Somatic Variation and Cultivar Innovation in Grapevine

Abstract

Paradoxically, continuous vegetative multiplication of traditional grapevine cultivars aimed to maintain cultivar attributes in this highly heterozygous species ends in the accumulation of considerable somatic variation. This variation has long contributed to cultivar adaptation and evolution under changing environmental and cultivation conditions and has also been a source of novel traits. Understanding how this somatic variation originates provides tools for genetics-assisted tracking of selected variants and breeding. Potentially, the identification of the mutations causing the observed phenotypic variation can now help to direct genome editing approaches to improve the genotype of elite traditional cultivars. Molecular characterization of somatic variants can also generate basic information helping to understand gene biological function. In this chapter, we review the state of the art on somatic variation in grapevine at phenotypic and genome sequence levels, present possible strategies for the study of this variation, and describe a few examples in which the genetic and molecular basis or very relevant grapevine traits were successfully identified.

Genetical, Morphological and Physicochemical Characterization of the Autochthonous Cultivar ‘Uva Rey’ (Vitis vinifera L.)

“…'Uva Rey' showed a very high density unlike 'Mantuo de Pilas' with a very low one. Similar phenotypic differences have been found between other cultivars such as 'Garnacha' and 'Garnacha Peluda' [47], both considered as somatic variants.…”

Genetic Resources of Olea europaea L. in the Garda Trentino Olive Groves Revealed by Ancient Trees Genotyping and Parentage Analysis of Drupe Embryos

“…Belaj et al [ 62 ] suggested that multiple bands for UDO43 may be the amplification products of two different loci. In this sense, we only found one genotype with three alleles at this locus ( Table S4 ) and it could also be due to mosaicism, a phenomenon more frequent during the senescent phase of a tree, which can accumulate mutations without phenotypic consequences [ 20 , 63 , 64 , 65 ].…”

“…In fact, until its unique phenotypic and agronomic features are clearly distinguished, a different genotype will not be considered to be a new cultivar (International Union for the Protection of New Varieties of Plants, 1991 in [ 20 ]). The number of somatic mutations appearing in a given variety is expected to increase proportionally with its age (the investigated trees were centuries-old) and cultivation area and some genotypes could be more prone to generate somatic variants [ 65 ]. Molecular variants have been commonly reported also in other olive cultivars widely cultivated in different areas, as well as in ancient and antique cultivars grown throughout history (i.e., ‘Ogliarola di Lecce’, ‘Ogliarola Barese’, ‘Ogliarola Garganica’, ‘Biancolilla’, ‘Giarraffa’, ‘Moresca’ (Italy), ‘Picholine Marocaine’ (Morocco), ‘Cirujal’, ‘Farga’, ‘Lechin de Granada’, ‘Verdial de Velez Malaga’ (Spain); [ 17 , 20 , 21 , 31 , 32 , 34 ].…”

“…It is likely that scion/rootstock genotype combinations are not randomly distributed, but selected by the growers to introduce genotypes with improved agronomic features and/or better adapted to the edaphoclimatic conditions, as suggested by [ 70 ]. The slightly genotypic differences found in some cases between the canopy and the basal part of the tree could be due to a real graft among clones of the same cultivar or to somatic point mutations [ 20 , 65 ].…”

Mechanisms and Candidate Genes for Seed and Fruit Set in Grapevine

“…In perennial plant species, where mutants are difficult to generate and to screen, natural somatic variants represent a unique resource to understand the genetic control of target traits, because they result from the effect of single mutation or epimutation events in a given genetic background [70][71][72][73].…”