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Detecting plant pathogens and diagnosing diseases are critical components of successful pest management. These key areas have undergone significant advancements driven by breakthroughs in molecular biology and remote sensing technologies within the realm of precision agriculture. Notably, nucleic acid amplification techniques, with recent emphasis on sequencing procedures, particularly next-generation sequencing, have enabled improved DNA or RNA amplification detection protocols that now enable previously unthinkable strategies aimed at dissecting plant microbiota, including the disease-causing components. Simultaneously, the domain of remote sensing has seen the emergence of cutting-edge imaging sensor technologies and the integration of powerful computational tools, such as machine learning. These innovations enable spectral analysis of foliar symptoms and specific pathogen-induced alterations, making imaging spectroscopy and thermal imaging fundamental tools for large-scale disease surveillance and monitoring. These technologies contribute significantly to understanding the temporal and spatial dynamics of plant diseases., Competing Interests: The author(s) declare no conflict of interest.

Strains of the bacterial pathogen Xylella fastidiosa subspecies multiplex ( Xfm ) and pauca ( Xfp ) isolated from symptomatic almond and olive plants in Spain and Italy were used in this study. Because of the risk of host jump and considering the importance of southern highbush blueberry production in Spain, we tested a small set of these strains for their potential to infect and cause disease symptoms in blueberries under greenhouse experiments. Xfm IVIA5901 (isolated from almonds in Alicante, Spain) caused symptoms similar to those caused by Xfm AlmaEm3 (isolated from blueberries in Georgia, U.S.A., and used as a reference strain capable of inducing severe symptoms in blueberry). Nevertheless, bacterial populations of Xfm IVIA5901 in planta were significantly lower than those of Xfm AlmaEm3. Xfm ESVL (isolated from almonds, Alicante, Spain) and Xfp XYL1961/18 (isolated from olives, Ibiza Island, Spain) caused limited symptoms, while Xfm XYL466/19 (isolated from wild olives, Mallorca Island, Spain) and Xfm XF3348 (isolated from almonds, Mallorca Island, Spain) and Xfp De Donno (isolated from olives, Puglia, Italy, and representative of the devastating olive quick decline syndrome) did not cause symptoms nor colonize blueberries. This study suggests that certain strains already found in Europe could infect blueberry if conditions conducive for a host jump in this region are met, such as proximity of blueberries to other infected hosts and presence of insect vectors that feed on these crops. Surveys on the presence of X. fastidiosa in blueberries in Spain and other European countries are needed to anticipate possible issues., Competing Interests: The author(s) declare no conflict of interest.

An unprecedented plant health emergency in olives has been registered over the last decade in Italy, arguably more severe than what occurred repeatedly in grapes in the United States in the last 140 years. These emergencies are epidemics caused by a stealthy pathogen, the xylem-limited, insect-transmitted bacterium Xylella fastidiosa. Although these epidemics spurred research that answered many questions about the biology and management of this pathogen, many gaps in knowledge remain. For this review, we set out to represent both the U.S. and European perspectives on the most pressing challenges that need to be addressed. These are presented in 10 sections that we hope will stimulate discussion and interdisciplinary research. We reviewed intrinsic problems that arise from the fastidious growth of X. fastidiosa , the lack of specificity for insect transmission, and the economic and social importance of perennial mature woody plant hosts. Epidemiological models and predictions of pathogen establishment and disease expansion, vital for preparedness, are based on very limited data. Most of the current knowledge has been gathered from a few pathosystems, whereas several hundred remain to be studied, probably including those that will become the center of the next epidemic. Unfortunately, aspects of a particular pathosystem are not always transferable to others. We recommend diversification of research topics of both fundamental and applied nature addressing multiple pathosystems. Increasing preparedness through knowledge acquisition is the best strategy to anticipate and manage diseases caused by this pathogen, described as "the most dangerous plant bacterium known worldwide.", Competing Interests: The author(s) declare no conflict of interest.

