Genetic structure of wild and cultivated olives in the central Mediterranean basin

BACKGROUND AND AIMS: Olive cultivars and their wild relatives (oleasters) represent two botanical varieties of Olea europaea subsp. europaea (respectively europaea and sylvestris). Olive cultivars have undergone human selection and their area of diffusion overlaps that of oleasters. Populations of genuine wild olives seem restricted to isolated areas of Mediterranean forests, while most other wild-looking forms of olive may include feral forms that escaped cultivation. METHODS: The genetic structure of wild and cultivated olive tree populations was evaluated by amplified fragment length polymorphism (AFLP) markers at a microscale level in one continental and two insular Italian regions. KEY RESULTS: The observed patterns of genetic variation were able to distinguish wild from cultivated populations and continental from insular regions. Island oleasters were highly similar to each other and were clearly distinguishable from those of continental regions. Ancient cultivated material from one island clustered with the wild plants, while the old plants from the continental region clustered with the cultivated group. CONCLUSIONS: On the basis of these results, we can assume that olive trees have undergone a different selection/domestication process in the insular and mainland regions. The degree of differentiation between oleasters and cultivated trees on the islands suggests that all cultivars have been introduced into these regions from the outside, while the Umbrian cultivars have originated either by selection from local oleasters or by direct introduction from other regions.     

Systematics, ecology and phylogeographic significance of Olea europaea L. ssp. maroccana (Greuter & Burdet) P. Vargas et al., a relictual olive tree in south-west Morocco

Within the genus Olea , the olive ( Olea europaea L.) possesses the largest geographic distribution, and several subspecies have been described. South-west Morocco harbours an endemic olive, O. europaea ssp. maroccana (Greuter & Burdet) P. Vargas et al. , located in the western part of the High Atlas (mainly on the southern slope of the Ida-ou-Tanane massif) and in the western Anti Atlas. The existence and the taxonomic position of this tree have long remained uncertain, but the combination of several morphological traits is unique. Nuclear and cytoplasmic DNA polymorphism also demonstrate that this tree is a well-differentiated and relictual taxon, probably originating from an ancestral unit within tropical Africa. Our findings refute the opinions of several authors who consider ssp. maroccana to be intermediate between the cultivated olive ( O. europaea ssp. europaea ) and the Saharan olive ( O. europaea ssp. laperrinei (Batt. & Trab.) Cif.). According to cpDNA and mtDNA analysis, the Moroccan olive and the Canarian olive ( O. europaea ssp. guanchica P. Vargas et al. ) are related and belong to the same sub-taxon. This biogeographical affinity is strongly supported by other recent phylogenetic studies. The long-term viability of ssp. maroccana is threatened by several factors: (1) limited distribution and reduced numbers of individuals within isolated populations, (2) fragmentation processes related to human and livestock pressures, and (3) putative gene flow between this taxon and the cultivated olive. In order to ensure the long-term survival of this endemic olive, a specific program of conservation should be implemented in the near future.     

(-)-olivil and (+)-1-acetoxypinoresinol from the olive tree (Olea europaea Linne; Oleaceae) as feeding stimulants of the olive weevil (Dyscerus perforatus)

Guided by a feeding stimulant activity test on the olive weevil (Dyscerus perforatus), two compounds that showed potent feeding stimulant activity were isolated from the olive tree (Olea europaea). Based on their spectral data and a literature survey, they were identified as (-)-olivil (1) and (+ )-1-acetoxypinoresinol (2). The activities of these minor lignans were significantly higher for the female than for the male weevil.     

Ethylene evolution from various developing organs of olive (Olea europaea) after excision

Ethylene evolution from leaves, stems, inflorescences and fruits of the olive plant ( Olea europaea L.) cv. Manzanillo was studied at various stages of their development. Mature non-growing organs, particularly leaves, have a constant, low, and uniform rate of ethylene evolution. Ethylene evolution from detached mature olive leaves was constant during the first 12 h after excision. Leaves on shoots maintained in vitro kept a constant rate of ethylene evolution for at least the first 5–6 days. Leaf injury significantly increased ethylene evolution. Ethylene evolution from injured and non-injured control leaves could be markedly inhibited aminoethoxyvinylglycine (AVG) applied to the leaves or fed to the shoot. The use of excised olive shoots and leaves as an in vitro model system for studies of induced metabolic processes such as abscission and developing water stress was suggested.     

