Roots Of Olive Trees Research Articles

Challenges of Salinity Intrusion and Drought Stress on Olive Tree Cultivation on Mljet Island.

Understanding genotype-specific responses to environmental stressors is vital for developing resilience strategies that ensure sustainable olive cultivation and productivity. In this work, cultivar 'Oblica' and several olive genotypes from the island of Mljet (Croatia) were exposed to short-term (21 days) salinity and drought treatments. In contrast to other olive genotypes, genotype M29 as well as cultivar 'Oblica' managed to maintain growth and chlorophyll a levels under salinity stress to the same level as the control. Drought, however, significantly reduced the growth parameters in all olive trees. Cultivar 'Oblica' accumulated the greatest amount of Na+ ions in the leaves compared to olive genotypes from the island of Mljet, demonstrating superior resistance by translocating Na+ to leaf vacuoles. The observed reduction in K+ content in the roots of olive trees under all treatments suggests a generalized stress response. On the other hand, effective Ca2+ uptake has been identified as a crucial energy-saving strategy that olive trees use to cope with brief periods of salinity and drought. The proline content and activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPOX) varied among the olive trees, highlighting the importance of antioxidative capacities and stress adaptation mechanisms. According to the obtained results, stress-resistant olive genotypes like 'Oblica' and M29 show potential for breeding resilient varieties.

Soil-applied nitrogen uptake by young olive cultivars intercropped or not with Paspalum notatum

Nitrogen (N) applications can be made in orchards to meet the N demand of the olive tree (Olea europaea L.), which may differ between cultivars. But part of the N in the fertilizer may be taken up by ground cover plant species, which can be native, such as Paspalum notatum (P. notatum), derived from the Pampa biome in South America and present in olive orchards. The study aimed to evaluate the recovery and distribution of N fertilizer by olive cultivars, grown alone and intercropped with P. notatum. Young plants of olive cultivars 'Arbosana', 'Coratina' and 'Picual', with and without intercropping with P. notatum, were grown in pots with sandy soil for 16 months. Urea enriched with 10% excess atoms of 15N (0.32 g N vase−1) was applied. Dry matter production and total N and 15N values in soil and plant organs were evaluated. Photosynthetic and chlorophyll a fluorescence parameters were determined. Fertilizer-derived N (Ndff), soil-derived N (Ndfs) and fertilizer-derived N recovery were calculated. The highest values of recovery of applied N were observed in the organs of olive trees grown without the presence of P. notatum. Ndff applied to the soil surface was accumulated mainly in the leaves and roots of olive trees. The recovery of applied N in cultivars 'Arbosana', 'Picual' and 'Coratina' were low, not exceeding 15% of the N supplied. P. notatum showed a great ability to compete with olive trees for mineral forms of N available in the soil. This is because it decreased growth and N in organs of the olive cultivars.

Arbuscular vesicular mycorrhizae in olive tree (Olea europaea L.)

The objective of the work was to determine the general and sanitary condition of olive seedlings (Olea europaea L.). For which the presence of the main microbial group that colonizes the roots of the seedlings of this crop was investigated. To determine and assess fungal root infection, colonization by native fungal organisms in roots of olive trees produced in a nursery in the Central Valley of the province of Catamarca (Argentina) was studied. The studies were carried out by microscopic observation of stained fungal structures within the root, using clarification and staining methodologies. Typical structures of endomycorrhizae such as hyphae, arbuscules and vesicles (MVA), and dark septate endophytic fungi (ESO) with septate, melanized hyphae and numerous microsclerotia were observed. This first condition is desirable in all plants due to its ability to promote plant growth of mycorrhizal-forming fungi

Characterization of endomycorrhizal fungi and their effect on the health status of olive plants (Olea europea L.) in western Algeria

