Xylella fastidiosa invasion of new countries in Europe, the Middle East and North Africa: Ranking the potential exposure scenarios

Performance of Artificial Diets for Zelus renardii (Hemiptera: Reduviidae) Rearing

Mass production is a prerequisite for using natural enemies in integrated pest management and organic farming. Natural enemies in agroecosystems include predators that prey on insects, which they can subdue while maintaining adequate pest population densities. The Leafhopper Assassin Bug (LAB), Zelus renardii, can be a natural enemy in agroecosystems, selecting its prey for size and mobility. Some of LAB's prey include Philaenus spumarius (L.), Bactrocera oleae (Rossi), Drosophila suzukii (Matsumura), and Macrohomotoma gladiata Kuwayama, suggesting this reduviid for biocontrol agent in various contexts. We reared LABs for two subsequent broods offering living prey and artificial diets. Our data show that the rearing of Z. renardii is feasible with oligidic, meridic, and holidic artificial formulations. Four artificial diets allowed the complete post-embryonic development of LABs in captivity for two successive generations. The accumulated degree-days (ADDs) accurately predict the growth of LABs based on heat accumulation, estimating that up to three generations could grow per year in captivity at the experimented T°C.

Nano-metals forming bacteria in Egypt. II. Efficacy towards biomolecules, ultrastructure, growth parameters, and eco-friendly therapeutic of soft rot/blackleg genera

The nanoparticles (NPs) formed by Enterococcus thailandicus, Pseudomonas putida, Marinobacter hydrocarbonoclasticus, and P. geniculate were tested against soft rot/blackleg genera. The effects of NPs recorded on bacterial DNA, proteins, and carbohydrates concentration of Pectobacterium carotovorum subsp. carotovorum, Enterobacter cloacae (soft rot), and Dickeya solani (soft rot/blackleg). Treated cells showed degradation in isolated DNA, decreased proteins and carbohydrates concentration compared with untreated cells. Using Scanning Electron Microscope (SEM), the treated cells showed collapsed and small pits in the cell wall. Using Transmission Electron Microscope (TEM), internal changes showed penetration of NPs inside the tested bacterial cells, the appearance of periplasmic space, formation of vacuoles, and condensation of cytoplasm. Disease severity ex vivo of potato tuber infected with tested genera demonstrated that NPs treatment didn't show any rotted tissue compared with untreated. The ability to uptake and accumulate FeNPs from the soil in potato (Solanum tuberosum) seedlings; Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) was used. It recorded an increase in iron content of treated potato (Solanum tuberosum) seedlings with NPs, compared with untreated. FeNPs can be used to control soft rot/blackleg diseases, instead of copper pesticides. It could be a new, approach for disease management and increase the plant's nutritional value.

Using 'sentinel' plants to improve early detection of invasive plant pathogens

Infectious diseases of plants present an ongoing and increasing threat to international biosecurity, with wide-ranging implications. An important challenge in plant disease management is achieving early detection of invading pathogens, which requires effective surveillance through the implementation of appropriate monitoring programmes. However, when monitoring relies on visual inspection as a means of detection, surveillance is often hindered by a long incubation period (delay from infection to symptom onset) during which plants may be infectious but not displaying visible symptoms. 'Sentinel' plants-alternative susceptible host species that display visible symptoms of infection more rapidly-could be introduced to at-risk populations and included in monitoring programmes to act as early warning beacons for infection. However, while sentinel hosts exhibit faster disease progression and so allow pathogens to be detected earlier, this often comes at a cost: faster disease progression typically promotes earlier onward transmission. Here, we construct a computational model of pathogen transmission to explore this trade-off and investigate how including sentinel plants in monitoring programmes could facilitate earlier detection of invasive plant pathogens. Using Xylella fastidiosa infection in Olea europaea (European olive) as a current high profile case study, for which Catharanthus roseus (Madagascan periwinkle) is a candidate sentinel host, we apply a Bayesian optimisation algorithm to determine the optimal number of sentinel hosts to introduce for a given sampling effort, as well as the optimal division of limited surveillance resources between crop and sentinel plants. Our results demonstrate that including sentinel plants in monitoring programmes can reduce the expected prevalence of infection upon outbreak detection substantially, increasing the feasibility of local outbreak containment.