Feeding stimulative activity of steroidal and secoiridoid glucosides and their hydrolysed derivatives toward the olive weevil (Dyscerus perforatus)

Beta-sitosteryl-D-glucoside and oleuropein isolated from the olive tree (Olea europaea) and their hydrolysed derivatives were tested by a feeding stimulative activity bioassay using the olive weevil (Dyscerus perforatus). Although the steroidal glucoside showed potent feeding stimulative activity, the activity of the aglycone (beta-sitosterol) was significantly lower than that of the glucoside. On the other hand, the difference in the activity between oleuropein, a secoiridoid glucoside, and the hydrolysed derivatives was not significant.     

Scolicidal effects of Olea europaea and Satureja khuzestanica extracts on protoscolices of hydatid cysts

Treatment of hydatid disease is mainly surgical, with medical treatment being reserved as a coadjuvant treatment. Use of effective scolicidal agents during surgery of cystic echinococcosis is essential to reduce the recurrence rate. The goal of this study was to evaluate the in vitro scolicidal effects of hydroalcoholic extracts of Satureja khuzestanica leaves and aqueous extracts of Olea europaea leaves on hydatid cyst protoscolices. Echinococcus granulosus protoscolices were collected from the liver of sheep infected with the hydatid cyst. Various concentrations of plant extracts were used in different exposure times for viability assay of protoscolices. Among the olive leaf extracts tested, 0.1% and 0.01% concentrations had strong scolicidal effects in 120 min. S. khuzestanica 0.1% had very strong scolicidal effects in 30, 60, and 120 min of exposure times and the mortality rate decreased with the lower concentration. The finding have shown that the scolicidal activity of S. khuzestanica against cystic echinococosis protoscolices were more effective, while the O. europaea extract showed less effects.     

Genetic diversity and population structure of wild olives from the North-Western Mediterranean assessed by SSR markers

BACKGROUND AND AIMS: This study examines the pattern of genetic variability and genetic relationships of wild olive (Olea europaea subsp. europaea var. sylvestris) populations in the north-western Mediterranean. Recent bottleneck events are also assessed and an investigation is made of the underlying population structure of the wild olive populations. METHODS: The genetic variation within and between 11 wild olive populations (171 individuals) was analysed with eight microsatellite markers. Conventional and Bayesian-based analyses were applied to infer genetic structure and define the number of gene pools in wild olive populations. KEY RESULTS: Bayesian model-based clustering identified four gene pools, which was in overall concordance with the Factorial Correspondence Analysis and Fitch-Margoliash tree. Two gene pools were predominantly found in southern Spain and Italian islands, respectively, in samples gathered from undisturbed forests of the typical Mediterranean climate. The other two gene pools were mostly detected in the north-eastern regions of Spain and in continental Italy and belong to the transition region between the temperate and Mediterranean climate zones. CONCLUSIONS: On the basis of these results, it can be assumed that the population structure of wild olives from the north-western Mediterranean partially reflects the evolutionary history of these populations, although hybridization between true oleasters and cultivated varieties in areas of close contact between the two forms must be assumed as well. The study indicates a degree of admixture in all the populations, and suggests some caution regarding genetic differentiation at the population level, making it difficult to identify clear-cut genetic boundaries between candidate areas containing either genuinely wild or feral germplasm.     

A new repetitive DNA sequence family in the olive (Olea europaea L.)

