Olive Leaf Spot Research Articles

No- or Low-Content Copper Compounds for Controlling Venturia oleaginea, the Causal Agent of Olive Leaf Spot Disease.

The efficacy of using a synthetic (azoxystrobin + difenoconazole), copper-based (copper oxychloride) and low-content copper compound (copper complexed with gluconate and lignosulphonate) fungicides for controlling Venturia oleaginea, the causal agent of olive spot disease, was evaluated in an olive (cv. Nabali) orchard located in the Kafr Qud area (Palestine) in 2017-2018. Treatments were applied at three different times (February, April, and August). In January 2017, at the beginning of the experiment, about 90% of the leaves grown in 2016 were infected. Defoliation was determined by counting the leaves on the labeled branches initially and then periodically. It increased gradually in both the control and treated trees, but those treated with azoxystrobin + difenoconazole or with copper complexed with gluconate and lignosulphonate showed a slower defoliation rate. During 2017, new shoots grew and new leaves developed. All treatments reduced the drop of new leaves with respect to the control, with positive effects on the reproductive activity (inflorescence growth and yield). Overall, all treatments significantly reduced the disease, thus indicating the possibility of greatly reducing infections if treatments are regularly applied each year, also with traditional (copper-based) fungicides. Due to their capability of penetrating inside the vegetative tissue, azoxystrobin + difenoconazole or copper complexed with gluconate and lignosulphonate reduced/slowed down the drop of infected leaves. The use of these fungicides is therefore particularly recommended when olive leaf spot disease is severe. The use of low-content copper compounds allows the amount of metallic copper used for the treatments against V. oleaginea to be greatly reduced.

First Molecular Phylogenetic Identification and Report of Pseudocercospora cannabina Causing Leaf Spot Disease on Cannabis sativa in Thailand

Cannabis sativa is gaining attention as an agronomically important crop in many countries around the world. The identification and control of leaf diseases in cannabis are very important for cannabis cultivators as leaves are the most economically important part of the cannabis plants. In 2022, several cannabis plants in cultivations showing olive leaf spot symptoms emerged from Chiang Rai province, Thailand. Preliminary studies indicated that the causal organism is Pseudocercospora sp. Species of Pseudocercospora are important plant pathogens that are now identified through morphological studies combined with DNA sequence data of Internal Transcribed Spacer (ITS), Actin (act), Translation Elongation Factor (tef), and RNA Polymerase II second largest subunit (rpb2) gene regions. We aimed to investigate and understand the emergence of olive leaf spot disease in cannabis plants in Chiang Rai province, Thailand, with a specific focus on the combined morpho-molecular identification of the pathogen. In our study, Pseudocercospora cannabina, the causal organism of olive leaf spot disease, was identified as the leaf spot-causing pathogen with both morphological and phylogenetic analyses. Our study is the first to provide molecular data for Ps. cannabina as the typenor Ps. cannabina isolates from previous studies have made molecular data available for this species. A pathogenicity test, re-isolation, and identification steps were performed to fulfill Koch’s postulates. This comprehensive approach enhances our understanding of the olive leaf spot disease and its causative agent in cannabis.

Linking Thermal Indices, Productivity, Phenotypic Traits, and Stressors for Assessing the Health of Centennial Traditional Olive Trees