Xylella fastidiosa is a vascular plant pathogenic bacterium native to the Americas that is causing significant epidemics and economic losses in olive and almonds in Europe, where it is a quarantine pathogen. Since its first detection in 2013 in Italy, mandatory surveys across Europe revealed the presence of the bacterium also in France, Spain, and Portugal. Combining Oxford Nanopore Technologies and Illumina sequencing data, we assembled high-quality complete genomes of seven X. fastidiosa subsp. fastidiosa strains isolated from different plants in Spain, the United States, and Mexico. Comparative genomic analyses discovered differences in plasmid content among strains, including plasmids that had been overlooked previously when using the Illumina sequencing platform alone. Interestingly, in strain CFBP8073, intercepted in France from plants imported from Mexico, three plasmids were identified, including two (plasmids pXF-P1.CFBP8073 and pXF-P2.CFBP8073) not previously described in X. fastidiosa and one (pXF5823.CFBP8073) almost identical to a plasmid described in a X. fastidiosa strain from citrus. Plasmids found in the Spanish strains here were similar to those described previously in other strains from the same subspecies and ST1 isolated in the Balearic Islands and the United States. The genome resources from this work will assist in further studies on the role of plasmids in the epidemiology, ecology, and evolution of this plant pathogen., Competing Interests: The author(s) declare no conflict of interest.

The recent introductions of the bacterium Xylella fastidiosa (Xf) into Europe are linked to the international plant trade. However, both how and when these entries occurred remains poorly understood. Here, we show how almond scorch leaf disease, which affects ~79% of almond trees in Majorca (Spain) and was previously attributed to fungal pathogens, was in fact triggered by the introduction of Xf around 1993 and subsequently spread to grapevines (Pierce's disease). We reconstructed the progression of almond leaf scorch disease by using broad phylogenetic evidence supported by epidemiological data. Bayesian phylogenetic inference predicted that both Xf subspecies found in Majorca, fastidiosa ST1 (95% highest posterior density, HPD: 1990-1997) and multiplex ST81 (95% HPD: 1991-1998), shared their most recent common ancestors with Californian Xf populations associated with almonds and grapevines. Consistent with this chronology, Xf-DNA infections were identified in tree rings dating to 1998. Our findings uncover a previously unknown scenario in Europe and reveal how Pierce's disease reached the continent.

Pathogen introductions have led to numerous disease outbreaks in naive regions of the globe. The plant pathogen Xylella fastidiosa has been associated with various recent epidemics in Europe affecting agricultural crops, such as almond, grapevine, and olive, but also endemic species occurring in natural forest landscapes and ornamental plants. We compared whole-genome sequences of X. fastidiosa subspecies multiplex from America and strains associated with recent outbreaks in southern Europe to infer their likely origins and paths of introduction within and between the two continents. Phylogenetic analyses indicated multiple introductions of X. fastidiosa subspecies multiplex into Italy, Spain, and France, most of which emerged from a clade with limited genetic diversity with a likely origin in California, USA. The limited genetic diversity observed in X. fastidiosa subspecies multiplex strains originating from California is likely due to the clade itself being an introduction from X. fastidiosa subspecies multiplex populations in the southeastern United States, where this subspecies is most likely endemic. Despite the genetic diversity found in some areas in Europe, there was no clear evidence of recombination occurring among introduced X. fastidiosa strains in Europe. Sequence type taxonomy, based on multilocus sequence typing (MLST), was shown, at least in one case, to not lead to monophyletic clades of this pathogen; whole-genome sequence data were more informative in resolving the history of introductions than MLST data. Although additional data are necessary to carefully tease out the paths of these recent dispersal events, our results indicate that whole-genome sequence data should be considered when developing management strategies for X. fastidiosa outbreaks. IMPORTANCE Xylella fastidiosa is an economically important plant-pathogenic bacterium that has emerged as a pathogen of global importance associated with a devastating epidemic in olive trees in Italy associated with X. fastidiosa subspecies pauca and other outbreaks in Europe, such as X. fastidiosa subspecies fastidiosa and X. fastidiosa subspecies multiplex in Spain and X. fastidiosa subspecies multiplex in France. We present evidence of multiple introductions of X. fastidiosa subspecies multiplex , likely from the United States, into Spain, Italy, and France. These introductions illustrate the risks associated with the commercial trade of plant material at global scales and the need to develop effective policy to limit the likelihood of pathogen pollution into naive regions. Our study demonstrates the need to utilize whole-genome sequence data to study X. fastidiosa introductions at outbreak stages, since a limited number of genetic markers does not provide sufficient phylogenetic resolution to determine dispersal paths or relationships among strains that are of biological and quarantine relevance., (Copyright © 2020 American Society for Microbiology.)