Two families of repeated DNA sequences were cloned from Olea europaea ssp sativa cv. "Picual". The first repetitive DNA is organized in a tandem repeat of monomers of 178 bp. Sequencing of several clones showed that it is relatively A-T rich (54.49%) and possesses short direct and inverted subrepeats as well as some palindromic sequences. Comparison between the monomers revealed heterogeneity of the sequence primary structure. This repetitive DNA is present in several cultivars of olive cultivates. Comparison of sequences with other repetitive DNAs described in Olea europaea has been carried out. No significant similarity was found. All the obtained results suggest that this repetitive DNA described here is a new family of repetitive DNA. The second repetitive DNA is organized in a tandem repeat of monomers of 78 bp. This second family of repetitive DNA showed significant similarity with other repetitive DNAs previously described in Olea europaea. Their existence in new cultivars of olive is shown.     

Induction of growth inhibition and differentiation of human leukemia HL-60 cells by a Tunisian gerboui olive leaf extract

Cancer protection associated with the consumption of olive products is well established, but not for leukemia. The protective effects of olive (Olea europaea L.) leaves were investigated by incubating human promyelocytic leukemia HL-60 cells with olive leaf extracts (OLEs) from seven principal Tunisian olive varieties, namely, Chemchali, Chemlali, Chétoui, Gerboui, Sayali, Zalmati and Zarrazi. The results showed significant growth inhibition of HL-60 cells incubated for 48 h with a 100-fold dilution of each OLE which had been obtained by incubating 10 g of dried leaves in 100 ml of 70% ethanol for one week with subsequent ultrafiltration. DNA fragmentation was observed in the cells incubated for 19 h with a 100-fold dilution of the Chemchali, Chemlali and Zalmati extracts. The results of a nitroblue tetrazolium (NBT) assay revealed NBT reduction, a differentiation marker, by the OLE-treated cells after an overnight incubation. The Gerboui extract showed the highest NBT reduction ability at more than 90%. An HPLC analysis revealed the presence of apigenin 7-glucoside in the extract, which was found in subsequent experiments to be responsible for the Gerboui extract-mediated cell differentiation.     

3-Hydroxypropyl amide formation from 1-aminocyclopropane-1-carboxylic acid by a cell-free ethylene-forming system from olive leaves

The low ethylene yield in a cell-free ethylene-forming system from olive tree leaves ( Olea europaea L. cv. Picual) was investigated. During the incubation, 1-aminocyclopropane-1-carboxylic acid (ACC) was extensively transformed into 3-hydroxypropyl amide (HPA). Enzyme extract, Mn²⁺ and oxygen are responsible for this reaction. Horseradish peroxidase (EC 1.11.1.7) can substitute for the enzyme extract in this reaction. HPA formation could be one reason for the poor in vitro conversion efficiency of ACC to ethylene.     

Penetration of UV-A, UV-B and blue light through the leaf trichome layers of two xeromorphic plants, olive and oak, measured by optical fibre microprobes

Quartz fibre-optic microprobes were used to monitor the light microenvironment beneath trichome layers of the xeromorphic leaves of two Mediterranean evergreen sclerophylls, Olea europaea and Quercus ilex . Young developing leaves of both plants were densely pubescent on both surfaces of the lamina, whereas the mature leaves were pubescent only on the abaxial side. Trichome layers of young as well as of mature leaves of both plants attenuated almost all incident ultraviolet (UV)-B (310 nm) and UV-A (360 nm) radiation and a considerable portion of blue light (430 nm). Abaxial trichome layers of young leaves were more effective in screening out the incident radiation compared to the adaxial ones of the same leaves and also compared to the abaxial layer of the mature leaves. The abaxial epidermis of dehaired mature leaves of O. europaea was ineffective in absorbing most of the incident UV-B and UV-A radiation. UV and visible spectra beneath trichome layers of O. europaea in mature leaves confirmed that the light microenvironment on the epidermis was deprived in the UV-B, UV-A and partly in the blue spectral regions. It is proposed that the occurrence of a dense trichome layer, especially in young leaves, may play a protective role against not only UV-B radiation damage, but also against high visible irradiance. This function is performed irrespective of the differing anatomy of individual hairs of both plants. The protection provided by the trichomes could afford advantages under stress conditions, especially during leaf development.     

