Olive Subspecies Research Articles

Chemical composition and antimicrobial activity of essential oils of two wild olive subspecies Olea europaea L.var. sylvestris and the endemic olive Olea europaea subsp. lapperinie from Algeria

Two wild olive subspecies are fixed in this research: Olea europaea L.var. sylvestris and Olea europaea subsp. laperrinei despite its ecological value, the chemical composition of subsp. laperrinei oil remains unknown. The samples were harvested from the different geographical area. Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-flame-ionization detection (GC-FID) analysis of Olea europaea L. var. sylvestris allowed the identification of 29 compounds oil with Nonanal (11.82%), theaspiranea A (9.81%), 3-hexen-1-ol,benzoate(9.31%) as a major constituents, while in the subspecies of the Saharan region 31 compounds were separated, where α-pinene (16%), β-Ocimene (12.82%), dl-Limonene (8.20%) were the main components. The results of the disc diffusion method showed that the two volatile oils have efficient antibacterial activity but, subsp. laperrinei essential oil has a higher range of inhibition, in which P. aeruginosa and B. subtilis showed an extreme sensitivity, while the K. pneumoniae bacterium shows a great resistance to the two essential oils.

Ensemble modeling to predict the impact of future climate change on the global distribution of Olea europaea subsp. cuspidata

Climate change is one of the significant factors influencing global species redistribution. As a result, a better understanding of the species' possible range change in future climate conditions is needed. Therefore, this study compiles global geographic occurrence data of a wild olive sub-species, Olea europaea subsp. cuspidate, and projected potential distribution models in current and future climate scenarios. This study using ensemble modeling predicted that the species will undergo a significant decrease in habitat suitability under future climatic conditions with a contraction ranging from ca. 41 and 42% under RCP4.5 2050 and to about 56 and 61% under RCP8.5 2070 for committee averaging and weighted mean, respectively. More specifically, there will be a decrease in habitat suitability in regions of the southeastern part of the United States in North America; coastal regions in South America; coastal regions in the majority of eastern Africa; coastal parts of Spain, France, Italy, and Greece in Europe; coastal parts of Yemen and Saudi Arabia; the southeastern parts of Pakistan and the southern part of China in Asia; and southwestern and eastern parts of Australia when compared to current habitat suitability. The results of this ensemble modeling could be extremely valuable in identifying cultivation hotspots for the effective restoration and protection of this olive lineage under future climatic conditions.

The De Novo Genome Assembly of Olea europaea subsp. cuspidate, a Widely Distributed Olive Close Relative.

The olive complex, comprising six subspecies, is a valuable plant for global trade, human health, and food safety. However, only one subspecies (Olea europaea subsp. europaea, OE) and its wild relative (Olea europaea subsp. europaea var. sylvestris, OS) have genomic references, hindering our understanding of the evolution of this species. Using a hybrid approach by incorporating Illumina, MGI, Nanopore, and Hi-C technologies, we obtained a 1.20-Gb genome assembly for the olive subspecies, Olea europaea subsp. cuspidate (OC), with contig and scaffold N50 values of 5.33 and 50.46 Mb, respectively. A total of 43,511 protein-coding genes were predicted from the genome. Interestingly, we observed a large region (37.5 Mb) of “gene-desert” also called “LTR-hotspot” on chromosome 17. The gene origination analyses revealed a substantial outburst (19.5%) of gene transposition events in the common ancestor of olive subspecies, suggesting the importance of olive speciation in shaping the new gene evolution of OC subspecies. The divergence time between OC and the last common ancestor of OE and OS was estimated to be 4.39 Mya (95% CI: 2.58–6.23 Mya). The pathways of positively selected genes of OC are related to the metabolism of cofactors and vitamins, indicating the potential medical and economic values of OC for further research and utilization. In summary, we constructed the de novo genome assembly and protein-coding gene pool for Olea europaea subsp. cuspidate (OC) in this study, which may facilitate breeding applications of improved olive varieties from this widely distributed olive close relative.

