Aggressiveness of Spanish Isolates of Xylella fastidiosa to Almond Plants of Different Cultivars Under Greenhouse Conditions.

Most studies of marine bacterial communities focus on functional attributes of the community, rather than on population or community structure, at least in part, because of the difficulty in enumerating individual species within complex communities. Here, we describe a study in which populations of three bacterial species were followed over time in replicate marine enrichment cultures using 16S rRNA-based oligonucleotide probes. Three identical enrichment microcosms were established with lignin-rich pulp mill waste as a sole carbon source, inoculated with coastal seawater, and transferred at two-week intervals. Population levels were assessed throughout a six-week period using species-specific 16S rRNA-based oligonucleotide probes directed toward three bacterial species that were numerically important (and culturable) members of the enrichments. Substantial differences in the population levels of each bacterial species were found among the triplicate incubations, despite the fact that the enrichments were inoculated and treated identically. Stochastic differences in the composition of the inoculum and/or ecological interactions within the enrichment replicates may have been important in determining final population levels. Functional ability, assessed as rates of degradation of a synthetic lignin preparation, were fairly similar among the three replicate enrichments (within 70%), despite the substantial differences in population levels of the representative lignin-degrading species.

In the Schnabel method of estimating number of animals, the number of recaptures has been assumed to follow a Poisson distribution. This approximation is useful in testing differences in population levels when the Schnabel method is used for estimation, since the distribution of recaptures from one population, conditional on the total number of recaptures from both populations, is approximately binomial with parameters n and p, where p is a function of the parameters of the two Poisson distributions. Tests based on this conditional binomial distribution are described. Confidence limits of the population numbers have been considered and a stop rule developed for the Schnabel experiment used at the second stage of a paired comparison. The Schnabel method (Schnabel 1938) of estimating numbers of animals from tagrecapture data is widely used in fish and game population studies. This method is popular because (1) computations are simple, (2) daily estimates are a feature of this method, enabling the field worker to see his results as the work progresses, and (3) the method is flexible and can reasonably be expected to provide useful results over a wide range of capture conditions. However, there is some hesitancy about using the Schnabel method, since the variances of these estimates are difficult to estimate. In addition, it has not been made clear whether tests of differences between estimated populations can safely be based on such estimates of variance, as is also true for confidence intervals about an estimate. Simple straightforward tests of differences in population level, as well as confidence limits for the population estimate, are possible by using the knowledge that the number recaptured has approximately a Poisson distribution (Chapman 1954). To estimate population size by the Schnabel method, let x x-= number of recaptures, (1) A(n,M,), (2) 1=1

Parasitoids of Aonidiella aurantii (Maskell) on citrus in South Africa were monitored using two types of yellow sticky trap. One of these traps was highly efficient, being fluorescent with peak reflectance at about 530 nm. Aphytis spp. populations were low before February and high thereafter. Citrus surrounded by natural bush was an isolated reservoir of high host and parasitoid population levels. Aphytis spatial distribution within the orchard was extremely patchy, with over 100-fold differences in population levels over a distance of a few metres. This patchiness mirrored that of its host. This contagious spatial pattern was maintained despite 1000-fold seasonal changes in population levels. These temporal changes were characteristic and general throughout an orchard, and independent of patchiness. Initial Aphytis population levels did not dictate the final population level at the end of the season. Comperiella bifasciata Howard and its hyperparasitoid Marietta javensis (Howard) also showed clear seasonal population trends, but not of the same magnitude as those of Aphytis. There was no statistically significant correlation between the spatial distribution of one parasitoid with that of another, even between C. bifasciata and M. javensis. The patchiness of these two species was not correlated with overall host density. Aphytis and C. bifasciata were partially mutually exclusive. Aphytis was by far the most economically important of the parasitoids. Pest management practices, therefore, should aim at conserving the pool of Aphytis within the orchard as far as practicable.

Chapter 1 - Overview

Pierce's disease of grapevine (PD), caused by the bacterial pathogen Xylella fastidiosa, remains a serious problem for grape production in California and elsewhere. This research examined induction of phenolic compounds in grapevines ('Thompson Seedless') infected with X. fastidiosa over a 6-month period. Two months postinoculation with X. fastidiosa, catechin, digalloylquinic acid, and astringin were found at greater levels in xylem sap; multiple catechins, procyanidins, and stilbenoids were found at greater levels in xylem tissues; and precursors to lignin and condensed tannins were found at greater levels in xylem cell walls. However, such large-scale inductions of phenolic compounds were not observed 4 months after inoculation. Six months after inoculation, infected plants had significantly reduced phenolic levels in xylem sap and tissues when compared with control plants, including lowered levels of lignin and condensed tannins. At 6 months, PD symptoms were severe in infected plants and most photosynthetic tissue was abscised. These results suggest that, even though grapevine hosts may initially respond to X. fastidiosa infections with increased production of phenolic compounds, ultimately, PD causes grapevines to enter a state of decline whereby diseased hosts no longer have the resources to support secondary metabolite production, including defense-associated phenolic compounds.