Temporal matching among diurnal photosynthetic patterns within the crown of the evergreen sclerophyll Olea europaea L

Trees are modular organisms that adjust their within-crown morphology and physiology in response to within-crown light gradients. However, whether within-plant variation represents a strategy for optimizing light absorption has not been formally tested. We investigated the arrangement of the photosynthetic surface throughout one day and its effects on the photosynthetic process, at the most exposed and most sheltered crown layers of a wild olive tree (Olea europaea L.). Similar measurements were made for cuttings taken from this individual and grown in a greenhouse at contrasted irradiance-levels (100 and 20% full sunlight). Diurnal variations in light interception, carbon fixation and carbohydrate accumulation in sun leaves were negatively correlated with those in shade leaves under field conditions when light intensity was not limiting. Despite genetic identity, these complementary patterns were not found in plants grown in the greenhouse. The temporal disparity among crown positions derived from specialization of the photosynthetic behaviour at different functional and spatial scales: architectural structure (crown level) and carbon budget (leaf level). Our results suggest that the profitability of producing a new module may not only respond to construction costs or light availability, but also rely on its spatio-temporal integration within the productive processes at the whole-crown level.     

The colonization history of Olea europaea L. in Macaronesia based on internal transcribed spacer 1 (ITS-1) sequences, randomly amplified polymorphic DNAs (RAPD), and intersimple sequence repeats (ISSR)

Phylogenetic relationships in the Olea europaea complex and the phylogeography of 24 populations of the Macaronesian olive (O. europaea ssp. cerasiformis) were assessed by using three molecular markers: nuclear ribosomal internal transcribed spacer 1 (ITS-1) sequences, randomly amplified polymorphic DNAs (RAPD), and intersimple sequence repeats (ISSR). Parsimony analysis of the ITS-1 sequences and Neighbour-joining (NJ) analyses of RAPD and ISSR banding variation revealed four major lineages in the O. europaea complex: (1) ssp. cuspidata; (2) ssp. cerasiformis from Madeira; (3) ssp. laperrinei; and (4) ssp. cerasiformis from the Canary Islands plus ssp. europaea. These results provide unequivocal support for two independent dispersal events of Olea to the Madeira and Canary Islands. Molecular and morphological evidence led to recognition of two separate olive taxa in Macaronesia, to date included in ssp. cerasiformis. NJ analyses of the combined RAPD and ISSR data suggest that the colonization of the Canaries by O. europaea may have followed an east to west stepping-stone model. An interisland dispersal sequence can be recognized, starting from the continent to Fuerteventura, Gran Canaria, Tenerife, La Gomera, and finally La Palma. High dispersal activity of the lipid-rich Olea fruits by birds in the Mediterranean region is congruent with multiple dispersal of olives to Macaronesia and successive colonization of the archipelagos. The observation of strong genetic isolation between populations of different islands of the Canary Islands suggests, however, that subsequent interisland dispersal and establishment has been very rare or may not have occurred at all.     

On chloroplast DNA variations in the olive ( Olea europaea L.) complex: comparison of RFLP and PCR polymorphisms

Previous papers have dealt with olive chloroplastic DNA (cpDNA) variation revealed using several methods (RFLPs, PCR-RFLPs and microsatellites) and have led to different conclusions. This paper aims to reconsider these divergences. A Southern approach was applied to reveal polymorphism. We used chloroplast DNA of Phillyrea media as a probe. Based on these data, only four chlorotypes were identified in the olive complex. The number of detected lineages was lower than reported in the literature using a direct cpDNA RFLP approach, and was insufficient to distinguish the North African subspecies europaea, maroccana, guanchica and laperrinei. Furthermore, one individual considered belonging to the subspecies laperrinei was questionable. Using other cpDNA and mitochondrial DNA (mtDNA) polymorphisms - based on PCR and RFLP methods, respectively - we showed that this individual displays the cytoplasmic lineage CE1-ME1 characteristic of most Eastern mediterranean cultivars and of Olea europaea subsp. laperrinei from Hoggar. However, based on RAPDs, this individual appeared as mislabelled and probably corresponded to a Mediterranean cultivar or a feral form. In addition, we checked O. e. subsp. laperrinei herbarium samples using two cpDNA microsatellites, which revealed polymorphisms. These also supported that both populations from Niger and Algeria displayed a chlorotype related to CE1. Consequently, based on cpDNA, the relationships of O. e. subsp. laperrinei from Hoggar with a Mediterranean lineage appeared well supported, whereas the South West Moroccan and Macaronesian olives appeared in a different clade using both mtDNA and cpDNA polymorphisms. We conclude that methods based on PCR reveal more polymorphisms in the cpDNA and lead to more-reliable results that the classical RFLP method.     

