Girardon K., Berud F., Jacquet O. and Coarer M., 2008. Champignons associés aux maladies du bois : une enquête en pépinières. Rhône VO., 3, 26-31.
• Larignon P., Fontaine F., Farine S., Clément C. and Bertsch C., 2009. Esca et Black Dead Arm : deux acteurs majeurs des maladies du bois chez la Vigne. C.R. Biologies, 332, 765-783. doi:10.1016/j.crvi.2009.05.005
• Lecomte P., Darrieutort G., Limiñana J.M., Louvet G., Guérin L., Tandonnet J.-P., Goutouly J.-P., Gaudillère J.-P. and Blancard D., 2008. (I) Eutypiose et Esca - Eléments de réflexion pour mieux appréhender ces phénomènes de dépérissement. (II) Esca de la vigne - Vers une gestion raisonnée des maladies de dépérissement. Phytoma, 615, 43-48 and 616, 37-41.
• Lecomte P., Darrieutort G., Laveau C., Blancard D., Louvet G., Goutouly J.-P., Rey P. and Guérin-Dubrana L., 2011. Impact of biotic and abiotic factors on the development of Esca decline disease. IOBC/WPRS Bull., 67, 171-180.
• Lecomte P., Darrieutort G., Liminana J.-M. and Comont G., 2012. New insights into esca of grapevine: the development of foliar symptoms and their association with xylem discoloration. Plant Dis., 96, 924-934. doi:10.1094/PDIS-09-11-0776-RE
• Luque J., Martos S., Aroca A., Raposo R. and Garcia-Figueres F., 2009. Symptoms and fungi associated with declining mature grapevine plants in northeast Spain. J. Plant Pathol., 91, 381-390.
• Maher N., Piot J., Bastien S., Vallance J., Rey P. and Guérin-Dubrana L., 2012. Wood necrosis in Esca-affected vines: types, relationships and possible links with foliar symptom expression. J. Int. Sci. Vigne Vin, 46, 15-27. http://dx.doi.org/10.20870/oeno-one.2012.46.1.1507
• Marchi G., Peduto F., Mugnai L., Di Marco S., Calzarano F. and Surico G., 2006. Some observations on the relationship of manifest and hidden esca to rainfall. Phytopathol. Mediterr., 45, 117-126.
• Mugnai L., Graniti G. and Surico G., 1999. Esca (black measles) and brown wood-streaking: two old and elusive diseases of grapevines. Plant Dis., 83, 404-418. doi:10.1094/PDIS.1999.83.5.404
• Murolo S. and Romanazzi G., 2014. Effects of grapevine cultivar, rootstock and clone on Esca disease. Australas. Plant Pathol., 43, 215-221. doi:10.1007/s13313-014-0276-9
• Retief E., McLeod A. and Fourie P.H., 2006. Potential inoculum sources of Phaeomoniella chlamydospora in South African grapevine nurseries. Eur. J. Plant Pathol., 115, 331-339. doi:10.1007/s10658-006-9025-4
• Romanazzi G., Murolo S., Pizzichini L. and Nardi S., 2009. Esca in young and mature vineyards, and molecular diagnosis of the associated fungi. Eur. J. Plant Pathol., 125, 277-290. doi:10.1007/s10658-009-9481-8
• Spagnolo A., Magnin-Robert M., Alayi T.D., Cilindre C., Schaeffer-Reiss C., Van Dorsselaer A., Clément C., Larignon P., Ramirez-Suero M., Chong J., Bertsch C., Abou-Mansour E. and Fontaine F., 2014. Differential responses of three grapevine cultivars to Botryosphaeria dieback. Phytopathology, 104, 1021-1035. doi:10.1094/PHYTO-01-14-0007-R
• Surico G., Marchi G., Braccini P. and Mugnai L., 2000. Epidemiology of esca in some vineyards in Tuscany (Italy). Phytopathol. Mediterr., 39, 190-205.
• Surico G., Bandinelli R., Braccini P., Di Marco S., Marchi G., Mugnai L. and Parrini C., 2004. On the factors that may have influenced the esca epidemic in the eighties in Tuscany. Phytopathol. Mediterr., 43, 136-143.
• Surico G., Mugnai L. and Marchi G., 2006. Older and more recent observations on Esca: a critical overview. Phytopathol. Mediterr., 45, 68-86.
• Travadon R., Rolshausen P.E., Gubler W.D., Cadle-Davidson L. and Baumgartner K., 2013. Susceptibility of cultivated and wild Vitis spp. to wood infection by fungal trunk pathogens. Plant Dis., 97, 1529-1536. doi:10.1094/PDIS-05-13-0525-RE
• Van Niekerk J., Fourie P.H., Halleen F. and Crous P.W., 2006. Botryosphaeria spp. as grapevine trunk disease pathogens. Phytopathol. Mediterr., 45, 43-54.
• Van Niekerk J., Bester W., Halleen F., Crous P.W. and Fourie P.H., 2011. The distribution and symptomatology of grapevine trunk disease pathogens are influenced by climate. Phytopathol. Mediterr., 50, 98-111.