An outbreak of Xylella fastidiosa subsp. multiplex sequence type ST6 was discovered in 2017 in mainland Spain affecting almond trees. Two cultured almond strains, "ESVL" and "IVIA5901," were subjected to high throughput sequencing and the draft genomes assembled. Phylogenetic analysis conclusively indicated they belong to the subspecies multiplex, and pairwise comparisons of the chromosomal genomes showed an average nucleotide identity higher than 99%. Interestingly, the two strains differ for the presence of the plasmids pXF64-Hb_ESVL and pUCLA-ESVL detected only in the ESVL strain. The availability of these draft genomes contribute to extend the European genomic sequence dataset, a first step toward setting new research to elucidate the pathway of introduction and spread of the numerous strains of this subspecies so far detected in Europe.

One of the main avocado diseases in southern Spain is white root rot caused by the fungus Rosellinia necatrix Prill. The use of organic soil amendments to enhance the suppressiveness of natural soil is an inviting approach that has successfully controlled other soilborne pathogens. This study tested the suppressive capacity of different organic amendments against R. necatrix and analyzed their effects on soil microbial communities and enzymatic activities. Two-year-old avocado trees were grown in soil treated with composted organic amendments and then used for inoculation assays. All of the organic treatments reduced disease development in comparison to unamended control soil, especially yard waste (YW) and almond shells (AS). The YW had a strong effect on microbial communities in bulk soil and produced larger population levels and diversity, higher hydrolytic activity and strong changes in the bacterial community composition of bulk soil, suggesting a mechanism of general suppression. Amendment with AS induced more subtle changes in bacterial community composition and specific enzymatic activities, with the strongest effects observed in the rhizosphere. Even if the effect was not strong, the changes caused by AS in bulk soil microbiota were related to the direct inhibition of R. necatrix by this amendment, most likely being connected to specific populations able to recolonize conducive soil after pasteurization. All of the organic amendments assayed in this study were able to suppress white root rot, although their suppressiveness appears to be mediated differentially., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Two haplotypes of Xylella fastidiosa subsp. pauca (Xfp) that correlated with their host of origin were identified in a collection of 90 isolates infecting citrus and coffee plants in Brazil, based on a single-nucleotide polymorphism in the gyrB sequence. A new single-nucleotide primer extension (SNuPE) protocol was designed for rapid identification of Xfp according to the host source. The protocol proved to be robust for the prediction of the Xfp host source in blind tests using DNA from cultures of the bacterium, infected plants, and insect vectors allowed to feed on Xfp-infected citrus plants. AMOVA and STRUCTURE analyses of microsatellite data separated most Xfp populations on the basis of their host source, indicating that they were genetically distinct. The combined use of the SNaPshot protocol and three previously developed multilocus SSR markers showed that two haplotypes and distinct isolates of Xfp infect citrus and coffee in Brazil and that multiple, genetically different isolates can be present in a single orchard or infect a single tree. This combined approach will be very useful in studies of the epidemiology of Xfp-induced diseases, host specificity of bacterial genotypes, the occurrence of Xfp host jumping, vector feeding habits, etc., in economically important cultivated plants or weed host reservoirs of Xfp in Brazil and elsewhere., (Copyright© by the Spanish Society for Microbiology and Institute for Catalan Studies.)