Resisting Aridification: Adaptation of Sap Conduction Performance in Moroccan Wild Olive Subspecies Distributed Over an Aridity Gradient.

In the current context of global change, the increasing frequency and the length of drought periods are testing the resistance capacities of plants of dry habitats. However, although the adaptation of plants to drought has been widely studied, the anatomical features of wood influencing the functional responses of plants to drought are still lacking at the intraspecific level, especially for species with a wide geographical distribution. As a result, we have studied the variation of wood anatomical traits related to sap conduction (i.e., vessel surface area, vessel density, and number of vessels joined by radial file) in two wild olive subspecies distributed in Morocco (i.e., Olea europaea subsp. europaea. var. sylvestris and Olea europaea subsp. maroccana), in relation to various drought conditions. This functional study, based on wood trait measurements of 351 samples from 130 trees and 13 populations, explores potential sap conduction in relation to environmental parameters and as a result, strategies to resist water stress. We found that (1) branch diameter (BD) captured 78% of total wood trait variation, (2) vessel size (SVS) expressed 32% of intraspecific variation according to cambium age, and (3) the positive relationship between SVS and BD could be explained by climate type, vegetation cover changes, and therefore available water resources. Taking into consideration the diameter of the branch as the main factor of anatomical variation, established reaction norms (linear models) at the intrapopulation scale of vessel lumen area according to aridity show for the first time how the functioning of the cambium modulates and controls sap conduction, according to aridity and thus available water resources. They pinpoint the risks incurred by the wild olive tree in the perspective of a dramatic increase in aridity, in particular, the inability of the cambium to produce large enough vessels to efficiently transport sap and irrigate the leaves. Finally, this study opens new and interesting avenues for studying at a Mediterranean scale, the resistance and the vulnerability of wild forms and cultivated varieties of olive to heterogeneous and changing environmental conditions.

Morphological, Molecular and Genomic Characterization of Two Inter-Subspecific Hybrids between Olive Cultivars and Olive Subspecies

Two inter-subspecific F1 hybrids have been obtained by crossing olive cultivars (‘Frantoio’ and ‘Coratina’) with pollen donors from olive subspecies (Olea europaea subsp. cuspidata) to enrich the germplasm of cultivated olive in southern China. This study aimed to investigate the characterization of morphological traits and molecular markers in the two hybrids and their parents of crosses. The morphological study showed a significant difference between genotypes according to the main discriminative parameters on qualitative and quantitative traits of leaf, fruit, and endocarp. A set of six co-dominant polymorphic simple sequence repeats (SSRs) were used for molecular identification, and SSR analysis confirmed that two progenies were the offspring of their cited parents based on the presence of parental specific SSR alleles. Three single-copy nuclear loci (SCNL) primer pairs were used for amplification of single-copy genes in the two progenies and their parents and after then PCR products were sequenced. Sequence alignment analysis on the effective data showed a total of 15 different base sites between two progenies, which were confirmed as true inter-specific hybrids between olive cultivars and subsp. cuspidata.

Comparative Oil Composition Study of the Endemic Moroccan Olive (Olea europaea subsp. maroccana) and Wild Olive (var. Sylvestris) in Central West Morocco

Six wild olive subspecies (Olea europaea L.) are currently recognised globally, with two taxa cooccurring in the argan tree area in Central West Morocco: the widespread Mediterranean subspecies europaea var. Sylvestris (the so-called oleaster) and the microendemic subspecies maroccana. Despite its taxonomic and ecological importance, the chemical composition of subsp. maroccana oil remains poorly known. Therefore, the aim of this study is to investigate the oil content and the chemical composition of subsp. maroccana and var. Sylvestris as well as comparing their proprieties during two consecutive years (2017 and 2018) from the same geographical area. The fatty acid and the sterol compositions were analysed using gas chromatography. Additionally, the tocopherol content was determined using high-performance liquid chromatography. The total amount of unsaturated fatty acids was higher in maroccana (85.24%) than that in oleasters (79.05%). Additionally, the tocopherol and phytosterol content of the maroccana oil (1232.35 mg/kg and 312.75 mg/100 g, resp.) was approximately twofold higher than in oleasters (661.35 mg/kg and 210.06 mg/100 g, resp.). Analysis of variance and principal component analysis (PCA) of the chemical composition highlighted a significant difference between the quantitative and qualitative properties of their oil. Finally, these findings suggest that maroccana oil could be considered as a potential source of vitamin E, essential fatty acids, and sterols and can provide a nutraceutical oil for the local population. While this work contributes to the study of olive tree biodiversity, further investigations are still necessary to guide the putative nutraceutical use of subspecies maroccana.

