Recent advances in genetic resources have revolutionized grapevine breeding methodologies. Current breeding programs develop and utilize Marker Assisted Selection (MAS) to efficiently select for bacterial and fungal disease resistance traits which are typically qualitative in nature. MAS is responsible for decreasing the time and funding devoted to large populations, and increasing the capacity for breeders to exercise selection within evaluated lines. This review of recent grapevine breeding examines the breeding history of bunch grapes, considers three breeding bandwagons, and discusses several prominent quantitative evaluations of heritability. Briefly exploring contemporary breeding goals, this paper concludes with a look into practical applications of grapevine breeding technologies used in the development of Pierce’s Disease (PD) resistant Vitis vinifera L. grapevine selections at the University of California Davis grape breeding program.
Cultivated European Grapevines
The European grapevine, Vitis vinifera L., is the most commonly cultivated species of bunch grape. Indigenous to Eurasia, V. vinifera is one of approximately 60 Vitis species worldwide (Alleweldt and Possingham, 1988; Martinez-Zapater et al., 2010). Domestication of V. sylvestris C.C. Gmelin, the progenitor of V. vinifera, is proposed to have occurred approximately 7,000 years ago with initial cultivation occurring as early as 3,500 BC (Zohary and Hopf, 1993).
Initial classifications of grape cultivars separated V. vinifera into three groups: occidentalis, orientalis, and pontica (Negrul, 1938). Western European wine grapes with smaller berries were classified as occidentalis, orientalis cultivars were table grapes from western Asia with large berries, and pontica cultivars, having intermediate berries, were named after the ancient country from Asia Minor and arose from eastern Europe and near the Black Sea and are typified by Greek and Italian grapes (Aradhya et al., 2003; Negrul, 1938). These classifications have been generally supported by genetic analysis of structure within populations of V. vinifera. Finding that human use and geography dictated the bulk of cultivar relatedness, Bacilieri et al. (2013) utilized STRUCTURE software to analyze 20 nuclear microsatellite loci across 2,096 V. vinifera genotypes via a Bayesian approach. Three main groups isolated when Ks clustering was set to three indicated two wine groups, West and Central Europe (42% of attributed cultivars) and Balkans and East Europe (36%), and one table grape group derived from the East (22%). Additionally discovered admixed genotypes were suggested to arise from human interactions, both transfer of plant materials and breeding.
Cluster analysis of a separate subset of eight microsatellite loci within 366 V. vinifera accessions clustered cultivars into three groups: Mediterranean table grapes, Western European wine grapes, and Central European grapes (Aradhya et al., 2003). Groups within cluster varied in the extent they typified occidentalis, orientalis, and pontica descriptions, but generally the Mediterranean table grapes resembled orientalis with some pontica, Western European wine grapes represented both occidentalis and pontica. Further analysis of an Unweighted Pair Group Method with Arithmetic Mean (UPGMA) phylogenetic tree depicted four main clusters with slight crossover between the three original grape classifications. The majority of genetic polymorphism variation was discovered to lay within groups, rather than between them, with the first two PCA vectors only accounting for 26% of variation.