Xylella fastidiosa in Europe: From the Introduction to the Current Status

Xylella fastidiosa is xylem-limited bacterium capable of infecting a wide range of host plants, resulting in Pierce's disease in grapevine, citrus variegated chlorosis, olive quick decline syndrome, peach phony disease, plum leaf scald, alfalfa dwarf, margin necrosis and leaf scorch affecting oleander, coffee, almond, pecan, mulberry, red maple, oak, and other types of cultivated and ornamental plants and forest trees. In the European Union, X. fastidiosa is listed as a quarantine organism. Since its first outbreak in the Apulia region of southern Italy in 2013 where it caused devastating disease on Olea europaea (called olive leaf scorch and quick decline), X. fastidiosa continued to spread and successfully established in some European countries (Corsica and PACA in France, Balearic Islands, Madrid and Comunitat Valenciana in Spain, and Porto in Portugal). The most recent data for Europe indicates that X. fastidiosa is present on 174 hosts, 25 of which were newly identified in 2021 (with further five hosts discovered in other parts of the world in the same year). From the six reported subspecies of X. fastidiosa worldwide, four have been recorded in European countries (fastidiosa, multiplex, pauca, and sandyi). Currently confirmed X. fastidiosa vector species are Philaenus spumarius, Neophilaenus campestris, and Philaenus italosignus, whereby only P. spumarius (which has been identified as the key vector in Apulia, Italy) is also present in Americas. X. fastidiosa control is currently based on pathogen-free propagation plant material, eradication, territory demarcation, and vector control, as well as use of resistant plant cultivars and bactericidal treatments.

Landscape and Vegetation Patterns Zoning Is a Methodological Tool for Management Costs Implications Due to Xylella fastidiosa Invasion

Philaenus spumarius (Linnaeus 1758, hereafter Ps) is considered one of the main insect vectors responsible for the spread of an alien biota, Xylella fastidiosa (Wells 1987, hereafter Xf), in the Salento area, Apulia region (Southern Italy). Effective management of this biological invader depends on the continuous surveillance and monitoring of its insect vector. As such, this research elicits the invasion drivers (i.e., landscape and vegetation indicators) that influence the abundance and the dynamics of this vector and, consequently, the spatial spread of this bacterium in this Italian region. For this purpose, a spatial pattern clustering methodological approach is considered. The results reveal that spatial variation and territorial differentiation may differ from zone to zone in the same invaded area, for which effective management and monitoring planning should be addressed. Further, six agro-ecosystems zones have been identified with respect to five indicators: (i) vegetation index, (ii) intensity of cultivation, (iii) cultural diversity, (iv) density of agricultural landscape elements, and (v) altitude. This paper has public implications and contributes to an understanding of how zoning of an infected area, by an alien biota, into homogenous zones may impact its effective management costs. This approach could also be applied in other countries affected or potentially affected by the phenomenon of Xf invasion.

Biological Approaches Promise Innovative and Sustainable Management of Powdery Mildew in Lebanese Squash

Biological management techniques act as a promising and sustainable alternative to alleviate pathogen-induced losses, improve ecosystem functions, and reinforce the resilience of agricultural systems. Lebanese squash production has been threatened by powdery mildew disease caused by the fungus Podosphaera xanthii. Very few studies, even unpublished ones, stress the evaluation of biological control approaches in the Lebanese agriculture sector. Here, we have aimed to evaluate the effect of five safe biological treatments (olive soap, sodium bicarbonate, garlic extract, horsetail, and compost tea) in the management of powdery mildew on Lebanese squash in organic open field conditions. Plants were treated after the first spots of powdery mildew appeared on leaves. We then examined the leaves to evaluate disease incidence and severity, and to compare the ability of the five treatments to reduce powdery mildew disease and incidence, in comparison with the untreated control. Plants treated with sodium bicarbonate and garlic extract were the least affected by powdery mildew regarding disease incidence and severity, while tea compost proved to be the least effective product. Organic management of vegetable crops is extremely important in order to ensure global food security and reduce pesticide applications.