Evaluation of early vigor traits in wild olive germplasm

The control of the olive tree vigor is a critical factor to ensure adequate production and longevity of high-density olive cultivation. To deal with this problem, we intend to take advantage of the genetic variability present in the wild subspecies of Olea europaea to identify genotypes of reduced vigor with optimal adaptability to diverse soils and adverse environmental conditions. In this work, early vigor traits have been characterized in different wild olive subspecies that could potentially be used as rootstocks to control the vigor of grafted cultivars. Significant differences between genotypes were obtained for all vigor traits and high values of broad sense heritability were obtained for most of them, indicating strong genetic effect and therefore good possibilities for selection. Compared to ‘Arbequina’ and ‘Picual’ cultivars, some of the wild genotypes evaluated showed a clearly lower vigor at the end of the experimental period. These genotypes could be tested as dwarfing rootstocks for high-density olive plantations.

An ecological and evolutionary perspective on the parallel invasion of two cross-compatible trees.

Invasive trees are generally seen as ecosystem-transforming plants that can have significant impacts on native vegetation, and often require management and control. Understanding their history and biology is essential to guide actions of land managers. Here, we present a summary of recent research into the ecology, phylogeography and management of invasive olives, which are now established outside of their native range as high ecological impact invasive trees. The parallel invasion of European and African olive in different climatic zones of Australia provides an interesting case study of invasion, characterized by early genetic admixture between domesticated and wild taxa. Today, the impact of the invasive olives on native vegetation and ecosystem function is of conservation concern, with European olive a declared weed in areas of South Australia, and African olive a declared weed in New South Wales and Pacific islands. Population genetics was used to trace the origins and invasion of both subspecies in Australia, indicating that both olive subspecies have hybridized early after introduction. Research also indicates that African olive populations can establish from a low number of founder individuals even after successive bottlenecks. Modelling based on distributional data from the native and invasive range identified a shift of the realized ecological niche in the Australian invasive range for both olive subspecies, which was particularly marked for African olive. As highly successful and long-lived invaders, olives offer further opportunities to understand the genetic basis of invasion, and we propose that future research examines the history of introduction and admixture, the genetic basis of adaptability and the role of biotic interactions during invasion. Advances on these questions will ultimately improve predictions on the future olive expansion and provide a solid basis for better management of invasive populations.

Spatial segregation and realized niche shift during the parallel invasion of two olive subspecies in south‐eastern Australia

AbstractAimGreater understanding of the processes underlying biological invasions is required to determine and predict invasion risk. Two subspecies of olive (Olea europaea subsp. europaea and Olea europaea subsp. cuspidata) have been introduced into Australia from the Mediterranean Basin and southern Africa during the 19th century. Our aim was to determine to what extent the native environmental niches of these two olive subspecies explain the current spatial segregation of the subspecies in their non‐native range. We also assessed whether niche shifts had occurred in the non‐native range, and examined whether invasion was associated with increased or decreased occupancy of niche space in the non‐native range relative to the native range.LocationSouth‐eastern Australia, Mediterranean Basin and southern Africa.MethodsEcological niche models (ENMs) were used to quantify the similarity of native and non‐native realized niches. Niche shifts were characterized by the relative contribution of niche expansion, stability and contraction based on the relative occupancy of environmental space by the native and non‐native populations.ResultsNative ENMs indicated that the spatial segregation of the two subspecies in their non‐native range was partly determined by differences in their native niches. However, we found that environmentally suitable niches were less occupied in the non‐native range relative to the native range, indicating that niche shifts had occurred through a contraction of the native niches after invasion, for both subspecies.Main conclusionsThe mapping of environmental factors associated with niche expansion, stability or contraction allowed us to identify areas of greater invasion risk. This study provides an example of successful invasions that are associated with niche shifts, illustrating that introduced plant species are sometimes readily able to establish in novel environments. In these situations the assumption of niche stasis during invasion, which is implicitly assumed by ENMs, may be unreasonable.

