Introduction

The European grapevine belongs to the botanical species Vitis vinifera, which is the most widely used around the world for wine production (about 7.4 million ha; FAO, 2002). Unfortunately, V. vinifera grapes are susceptible to various diseases, mildew (Reisch , 2012) and insect damage, Phylloxera in particular, and despite being grafted onto resistant rootstocks, they need frequent treatments against several pathogens. Until recently, the range of pesticides available (fungicides and insecticides) ensured that winemakers enjoyed a high quality harvest while protecting yields. It is only relatively recently that the winemaking sector has become aware of the need to reduce the use of pesticides. Winemakers and their workers have often been unaware of the risks to their health. The 2001ban on the use of sodium arsenite (a carcinogenic product) in the winemaking sector to treat the main vine trunk disease (Esca) only served to confirm the general criticisms levelled at pesticides by ecologists. There were also some complaints reported by the press with regard to a slight intoxication suffered by school children when the product was sprayed near their school. The data concerning the proportion of pesticides used by the winemaking sector in Europe have also heaped further disgrace on the sector. The French Ministry of Agriculture launched the Ecophyto 2018 plan with a view to satisfying this social demand, requiring a commitment from the stakeholders to reduce the use of pesticides across the country by 50%, if possible within a time frame of 10 years. The fear of facing legal proceedings, as in the case of asbestos, for having failed to provide agricultural workers with sufficient protection against these risks further increased awareness within the sector, drawing operators’ attention to all possible improvements in this sphere as well as the potential contributions of new resistant varieties. The reduced use of pesticides in the winemaking sector has therefore come to represent an essential social demand (Montaigne , 2016). Massive use of pesticides is unsustainable from an environmental and economic point of view, and leads to pesticide resistance (Barnaba , 2017). Inter-specific hybridization of grapevines began in the 19th century and was initially aimed at introducing pest and disease resistance in offspring (Galet, 1999). Later, several breeding programmes implemented worldwide led to the development of varieties showing different characteristics such as cold-hardiness, short/long growing season, and pest resistance (Reynolds, 2015). From a historical standpoint, innovation in wine-growing plant material has focussed more on sanitary and clonal selection since 1962 than on plant breeding. This line of research has transformed the value chain by eradicating the main viral diseases and thus supplying the entire world with plants boasting unparalleled levels of productivity and quality. The new varieties produced by the cross-breeding programmes launched in 1956, at least in France, did not have this impact. Since 1974 for the pioneering work of Alain Bouquet, and since the beginning of the new millennium for French viticulture research, the increasing social demand for sustainable development and reduced pesticide use has renewed the technological paradigms of plant breeding along with the attention paid by policy-makers and researchers to this road to progress that had been almost completely abandoned in France (Montaigne , 2016).

Few examples of studies

Variation of grape and wine composition in the frame of disease-resistant varieties

To model grape and wine quality from resistant vine varieties, it is necessary to understand the genetic, chemical and biochemical basis of wine quality attributes related to consumer preferences for colour, aroma, taste and texture. For this purpose, it is also necessary to measure grape and wine quality, including attributes that are desirable and undesirable to consumers. A last aspect concerns the identification of viticultural and winemaking practices that produce grape and wine with desirable characteristics. V. vinifera grapes have preferred flavour characteristics for wine production, but they tend to be susceptible to pests, diseases, and extreme temperatures; species native to North America and East Asia are generally better adapted to these stressors. For example, V. riparia can tolerate winter temperatures down to -40 °C and V. muscadinia is resistant to several diseases capable of devastating vinifera (e.g., Pierce’s disease caused by an insect-transmitted bacteria) (Reisch , 2012). However, these wild species tend to be low yielding and produce wines with undesirable sensory characteristics, including high acidity, low astringency, and excessive herbaceous aromas. Native American grape (Vitis) species have many desirable properties for winegrape breeding, but hybrids of these non-vinifera wild grapes with V. vinifera often have undesirable aromas. Other than the foxy-smelling compounds in V. labrusca and V. rotundifolia, the aromas inherent to American Vitis species are not so well characterized. Some key odorants in wine produced from the American grape species V. riparia and V. cinerea were characterized in comparison to wine produced from European wine grapes (V. vinifera). Grape-derived volatile compounds with fruity and floral aromas were at similar potency, but non-vinifera wines had higher concentrations of odorants with vegetative and earthy aromas: eugenol, cis-3-hexenol, 1,8-cineole, 3-isobutyl-2-methoxypyrazine (IBMP) and 3-isopropyl-2-methoxypyrazine (IPMP). Concentrations of IBMP and IPMP were well above sensory threshold in both non-vinifera wines. IBMP and IPMP were surveyed in 31 accessions of V. riparia, V. rupestris and V. cinerea. Some accessions had concentrations of >350 pg/g IBMP or >30 pg/g IPMP, well above concentrations reported in previous studies of harvest-ripe vinifera grapes. Methyl anthranilate and 2-aminoacetophenone, key odorants responsible for the foxiness of V. labrusca grapes, were undetectable in both the V. riparia and V. cinerea wines (<10 μg/L; Sun , 2011).