This study concerned the characterization of endomycorrhizal fungi associated to a variety of olive tree which is endemic to Algeria ; the Sigoise variety (Olea europea L.). The study was carried out in western Algeria where the cultivation of this variety is dominant. As methodological approaches, we used techniques that allow to highlight several biological aspects of endomycorrhization. Indeed, the estimation of the natural endomycorrhizal infection in the roots of olive trees was carried out as well as the study of the endomycorrhizal potential of the soil (EMP). Also, an estimation and identification of natural endomycorrhizal fungi of the soil and their effects on the sanitary state (growth) of the olive plants were undertaken in the greenhouse. In results, microscopic examinations of olive tree root fragments revealed a very high mycorrhization rate (more than 80%) with the presence of different structures characteristic of arbuscular endomycorrhizae : arbuscules, vesicles and pellets, independently of the age and season of sampling. Morphological characterization of fungal spores, isolated from rhizospheric soils of olive tree, revealed the presence of three genera belonging to the order of Glomales: Glomus sp., Acaulospora sp. and Gigaspora sp. with a predominance of Glomus. Moreover, the growth parameters of the aerial and underground parts of the olive plants were positively affected after inoculation, which reflects a good sanitary condition of the plants. In conclusion, our work provided additional knowledge on the controlled mycorrhization of olive plants and opened interesting perspectives for the application of this biotechnology to the production of olive plants in greenhouses.

Morphological characterization of Verticillium dahliae isolated from olive trees in District Mardan

Verticillium dahliae is a soil-borne fungus that causes Verticillium wilt, a destructive disease of Olive trees worldwide. The common symptoms of Verticillium wilt in Olive trees include wilting, leaf rolling, chlorosis, defoliation, and dead brown leaves on sunny days. During the year 2020-21, one field of Olive Arched (17-acre area) was investigated for the incidence of Verticillium wilt located in Mardan District of Khyber Pakhtunkhwa. Root, stem and leaves, samples were collected from suspected plants, and cultured on potato dextrose agar (PDA) media for the isolation of Verticillium dahliae. Spores of the isolated fungal colonies were counted using a hemocytometer. The diameter of colonies was measured on PDA and complete media (CM) using a ruler with intervals of three days. Verticillium dahliae was isolated only from the olive tree roots, while no isolation of Verticillium dahliae was observed in stem and leaves samples. The average colony diameter after seven days on PDA and CM media was 4.6 cm and 2.4 cm respectively. Spores count for the pure colony was 3.44 x 107/ml conidia. It was concluded that the wilting observed in Olive trees was due to Verticillium dahliae in district Mardan.

Foliar application of fertilizers and biostimulant has a strong impact on the olive (Olea europaea) rhizosphere microbial community profile and the abundance of arbuscular mycorrhizal fungi

Many studies on biostimulants and nutrient-based fertilizers of olive trees have been focused on the ability of these products to increase olive productivity and ameliorate oil quality. However, little information is available on their effects on rhizosphere microbial communities; whereas it is well known that microorganisms associated with plants play a key role on the productivity and the health of their host. The aim of this study was to evaluate the effects of foliar application of a biostimulant and nutrient fertilizers on photosynthesis, carbohydrate profile of the roots and soil microbial community structure. Specific attention was paid to arbuscular mycorrhizal (AM) fungi. The phospholipid fatty acid (PLFA) 16:1ω5 and the neutral lipid fatty acid (NLFA)16:1ω5 in the roots (intraradical mycelium) and in the soil (extraradical mycelium) were used as biomarkers for AM fungi. Experimentation consists of the annual foliar application of six nutrient-based treatments during two successive growing seasons: TC (untreated trees), T1 (nitrogen-based fertilizer), T2 (biostimulant rich in boron, magnesium, sulfur, manganese and amino acids), T3 (products rich in phosphorus, potassium and boron), T4 (product rich in phosphorus, calcium and zinc), T12 (application of T1 and T2) and T1234 (application of T1, T2, T3 and T4). At the end of the experiment, statistical analysis revealed a significant modification of macronutrient and micronutrient profiles of olive leaves, which caused a significant increase of photosynthesis and induced quantitative changes in the most of individual root sugars, essentially the translocated forms of sugars (sucrose and mannitol). Foliar application of fertilizers and biostimulant increased the PLFA biomarkers indicative of Gram-positive bacteria (i15:0, i16:0), Gram-negative bacteria (16:1ω7, 16:1ω9, cy17:0, 18:1ω7 and cy19:0) and actinobacteria (10Me16:0). The level of NLFA 16:1ω5 in both the rhizosphere and roots, increased significantly under foliar fertilization, however the level of PLFA 16:1ω5 did not appear to be significantly influenced, suggesting that spore and vesicle formation was more sensitive to foliar fertilization than the hyphae development. The NLFA 16:1ω5/PLFA 16:1ω5 ratio, in the roots of olive trees, showed a significant increase, indicating that AM fungi allocated high carbon to storage structures following foliar fertilization. Our study provides evidence that foliar fertilization induces rapid changes in specific microbial groups, which in turn increase the rhizosphere carbon metabolism.