Centennial olive trees, integral components of traditional Mediterranean agroecosystems, hold immense value as repositories of biodiversity and cultural heritage due to their physiological attributes and life history, making them crucial for the conservation of High Nature Value ancient olive orchards. However, they are increasingly confronted with physiological challenges exacerbated by various biotic and abiotic stressors jeopardizing their health and productivity, underscoring the urgency for ongoing monitoring and conservation measures to secure their long-term existence. To monitor these challenges, in recent years, the adoption of non-invasive techniques like infrared thermography (IRT) has become prevalent. In this study, we aimed to comprehensively assess the health state of traditional centennial olive trees, with a particular focus on their productivity. To achieve this, we monitored 44 centennial olive trees from a traditional olive grove on the island of Naxos, Greece, a representative location for Mediterranean olive groves, during the period from 2017 to 2020. We established connections between a set of trunk and canopy thermal and humidity indices, phenotypic traits, and the two most prevalent stressors affecting olive trees not only within the context of the island but also more broadly in similar Mediterranean environments worldwide: the olive leaf spot disease (OLS) and crop water stress, assessed through the crop water stress index (CWSI). To evaluate their interrelationships, we initially assessed intraspecific thermal and humidity pattern variations, and we developed linear and logistic regression models to gain insights into the factors influencing olive tree productivity, water stress, and the OLS presence. Results indicated that combining thermal and humidity indices can substantially explain olive tree productivity, water stress, and OLS, providing a valuable tool for assessing and monitoring the health and overall state of centennial olive trees, while offering a comprehensive approach to understanding the complex interactions shaping traditional olive grove dynamics. By identifying key indicators such as tree thermal patterns and water stress levels, olive growers and conservationists can make informed decisions to enhance the vitality and longevity of these culturally and ecologically significant trees.

Differential Response of Olive Cultivars to Leaf Spot Disease (Fusicladium oleagineum) under Climate Warming Conditions in Morocco

Olive leaf spot (OLS), also called olive scab and peacock eye, caused by Fusicladium oleagineum, is a major disease that causes significant damage to olive trees. However, we still lack information about how cultivar and environmental factors influence disease development. In this study, evaluation of the incidence and severity on twenty olive cultivars (Olea europaea L.), maintained in an ex situ collection in Morocco, was carried out monthly during the period from March to July 2021. Biochemical parameters were also evaluated for each cultivar including leaf chlorophyll, polyphenols and flavonoid contents. Results revealed that the OLS incidence was highly correlated with severity (r = 0.94) and found to be related to climatic conditions and cultivars. The studied cultivars were classified into four major groups, i.e., susceptible, moderately susceptible, moderately resistant and resistant. Finally, our investigations revealed a partial relationship between resistance to the OLS disease and phenolic and flavonoid leaf contents, supporting the assumption of the potential involvement of such components in cultivar resistance to the disease. Overall, our work highlights the importance of characterizing olive cultivar resistance to OLS in driving the choice of the best varieties for an effective control of the disease in specific warming regions such as Morocco.

Deciphering plant health status: The link between secondary metabolites, fungal community and disease incidence in olive tree.

Plant-associated microorganisms are increasingly recognized to play key roles in host health. Among several strategies, associated microorganisms can promote the production of specific metabolites by their hosts. However, there is still a huge gap in the understanding of such mechanisms in plant-microorganism interaction. Here, we want to determine whether different levels of olive leaf spot (OLS) disease incidence were related to differences in the composition of fungal and secondary metabolites (i.e. phenolic and volatile compounds) in leaves from olive tree cultivars with contrasting OLS susceptibilities (ranging from tolerant to highly susceptible). Accordingly, leaves with three levels of OLS incidence from both cultivars were used to assess epiphytic and endophytic fungal communities, by barcoding of cultivable isolates, as well as to evaluate leaf phenolic and volatile composition. Fungal and metabolite compositions variations were detected according to the level of disease incidence. Changes were particularly noticed for OLS-tolerant cultivars, opposing to OLS-susceptible cultivars, suggesting that disease development is linked, not only to leaf fungal and metabolite composition, but also to host genotype. A set of metabolites/fungi that can act as predictive biomarkers of plant tolerance/susceptibility to OLS disease were identified. The metabolites α-farnesene and p-cymene, and the fungi Fusarium sp. and Alternaria sp. were more related to disease incidence, while Pyronema domesticum was related to the absence of disease symptoms. Cultivar susceptibility to OLS disease is then suggested to be driven by fungi, volatile and phenolic host leaves composition, and above all to plant-fungus interaction. A deeper understanding of these complex interactions may unravel plant defensive responses.

Olive leaf spot caused by Venturia oleaginea: An updated review.

