A comparative analysis of genetic variation in rootstocks and scions of old olive trees – a window into the history of olive cultivation practices and past genetic variation

Abstract

BackgroundPast clonal propagation of olive trees is intimately linked to grafting. However, evidence on grafting in ancient trees is scarce, and not much is known about the source of plant material used for rootstocks. Here, the Simple Sequence Repeat (SSR) marker technique was used to study genetic diversity of rootstocks and scions in ancient olive trees from the Levant and its implications for past cultivation of olives. Leaf samples were collected from tree canopies (scions) and shoots growing from the trunk base (suckers). A total of 310 trees were sampled in 32 groves and analyzed with 14 SSR markers.ResultsIn 82.7% of the trees in which both scion and suckers could be genotyped, these were genetically different, and thus suckers were interpreted to represent the rootstock of grafted trees. Genetic diversity values were much higher among suckers than among scions, and 194 and 87 multi-locus genotypes (MLGs) were found in the two sample groups, respectively. Only five private alleles were found among scions, but 125 among suckers. A frequency analysis revealed a bimodal distribution of genetic distance among MLGs, indicating the presence of somatic mutations within clones. When assuming that MLGs differing by one mutation are identical, scion and sucker MLGs were grouped in 20 and 147 multi-locus lineages (MLLs). The majority of scions (90.0%) belonged to a single common MLL, whereas 50.5% of the suckers were single-sample MLLs. However, one MLL was specific to suckers and found in 63 (22.6%) of the samples.ConclusionsOur results provide strong evidence that the majority of olive trees in the study are grafted, that the large majority of scions belong to a single ancient cultivar containing somatic mutations, and that the widespread occurrence of one sucker genotype may imply rootstock selection. For the majority of grafted trees it seems likely that saplings were used as rootstocks; their genetic diversity probably is best explained as the result of a long history of sexual reproduction involving cultivated, feral and wild genotypes.

Genetic variation of naturally growing olive trees in Israel: from abandoned groves to feral and wild?

“…Analysis of multi-locus genotypes (MLGs) and grouping of MLGs into multi-locus lineages (MLLs) reduced the probability of mistakes resulting from SSR genotyping errors, thus permitting the comparison of naturally growing populations with grafted old olive trees [30]. The multi-locus lineage analysis (Table 2) showed that 10 trees each of the naturally growing and cultivated trees at BGR belonged to the most commonly cultivated regional clone MLL1 [33]. One of the remaining nine trees belonged to MLL7 and the remaining eight trees were assigned to site-specific single occurrence MLLs of which seven were found in naturally growing trees.…”

“…For comparison, MLLs of suckers and scions of cultivated old olive trees are indicated. Site-specific and single occurrence (SO) MLLs are indicated in bold; MLL1 and 7 represent the most common MLLs found in scions and suckers of old cultivated trees, respectively [33]. MLLs in the BGR population represent the supposedly cultivated (C) and naturally growing (wild) trees…”

“…europaea ) or perhaps as abandoned groves, we used SSR markers for the analysis of six naturally growing olive populations sampled at close to far distances from extant cultivated groves. In a previous study we already used a multi-locus lineage (MLL) analysis with the same SSR markers to infer cultivar identity in the same region [33]. We could show the dominance of one clone in scions, and that another clone is frequent in rootstocks of grafted trees.…”

Recent developments in olive (Olea europaea L.) genetics and genomics: applications in taxonomy, varietal identification, traceability and breeding

“…Ancient trees have been recently investigated using SSR markers (Lazović et al 2016;Sakar et al 2016b;Barazani et al 2014;Petruccelli et al 2014;Salimonti et al 2013). Chalak et al (2015) analysed 73 olive trees, including six monumentals from four main Lebanese areas, with 12 nuclear SSRs and 39 plastid DNA markers.…”

Savoirs paysans autour des huiles d’olive, (zaytun, Olea europaea var. europaea) et d’oléastre, (əl-bərri, Olea europaea var. sylvestris) Rif, nord du Maroc

“…(Brun 1986). Cette technique fort ancienne existe à l'état de trace désormais en Espagne et au Levant et elle a attiré l'attention récemment des généticiens (Diez et al 2011, Barazani et al 2014. Ces derniers suggèrent que cette méthode a pu être une des anciennes techniques de domestication de l'olivier et serait passée quelque peu inaperçue.…”