Mineral and carbohydrates changes in leaves and roots of olive trees receiving biostimulants and foliar fertilizers

Fertilization practices in Tunisian olive growing are widely used in order to improve the yields and the mineral status of the trees grown under rain-fed conditions (low received rainfall). The aim of this study is to assess the effect of foliar fertilization on mineral composition and primary metabolites (soluble sugars) in leaves and roots of cultivar Chemlali. A nitrogen based fertilizer and two biostimulants were sprayed separately in different seasons and the treatments were the following: F1 (nitrogen based fertilizer), F2 (biostimulant rich in boron), F3 (combination of F1 and F2), F4 (biostimulant with a calcium base) and F5 (Combination of F1, F2 and F4). Untreated trees (no foliar fertilization) were used as control (C). Leaf and root samples of treatments F1, F2 and F3 were collected at different phenological stages while samples of F4 and F5 were collected at fruit growth. Mineral content and carbohydrate composition were carried out in all the samples. Results showed that foliar fertilization generally improved the mineral profile of leaves for both macro and micronutrients. Macronutrient concentrations were more important in leaves than in roots while the micronutrients were the highest in roots. Concerning carbohydrates status, the most abundantly soluble sugar in leaves and roots was mannitol followed by glucose. Differences in carbohydrates concentration were observed in leaves through the season and the treatments. The combined treatment F3 induced a positive effect on the pool of soluble sugars in leaves at flowering. Then, both mannitol and glucose decreased in July compared to the levels in May, a fact which can be explained by the high carbohydrate demand for fruit growth during this period. Roots accumulated lower contents of carbohydrates. The ratios macronutrients/total carbohydrates and micronutrients/total carbohydrates were higher in the roots than in the leaves. All these results showed the impact of foliar fertilization on the mineral and carbohydrate status and highlighted a relationship between them for different organs of the olive tree cultivated under rain-fed conditions.

Root structural plasticity enhances salt tolerance in mature olives

Roots are the first plant organ to encounter, sense, and respond to soil salinity. Like for many moderately salt tolerant species, roots of olive (Olea eurpaea) trees are the principal players in salt tolerance. We studied roots of mature olive trees in order to illuminate the yet vague mechanism(s) of root salt exclusion.Root structural traits were examined in olive trees grown in lysimeters and from a long-term salinity field trial. The distribution of salts was detected in root cross-sections using scanning electron microscopy combined with energy dispersive spectroscopy.Increased soil salinity caused a continuous decline in specific root length and an increase in root diameter, periderm thickness, and specific hydraulic conductivity. While periderm cell number was not modified, cell diameter increased linearly by a total of 50 % as root zone salinity increased nearly eight-fold. Strong compartmentation of Na within the periderm was found, with highest content in the outer periderm layer and lowest content in the stele. Increase in soil salinity was associated with decrease in stele area, yet, hydraulic conductivity was doubled due to higher fraction of large diameter xylem vessels.Our results indicate significant root structural plasticity, which underlies the salt resistance mechanisms. The dominant trait enabling salt tolerance of olive trees is the enlarged periderm serving as an apoplastic barrier that enhances salt compartmentation and exclusion from the vascular tissues.

First Report of Root Rot Caused by Phytophthora bilorbang on Olea europaea in Italy.

Leaf chlorosis, severe defoliation and wilt associated with root rot were observed on mature olive trees cv. Nera di Gonnos in an experimental orchard at Mirto Crosia (Calabria, southern Italy). An oomycete was consistently isolated from rotten roots of symptomatic olive trees. It was identified as Phytophthora bilorbang by morphological characters and sequencing of Internal Transcribed Spacer (ITS) regions of ribosomal DNA (rDNA). Pathogenicity was verified by inoculating potted two-month-old rooted cuttings of Olea europaea var. Nera di Gonnos in a soil infestation trial. P. bilorbang was re-isolated from roots of symptomatic, artificially inoculated olive cuttings to fulfill Koch’s postulates. This is the first report of P. bilorbang on O. europaea L. and on a species of the Oleaceae family worldwide.