This work has studied for the first time the structure and diversity of plant-parasitic nematodes (PPNs) infesting olive orchard soils in a wide-region in Spain that included 92 locations. It aims at determining which agronomical or environmental factors associated to the olive orchards are the main drivers of the PPNs community structure and diversity. Classical morphological and morphometric identification methods were used to determine the frequency and densities of PPNs. Thirteen families, 34 genera and 77 species of PPNs were identified. The highest diversity was found in Helicotylenchus genus, with six species previously reported in Spain and with H. oleae being a first report. Neodolichorhynchus microphasmis and Diptenchus sp., Diphtherophora sp., and Discotylenchus sp., usually considered fungal feeders, were also reported for the first time associated to olive rhizosphere. PPNs abundance ranged from 66 to 16,288 individuals/500-cm3 of soil with Helicotylenchus digonicus being the most prevalent species, followed by Filenchus sp., Merlinius brevidens and Xiphinema pachtaicum. Nematode abundance and diversity indexes were influenced by olive cultivar, and orchard and soil management practices; while olive variety and soil texture were the main factors driving PPN community composition. Soil physicochemical properties and climatic characteristics most strongly associated to the PPN community composition included pH, sand content and exchangeable K, and maximum and minimum average temperature of the sampled locations. Our data suggests that there is a high diversity of PPNs associated to olive in Southern Spain that can exert different damage to olive roots depending on the olive variety and their abundance. Further analysis to determine the resistance levels of most common olive varieties to the prevalent PPNs in Spain will help to choose the most appropriate ones for the establishment of new plantations. This choice will take into consideration the specific soils and environments where those olive varieties will be established.

Populations of Sclerotium rolfsii, the causal organism of Sclerotium root-rot on a wide range of hosts, can be placed into mycelial compatibility groups (MCGs). In this study, we evaluated three different molecular approaches to unequivocally identify each of 12 previously identified MCGs. These included restriction fragment length polymorphism (RFLP) patterns of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (rDNA) and sequence analysis of two protein-coding genes: translation elongation factor 1α (EF1α) and RNA polymerase II subunit two (RPB2). A collection of 238 single-sclerotial isolates representing 12 MCGs of S. rolfsii were obtained from diseased sugar beet plants from Chile, Italy, Portugal, and Spain. ITS-RFLP analysis using four restriction enzymes (AluI, HpaII, RsaI, and MboI) displayed a low degree of variability among MCGs. Only three different restriction profiles were identified among S. rolfsii isolates, with no correlation to MCG or to geographic origin. Based on nucleotide polymorphisms, the RPB2 gene was more variable among MCGs compared with the EF1α gene. Thus, 10 of 12 MCGs could be characterized utilizing the RPB2 region only, while the EF1α region resolved 7 MCGs. However, the analysis of combined partial sequences of EF1α and RPB2 genes allowed discrimination among each of the 12 MCGs. All isolates belonging to the same MCG showed identical nucleotide sequences that differed by at least in one nucleotide from a different MCG. The consistency of our results to identify the MCG of a given S. rolfsii isolate using the combined sequences of EF1α and RPB2 genes was confirmed using blind trials. Our study demonstrates that sequence variation in the protein-coding genes EF1α and RPB2 may be exploited as a diagnostic tool for MCG typing in S. rolfsii as well as to identify previously undescribed MCGs.

Background: Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris, a main threat to global chickpea production, is managed mainly by resistant cultivars whose efficiency is curtailed by Fusarium oxysporum f. sp. ciceris races., Methodology: We characterized compatible and incompatible interactions by assessing the spatial-temporal pattern of infection and colonization of chickpea cvs. P-2245, JG-62 and WR-315 by Fusarium oxysporum f. sp. ciceris races 0 and 5 labeled with ZsGreen fluorescent protein using confocal laser scanning microscopy., Findings: The two races colonized the host root surface in both interactions with preferential colonization of the root apex and subapical root zone. In compatible interactions, the pathogen grew intercellularly in the root cortex, reached the xylem, and progressed upwards in the stem xylem, being the rate and intensity of stem colonization directly related with the degree of compatibility among Fusarium oxysporum f. sp. ciceris races and chickpea cultivars. In incompatible interactions, race 0 invaded and colonized 'JG-62' xylem vessels of root and stem but in 'WR-315', it remained in the intercellular spaces of the root cortex failing to reach the xylem, whereas race 5 progressed up to the hypocotyl. However, all incompatible interactions were asymptomatic., Conclusions: The differential patterns of colonization of chickpea cultivars by Fusarium oxysporum f. sp. ciceris races may be related to the operation of multiple resistance mechanisms.