Continuous Pest Surveillance and Monitoring Constitute a Tool for Sustainable Agriculture: Case of Xylella fastidiosa in Morocco

Climate and trade changes are reshaping the cartographic distribution of lethal pervasive pathogens. Among serious emerging challenges is Xylella fastidiosa (Xf), a xylem-limited phytopathogenic bacterium that produces losses and damages to numerous crops of high economic and agronomic importance. Lately, this grave quarantine pathogen has expended its distribution by arriving to several European countries and infecting both wild and cultivated plants, and no cure has been identified so far. Countries without current outbreaks like Morocco, need to monitor theirs crops frequently because detecting diseases in the early stages may reduce the huge losses caused by Xf. For that purpose, inspections were managed in different regions in Morocco from March 2020 to July 2021 to assess the presence of Xf in several growing areas of vulnerable economic crops (i.e., almond, citrus and olive). To extend the likelihood of detection, hosts have been inspected and sampled randomly over different environments including symptomatic and asymptomatic plants. Each sample was screened for the existence of Xf by using the DAS-ELISA commercial kit, while, further analyses were carried out for doubtful samples, by PCR. Results of both tests did not show any positive sample in the investigated areas. This finding is an update on the Xf situation in Morocco and confirms that this country is still a free territory from this bacterium, at least in the monitored regions.

The potential direct economic impact and private management costs of an invasive alien species: Xylella fastidiosa on Lebanese wine grapes

Since its outbreak in 2013 in Italy, the harmful bacterium Xylella fastidiosa has continued to spread throughout the Euro-Mediterranean basin and, more recently, in the Middle East region. Xylella fastidiosa subsp. fastidiosa is the causal agent of Pierce’s disease on grapevines. At present, this alien subspecies has not been reported in Lebanon but if this biological invader was to spread with no cost-effective and sustainable management, it would put Lebanese vineyards at a certain level of risk. In the absence of an Xylella fastidiosa subsp. fastidiosa outbreak, the gross revenue generated by Lebanese wine growers is estimated as close to US$22 million/year for an average period of 5 years (2015–2019). The potential quantitative economic impacts of an Xylella fastidiosa subsp. fastidiosa outbreak and particularly, the private control costs have not been assessed yet for this country as well as for others which Xylella fastidiosa may invade. Here, we have aimed to estimate the potential direct economic impact on growers’ livelihoods and provide the first estimate of the private management costs that a theoretical Xylella fastidiosa subsp. fastidiosa outbreak in Lebanon would involve. For this purpose, we used a Partial Budget approach at the farm gate. For the country as a whole, we estimated that a hypothetical full spread of Xylella fastidiosa subsp. fastidiosa on Lebanese wine grapes would lead to maximum potential gross revenue losses of almost US$ 11 million for an average recovery period of 4 years, to around US$ 82.44 million for an average grapevine life span period of 30 years in which infected plants are not replaced at all. The first yearly estimated additional management cost is US$853 per potentially infected hectare. For a recovery period of 4 years, the aggregate estimated additional cost would reach US$2374/ha, while the aggregate net change in profit would be US$-4046/ha. Furthermore, additional work will be needed to estimate the public costs of an Xylella fastidiosa subsp. fastidiosa outbreak in Lebanon. The observed costs in this study support the concerned policy makers and stakeholders to implement a set of reduction management options against Xylella fastidiosa subsp. fastidiosa at both national and wine growers’ levels. This re-emerging alien biota should not be neglected in this country. This understanding of the potential direct economic impact of Xylella fastidiosa subsp. fastidiosa and the private management costs can also benefit further larger-scale studies covering other potential infection areas and plant hosts.

