Grape Species and Varieties

The distinctive structural and genetic nature of genus Vitis is covered, followed by a discussion of its geographic origin and distribution, notably V. vinifera – the wine grape. Subsequently, the domestication of V. vinifera is explored, as well as modern views on the likely origins of grape cultivars, their selection, and spread. This includes the development of rootstocks, demanded as a consequence of the European invasion by phylloxera. Standard as well as modern breeding techniques are noted, including clonal selection. The chapter ends with a discourse on the methods used in cultivar identification, origin studies, and the distinctive attributes of some of the more significant cultivars.

Keywords

Vitis; Vitis vinifera; wine grapes; grape cultivars; cultivar origin; rootstocks; grape breeding; cultivar identification

Introduction

Grapevines are classified in the genus Vitis, within the Vitaceae. Other well-known members of the family are the Boston Ivy (Parthenocissus tricuspidata) and Virginia Creeper (P. quinquefolia). Members of the Vitaceae are typically woody, show a climbing habit, have leaves that develop alternately on shoots (Fig. 2.1), and possess swollen or jointed nodes. These may generate tendrils or flower clusters opposite the leaves. The flowers are minute, uni- or bisexual, and occur in large clusters. Most flower parts appear in groups of fours or fives, with the stamens developing opposite the petals. The ovary consists of two carpels, partially enclosed by a receptacle that develops into a two-compartmented berry. The fruit contains up to four seeds.

The Vitaceae is predominantly a tropical to subtropical family, containing about 900 species, divided among some 14 genera (Galet, 1988). In contrast, Vitis is primarily a temperate-zone genus, occurring indigenously only in the Northern Hemisphere. Related genera include Acareosperma, Ampelocissus, Ampelopsis, Cayratia, Cissus, Clematicissus, Cyphostemma, Nothocissus, Parthenocissus, Pterisanthes, Pterocissus, Rhoicissus, Tetrastigma, and Yua.

The Genus Vitis

Grapevines are distinguished from related genera primarily on floral characteristics. The flowers are typically functionally unisexual, being either male (possessing erect, functional anthers, and lacking a fully developed pistil) or female (containing a functional pistil, and either producing recurved stamens and sterile pollen, or lacking anthers) (Fig. 2.2). The petals are fused, forming a calyptra or cap. The petals remain connected at the apex, only splitting along the base at maturity, when the calyptra is shed (see Plate 3.6). Occasionally, though, the petals may separate at the top, while remaining attached at the base (Plate 2.1). These ‘star’ flowers possess an appearance resembling typical flowers. This situation characterizes some members of the Vitaceae, for example Cissus. In some cultivars, star flower production is induced by cool temperatures, whereas in others it is a constitutional property (Longbottom et al., 2008). The trait is not genetically transmissible because star flowers are sterile, generating seedless berries (Chardonnay), or no fruit (Shiraz).

Swollen nectaries occur at the base of the ovary (see Fig. 3.25C). Despite their name, they do not produce nectar, but they produce a mild fragrance that attracts pollinating insects. The sepals of the calyx form only as vestiges and degenerate early in flower development. The fruit is juicy and acidic.

The genus has typically been divided into two subgenera, Vitis1 and Muscadinia. Vitis (bunch grapes) is the larger of the two subgenera, containing all species except V. rotundifolia and V. popenoei. The latter are placed in the subgenus Muscadinia (muscadine grapes). The two subgenera are sufficiently distinct to have induced some taxonomists to separate the muscadine grapes into their own genus, Muscadinia.

Members of the subgenus Vitis are characterized by having shredding bark, nonprominent lenticels, a pith interrupted at nodes by woody tissue (the diaphragm), tangentially positioned phloem fibers, branched tendrils, elongated flower clusters, berries that adhere to the fruit stalk at maturity, and pear-shaped seed possessing a prominent beak and smooth chalaza. The chalaza is a pronounced, circular, depressed region on the dorsal (back) side of the seed (Fig. 2.3C). In contrast, species in the subgenus Muscadinia possess a tight, nonshredding bark, prominent lenticels, no diaphragm interrupting the pith at nodes, radially arranged phloem fibers, unbranched tendrils, small floral clusters, berries that separate individually from the cluster at maturity, and boat-shaped seed with a wrinkled chalaza. Some of these characteristics are diagrammatically illustrated in Fig. 2.3. Plate 2.2 illustrates the appearance of Muscadinia grapes and leaves.

The two subgenera also differ in their chromosomal composition. Vitis species contain 38 chromosomes (2n=6x=38), whereas Muscadinia species possess 40 chromosomes (2n=6x=40). The symbol n refers to the number of chromosome pairs formed during meiosis, and x refers to the number of chromosome complements (genomes that were involved in their evolution).

Successful crosses can be experimentally produced between species of the two subgenera, primarily when V. rotundifolia is used as the pollen source. When V. vinifera is used as the male plant, the pollen germinates, but does not effectively penetrate the style of the V. rotundifolia flower (Lu and Lamikanra, 1996). This may result from the synthesis of inhibitors, such as quercetin glycosides in the pistil (Okamoto et al., 1995). Although generally showing vigorous growth, the progeny frequently are infertile. This probably results from imprecise pairing of the unequal number of chromosomes (19+20) and the consequential imbalanced separation of the chromosomes during meiosis. The genetic instability so produced disrupts pollen growth, resulting in infertility.

The evolution of the Vitaceae appears to have involved hybridization and subsequent chromosome doubling, a feature common in many plants (Soltis and Soltis, 2009). In the Vitaceae, three separate whole-genome duplication events are suspected, based on DNA genomic analyses (Jaillon et al., 2007; Velasco et al., 2007). Their proposals differ basically only in the timing of the duplications – whether the last duplication occurred before or after the progenitors of the Vitaceae split from other rosid dicotyledons. Velasco et al. (2007) consider that the last duplication involved at least 10 chromosomes. These views differ from the proposals of Patel and Olmo (1955). They viewed the timing of the ploidy events occurring after the genus Vitis evolved from other Vitaceae. Patel and Olmo used cytogenetic evidence to envision two duplication events – the first involving hybridization between progenitors with six and seven chromosome pairs (6+7=13, doubling to 26). Later, a second set of hybridization events of such tetraploids, with diploids of 12 and 14 chromosomes respectively, followed by chromosome doubling, gave rise to current day hexaploids – the subgenera Vitis (13+6=19, doubling to 38) and Muscadinia (13+7=20, doubling to 40) (Fig. 2.4). Variations in the chromosome numbers of other genera in the Vitaceae could be viewed as later modifications, involving phenomena such as chromosome loss, fusion, translocation, and/or doubling. For example, other Vitaceae possess 22 chromosomes (Cyphostemma); 22, and occasionally 44 (Tetrastigma); 24, and occasionally 22 or 26 (Cissus); 32, 72, or 98 (Cayratia), and 40 (Ampelocissus and Ampelopsis).

Older cytogenetic evidence, consistent with polyploidy, involves the apparent association of four nucleoli in species possessing 24 and 26...