Severity of Verticillium wilt in olive trees in Andalusia, southern Spain is associated with the spread of a highly virulent, defoliating (D) Verticillium dahliae pathotype of vegetative compatibility group 1A (VCG1A) but the extent of this spread and the diversity of the pathogen population have never been documented. VCG typing of 637 V. dahliae isolates from 433 trees in 65 orchards from five olive-growing provinces in Andalusia indicated that 78.1% were of VCG1A, 19.8% of VCG2A, 0.6% of VCG2B, 1.4% of VCG4B, and one isolate was heterokaryon self-incompatible. A single VCG prevailed among isolates within most orchards but two and three VCGs were identified in 12 and 3 orchards, respectively, with VCG1A+VCG2A occurring in 10 orchards. VCG1A was the predominant VCG in the three most important olive-growing provinces, and was almost as prevalent as VCG2A in another one. Molecular pathotyping of the 637 isolates using specific polymerase chain reaction assays indicated that VCG1A isolates were of the D pathotype whereas isolates of VCG2A, -2B, and -4B were of the less virulent nondefoliating (ND) pathotype. The pathotype of isolates correlated with the disease syndrome affecting sampled trees. Only three (seq1, seq2, and seq4) of the seven known sequences of the V. dahliae-specific 539- or 523-bp amplicon were identified among the 637 isolates. Distribution and prevalence of VCGs and seq sequences among orchards indicated that genetic diversity within olive V. dahliae in Andalusia is higher in provinces where VCG1A is not prevalent. Log-linear analysis revealed that irrigation management, source of irrigation water, source of planting stock, and cropping history of soil were significantly associated with the prevalence of VCG1A compared with that of VCG2A. Multivariate analyses using a selected set of agricultural factors as variables allowed development of a discriminant model for predicting the occurrence of D and ND pathotypes in the area of the study. Blind tests using this model correctly indentified the V. dahliae pathotype occurring in an orchard. The widespread occurrence and high prevalence of VCG1A/D pathotype in Andalusia have strong implications for the management of the disease.

A sensitive nested-polymerase chain reaction (PCR) protocol was developed using either of two primer pairs that improves the in planta detection of Peronospora arborescens DNA. The new protocol represented an increase in sensitivity of 100- to 1,000-fold of detection of the oomycete in opium poppy tissue compared with the detection limit of single PCR using the same primer pairs. The new protocol allowed amplification of 5 to 0.5 fg of Peronospora arborescens DNA mixed with Papaver somniferum DNA. The protocol proved useful for amplifying Peronospora arborescens DNA from 96-year-old herbarium specimens of Papaver spp. and to demonstrate that asymptomatic, systemic infections by Peronospora arborescens can occur in wild Papaver spp. as well as in cultivated opium poppy. Also, the increase in sensitivity of the protocol made possible the detection of seedborne Peronospora arborescens in commercial opium poppy seed stocks in Spain with a high frequency, which poses a threat for pathogen spread. Direct sequencing of purified amplicons allowed alignment of a Peronospora arborescens internal transcribed spacer (ITS) ribosomal DNA (rDNA) sequence up to 730-bp long when combining the sequences obtained with the two primer sets. Maximum parsimony analysis of amplified Peronospora arborescens ITS rDNA sequences from specimens of Papaver dubium, P. hybridum, P. rhoeas, and P. somniferum from different countries indicated for the first time that a degree of host specificity may exist within populations of Peronospora arborescens. The reported protocol will be useful for epidemiological and biogeographical studies of downy mildew diseases as well as to unravel misclassification of Peronospora arborescens and Peronospora cristata, the reported causal agents of the opium poppy downy mildew disease.