Sequence analysis of single-copy genes in two wild olive subspecies: nucleotide diversity and potential use for testing admixture.

The wild olive distribution extends from the Mediterranean region to south Asia and Austral Africa. The species is also invasive, particularly in Australia. Here, we investigated the sequence variation at five nuclear single-copy genes in 41 native and invasive accessions of the Mediterranean and African olive subspecies. The nucleotide diversity was assessed and the phylogenetic relationships between alleles were depicted with haplotype networks. A Bayesian clustering method (STRUCTURE) was applied to identify the main gene pools. We found an average of 18.4 alleles per locus. Native Mediterranean and African olives only share one allele, which testifies for ancient admixture on the Red Sea hills. The presence of divergent alleles in the Mediterranean olive, as well as the identification of two main genetic clusters, suggests a complex origin with two highly differentiated gene pools from the eastern and western Mediterranean that recently admixed. In the invasive range, relatively high nucleotide diversity is observed as a consequence of the introduction of alleles from two subspecies. Our data confirm that four invasive individuals are early-generation hybrids. Finally, the utility of single-copy gene sequences in olive population genomic and phylogenetic studies is briefly discussed.

Comparison of methods used in the recovery of Phylloplane bacteria: a case study of Pseudomonas savastanoi pv. savastanoi applied to the Phylloplane of Olea europaea sub-species

Abstract An efficient and accurate method of sampling, recovery, and enumeration of epiphytic bacterial populations are of fundamental importance for their precise estimation. In this study, effectiveness and reliability of processing methods, sampling type, sample storage, and plating techniques, for the recovery of the epiphytic bacterial populations, were evaluated. Pseudomonas savastanoi pv. savastanoi, the causal agent of olive knot disease, and two olive sub-species were used. Bulk-leaf sampling allowed for a higher number of the bacterial recovery. The use of a lab blender was the most effective and reliable method among the four commonly used processing methods. A short storage of leaf samples was possible through freezing. Bacterial survival was not influenced as long as the samples were processed within 5 days and frozen without a buffer. No difference was observed among the drop and spread platings, suggesting that one of them can be used and the choice depends on the cost and time required.

Epiphytic Pseudomonas savastanoi pv. savastanoi can infect and cause olive knot disease on Olea europaea subsp. cuspidata

Endophytic and epiphytic survival and population growth of Pseudomonas savastanoi pv. savastanoi (Psav), the causal agent of olive knot disease, were studied for the first time in Olea europaea subsp. cuspidata. Five different strains of Psav, isolated from different geographic areas, were inoculated into wounds of O. europaea subsp. cuspidata and European olive (O. europaea subsp. europaea) plants that were 3, 9, or 20 months of age to evaluate endophytic survival. Epiphytic survival of two strains of Psav sprayed on leaves of 2-year old plants was also assessed. Pathogenicity tests showed that O. europaea subsp. cuspidata is susceptible to Psav. Pathogen survival and population growth rates did not differ significantly between the two olive subspecies. No correlation was observed between knot weight and endophytic pathogen population density. Plant age did not significantly influence the host–pathogen interaction. Epiphytic survival showed that Psav, regardless of strain, reproduced better on O. europaea subsp. cuspidata than on the European olive. Together, these results indicate that control measures are necessary to prevent the spread of introduced Psav in areas where O. europaea subsp. cuspidata is native.