Native mycorrhizal communities of olive tree roots as affected by protective green cover and soil tillage

Arbuscular mycorrhizal fungi (AMF) are beneficial symbionts associated with the roots of most food crops and improve plant nutrient uptake and tolerance to biotic and abiotic stresses. AMF implementation in food production requires targeted studies on the factors affecting their development in differently managed agroecosystems. Here, we investigated the diversity and community composition of native AMF in the roots of olive trees, as affected by a long-term permanent green cover and shallow tillage, at two different soil depths, in a high-density olive orchard under Mediterranean climate conditions, by using a molecular approach, PCR-denaturating gradient gel electrophoresis (PCR-DGGE) of partial 18S rRNA gene. Olive root colonization was 20–30%. Analysis of similarities (ANOSIM) of PCR-DGGE clusters revealed significant differences in AMF community composition of olive tree root samples collected from permanent cover versus tillage treatment. The DGGE bands, excised, sequenced and affiliated to AMF species using Basic Local Alignment Search Tool and phylogenetic trees analyses, allowed, for the first time, the identification of native mycorrhizal microbiota colonizing olive tree roots. This is the first work showing that two different managements of olive orchard floor - permanent green cover versus shallow tillage - are able to shape AMF community composition in olive tree roots, regardless of soil depth. Moreover, the finding that most sequences retrieved from olive tree roots (86%) were affiliated to sequences of forest and fruit trees represents an excellent clue for studying host preference of specific AMF for trees, also in relation to their functional significance, in the years to come.

Olea europaea L. Root Endophyte Bacillus velezensis OEE1 Counteracts Oomycete and Fungal Harmful Pathogens and Harbours a Large Repertoire of Secreted and Volatile Metabolites and Beneficial Functional Genes.

Oomycete and fungal pathogens, mainly Phytophthora and Fusarium species, are notorious causal agents of huge economic losses and environmental damages. For instance, Phytophthora ramorum, Phytophthora cryptogea, Phytophthora plurivora and Fusarium solani cause significant losses in nurseries and in forest ecosystems. Chemical treatments, while harmful to the environment and human health, have been proved to have little or no impact on these species. Recently, biocontrol bacterial species were used to cope with these pathogens and have shown promising prospects towards sustainable and eco-friendly agricultural practices. Olive trees prone to Phytophthora and Fusarium disease outbreaks are suitable for habitat-adapted symbiotic strategies, to recover oomycetes and fungal pathogen biocontrol agents. Using this strategy, we showed that olive trees-associated microbiome represents a valuable source for microorganisms, promoting plant growth and healthy benefits in addition to being biocontrol agents against oomycete and fungal diseases. Isolation, characterization and screening of root microbiome of olive trees against numerous Phytophthora and other fungal pathogens have led to the identification of the Bacillus velezensis OEE1, with plant growth promotion (PGP) abilities and strong activity against major oomycete and fungal pathogens. Phylogenomic analysis of the strain OEE1 showed that B. velezensis suffers taxonomic imprecision that blurs species delimitation, impacting their biofertilizers’ practical use. Genome mining of several B. velezensis strains available in the GenBank have highlighted a wide array of plant growth promoting rhizobacteria (PGPR) features, metals and antibiotics resistance and the degradation ability of phytotoxic aromatic compounds. Strain OEE1 harbours a large repertoire of secreted and volatile secondary metabolites. Rarefaction analysis of secondary metabolites richness in the B. velezenis genomes, unambiguously documented new secondary metabolites from ongoing genome sequencing efforts that warrants more efforts in order to assess the huge diversity in the species. Comparative genomics indicated that B. velezensis harbours a core genome endowed with PGP features and accessory genome encoding diverse secondary metabolites. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of OEE1 Volatile Organic Compounds (VOCs) and Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS) analysis of secondary metabolites identified numerous molecules with PGP abilities that are known to interfere with pathogen development. Moreover, B. velezensis OEE1 proved effective in protecting olive trees against F. solani in greenhouse experiments and are able to inhabit olive tree roots. Our strategy provides an effective means for isolation of biocontrol agents against recalcitrant pathogens. Their genomic analysis provides necessary clues towards their efficient implementation as biofertilizers.

