Grapes belong to the Vitis genus, which includes about 80 species and is considered as two sub-genera, including Euvitis and Muscadinia. Muscadine grapes are sometimes considered as a separate genus in different classification systems and include three species: Muscadinia rotundifolia, Muscadinia munsoniana, and Muscadinia popenoei. The Euvitis sub-genus includes the most commercially important grape varieties. Euvitis is divided into three groups. 1) The American group consists of about 30 species that are important for rootstock breeding; 2) The Asian group consists of about 50 species, which, up to this point, have been underutilized for grape cultivation; and 3) The Eurasian group consists of a single species, Vitis vinifera L., which includes two sub-species of V. vinifera: V. vinifera subsp. sylvestris, considered to be the wild form of grape; and V. vinifera subsp. vinifera, refers to cultivated forms. Of all species in the genus Vitis, the V. vinifera, is undoubtedly the most important worldwide for commercializing grapes and represents the most cultivated varieties worldwide. Other grape species contributed to breeding programs beyond the traditional efforts of rootstock hybridization from wild species. An aphid-like pest, phylloxera (Daktulosphaira vitifoliae), causes damage by feeding on the structural roots of V. vinifera, eventually leading to vine death. In an effort, American Vitis species that coevolved with phylloxera were eventually used as rootstocks for the widely planted V. vinifera scion cultivars. Later, crosses between these wild species became common, and historical breeding efforts led to the modern grape rootstock breeding programs currently active worldwide. Two-thirds of American species have already been used for rootstock breeding. However, it has been reported that the most commonly available rootstocks are derived from just three American species (Vitis berlandieri, Vitis rupestris, and Vitis riparia). Therefore, the most common grape rootstocks have a narrow genetic base, and efforts to extend the gene pools for breeding programs by using other species are of ongoing importance to the industry and scientific community. There are around 1500 grape rootstocks developed in the world, of which around 50 are commonly used as commercial rootstock and play a fundamental role in resistance to biotic and abiotic stresses and adaptation of grapevine to different environmental conditions, a factor that has opened commercial grape growing to regions that might otherwise be overlooked.