Genetic relationships among and within wild and cultivated olives based on RAPDs

We examined genetic relationships among wild and cultivated olives, which is a very important crop in the economy of the Aegean region. We used RAPD analysis to evaluate relationships among and within 22 olive subspecies from Manisa, Mugla and Izmir provinces in Turkey. Twelve of the subspecies were wild and 10 were cultivated olives. Fifty-two primers were used (OP-Q 1-20, OP-I 1-20, OP-F 14-15-16-17, and OP-K 1-8) and 49 polymorphic bands were selected and used for analysis. The dendrogram based on unweighted pair-group cluster analysis using the Sorensen-Dice coefficient of similarity index indicated two major groups, dividing wild olives from cultivated olives. The patterns of genetic relationships among and within the different olives were analyzed by means of analysis of molecular variance. We found significant differences between wild and cultivated olives (Phi(st) = 0.1507; P < 0.001). In order to determine the genetic relationship among wild and cultivated olives, principal coordinate analysis was used to examine the variation among subspecies. The wild and cultivated olives formed two main groups, one on the right side and the other on the left side of the principal coordinates graph, respectively. This was compatible with the results we obtained from analysis of molecular variance.

Coexistence of diploids and triploids in a Saharan relict olive: Evidence from nuclear microsatellite and flow cytometry analyses

Polyploidy was recently reported in two endangered olive subspecies from North-West Africa. The origin of this phenomenon remains unclear. In the present study, 106 genotypes of a relict Laperrine's olive population form Hoggar (Algeria) were analysed using eight nuclear microsatellites. Diploid and triploid genetic profiles were observed. A flow cytometry analysis confirmed that trees displaying three alleles at several loci are effectively triploid. This report constitutes the first evidence for the coexistence of two ploidy types in an olive population. The triploid genotypes, probably in mean more vigorous than diploid trees, may be positively selected in the absence of sexual regeneration since a very long time, explaining their relative high frequency in the investigated population. To cite this article: G. Besnard, D. Baali-Cherif, C. R. Biologies 332 (2009).

Molecular characterization of some selected wild olive (Olea oleaster L.) ecotypes grown in Turkey

The wild olive subspecies oleaster called Karadelice in Turkish is a small tree or bush of rather irregular growth, with thorny branches and oppositely positioned oblong pointed leaves, dark grayish- green on the leaf surface and, in the early growth state, hoary on the lower surface with whitish scales. Generally, it is used as a dwarf rootstock; however, it has some grafting incompatibility with certain important olive cultivars. Some wild olive plants were selected from the village Kayadibi, 20 km distant from the city of �zmir in Turkey. This region is a very unique place for this type of wild olive. These ecotypes were differentiated by molecular markers using RAPD-PCR. Since they can be used as a dwarf rootstock, the correlations with some important olive cultivars were analyzed. For that reason Ayvalok cv, which is the most important olive cultivar for olive oil production was used primarily. Since Ayvalok cv and KD-8 are 97% similar, it was expected that they may have grafting compability. In the second part of the study, the comparison were done with Memecik and Tavan Yurei cultivars which are important olive oil and table olive cultivars, respectively. Since Memecik and Tavan Yurei were 100% similar therefore, it was considered that they may have more grafting compability with oleasters KD-3 and KD-8. Both studies were carried out to find similarities in 9 olive oleasters growing at Kayadibi ofzmir province which are said to have confused and low level morphologic variations in their features.