Vascular pathogens are the causal agents of some of the most devastating plant diseases in the world, which can cause, under specific conditions, the destruction of entire crops. These plant pathogens activate a range of physiological and immune reactions in the host plant following infection, which may trigger the proliferation of a specific microbiome to combat them by, among others, inhibiting their growth and/or competing for space. Nowadays, it has been demonstrated that the plant microbiome can be modified by transplanting specific members of the microbiome, with exciting results for the control of plant diseases. However, its practical application in agriculture for the control of vascular plant pathogens is hampered by the limited knowledge of the plant endosphere, and, in particular, of the xylem niche. In this review, we present a comprehensive overview of how research on the plant microbiome has evolved during the last decades to unravel the factors and complex interactions that affect the associated microbial communities and their surrounding environment, focusing on the microbial communities inhabiting the xylem vessels of olive trees (Olea europaea subsp. europaea), the most ancient and important woody crop in the Mediterranean Basin. For that purpose, we have highlighted the role of xylem composition and its associated microorganisms in plants by describing the methodological approaches explored to study xylem microbiota, starting from the methods used to extract xylem microbial communities to their assessment by culture-dependent and next-generation sequencing approaches. Additionally, we have categorized some of the key biotic and abiotic factors, such as the host plant niche and genotype, the environment and the infection with vascular pathogens, that can be potential determinants to critically affect olive physiology and health status in a holobiont context (host and its associated organisms). Finally, we have outlined future directions and challenges for xylem microbiome studies based on the recent advances in molecular biology, focusing on metagenomics and culturomics, and bioinformatics network analysis. A better understanding of the xylem olive microbiome will contribute to facilitate the exploration and selection of specific keystone microorganisms that can live in close association with olives under a range of environmental/agronomic conditions. These microorganisms could be ideal targets for the design of microbial consortia that can be applied by endotherapy treatments to prevent or control diseases caused by vascular pathogens or modify the physiology and growth of olive trees. [ABSTRACT FROM AUTHOR]

Summary: Xylella fastidiosa is the causal agent of important crop diseases and is transmitted by xylem‐sap‐feeding insects. The bacterium colonizes xylem vessels and can persist with a commensal or pathogen lifestyle in more than 500 plant species. In the past decade, reports of X. fastidiosa across the globe have dramatically increased its known occurrence. This raises important questions: How does X. fastidiosa interact with the different host plants? How does the bacterium interact with the plant immune system? How does it influence the host's microbiome? We discuss recent strain genetic typing and plant transcriptome and microbiome analyses, which have advanced our understanding of factors that are important for X. fastidiosa plant infection. [ABSTRACT FROM AUTHOR]

Based on sequence data from ITS rDNA, cox1 and cox2, six Peronospora species are recognised as phylogenetically distinct on various Papaver species. The host ranges of the four already described species P. arborescens, P. argemones, P. cristata and P. meconopsidis are clarified. Based on sequence data and morphology, two new species, P. apula and P. somniferi, are described from Papaver apulum and P. somniferum, respectively. The second Peronospora species parasitizing Papaver somniferum, that was only recently recorded as Peronospora cristata from Tasmania, is shown to represent a distinct taxon, P. meconopsidis, originally described from Meconopsis cambrica. It is shown that P. meconopsidis on Papaver somniferum is also present and widespread in Europe and Asia, but has been overlooked due to confusion with P. somniferi and due to less prominent, localized disease symptoms. Oospores are reported for the first time for P. meconopsidis from Asian collections on Papaver somniferum. Morphological descriptions, illustrations and a key are provided for all described Peronospora species on Papaver. cox1 and cox2 sequence data are confirmed as equally good barcoding loci for reliable Peronospora species identification, whereas ITS rDNA does sometimes not resolve species boundaries. Molecular phylogenetic data reveal high host specificity of Peronospora on Papaver, which has the important phytopathological implication that wild Papaver spp. cannot play any role as primary inoculum source for downy mildew epidemics in cultivated opium poppy crops. [ABSTRACT FROM AUTHOR]