Olive leaf spot (OLS) caused by Venturia oleaginea is widespread in all olive-growing areas and continents, where can cause severe yield losses. The disease is often underestimated for the difficulty to reveal early leaf symptoms and for the pathogen-induced phylloptosis, which creates the illusion of healthy and restored plants. The present review provide updated information on taxonomy, pathogen life style and cycle, epidemiology, diagnosis, and control. Application of copper-based fungicides is the main method to control OLS. However, the regulation 2009/1107 of the European Commission include these fungicides in the list of substances candidates for substitution. It is therefore urgent to find alternative control strategies especially for organic agriculture. Among new approaches/strategies for controlling OLS, promising results have been obtained using nanotechnology, endophytic microbes, and biostimulants.

An Insight into an Olive Scab on the "Istrska Belica" Variety: Host-Pathogen Interactions and Phyllosphere Mycobiome.

The olive tree is one of the most important agricultural plants, affected by several pests and diseases that cause a severe decline in health status leading to crop losses. Olive leaf spot disease caused by the fungus Venturia oleaginea can result in complete tree defoliation and consequently lower yield. The aim of the study was to obtain new knowledge related to plant-pathogen interaction, reveal mechanisms of plant defense against the pathogen, and characterize fungal phyllosphere communities on infected and symptomless leaves that could contribute to the development of new plant breeding strategies and identification of novel biocontrol agents. The highly susceptible olive variety "Istrska Belica"' was selected for a detailed evaluation. Microscopy analyses led to the observation of raphides in the mesophyll and parenchyma cells of infected leaves and gave new insight into the complex V. oleaginea pathogenesis. Culturable and total phyllosphere mycobiota, obtained via metabarcoding approach, highlighted Didymella, Aureobasidium, Cladosporium, and Alternaria species as overlapping between infected and symptomless leaves. Only Venturia and Erythrobasidium in infected and Cladosporium in symptomless samples with higher abundance showed statistically significant differences. Based on the ecological role of identified taxa, it can be suggested that Cladosporium species might have potential antagonistic effects on V. oleaginea.

Agroecological Screening of Copper Alternatives for the Conservation of Soil Health in Organic Olive Production

The efficacy of soil conditioner (vermicompost tea), fertiliser (potassium silicate), and biological control agents (BCAs) as practical agroecological copper alternatives against olive leaf spot (Spilocaea oleaginea (Cast.) Hughe.) disease was investigated between 2018 and 2021 under organic management in a Mediterranean climate. In total, 9 agroecological alternatives to copper oxychloride (vermicompost tea, potassium silicate, Bacillus subtilis EU 007 WP, Platanus orientalis leaf extract, Mycorrhiza mix, seaweed commercial product, Trichoderma citrinoviride TR1, vermicompost tea+Platanus orientalis mix, Penicillium (Mouldy bread pieces)) were applied to olive trees in a randomised block design with 4 replicationsTotal water soluble phenol compounds (TWSP) were found to be the main bioindicator to assess the alternatives and their potential to phase-out copper application. Results related to TWSP indicated that copper oxychloride (control), potassium silicate and vermicompost tea showed significantly higher content of TWSP as we compared zero application of copper and other treatments. These stimulate the antioxidant capacity in olive fruits and reduce the olive leaf spot disease incidence. The pollution effect of copper was monitored during the trial to identify soil pollution in the organic in-conversion experimental land. The total annual ‘active copper’ application was 4.7 kg.ha−1.year−1 and this is in accordance with the legal organic legislation of Turkey. During the conversion period from conventional to organic management, we determined approximately 50% reduced copper content in the soil 0–30 cm depth samples in 2020 (3.70 mg.kg−1) as it is compared to those initial samples (6.43 mg.kg−1) in 2018. We conclude that alternatives to copper that are easily accessible, e.g., vermicompost tea, have a potential for use in organic olive production to replace copper in mitigating olive leaf spots. Furthermore, we find that reduced copper application in organic management with the aim to decrease copper accumulation in soil, fruits and leaves was not yet enough to reduce copper to satisfactory levels. We conclude that further research with the aim of a total replacement of copper fungicide treatments in organic and non-organic systems is needed.