Assessment of Ionomic, Phenolic and Flavonoid Compounds for a Sustainable Management of Xylella fastidiosa in Morocco

Morocco belongs to the countries ranked at a high-risk level for entry, establishment, and spread of Xylella fastidiosa, which has recently re-emerged as a plant pathogen of global importance causing olive quick decline syndrome (OQDS). Symptomatic infection by X. fastidiosa leads to devastating diseases and important economic losses. To prevent such losses and damages, countries without current outbreaks like Morocco need to first understand their host plant responses to X. fastidiosa. The assessment of the macro and micro-elements content (ionome) in leaves can give basic and useful information along with being a powerful tool for the sustainable management of diseases caused by this devastating pathogen. Herein, we compare the leaf ionome of four important autochthonous Moroccan olive cultivars (‘Picholine Marocaine’, ‘Haouzia’, ‘Menara’, and ‘Meslalla’), and eight Mediterranean varieties introduced in Morocco (‘Arbequina’, ‘Arbosana’, ‘Leccino’, ‘Ogliarola salentina’, ‘Cellina di Nardo’, ‘Frantoio’, ‘Leucocarpa’, and ‘Picholine de Languedoc’), to develop hypotheses related to the resistance or susceptibility of the Moroccan olive trees to X. fastidiosa infection. Leaf ionomes, mainly Ca, Cu, Fe, Mg, Mn, Na, Zn, and P, were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES). These varieties were also screened for their total phenolics and flavonoids content. Data were then involved in a comparative scheme to determine the plasticity of the pathogen. Our results showed that the varieties ‘Leccino’, ’Arbosana’, ‘Arbequina’ consistently contained higher Mn, Cu, and Zn and lower Ca and Na levels compared with the higher pathogen-sensitive ‘Ogliarola salentina’ and ‘Cellina di Nardò’. Our findings suggest that ‘Arbozana’, ‘Arbiquina’, ‘Menara’, and ‘Haouzia’ may tolerate the infection by X. fastidiosa to varying degrees, provides additional support for ‘Leccino’ having resistance to X. fastidiosa, and suggests that both ‘Ogliarola salentina’ and ‘Cellina di Nardö’ are likely sensitive to X. fastidiosa infection.

Landscape restoration due to Xylella fastidiosa invasion in Italy: Assessing the hypothetical public’s preferences

Since 2013, the olive landscapes have gradually degenerated due to the spread and establishment of Xylella fastidiosa subsp. pauca (hereafter Xf) in Apulia, southern Italy. From 2013 to 2019, a total of approximately 54,000 hectares of olive orchards in the south of this region have been seriously damaged, and their restoration will progressively regenerate the economic, social, cultural and environmental nonmarket benefits. Since there is a willingness to restore the affected landscape in the best interest of the local citizens, this research aims to predict their preference heterogeneity and willingness to pay (WTP) to improve this landscape and continue research and experimentation in relation to Olive Quick Decline Syndrome Disease by the bacterium. For this purpose, a choice experiment method is used. The social field survey includes a representative sample of 683 respondents in three major cities (Foggia, Bari and Lecce) of Apulia region. The results reveal that for the local citizens interviewed, the most appreciated olive landscape services are cultural heritage and aesthetic values. In addition, the findings revealed citizens’ positive appreciation of improving the damaged olive landscape, while respondents are not willing to pay a premium for research. The results show that the average value that Apulians are willing to pay for landscape restoration is about 5.7 million of € per year. Further, this research has implications for land use planners in the study area, which faces issues of harmful pathogen management and land revival.

Semi-Automatic Method for Early Detection of Xylella fastidiosa in Olive Trees Using UAV Multispectral Imagery and Geostatistical-Discriminant Analysis

Xylella fastidiosa subsp. pauca (Xfp) is one of the most dangerous plant pathogens in the world. Identified in 2013 in olive trees in south–eastern Italy, it is spreading to the Mediterranean countries. The bacterium is transmitted by insects that feed on sap, and causes rapid wilting in olive trees. The paper explores the use of Unmanned Aerial Vehicle (UAV) in combination with a multispectral radiometer for early detection of infection. The study was carried out in three olive groves in the Apulia region (Italy) and involved four drone flights from 2017 to 2019. To classify Xfp severity level in olive trees at an early stage, a combined method of geostatistics and discriminant analysis was implemented. The results of cross-validation for the non-parametric classification method were of overall accuracy = 0.69, mean error rate = 0.31, and for the early detection class of accuracy 0.77 and misclassification probability 0.23. The results are promising and encourage the application of UAV technology for the early detection of Xfp infection.