Root verbascoside and oleuropein are potential indicators of drought resistance in olive trees (Olea europaea L.)

Polyphenols are constituents of all higher plants. However, their biosynthesis is often induced when plants are exposed to abiotic stresses, such as drought. The aim of the present work was to determine the phenolic status in the roots of olive trees grown under water deficit conditions. The results revealed that roots of water-stressed plants had a higher content of total phenols. The main compound detected in well-watered olive tree roots was verbascoside. Oleuropein was established as the predominant phenolic compound of water-stressed plants. The oleuropein/verbascoside ratio varied between 0.31 and 6.02 in well-watered and water-stressed plants respectively, which could be a useful indicator of drought tolerance in olive trees. Furthermore, this study is the first to provide experimental evidence showing that luteolin-7-rutinoside, luteolin-7-glucoside and apigenin-7-glucoside were the dominant flavonoid glucosides in olive tree roots and showed the most significant variations under water stress.

Organic carbon pools and storage in the soil of olive groves of different age

SummaryCompared with annual crop cultivation, tree groves might represent a relevant land‐use system to improve C sequestration, but few data are available to support this hypothesis. To evaluate the potential of olive tree (Olea europaea L., 1753) cultivation to store soil organic C (SOC), we assessed (i) the distribution of organic C in active (water‐extractable and particulate organic C, WEOC and POC, respectively), intermediate (organic matter associated with stable sand‐size aggregates and silt‐ and clay‐size aggregates, SSAs and SCAs, respectively) and passive (organic matter resistant to oxidation, rSOM) pools, (ii) the phenol content of the C pools, (iii) the humic‐C distribution of the intermediate C pool and (iv) the stocks of SOC pools in two olive groves of different age (7 years (OG7) and 30 years (OG30)) compared with a nearby site with cereal crops (arable soil, AS). In OG30 the organic C stock of the olive grove was no different from that of the AS, but the distribution of SOC pools changed with the age of the olive groves. The WEOC and POC increased in the Ap horizon of OGs, probably because of the herbaceous cover and distribution of chipped prunings on the soil. There were fewer SSAs in OG7 than AS, possibly because of pedoturbations from deep tillage before the olive trees were established, but they increased in OG30. The increase in SSAs and SCAs in the Bw and BC horizons of OG30 was associated with humic‐C and unextractable‐C and a smaller phenol content than AS. This suggested that the olive tree roots had a positive role through rhizodeposition and root turnover, which favoured the stabilization of organic matter into aggregates at depth. In contrast to the active and intermediate C pools, the passive C pool did not vary following the change in land use from arable to olive grove.Highlights Effects of land‐use change from arable to olive grove on soil organic C pools and stocks. Soil organic C stock increased from 7‐ to 30‐year‐old olive orchard. Olive tree cultivation affected active and intermediate C pools, but not the passive C pool. After 30 years, the olive grove stored an amount of SOC similar to that of the arable system.

English

Arbuscular Mycorrhizal Fungi (AMFs) are known as a symbiotic microorganism which ameliorates growth and tolerance against stressful conditions of their host plants. It is characterized by morphological, physiological and biochemical events that are controlled by the interaction of both plants and fungus. The aim of this research was to evaluate the intensity (M%) and the Arbuscules abundance (A%) of mycorrhizal infection with Glomus intraradices in olive (Olea europaea L.) tree roots of five Tunisian local cultivars (cvs Oueslati, Meski, Jarboui, Chemlali and Chetoui). After 2 weeks of acclimatization in a greenhouse, the olive plantlets were inoculated with “G. intraradices”. The estimate of percentage of root colonization was calculated using an adequate method. This method consists of putting fragments of colored roots from each cultivar and observing them in a light microscope. These fragments were noted in a grid based on a scale class. Differences obtained in values were detected in all cultivars. This paper suggests the presence of cultivar-dependent differences in both the M% and A% that can be modified by AM fungi as well as by its interaction with olive roots. Results confirm also that oueslati cv has the best compatibility with G. intraradices. These findings open up many opportunities for mycorrhiza inoculation in the oleaster plants production in Tunisia. Key words: Olea europaea L., Glomus intraradices, arbuscules, Oueslati cv.