Survey and evaluation of Olive Leaf Spot caused by Venturia oleaginea (Castagne) Rossman & Crous (2015) on olive trees in Algeria

Objective: Olive Leaf Spot fungal disease caused by Venturia oleaginea (Castagne) Rossman & Crous (2015). It has a significant negative impact on certain olive growing regions of Algeria. Methodology and results: A survey was conducted from 2013 to 2015 during periods at risk of contamination (i.e. autumn, winter and early spring) to map the geographical distribution of this pathogen. The results obtained showed that Olive Leaf Spot is present in all olive- growing regions in Algeria but not in all states. Twenty seven (27) states out of the 35 surveyed states were reported to be infested, with a total of 1163 infected orchards out of the 1696 orchards surveyed, and a percentage of infection also varying from one region to another and depending on the year. The results of the statistical analyses based on Tukey HSD test at P<0.05 show very highly significant differences between the Wilayas affected. The western regions are very highly significant, whereas in the east the infection is less important. This difference may be explained by the more favourable climatic conditions, the dominance of a single olive variety “Sigoise” which seems to be more susceptible to the disease and the lack of a technical itinerary. Conclusion and application of results: This survey is the first on the situation of olive leaf spot in the olive growing regions located in the East, West and Center of the country, allowing to map the distribution of this pathogen, and the use of resistant varieties as biological control agents in the treatment of OLS disease in Algeria. Keywords: Infected, Venturia oleaginea, Olive Leaf Spot, survey, variety.

Control of olive anthracnose and leaf spot disease by bloom treatments with a pomegranate peel extract

Olive anthracnose (OA) caused by Colletotrichum spp. and olive leaf spot (OLS) caused by Ventuaria oleaginea are two of the most important diseases affecting olive trees. OA mainly affects mature olive drupes while OLS is typically known as a defoliating pathogen. Field treatments with a pomegranate peel extract (PGE) at 3, 6 or 12 g/l seven days before the expected full bloom prevented the colonization of flowers by Colletotrichum spp. and reduced latent infections in small olive drupes over the summer period by 53-100%. The same treatments significantly reduced or completely prevented the latent infections of V. oleaginea in olive leaves. Interestingly, PGE at the higher concentration (12 g/l) proved always more effective that Flint Max, a chemical formulate recently registered in Europe on olive. On plants sprayed with PGE, the lower quantity of over-summering inoculum of Colletotrichum spp. effectively delayed the disease outbreak in autumn of approximately ten days. In particular, PGE at 12 g/l reduced the incidence of anthracnose by 84.5% as compared to the untreated control. Treatments also reduced the premature defoliation of plants. Similar results to those described for a single PGE treatment made before the full bloom where achieved with two applications made before and after flowering. Overall, the present study highlighted the importance of controlling the establishment of latent infections of both Colletotrichum spp. and V.oleaginea to effectively protect olive trees . These results together with previous reports suggest the possible use of PGE as a key natural antifungal preparation to control the olive diseases affecting aerial plant organs.

Effectiveness of Low Copper-Containing Chemicals against Olive Leaf Spot Disease Caused by Venturia oleaginea

The high level of copper (Cu) accumulation in the soil, the risk of surface water contamination, and the potential public health problems due to Cu entering the food chain have raised concerns on the use of Cu compounds in agriculture, including olive growing. As a consequence, there is worldwide regulatory pressure on agricultural systems to limit the use of Cu compounds. Hence, a field trial was carried out to evaluate the effectiveness of low copper containing chemicals to control olive leaf spot (OLS) disease caused by Venturia oleaginea. The trial was conducted in 2021 in an olive (cv. Nabali Baladi) grove in Palestine. Copper complexed with lignosulphonate and gluconate (Disper Cu Max®) and the self-defense inducer Disper Broton GS® were evaluated and compared to dodine and the traditionally and frequently used copper hydroxide. In addition, untreated trees were used as the control. Treatments were made in March, July, and August. In March 2021, leaves grown in 2020 were present and 100% infected. V. oleaginea infections caused defoliation in untreated and treated olive trees with varying degrees of intensity: the Control had the most defoliation, followed by copper hydroxide and Disper Cu Max®, whereas dodine and, in particular, Disper Broton GS® had the least. All treatments reduced symptomatic leaves but their efficacy varied significantly: copper hydroxide was the least effective, Disper Cu Max® was intermediate, dodine and, mainly, Disper Broton GS® were the most effective. Overall, the results are promising since Disper Cu Max® and Disper Broton GS® were able to significantly reduce OLS damage and the amount of copper used for treatments.