Background: Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris, a main threat to global chickpea production, is managed mainly by resistant cultivars whose efficiency is curtailed by Fusarium oxysporum f. sp. ciceris races. Methodology: We characterized compatible and incompatible interactions by assessing the spatial-temporal pattern of infection and colonization of chickpea cvs. P-2245, JG-62 and WR-315 by Fusarium oxysporum f. sp. ciceris races 0 and 5 labeled with ZsGreen fluorescent protein using confocal laser scanning microscopy. Findings: The two races colonized the host root surface in both interactions with preferential colonization of the root apex and subapical root zone. In compatible interactions, the pathogen grew intercellularly in the root cortex, reached the xylem, and progressed upwards in the stem xylem, being the rate and intensity of stem colonization directly related with the degree of compatibility among Fusarium oxysporum f. sp. ciceris races and chickpea cultivars. In incompatible interactions, race 0 invaded and colonized ‘JG-62’ xylem vessels of root and stem but in ‘WR-315’, it remained in the intercellular spaces of the root cortex failing to reach the xylem, whereas race 5 progressed up to the hypocotyl. However, all incompatible interactions were asymptomatic. Conclusions: The differential patterns of colonization of chickpea cultivars by Fusarium oxysporum f. sp. ciceris races may be related to the operation of multiple resistance mechanisms. [ABSTRACT FROM AUTHOR]

Incidence and nematode population densities of plant-parasitic nematodes were determined in 64 samples of soil and grapevine roots collected from commercial vineyards in southern Spain between October 2003 and May 2005. In addition, a histopathological study was done of root- stock roots naturally infected by root-knot nematodes (Meloidogyne spp.). Nematodes infecting the rootstocks were identified according to conventional procedures, and the Meloidogyne spp. were furthermore identified by sequence characterized amplified region-polymerase chain reaction (SCAR-PCR) and isozyme esterase analyses. The most important plant-parasitic nematodes detected, in order of decreasing frequency of total soil infestation and root infection (percentage of samples), were Mesocriconema xenoplax (34.4%), Meloidogyne incognita (26.6%), Meloidogyne javanica (14.1%), Xiphinema index (12.5%), Xiphinema italiae (10.9%), Pratylenchus vulnus (6.3%), and Meloidogyne arenaria (1.6%). No disease symptoms were observed on aboveground plant parts of the infected grapevines, except for plants in some fields where soil was infested with the virus-vector nematodes X. index and X. italiae. Those grapevines showed a yellow mosaic pattern in leaves early in the growing season and the internode shortening characteristic of infections by Grapevine fanleaf virus. Rootstocks infected by root-knot nematodes (Meloidogyne spp.) showed distorted feeder roots and large- to moderate-sized root galls, present either singly or in clusters. Histopathology of galled roots showed a typical susceptible response to infection by root-knot nematodes: cellular alterations were induced in the cortex, endodermis, pericycle, and vascular system, including giant-cell formation and severe distortion of vascular tissues. Most Meloidogyne egg masses occurred on the surface of the galled root tissues, a position that could facilitate dispersion of the nematode eggs and juveniles and the occurrence of secondary infections. Some of the grapevine rootstocks surveyed in this study (Paulsen 1103, Richter 110, Rupestris du Lot, and SO4) had previously been reported to be resistant to Meloidogyne spp.; however, the population densities of these nematodes found in soil and roots sampled in the present study, as well as the compatible host-parasite relationship revealed by histopathology, indicate a susceptible response to Meloidogyne spp. from southern Spain. [ABSTRACT FROM AUTHOR]

Races 0 (Foc-0) and 5 (Foc-5) of Fusarium oxysporum f. sp. ciceris differ in virulence and induce yellowing or wilting syndrome, respectively, in chickpea. We modeled the combined effects of soil temperature and inoculum density of Foc-0 and Foc-5 on disease developed in chickpea cvs. P-2245 and PV-61 differing in susceptibility to those races, using quantitative nonlinear models. Disease development over time in the temperature range of 10 to 30°C and inoculum densities between 6 and 8,000 chlamydospores g-1 of soil was described by the Weibull function. Four response variables (the reciprocal incubation period, the final disease intensity, the standardized area under the disease progress curve, and the intrinsic rate of disease development) characterized the disease development. Response surface models that expressed the combined effect of inoculum density and temperature were developed by substituting the intrinsic rate of disease development in the Weibull or exponential functions with a beta function describing the relationship of response variables to temperature. The models estimated 22 to 26°C as the most favorable soil temperature for infection of cvs. P-2245 and PV- 61 by Foc-5, and 24 to 28°C for infection of cv. P-2245 by Foc-0. At 10°C, no disease developed except in cv. P-2245 inoculated with Foc-5. At optimum soil temperature, maximum disease intensity developed with Foc-5 and Foc-0 at 6 and 50 chlamydospores g-1 of soil respectively, in cv. P-2245, and with Foc-5 at 1,000 chlamydospores g-1 of soil in cv. PV- 61. The models were used to construct risk threshold charts that can be used to estimate the potential risk of Fusarium wilt epidemics in a geographical area based on soil temperature, the race and inoculum density in soil, and the level of susceptibility of the chickpea cultivar. [ABSTRACT FROM AUTHOR]