Xylella fastidiosa is a plant pathogenic bacterium that has been introduced in the European Union (EU), causing significant yield losses in economically important Mediterranean crops. Almond leaf scorch (ALS) is currently one of the most relevant diseases observed in Spain, and no cure has been found to be effective for this disease. In previous reports, the peptide BP178 has shown a strong bactericidal activity invitro against X. fastidiosa and to other plant pathogens, and to trigger defense responses in tomato plants. In the present work, BP178 was applied by endotherapy to almond plants of cultivar Avijor using preventive and curative strategies. The capacity of BP178 to reduce the population levels of X. fastidiosa and to decrease disease symptoms and its persistence over time were demonstrated under greenhouse conditions. The most effective treatment consisted of a combination of preventive and curative applications, and the peptide was detected in the stem up to 60 days posttreatment. Priming plants with BP178 induced defense responses mainly through the salicylic acid pathway, but also overexpressed some genes of the jasmonic acid and ethylene pathways. It is concluded that the bifunctional peptide is a promising candidate to be further developed to manage ALS caused by X. fastidiosa.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Sex-attractant traps were used to monitor the relative abundances of eight species of cutworm and army worm moths at 81 locations in a 13 000-km2 (5000-mi2) area of southern Alberta from 1978 to 1983. Clover cutworm (Discestra trifolii (Hufn.)), variegated cutworm (Peridroma saucia (Hbn.)), bertha armyworm (Mamestra configurata Wlk.), and Leucania commoides Gn. were monitored during spring and early summer, and redbacked cutworm (Euxoa ochrogaster (Gn.)), darksided cutworm (Euxoa messoria (Harr.)), pale western cutworm (Agrotis orthogonia Morr.), and army cutworm (Euxoa auxiliaris (Grt.)) during late summer and fall.The ranking of moth catches among locations within years was highly consistent, indicating that the spatial pattern of abundance within the survey area remained stable during each flight period. The corollary is that differences in population levels among locations were being consistently detected. Most of the species also exhibited a considerable degree of consistency of pattern of abundance between consecutive years and to some extent over all years.Estimates of the variability associated with individual traps, between duplicate traps, and among locations were obtained for each species. The within-location variability was always much less than the among-location variability, indicating that a meaningful measure of the relative population level at each location was being obtained. When abundance levels approached economic thresholds the likelihood of moth catches in duplicate traps being within 20% of the mean catch for a location was usually greater than 80%. Year-to-year differences in mean trap catches were frequently significant at the 95% confidence level and the monitoring system could detect relatively small changes in population level between years. Season cumulative trap catches are a composite measure of abundance and the mate-searching activity of males. Weather conditions that restrict male activity are also likely to reduce oviposition by females. Cumulative trap catches may therefore be closely correlated with realized fecundity.

The Pythium flora of 38 soils from different sections of the West Bank and Gaza Strip was determined using a selective agar medium and a surface - soil - dilution plating technique. A total of 23 species were recovered. Sixteen of these species possessed subglobose sporangia and/or hyphal swellings and constituted 92 % of the total number of Pythium propagules. The remaining species had filamentous or lobulate sporangia. Considerable differences in population levels in the different localities were found. The Nablus locality harboured the highest mean level of Pythium propagules followed by the localities in Jenin, Bethlehem, Jericho, Tulkarm, Ramallah, Gaza Strip, and Hebron. Solis in the different localities differed also in population levels and composition of species. Associations between Pythium population levels and soil factors and agricultural practices are discussed.