Measuring plant disease severity in R: introducing and evaluating the pliman package

Image analysis based on color thresholding is the reference method for measuring severity as percent area affected. It is deemed to produce accurate results, usually considered the “true” severity value. More than a dozen applications have been used for the task in phytopathometry studies, but none was coded in R language. Here we introduced and evaluated pliman, a suite for the analysis of plant images. In particular, we show functions for computing percent severity based on RGB information contained in image palettes prepared by the user. Six image collections, totaling 249 images, from different diseases (wheat tan spot, soybean rust, olive leaf spot, rice brown spot, bean angular spot, and Xyllela fastidiosa on tobacco) exhibiting a range of symptomatic patterns and severity were used to evaluate the agreement of pliman predictions with measures by three other software: APS Assess, LeafDoctor, and ImageJ. Three users independently prepared three image palettes (each representing leaf background, symptomatic, or healthy leaf tissue) by manually inspecting and subsetting these target areas of the images. Pliman predictions by a joint palette (by joining images by the three users into one) were highly concordant (ρc > 0.98) with measures by the other software for all but Xylella fastidiosa on tobacco (ρc = 0.49). The error for the latter may be due to the low contrast between symptomatic and healthy tobacco tissues. Users showed to be a source of variation in the overall concordance depending on the disease. Reduction in the image resolution (< 1 megapixel) did not impact the results. Combined with parallel processing, the use of low image resolution (1078 × 680) decreased processing time, resulting in pliman being ~ 150 to ~ 700 times faster than existing tools for disease quantification. Pliman showed great potential to produce accurate measures and accelerate studies involving plant disease severity measurements, especially for the batch processing of large sets of image collections.

Fungal Phytopathogenic Spore First Assessment in an Olive Orchard of Northwestern Spain

The most common fungal diseases of Olea europaea are olive leaf spot (Fusicladium oleagineum), anthracnose (Colletotrichum spp.) and cercospora leaf spot (Pseudocercospora cladosporioides). To know the fungal load during the vegetative olive cycle, an aerobiological and phenological study was conducted in an olive grove in North-West Spain. For the aerobiological study, the Spanish Aerobiological Network protocol was followed using a Hirst-type spore trap. The goal of the study was to assess the spore concentrations in the atmosphere of the olive grove and their relationship with the meteorological parameters by applying statistical procedures, including a Cluster analysis, Spearman’s correlation test and PCA analysis. The most abundant spores belong to Fusicladium, registering the double of values than Colletotrichum and Pseudocercospora. The hours with the highest spores’ presence were from 11:00 to 12:00 for Fusicladium and Colletotrichum, and from 17:00 to 18:00 for Pseudocercospora. The Spearman’s and PCA test showed a positive association between temperature and relative humidity with the spores’ concentrations. The combination of meteorological, phenological and aerobiological parameters is a useful tool to understand the ecological behavior of the considered phytopathogenic fungal spores in order to develop futures strategies for the integrated management of fungal olive diseases in areas at the limit of this tree distribution.

Estimating Productivity, Detecting Biotic Disturbances, and Assessing the Health State of Traditional Olive Groves, Using Nondestructive Phenotypic Techniques

Conservation of traditional olive groves through effective monitoring of their health state is crucial both at a tree and at a population level. In this study, we introduce a comprehensive methodological framework for estimating the traditional olive grove health state, by considering the fundamental phenotypic, spectral, and thermal traits of the olive trees. We obtained phenotypic information from olive trees on the Greek island of Lesvos by combining this with in situ measurement of spectral reflectance and thermal indices to investigate the effect of the olive tree traits on productivity, the presence of the olive leaf spot disease (OLS), and olive tree classification based on their health state. In this context, we identified a suite of important features, derived from linear and logistic regression models, which can explain productivity and accurately evaluate infected and noninfected trees. The results indicated that either specific traits or combinations of them are statistically significant predictors of productivity, while the occurrence of OLS symptoms can be identified by both the olives’ vitality traits and by the thermal variables. Finally, the classification of olive trees into different health states possibly offers significant information to explain traditional olive grove dynamics for their sustainable management.