Chloroplast DNA variations in Mediterranean olive

SummaryOver ten years, several European teams have characterised polymorphism in the olive chloroplast genome (cpDNA). A particularly low level of cpDNA polymorphism was detected; but, in a recent study based on 14 Mediterranean trees, an intergenic (trnD-trnT) spacer was reported to be sufficiently variable to distinguish at least six haplotypes in cultivated olive. Compared to previous studies, the level of polymorphism described (nine substitutions and seven short indels on a segment of approx. 1 kbp) was particularly high. In order to enlarge upon the sample analysed, new trnD-trnT sequences were generated from 18 olive trees originating from the Mediterranean Basin, Macaronesia, S. Algeria, Kenya, Yemen, Reunion Island, Hawaii, Iran, and China. Only two base substitutions were detected in this enlarged sample, one of which discriminated between Olea europaea subsp. cuspidata and other olive sub-species. Length variation at a (poly-T) microsatellite motif was also found. The relatively low variation revealed between distant populations of olive suggests that sequencing problems might be the origin of the high polymorphism previously reported in the trnD-trnT spacer. Furthermore, length polymorphism at the poly-T motif was investigated in 55 Mediterranean olive trees which had previously been analysed for other cpDNA polymorphisms. Two alleles were found in Mediterranean olive, but they did not permit detection of new cpDNA haplotypes. It is proposed that proper analyses of cpDNA polymorphism in Mediterranean olive should use a combination of seven markers in order to detect its correct phylogeographic structure.

Polyploidy in the Olive Complex (Olea europaea): Evidence from Flow Cytometry and Nuclear Microsatellite Analyses

Phylogenetic and phylogeographic investigations have been previously performed to study the evolution of the olive tree complex (Olea europaea). A particularly high genomic diversity has been found in north-west Africa. However, to date no exhaustive study has been addressed to infer putative polyploidization events and their evolutionary significance in the diversification of the olive tree and its relatives. Representatives of the six olive subspecies were investigated using (a) flow cytometry to estimate genome content, and (b) six highly variable nuclear microsatellites to assess the presence of multiple alleles at co-dominant loci. In addition, nine individuals from a controlled cross between two individuals of O. europaea subsp. maroccana were characterized with microsatellites to check for chromosome inheritance. Based on flow cytometry and genetic analyses, strong evidence for polyploidy was obtained in subspp. cerasiformis (tetraploid) and maroccana (hexaploid), whereas the other subspecies appeared to be diploids. Agreement between flow cytometry and genetic analyses gives an alternative approach to chromosome counting to determine ploidy level of trees. Lastly, abnormalities in chromosomes inheritance leading to aneuploid formation were revealed using microsatellite analyses in the offspring from the controlled cross in subsp. maroccana. This study constitutes the first report for multiple polyploidy in olive tree relatives. Formation of tetraploids and hexaploids may have played a major role in the diversification of the olive complex in north-west Africa. The fact that polyploidy is found in narrow endemic subspecies from Madeira (subsp. cerasiformis) and the Agadir Mountains (subsp. maroccana) suggests that polyploidization has been favoured to overcome inbreeding depression. Lastly, based on previous phylogenetic analyses, we hypothesize that subsp. cerasiformis resulted from hybridization between ancestors of subspp. guanchica and europaea.

On the origin of the invasive olives (Olea europaea L., Oleaceae)

The olive tree (Olea europaea) has successfully invaded several regions in Australia and Pacific islands. Two olive subspecies (subspp. europaea and cuspidata) were first introduced in these areas during the nineteenth century. In the present study, we determine the origin of invasive olives and investigate the importance of historical effects on the genetic diversity of populations. Four invasive populations from Australia and Hawaii were characterized using eight nuclear DNA microsatellites, plastid DNA markers as well as ITS-1 sequences. Based on these data, their genetic similarity with native populations was investigated, and it was determined that East Australian and Hawaiian populations (subsp. cuspidata) have originated from southern Africa while South Australian populations (subsp. europaea) have mostly derived from western or central Mediterranean cultivars. Invasive populations of subsp. cuspidata showed significant loss of genetic diversity in comparison to a putative source population, and a recent bottleneck was evidenced in Hawaii. Conversely, invasive populations of subsp. europaea did not display significant loss of genetic diversity in comparison to a native Mediterranean population. Different histories of invasion were inferred for these two taxa with multiple cultivars introduced restoring gene diversity for europaea and a single successful founder event and sequential introductions to East Australia and then Hawaii for cuspidata. Furthermore, one hybrid (cuspidata x europaea) was identified in East Australia. The importance of hybridizations in the future evolution of the olive invasiveness remains to be investigated.