Allozyme variation of oleaster populations (wild olive tree) (Olea europaea L.) in the Mediterranean Basin

As a result of the early domestication and extensive cultivation of the olive tree throughout the Mediterranean Basin, the wild-looking forms of olive (oleasters) presently observed constitute a complex, potentially ranging from wild to feral forms. Allozyme variation was analysed at 10 loci in 31 large and 44 small oleaster populations distributed in various habitats of the Mediterranean Basin and in two populations of the wild subspecies Olea europaea subsp (ssp) guanchica, endemic to the Canary islands and closely related to oleasters. At eight polymorphic loci, 25 alleles were identified. Genetic evidence that nondomesticated oleasters still survive locally was provided by the occurrence of four and one alleles shared exclusively by the eight western and two eastern oleaster populations, respectively, which were collected in forests potentially containing genuinely wild forms according to environmental, historical and demographic criteria. As reported previously from cytoplasmic and RAPDs analysis, substantial genetic differentiation was observed between the eastern oleaster populations genetically close to most olive clones cultivated in the Mediterranean Basin, and the western populations that are related to the wild Canarian populations. In addition, the occurrence of significantly lower heterozygosity in cultivated olive than in oleasters, whatever their origin, suggests that intensive selection involving inbreeding has taken place under cultivation to obtain particular characteristics in the olive cultivars.     

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.     

Combination of chloroplast and mitochondrial DNA polymorphisms to study cytoplasm genetic differentiation in the olive complex ( Olea europaea L.)

Four hundred and four individuals belonging to the species Olea europaea were characterised using mitochondrial DNA (mtDNA) RFLPs. Twelve mitotypes were distinguished. The combination of mtDNA information with cpDNA polymorphism (characterised in a previous study) led us to recognise 20 cytoplasmic lineages of which seven were found in the Mediterranean area (oleasters, cultivars and O. e. subsp. maroccana). In the olive complex, strong cytoplasm genetic differentiation was revealed ( F(st) = 0.73). Very strong linkage disequilibrium between cpDNA and mtDNA polymorphisms was observed, particularly in the Mediterranean subspecies europaea. This high congruence between genetic structure based on cpDNA or mtDNA sustains a low level of recurrent mutation in both organelle DNAs and, thus, the polymorphisms used in this study were pertinent to reconstruct olive phylogeography. In the Mediterranean area, genetic drift due to population regression during Quaternary glaciations, and founder effects associated with the postglacial seed dissemination, have probably contributed to the existence of a high genetic linkage disequilibrium between cpDNA and mtDNA polymorphisms. Thus, four Mediterranean cytoplasmic lineages, clearly distinguished both by cpDNA and mtDNA polymorphisms, most likely reflect four distinct relic populations during Quaternary glaciations. Finally, O. e. subsp. maroccana from South Morocco, which also displayed specific cytoplasmic lineages, should be considered as another relic Mediterranean population.     

Ultraviolet-B radiation absorbing capacity of leaf hairs

Pubescence layers with their native structure and orientation were isolated from the leaves of Olea europaea L. and Olea chrysophylla L. They were almost transparent in the visible, but considerable absorptance was evident in the ultraviolet-B region (UV-B), with maximum at 310 nm. Methanolic extracts of hairs from Olea and a variety of other pubescent species consistently showed the existence of UV-screening pigments. Absorptance of trichomes varied, but a trend towards more effective UV-B radiation attenuation in the sub-alpine Verbascum species may be claimed. In all cases, pigments were located within hair cells and in Olea they were characterized as phenolics with considerable flavonoid contribution. It is suggested that leaf hairs, besides other functions, may constitute a shield against UV-B radiation.