Synthesis and Characterization of Novel Copper Nanoparticles for the Control of Leaf Spot and Anthracnose Diseases of Olive.

Olive crop is frequently treated with copper fungicides to combat foliar and fruit diseases such as olive leaf spot caused by Fusicladium oleagineum and anthracnose caused by Colletotrichum spp. The replacement of copper-based products with more eco-friendly alternatives is a priority. Metal nanoparticles synthesized in several ways have recently revolutionized crop protection with applications against important crop pathogens. In this study, we present the development of four copper-based nanoparticles (CuNP Type 1 to 4) synthesized with a wet chemistry approach. The CuNPs were characterized using Transmission Electron Microscopy, Dynamic Light Scattering, Laser Doppler Electrophoresis, and Attenuated Total Reflection measurements. In addition, the activity of the four CuNP types was tested in vitro and in planta against F. oleagineum and Colletotrichum spp. In vitro sensitivity measurements showed that for both pathogens, mycelial growth was the most susceptible developmental stage to the tested compounds. Against both pathogens, CuNP Type 1 and Type 2 were found to be more active in reducing mycelial growth compared to the reference commercial compounds of copper oxide and copper hydroxide. In planta experiments showed that CuNP Type 3 and CuNP Type 4 exhibited a strong protectant activity against both F. oleagineum and Colletotrichum acutatum with control efficacy values significantly higher than those achieved by the applications of either reference product.

Evaluation of Two Predictive Models for Forecasting Olive Leaf Spot in Northern Greece.

Olive leaf spot (Venturia oleaginea) is a very important disease in olive trees worldwide. The introduction of predictive models for forecasting the appearance of a disease can lead to improved disease management. One of the aims of this study was to investigate the effect of temperature and leaf wetness on conidial germination of local isolates of V. oleaginea. The results showed that a temperature range of 5 to 25 °C was appropriate for conidial germination, with 20 °C being the optimum. It was also found that at least 12 h of leaf wetness was required to start the germination of V. oleaginea conidia at the optimum temperature. The second aim of this study was to validate the above generic model and a polynomial model for forecasting olive leaf spot disease under the field conditions of Potidea Chalkidiki, Northern Greece. The results showed that both models correctly predicted infection periods. However, there were differences in the severity of the infection, as demonstrated by the goodness-of-fit for the data collected on leaves of olive trees in 2016, 2017 and 2018. Specifically, the generic model predicted lower severity, which fits well with the incidence of the disease symptoms on unsprayed trees. In contrast, the polynomial model predicted high severity levels of infection, but these did not fit well with the incidence of disease symptoms.

Laminarin Induces Defense Responses and Efficiently Controls Olive Leaf Spot Disease in Olive.

Olive leaf spot (OLS) caused by Fusicladium oleagineum is mainly controlled using copper fungicides. However, the replacement of copper-based products with eco-friendly alternatives is a priority. The use of plant resistance-inducers (PRIs) or biological control agents (BCAs) could contribute in this direction. In this study we investigated the potential use of three PRIs (laminarin, acibenzolar-S-methyl, harpin) and a BCA (Bacillus amyloliquefaciens FZB24) for the management of OLS. The tested products provided control efficacy higher than 68%. In most cases, dual applications provided higher (p < 0.05) control efficacies compared to that achieved by single applications. The highest control efficacy of 100% was achieved by laminarin. Expression analysis of the selected genes by RT-qPCR revealed different kinetics of induction. In laminarin-treated plants, for most of the tested genes a higher induction rate (p < 0.05) was observed at 3 days post application. Pal, Lox, Cuao and Mpol were the genes with the higher inductions in laminarin-treated and artificially inoculated plants. The results of this study are expected to contribute towards a better understanding of PRIs in olive culture and the optimization of OLS control, while they provide evidence for potential contributions in the reduction of copper accumulation in the environment.

