Abstract
The domesticated grapevine spread along the Mediterranean basin from the primary Near East domestication area, where the greatest genetic diversity is found in its ancestor, the wild vine populations. Portuguese wild populations are on the southwestern fringe of the distribution of the Vitis vinifera L. ssp. sylvestris (C.C. Gmel.) Hegi in Europe. During the last Glacial Period they became isolated from the previous continuum that had been the territory of wild vine populations. Archaeological remains of domesticated vinifera grapevines in Portugal date back from 795 Before Common Era (BCE) in the lower Tagus river basin. In this work, 258 Portuguese vinifera varieties and sylvestris plants were characterized using 261 single nucleotide polymorphism (SNP) markers. The study of the genetic diversity of this local germplasm, its population structure and kinship, all framed in their historical and geographical backgrounds, revealed a complex network of first-degree relationships, where only Iberian varieties are involved. Some Iberian genotypes, like Alfrocheiro (Bruñal, in Spain), Sarigo (Cayetana Blanca), Mourisco Branco (Hebén), Amaral (Caiño Bravo), and Marufo (Moravia Dulce) are ancestors of a considerable fraction of all the autochthonous analyzed varieties. A part of the diversity developed was mostly local in some cases as shown by the closeness of several varieties (Vinhos Verdes) to the wild cluster in different analyses. Besides, several evidences of introgression of domesticated germplasm into wild vines was found, substantiating the high risk of genetic contamination of the sylvestris subspecies. All these findings together to the known matching between the wild maternal lineage of the Iberian Peninsula and an important number of Portuguese grapevine varieties (chlorotype A), point out that some of these varieties derive, directly or indirectly, from originally local wild populations, supporting the possible occurrence of secondary events of local domestication, or, at least, of an introgression process of wild into cultivated grapevines.
Highlights
The domesticated grapevine (Vitis vinifera L. ssp. vinifera) is the most cultivated fruit crop of the Vitis genus, which contains about 60 inter-fertile wild species (This et al, 2006; Emanuelli et al, 2013)
A total of 258 accessions (27 wild vines and 231 grapevine varieties) from the Portuguese Ampelographic Collection bearing non-redundant genotypes when analyzed with 48 single nucleotide polymorphism (SNP) (Cunha et al, 2016) were genotyped with up to 261 SNP markers
The results obtained, including those considering the sample sizes, indicate what other previous works have pointed out: the existence of a reduced diversity in the sylvestris subspecies (Marrano et al, 2017; Marrano et al, 2018). This unexpected situation is caused by the small sizes commonly found in wild populations, due to their isolation by natural barriers, human actions, and the severe bottleneck that began in the 19th century with the pathogens introduced from North America that has converted in relict the surviving populations
Summary
The domesticated grapevine (Vitis vinifera L. ssp. vinifera) is the most cultivated fruit crop of the Vitis genus, which contains about 60 inter-fertile wild species (This et al, 2006; Emanuelli et al, 2013). Domesticated grapevines were disseminated along with the spreading of wine culture from their primary domestication sites in the Near East in a process that lasted over 5000 years (McGovern et al, 2017) but likely a reduced number of sexual generations, given their vegetative multiplication (Arroyo-García et al, 2006). Along this time, introgression from local populations or even secondary domestication events could have taken place as suggested by Arroyo-García et al (2006); Imazio et al (2006); or Myles et al (2011)
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