MIP diversity from Trichoderma: Structural considerations and transcriptional modulation during mycoparasitic association with Fusarium solani olive trees

Major intrinsic proteins (MIP) are characterized by a transmembrane pore-type architecture that facilitates transport across biomembranes of water and a variety of low molecular weight solutes. They are found in all parts of life, with remarkable protein diversity. Very little is known about MIP from fungi. And yet, it can legitimately be stated that MIP are pivotal molecular components in the privileged relationships fungi enjoy with plants or soil fauna in various environments. To date, MIP have never been studied in a mycoparasitism situation. In this study, the diversity, expression and functional prediction of MIP from the genus Trichoderma were investigated. Trichoderma spp. genomes have at least seven aquaporin genes. Based on a phylogenetic analysis of the translated sequences, members were assigned to the AQP, AQGP and XIP subfamilies. In in vitro and in planta assays with T. harzianum strain Ths97, expression analyses showed that four genes were constitutively expressed. In a mycoparasitic context with Fusarium solani, the causative agent of fusarium dieback on olive tree roots, these genes were up-regulated. This response is of particular interest in analyzing the MIP promoter cis-regulatory motifs, most of which are involved in various carbon and nitrogen metabolisms. Structural analyses provide new insights into the possible role of structural checkpoints by which these members transport water, H2O2, glycerol and, more generally, linear polyols across the membranes. Taken together, these results provide the first evidence that MIP may play a key role in Trichoderma mycoparasitism lifestyle.

Transcriptomic Analysis of L. Roots during the Early Infection Process.

Olive cultivation is affected by a wide range of biotic constraints. Verticillium wilt of olive is one of the most devastating diseases affecting this woody crop, inflicting major economic losses in many areas, particularly within the Mediterranean Basin. Little is known about gene-expression changes during plant infection by of woody plants such as olive. A complete RNA-seq transcriptomic analysis of olive tree roots was made. Trinity assembler proved to be the best option to assemble the olive and transcriptomes. The olive transcriptome (Oleup) consisted of 68,259 unigenes (254,252 isoforms/transcripts), and the transcriptome (Vedah) consisted of 37,425 unigenes (52,119 isoforms/transcripts). Most unigenes of the Oleup transcriptome corresponded to cellular processes (12,339), metabolic processes (10,974), single-organism processes (7263), and responses to stimuli (5114). As for the Vedah transcriptome, most unigenes correspond to metabolic processes (25,372), cellular processes (23,718), localization (6385), and biological regulation (4801). Differential gene-expression analysis of both transcriptomes was made at 2 and 7 d post-infection. The induced genes of both organisms during the plant-pathogen interaction were clustered in six subclusters, depending on the expression patterns during the infection. Subclusters A to C correspond to plant genes, and subcluster D to F correspond to genes. A relevant finding was that the differentially expressed gene (DEGs) included in subclusters B and C were highly enriched in proteolysis as well as protein-folding and biosynthesis genes. In addition, a reactive oxygen species (ROS) defense was induced first in the pathogen and later in the plant roots.

Correlations between morpho-anatomical changes and radial hydraulic conductivity in roots of olive trees under water deficit and rewatering

The effects of prolonged drought were studied on olive (Olea europaea L.; drought-sensitive cultivar Biancolilla and drought-tolerant cultivar Coratina) to examine how morpho-anatomical modifications in roots impact on root radial hydraulic conductivity (Lpr). Two-year-old self-rooted plants were subjected to a gradual water depletion. The levels of drought stress were defined by pre-dawn leaf water potentials (Ψw) of -1.5, -3.5 and -6.5 MPa. After reaching the maximum level of drought, plants were rewatered for 23 days. Progressive drought stress, for both cultivars, caused a strong reduction in Lpr (from 1.2 to 1.3 × 10(-5) m MPa(-1) s(-1) in unstressed plants to 0.2-0.6 × 10(-5) m MPa(-1) s(-1) in plants at Ψw = -6.5 MPa), particularly evident in the more suberized (brown) roots, accompanied with decreases in stomatal conductance (gs). No significant differences in Lpr and gs between the two olive cultivars were observed. Epifluorescence microscopy and image analyses revealed a parallel increase of wall suberization that doubled in white stressed roots and tripled in brown ones when compared with unstressed plants. In drought-stressed plants, the number of suberized cellular layers from the endodermis towards the cortex increased from 1-2 to 6-7. Recovery in Lpr during rewatering was correlated to the physical disruption of hydrophobic barriers, while the time necessary to obtain new mature roots likely accounted for the observed delay in the complete recovery of gs. Radial hydraulic conductivity in olive roots was strongly influenced by soil and plant water availability and it was also modulated by structural root modifications, size, growth and anatomy. These findings could be important for maintaining an optimal water status in cultivated olive trees by scheduling efficient irrigation methods, saving irrigation water and obtaining yield of high quality.