Antifungal Effect of Ambrosia artemisiifolia L. Extract and Chemical Fungicide Against Spilocaea oleagina Causing Olive Leaf Spot

Olive leaf spot or peacock eye disease caused by Spilocaea oleagina is one of the most common diseases attacking olive trees all over the world. Control of the disease by application of copper fungicides is not always feasible and requires proper management practices. The use of plant extract is considered a safe alternative to the harmful effect of chemical fungicides. In this work, different concentrations (0.5, 1.0, 1.5, 2.0, 2.5, 5.0 and 10% w/v) of Ambrosia artimisiifolia aqueous leaf extract were tested for their efficacy against OLS spore germination. All concentrations proved to have an inhibitory effect on conidial germination under in vitro conditions. The concentrations 2.5 and 5% were the most effective with germination rates of 8.3 and 2.8%, respectively. The results of this work provided new possibilities to control the disease using A. artimisiifolia leaf extract.

The Application of Trichoderma Strains or Metabolites Alters the Olive Leaf Metabolome and the Expression of Defense-Related Genes

Biocontrol fungal strains of the genus Trichoderma can antagonize numerous plant pathogens and promote plant growth using different mechanisms of action, including the production of secondary metabolites (SMs). In this work we analyzed the effects of repeated applications of selected Trichoderma strains or SMs on young olive trees on the stimulation of plant growth and on the development of olive leaf spot disease caused by Fusicladium oleagineum. In addition, metabolomic analyses and gene expression profiles of olive leaves were carried out by LC–MS Q-TOF and real-time RT-PCR, respectively. A total of 104 phenolic compounds were detected from olive leave extracts and 20 were putatively identified. Targeted and untargeted approaches revealed significant differences in both the number and type of phenolic compounds accumulated in olive leaves after Trichoderma applications, as compared to water-treated plants. Different secoiridoids were less abundant in treated plants than in controls, while the accumulation of flavonoids (including luteolin and apigenin derivatives) increased following the application of specific Trichoderma strain. The induction of defense-related genes, and of genes involved in the synthesis of the secoiridoid oleuropein, was also analyzed and revealed a significant variation of gene expression according to the strain or metabolite applied.

Biological control of Peacock spot disease caused by Spilocaea oleagina on Olive using bacteria.

The olive leaf spot disease caused by the fungus Spilocaea oleagina (Cast.) Hughes (syn. Cycloconium oleagina) is one of the most destructive diseases on olive trees causing losses that may reach 20% of the yield. The disease is controlled by the application of chemical fungicides which is not always feasible in providing proper protection against the pathogen. In this work we report the efficacy of Pseudomonas fluorescenc isolate ORS3 and Bascillus atrophaeus isolate Bat in controlling the disease under field conditions. An Olive field in, Tulkarm governorate, Palestine was selected. The olive trees were 5-10 years old and were highly infected with the olive leaf spot. Trees were sprayed with bacteria formulated in oil. Control trees were sprayed with water. For evaluation of bacterial efficacy against the disease, olive leaves were collected before and after application of the bacteria. Germination of conidia latent infection and severity were determined. In addition to that, bacterial viability was assessed. Results of the work revealed that the bacteria were able to inhibit conidial germination of the fungus. The percent of reduction in conidial germination (85.8 and 70.2%) in the presence of P. fluorescenc isolate ORS and B. atrophaeus isolate Bat, respectively was significantly lower than that in the control or in leaves sprayed with 10% oil (69.1 and 56.1%, respectively). After two weeks of spraying, the percent of latent infectoin (figure 4) was significantly (p&lt;0.05) lower on leaves sprayed with P. fluorescenc isolate ORS3 and B. atrophaeus isolate BAT (5.1 and 3.8% latent infection, respectively). However, bacterial shelf life on the surface of olive leaves was reduced after three days of spraying (i.e no bacteria were re-isolated). The results indicated that the bacteria can be used for control of the leaf spot disease. Further studies are required to evaluate the efficacy of the bacteria under different environmental conditions.