Georgian Grapevine Cultivars: Ancient Biodiversity for Future Viticulture

Abstract

Grapevine (Vitis vinifera) is one of the most widely cultivated plant species of agricultural interest, and is extensively appreciated for its fruits and the wines made from its fruits. Considering the high socio-economic impact of the wine sector all over the world, in recent years, there has been an increase in work aiming to investigate the biodiversity of grapevine germplasm available for breeding programs. Various studies have shed light on the genetic diversity characterizing the germplasm from the cradle of V. vinifera domestication in Georgia (South Caucasus). Georgian germplasm is placed in a distinct cluster from the European one and possesses a rich diversity for many different traits, including eno-carpological and phenological traits; resistance to pathogens, such as oomycetes and phytoplasmas; resistance to abiotic stresses, such as sunburn. The aim of this review is to assess the potential of Georgian cultivars as a source of useful traits for breeding programs. The unique genetic and phenotypic aspects of Georgian germplasm were unraveled, to better understand the diversity and quality of the genetic resources available to viticulturists, as valuable resources for the coming climate change scenario.

Keywords: Vitis vinifera L.; climate change; genetic diversity; phenotypical characterization; resistance to diseases.

FIGURE 1

Map of Georgia and location of 12 Georgian wine-growing regions: 1 – Abkhazeti; 2 – Samegrelo; 3 – Guria; 4 – Adjara; 5 – Svaneti; 6 – Lechkhumi; 7 – Racha; 8 – Imereti; 9 – South Kartli; 10 – Inner Kartli; 11 – Lower Kartli; 12 – Kakheti. Image is obtained by Google Earth. Pin indicates Tbilisi position. Map on the right reports the Winkler classification based on yearly average Winkler index calculated for the period 1994–2013 in Georgia (Caucasus). The analysis is limited to the areas below 1250 m above sea level. Description of Winkler indices: (I–) GDD (Growth Degree Days) < 850, viticultural climate is very cool, vinicultural aptitude is very early ripening grapes for fresh and fruity wines or sparkling wine bases. (I) GDD 850–1400, viticultural climate is cool, vinicultural aptitude is early ripening grapes for fresh and fruity wines or sparkling wine bases. (II) GDD 1400–1650, viticultural climate is temperate cool, vinicultural aptitude is early ripening grapes for wines to be aged. Medium ripening grapes for white or red wines ready to drink. (III) GDD 1650–1950, viticultural climate is temperate, vinicultural aptitude is medium ripening grapes for white or red wines ready to be aged. (IV) GDD 1950–2200, viticultural climate is temperate warm, vinicultural aptitude is late ripening grapes for white or red wines ready to be aged. (V) GDD 2200–2700, viticultural climate is hot, vinicultural aptitude is late ripening grapes for bodied red wines to be aged. (V+) GDD > 2700, viticultural climate is very hot; vinicultural aptitude is very late ripening grapes for bodied red wines to be aged.

FIGURE 2

Phenological timing simulation for three relevant Georgian cultivars, compared with Chardonnay and Cabernet sauvignon, using meteorological data of Perugia (Italy) (years 1990–2019). Phenology is represented following the reference BBCH scale: (i) 53–59 development of flowers; (ii) 60–69 flowering; (iii) 70–79 development of fruits; (iv) 80–89 ripening.

FIGURE 3

Two-dimension DAPC (discriminant analysis of principal component) scatter plot. Reworking of genetic profiles of grapevine cultivars coming from France, Georgia, Italy, and Spain, genotyped by 20 SSRs (A) and 18k SNPs (B), using data reported in De Lorenzis et al. (2015), Laucou et al. (2018), Riaz et al. (2018), and De Lorenzis et al. (2019). DAPC was performed to identify genetic clusters using the package adegenet of R software. Black dotted lines represent a minimum-spanning tree.

FIGURE 4

Frequency distribution of the entire V. vinifera species (orange) in comparison with the Georgian (green) records concerning the traits: titratable acidity (A); % of skin (B) and skin phenolics (C) (reworking of the results published in Rustioni et al., 2014, and Abashidze et al., 2015).

FIGURE 5

Symptoms of grapevine downy mildew on leaves (A–C), shoot (D) and bunches (E,F). (A) Oilspot (yellow circular spots with an oily appearance) on the upper side of the leaf; (B) mosaic symptom (yellow spot restricted by veins to form yellow-to-brown small, angular spots in a mosaic pattern) on the upper side of the leaf; (C) sporulation (sporangiophores and sporangia appearing as a bright white, fluffy growth) on the undersides of leaves; (D) shoot covered by sporulation turning brown; (E) distorted bunch (U-shaped) turning necrotic; (F) shrinking berries turning violet.

FIGURE 6

Distribution of resistance loci to P. viticola (Rpv) overall the 19 grapevine chromosomes. In red: loci identified in Northern American Vitis species. In green: loci identified in Asian Vitis species. In blue: loci identified in V. vinifera genetic background (Georgian germplasm). No information is now available for Rpv15 and Rpv16 detected in Vitis piasezkii Maxim (Pap et al., unpublished).

FIGURE 7

Symptoms observed on ‘Candidatus Phytoplasma solani’ infected grapevine cultivars in Georgia. Severe symptoms on international cultivar Chardonnay (A) and Georgian cultivar Kisi (B); moderate symptoms on Georgian cultivar Goruli Mtsvane (C); mild symptoms on Georgian cultivar Tsitska (D).