Xylella fastidiosa infects a wide range of plant hosts and causes Pierce's disease (PD) of grapevines. The type 1 multidrug resistance (MDR) efflux system is essential for pathogenicity and survival of bacterial pathogens in planta. X. fastidiosa, with a single MDR system, is significantly more vulnerable to inhibition by small-molecule treatments than most bacterial pathogens that typically carry redundant MDR systems. A high-throughput cell viability assay using a green fluorescent protein-marked strain of X. fastidiosa Temecula 1 was developed to screen two Prestwick combinatorial small-molecule libraries of drugs and phytochemicals (1,600 chemicals in total) approved by the Food and Drug Administration and European Medicines Agency for cell growth inhibition. The screens revealed 215 chemicals that inhibited bacterial growth by >50% at 50 µM concentrations. Seven chemicals proved to lyse X. fastidiosa cells at 25 µM, including four phytochemicals. Menadione (2-methyl-1,4-naphthoquinone, vitamin K) from the phytochemical library and benzethonium chloride (a topical disinfectant) from the chemical library both showed significant bactericidal activity against X. fastidiosa. Both menadione and benzethonium chloride foliar spray (15 and 5 mM, respectively) and soil drench (5 and 25 mM, respectively) treatments were equally effective in reducing PD symptoms by 54 to 59% and revealed that the effects of both chemical treatments became systemic. However, menadione was phytotoxic when applied as a foliar spray at effective concentrations, causing significant loss of photosynthetic capacity.

BackgroundThe recent Xylella fastidiosa subsp. pauca (Xfp) outbreak in olive (Olea europaea) groves in southern Italy is causing a destructive disease denoted Olive Quick Decline Syndrome (OQDS). Field observations disclosed that Xfp-infected plants of cv. Leccino show much milder symptoms, than the more widely grown and highly susceptible cv. Ogliarola salentina. To determine whether these field observations underlie a tolerant condition of cv. Leccino, which could be exploited for lessening the economic impact of the disease on the local olive industry, transcriptional changes occurring in plants of the two cultivars affected by Xfp were investigated.ResultsA global quantitative transcriptome profiling comparing susceptible (Ogliarola salentina) and tolerant (Leccino) olive cultivars, infected or not by Xfp, was done on messenger RNA (mRNAs) extracted from xylem tissues. The study revealed that 659 and 447 genes were differentially regulated in cvs Leccino and Ogliarola upon Xfp infection, respectively, whereas 512 genes were altered when the transcriptome of both infected cultivars was compared. Analysis of these differentially expressed genes (DEGs) shows that the presence of Xfp is perceived by the plants of both cultivars, in which it triggers a differential response strongly involving the cell wall. Up-regulation of genes encoding receptor-like kinases (RLK) and receptor-like proteins (RLP) is the predominant response of cv. Leccino, which is missing in cv. Ogliarola salentina. Moreover, both cultivars react with a strong re-modelling of cell wall proteins. These data suggest that Xfp elicits a different transcriptome response in the two cultivars, which determines a lower pathogen concentration in cv. Leccino and indicates that this cultivar may harbor genetic constituents and/or regulatory elements which counteract Xfp infection.ConclusionsCollectively these findings suggest that cv. Leccino is endowed with an intrinsic tolerance to Xfp, which makes it eligible for further studies aiming at investigating molecular basis and pathways modulating its different defense response.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2833-9) contains supplementary material, which is available to authorized users.

In the last decade or so several studies have looked into the impacts of transport infrastructure improvements on decreasing territorial disparities. In those studies population levels are usually assumed static, although future population levels likely change in response to changing accessibility levels as well as to other factors. To test how much accessibility impacts may be affected by changes in population levels, this study explores the effects of foreseeable population changes on the accessibility improvements offered by large scale transport infrastructure investments. In this study we compare accessibility measures from four cases, namely the current situation; one case in which only transport investments are taken into account; and two cases that include transport investments and two scenarios with differing future population distributions that in turn are simulated by the LUISA land-use model. The modelled transport investments are assumed to improve travel times. The study concentrates on accessibility effects in Austria, Czech Republic, Germany and Poland. To provide a reference to the found results, the same computations are repeated with historical population and road network changes. The results indicate that differences in local population levels have a limited effect on average accessibility levels, but may have a large impact on territorial inequalities related to accessibility. The findings in this study underpin the importance of incorporating future local population levels when assessing the impacts of infrastructure investments on territorial disparities.