Use of resistant cultivars and adjustment of sowing dates are important measures for management of Fusarium wilt in chickpeas (Cicer arietinum). In this study, we examined the effect of temperature on resistance of chickpea cultivars to Fusarium wilt caused by various races of Fusarium oxysporum f. sp. ciceris. Greenhouse experiments indicated that the chickpea cultivar Ayala was moderately resistant to F. oxysporum f. sp. ciceris when inoculated plants were maintained at a day/night temperature regime of 24/21°C but was highly susceptible to the pathogen at 27/25°C. Field experiments in Israel over three consecutive years indicated that the high level of resistance of Ayala to Fusarium wilt when sown in mid- to late January differed from a moderately susceptible reaction under warmer temperatures when sowing was delayed to late February or early March. Experiments in growth chambers showed that a temperature increase of 3°C from 24 to 27°C was sufficient for the resistance reaction of cultivars Ayala and PV-1 to race 1A of the pathogen to shift from moderately or highly resistant at constant 24°C to highly susceptible at 27°C. A similar but less pronounced effect was found when Ayala plants were inoculated with E oxysporum f. sp. ciceris race 6. Conversely, the reaction of cultivar JG-62 to races 1A and 6 was not influenced by temperature, but less disease developed on JG-62 plants inoculated with a variant of race 5 of F. oxysporum f. sp. ciceris at 27°C compared with plants inoculated at 24°C. These results indicate the importance of appropriate adjustment of temperature in tests for characterizing the resistance reactions of chickpea cultivars to the pathogen, as well as when determining the races of isolates of E oxysporum f. sp. ciceris. Results from this study may influence choice of sowing date and use of chickpea cultivars for management of Fusarium wilt of chickpea. [ABSTRACT FROM AUTHOR]

The article offers information on the 15th Congress of the Mediterranean Phytopathological Union, which will held in Córdoba (Spain), from June 20–23, 2017 to promote dissemination of latest plant pathology knowledge.

The article focuses on the presence of plant-parasitic nematodes in the roots and rhizosphere of chickpea in the major growing regions in the world. However, only certain nematode species are considered constraints to chickpea producing, causing an estimated 14% in annual yield losses. The symptoms and signs of nematode parasitism on chickpea differ depending on the nematode's feeding habit. Symptoms caused by nematode attack are nonspecific and nondescript, and they are largely a consequence of disruption of normal processes of plant growth, and absorption and translocation of water and nutrients.

Abstract: The proper identification and quantification of F. oxysporum populations inhabiting soil and plant rhizosphere niches are of importance for soil microbial ecology and plant pathology. In this study, we report the improvement of a PCR protocol for the specific identification of the F. oxysporum species complex and its conversion into a real-time qPCR assay for the quantification up to 1pg of the fungus DNA in soil and different plant tissues. The amplification efficiency, sensibility and reproducibility of qPCR assays were not influenced by presence of non-target DNA from either plant or soil. The applicability of the newly developed qPCR protocol for F. oxysporum population studies was demonstrated using the technique for quantifying the fungus in different complex environmental samples. The use of the qPCR protocol allowed to accurately quantify up to 25pg of F. oxysporum/g of naturally infested field soil, as well as to identify significant differences in the amount of F. oxysporum DNA in roots of different chickpea cultivars grown in a field soil infested with diverse pathogenic and nonpathogenic F. oxysporum populations. This qPCR protocol may be especially important for studies on soil microbial ecology and plant pathology since it provides a new opportunity for analyzing F. oxysporum populations and their interactions with the soil microflora, environment and plant host genotypes. [ABSTRACT FROM AUTHOR]