Accumulation of flavonoids and phenolic compounds in olive tree roots in response to mycorrhizal colonization: A possible mechanism for regulation of defense molecules

The arbuscular mycorrhizal (AM) fungus promotes plant growth and can alter the production of primary and secondary metabolites. The aim of this work was to determine the influence of AM fungi colonization on the content of phenolic compounds, flavonoids and soluble carbohydrates in olive (Olea europaea L.) tree roots. The results revealed that mycorrhizal plants had a higher content of flavonoids and total phenols. Analysis of sugar contents showed enhanced levels of sucrose and fructose in mycorrhizal roots, while glucose amounts stayed constant. The DPPH radical-scavenging activity of the mycorrhizal root methanolic extracts was higher than that of the non- mycorrhizal root methanolic extracts. These results indicated that olive tree roots contain significant amounts of phenolic compounds, important factors for antioxidant capacity, which can be substantially modified by colonization of olive trees with AM fungi.

Determination of mannitol sorbitol and myo-inositol in olive tree roots and rhizospheric soil by gas chromatography and effect of severe drought conditions on their profiles.

This study reports a method for the analysis of mannitol, sorbitol and myo-inositol in olive tree roots and rhizospheric soil with gas chromatography. The analytical method consists of extraction with a mixture of dichloromethane:methanol (2:1, v/v) for soil samples and a mixture of ethanol:water (80:20) for root samples, silylation using pyridine, hexamethyldisilazane (HMDS) and trimethylchlorosilane (TMCS). The recovery of mannitol sorbitol and myo-inositol (for extraction and analysis in dichloromethane:methanol and ethanol:water) was acceptable and ranged from 100.3 to 114.7%. The time of analysis was <24 min. Among identified polyols extracted from rhizosphere and roots of olive plants, mannitol was the major compound. A marked increase in mannitol content occurred in rhizosphere and roots of water-stressed plants, suggesting a much broader role of mannitol in stress response based on its ability to act as a compatible solute.

Agronomic Application of Olive Mill Wastewater with Rock Phosphate Influence Soil Phosphorus Availability, Arbuscular Mycorrhizal Fungal Colonisation and Olive Tree Performance under Long-Term Field Conditions

The use of organic acids and phenolic compounds that are present in olive mill wastewater (OMW) represents a new perspective in rock phosphate (RP) research and a possible solution for the recycling of the OMW. To test the hypothesis that OMW applied in combination with Gafsa RP to olive tree plants can affect P mobilisation from RP to olive trees, a field experiment was conducted to evaluate the potential use of OMW with RP as soil amendment on olive tree alkaline soils. Treatment included three levels of OMW and RP application: M0 (non-amended control), M1PN (30 m3 ha-1 of OMW+150 kg ha-1 of RP) and M2PN (60 m3 ha-1 of OMW+150 kg ha-1 of RP). Five years after the start of the experiment, the available phosphorus decreased significantly. Amended olive trees had lower rate of photosynthates compared to the control, mostly due to decreased sink demand for carbon by the root. The biomass of arbuscular mycorrhizal (AM) fungi and the development of colonisation in the olive tree roots decreased dramatically by the application of OMW and RP. Phenols accumulation in leaves was significantly higher in the OMW and RP amended soils, whereas total chlorophyll, chlorophyll a, and chlorophyll b in olive trees leaves decreased significantly after agronomic application of OMW and RP. Taken with data from experiments in field conditions, our results suggest that the use of OMW in combination with RP, in order to mobilise P from RP to olive trees, are expected to have a major negative impact on plant performance.