For example, table 1 gives representative reported concentrations of some key wine components that differentiate typical red vinifera varieties from V. riparia and V. labrusca (Concord) (Waterhouse , 2016).

Anthocyanidins are widely present in the plant kingdom, mainly in the form of glycosides, especially in black/red grape skins, where they are responsible for the colours red, blue, and purple depending on the pH of the cell compartment (Burns , 2002). The most common anthocyanidins are pelargonidin, cyanidin, delphinidin, peonidin, and malvidin, but these compounds are only present under their glycosylated forms, called anthocyanins. Anthocyanidins are also capable of conjugation with hydroxycinnamic acids (e.g., p-coumaric acid, caffeic acid) and other organic acids (e.g., malic and acetic acids). Unlike other species, North American Vitis species have significant levels of diglycosylated anthocyanins in positions C3 and C5; V. vinifera contains only traces of these and is characterized by the presence of a majority of anthocyanin monoglucosides, particularly malvidin-3-O-glucoside and its acylated derivatives. Anthocyanins are present in red grapes at about 500-3000 mg/kg, but can reach higher values in “dyers” cultivars such as Alicante Bouschet (5000 mg/kg) in which the anthocyanin concentration in pulp is also high (Teissedre , 2013).

We previously compared grape seed proanthocyanidin composition of Croatian V. vinifera spp. and different American Vitis spp. (Ćurko , 2012). Important significant differences were observed not just in concentration of monomeric and oligomeric flavan-3-ols, but also in structural characteristics such as mDP (mean Degree of Polymerization) and %G (% of Galloylation). Significantly higher concentrations of monomeric and oligomeric flavan-3-ols were observed in both cultivars of V. vinifera spp. V. doaniana and V. champinii showed significantly high %G, which was not previously reported in the literature. Since there has been a lack of studies comparing differences in proanthocyanidin composition between species of the genus Vitis, this research provides basic data for future studies.

For total anthocyanins and anthocyanin 3,5-diglucosides, differences amongst red, white and pink grapes can largely be explained by allelic variation in a transcription factor (VvmybA1) responsible for the expression of a 3-O-glycosyltransferase (UDGT) involved in the final step of anthocyanin biosynthesis (This , 2007). Similarly, anthocyanin 3,5-diglucoside production is not observed in vinifera due to a mutation in a 5-O-glycosyltransferase gene (Janvary , 2009). Differences in methoxypyrazine (MP) formation between Cabernet Sauvignon (high MP) and Pinot Noir (low MP) could be explained by allelic variation in VvOMT3, a methyltransferase involved in the final step of MP biosynthesis (Dunlevy , 2013). For monoterpenes, the higher monoterpene content of Muscat varieties could be explained by variations in the 1-deoxy-d-xylulose 5-phosphate synthase gene (VvDXS). Analogous genes are known to be responsible for the first steps of monoterpene biosynthesis in other plants (Emanuelli , 2010).

Knowledge of the genes controlling fruit quality and other traits should assist grape breeders in their efforts to produce new varieties (Waterhouse , 2016). However, how can the gene expression of phenolics and aroma precursors be affected by new disease-resistance genes introduced in Vitis species?

Assays carried out to improve the quality of wine from Fungus Resistant Grapes varieties (FRG) were primarily meant to reduce the occurrence of foxy flavours with the use of different winemaking processes (Pedneault and Provost, 2016). In 1974, carbonic maceration (CM) was found to efficiently reduce foxy flavours in red Concord (V. labrusca) wines (Fuleki, 1974). CM was initially developed to reduce oxidation reactions occurring spontaneously in grapes in order to preserve fruit flavours (Paul, 1996). In organic wine production, restricting contact between berries and air using CM may be of particular interest because organic grapes have been shown to carry twice as much polyphenol oxidase activity compared to conventional grapes (Núnez-Delicado , 2005). White FRG wines such as Chardonel, Solaris and La Crescent generally present desirable floral notes that may be related to compounds such as C13-norisoprenoids (e.g., ß-damascenone) and monoterpenes (e.g., linalool) located in the berry skin (Cadwallader , 2009; Savits, 2014; Liu , 2015). In fact, extended skin maceration (24 h cold-soak and 30 h on-skin fermentation) significantly improved the intensity of floral notes in Solaris wines, but also increased green vegetable notes (Zhang , 2015). Conversely, short cold-soaks (3-8 h) did not improve the aroma intensity of Traminette wine (Skinkis , 2010). A recent study reported for the first time the presence of 3-mercaptohexanol in the FRG variety Cayuga, at a concentration of 195 ng/L (Musumeci , 2015). This compound is a highly odour potent thiol (odour perception threshold: 60 ng/L) that produces a grapefruit aroma in white wine (Musumeci , 2015).

Future research and alternatives

The question for winemakers in a near future is not which variety of resistant vine should they plant, but rather what choice of resistant variety for what types of wines: Generic, Protected Geographical Indication, Protected Origin Appellation?