The aggressiveness of seventeen X. fastidiosa strains, representing different subspecies and sequence types (STs), was studied in the surrogated host N. benthamiana by the analysis of the population levels and symptoms dynamics, dose-response relationships and the transcriptomic response of the plant. Colonization of all strains was observed after 7 days post inoculation (dpi), and the first symptoms appeared after 14 dpi. Differences in patterns of population dynamics and symptoms development were observed between strains and there was neither a relationship between population growth and symptoms severity, nor between strains of the same subspecies and STs. Strains IVIA 5387, DeDonno, CN28 and GP18 showed a typical S-shaped dose-effect curve, and the minimum infective dose in N. benthamiana was established at 300 UFC/plant for all strains. The plant response to the infection by the subsp. pauca ST53 strains DeDonno, CN28 and GP18 was studied in relation to the expression of defense genes. A strain-dependent modulation depending on time was observed, where CN28 infection showed the highest gene overexpression (12 out of 19 genes), and DeDonno the lowest (8 of 19 genes). At 4 dpi, all strains upregulated the genes PR1, PR1a and ERF1 and downregulated the PDF1.2 gene, while at 30 dpi most of the genes were downregulated, especially the pathogenesis related (PR) genes, suggesting an immune evasion by the pathogen. Our findings are expected to provide valuable insights into the interaction between X. fastidiosa and its hosts, highlighting the importance of considering differences in aggressiveness among strains and in plant response.

In 2017, Xylella fastidiosa, a quarantine plant-pathogenic bacterium in Europe, was detected in almond trees associated with leaf scorch symptoms in Alicante, a Mediterranean area in southeastern mainland Spain. The bacterium was detected by serological and molecular techniques, isolated in axenic culture from diseased almond trees, and identified as X. fastidiosa subsp. multiplex sequence type (ST) 6. Inoculation experiments on almond plants in greenhouse trials with a characterized strain of X. fastidiosa subsp. multiplex ST6 isolated in the outbreak area have proved that it was able to multiply and systemically colonize inoculated plants. Disease symptoms characteristic of leaf scorch like those observed in the field were observed in the inoculated almond trees after 1 year. Furthermore, the pathogen was reisolated and identified by molecular tests. With the fulfillment of Koch's postulates, we have demonstrated that X. fastidiosa is the causal agent of the almond leaf scorch disease in the Alicante outbreak.

The activity of Eucalyptus essential oil against eleven strains pertaining to six species of plant pathogenic bacteria was studied using growth inhibition and contact assays. All strains were susceptible to the formulation EGL2, and Xylella fastidiosa subspecies and Xanthomonas fragariae were the most sensitive. The bactericidal effect was strong causing 4.5 to 6.0 log reductions in survival in 30 min at concentrations in the range of 0.75 to 15.0 μl/ml depending on the bacteria tested. Transmission electron microscopy of the formulation EGL2 against the three X. fastidiosa subspecies studied allowed the observation of a strong lytic effect on bacterial cells. In addition, the preventive spray application of EGL2 to potted pear plants subsequently inoculated with Erwinia amylovora significantly decreased the severity of infections. Almond plants treated by endotherapy or soil drenching, and then inoculated with X. fastidiosa showed a significant decrease in disease severity as well as in the levels of the pathogen, depending on the strategy used (endotherapy/soil drenching, preventive/curative). The treatment by endotherapy in almond plants induced the expression of several genes involved in plant defense. It was concluded that the reduction of infections by the Eucalyptus oil treatments was due to the combination of its bactericidal and plant defense induction activities.

Sweetgum dieback and leaf scorch of purple-leafed plum are two new diseases of southern California landscape ornamentals. Samplings were conducted in 2003 and 2004 and 28 of 105 sweetgum (Liquidambar styraciflua) and 38 of 62 purple-leafed plum (Prunus cerasifera) plants tested positive for Xylella fastidiosa by enzyme linked immunosorbent assay. In all, 3 strains of X. fastidiosa were isolated from sweetgum and 13 from purple-leafed plum. All sweetgum strains and some purple-leafed plum strains grew on PW but not PD3 media. Strain PC045 from purple-leafed plum and strain LS022 from sweetgum were inoculated into their original hosts in addition to almond, oleander, and grapevine plants. Sweetgum plants also were inoculated with strains causing Pierce's disease, almond leaf scorch, and oleander leaf scorch. Strain PC045 caused symptoms in purple-leafed plum and almond plants within 6 months, and the pathogen was recovered from 93 and 100% of inoculated plants, respectively. Inoculation of grapevine and oleander plants with PC045 did not result in disease or recovery of the pathogen. In all, 5 of 25 sweetgum plants inoculated with LS022 showed symptoms after 9 months, and the pathogen was recovered from 3 of these plants. Inoculation of grapevine, oleander, and almond with LS022 resulted in no disease or recovery of the pathogen from the plants. A strain of Pierce's disease, a strain of oleander leaf scorch, and two strains from almond did not cause disease in sweetgum. These results confirm the role of X. fastidiosa strains as pathogens of purple-leafed plum and sweetgum, and that strains from sweetgum are unique in their host range.