Multilocus sequence analysis of xanthomonads causing bacterial spot of tomato and pepper plants reveals strains generated by recombination among species and recent global spread of Xanthomonas gardneri

Four Xanthomonas species are known to cause bacterial spot of tomato and pepper, but the global distribution and genetic diversity of these species are not well understood. A collection of bacterial spot-causing strains from the Americas, Africa, Southeast Asia, and New Zealand were characterized for genetic diversity and phylogenetic relationships using multilocus sequence analysis of six housekeeping genes. By examining strains from different continents, we found unexpected phylogeographic patterns, including the global distribution of a single multilocus haplotype of X. gardneri, possible regional differentiation in X. vesicatoria, and high species diversity on tomato in Africa. In addition, we found evidence of multiple recombination events between X. euvesicatoria and X. perforans. Our results indicate that there have been shifts in the species composition of bacterial spot pathogen populations due to the global spread of dominant genotypes and that recombination between species has generated genetic diversity in these populations. (Résumé d'auteur

Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity

Citation: Schwartz, A. R., Potnist, N., Milsina, S., Wilson, M., Patane, J., Martins, J., . . . Staskawicz, B. J. (2015). Phylogenomics of Xanthomonas field strains infecting pepper and tomato reveals diversity in effector repertoires and identifies determinants of host specificity. Frontiers in Microbiology, 6, 17. https://doi.org/10.3389/fmicb.2015.00535Bacterial spot disease of pepper and tomato is caused by four distinct Xanthomonas species and is a severely limiting factor on fruit yield in these crops. The genetic diversity and the type Ill effector repertoires of a large sampling of field strains for this disease have yet to be explored on a genomic scale, limiting our understanding of pathogen evolution in an agricultural setting. Genomes of 67 Xanthomonas euvesicatoria (Xe), Xanthomonas perforans (Xp), and Xanthomonas gardneri (Kg) strains isolated from diseased pepper and tomato fields in the southeastern and midwestern United States were sequenced in order to determine the genetic diversity in field strains. Type Ill effector repertoires were computationally predicted for each strain, and multiple methods of constructing phylogenies were employed to understand better the genetic relationship of strains in the collection. A division in the Xp population was detected based on core genome phylogeny, supporting a model whereby the host-range expansion of Xp field strains on pepper is due, in part, to a loss of the effector AvrBsT. Xp-host compatibility was further studied with the observation that a double deletion of AvrBsT and XopQ allows a host range expansion for Nicotiana benthamiana. Extensive sampling of field strains and an improved understanding of effector content will aid in efforts to design disease resistance strategies targeted against highly conserved core effectors.Additional Authors: Goss, E.;Bart, R. S.;Setubal, J. C.;Jones, J. B.;Staskawicz, B. J

Immigrants and Native Workers: An Analysis of the Long Run Impact of Immigrants on Native Workers

In this study I examine how new labor market entrants affect employment, poverty, and income and how this varies for different subcategories of the population within Combined Statistical Areas (CSAs) and metropolitan and micropolitan statistical areas not within a CSA. These subcategories are sorted by nativity and education level and I specifically look at how foreign born workers impact native workers. The effect can be measured by looking at the changes in population for high-skilled/low-skilled natives and migrants and comparing this to the changes in the number of persons employed, unemployed, in poverty, out of poverty, etc. The time period for the population change is adjusted relative to the time period for the employment change to look at the short run and long run effects of immigration. I use the initial population size for each subgroup as a control. My data source is the American Community Survey from the United States Census Bureau. I find that most of the effect that immigrants have on native workers is negative, however these effects are very minimal for an increase in the low-skilled immigrant population. An increase in the high-skilled immigrant population has a larger negative effect on native workers than an increase in the low-skilled immigrant population. An increase in the native population has the greatest negative impact on native workers

Prospects for plant defence activators and biocontrol in IPM - Concepts and lessons learnt so far

There is an urgent need to develop new interventions to manage pests because evolution of pesticide resistance and changes in legislation are limiting conventional control options for farmers. We investigated β-aminobutyric acid (BABA), jasmonic acid (JA) and fructose as possible plant defence activators against grey mould disease, . Botrytis cinerea, and root knot nematode, . Meloidogyne incognita. We also tested . Trichogramma achaeae parasitoid wasps and an antifeedant plant extract for biocontrol of the invasive tomato leafminer, . Tuta absoluta. BABA and JA enhanced resistance of tomato plants to . B. cinerea but neither treatment provided complete protection and the efficacy of treatment varied over time with BABA being more durable than JA. Efficacy was partly dependent on tomato cultivar, with some cultivars responding better to BABA treatment than others. Furthermore, treatment of tomato with BABA, JA and fructose led to partial suppression of . M. incognita egg mass development. Biocontrol agent, . T. achaeae, performance against . T. absoluta could be enhanced by adjusting the rearing conditions. Both attack rate and longevity were improved by rearing the parasitoids on . T. absoluta rather than on other insects. Finally, . Ajuga chamaepitys extract was shown to have significant antifeedant activity against . T. absoluta. Our findings suggest that there are potential new solutions for protection of crops but they are more complicated to deploy, more variable and require more biological knowledge than conventional pesticides. In isolation, they may not provide the same level of protection as pesticides but are likely to be more potent when deployed in combination in IPM strategies

Enhanced Botrytis cinerea resistance of Arabidopsis plants grown in compost may be explained by increased expression of defense-related genes, as revealed by microarray analysis

Composts are the products obtained after the aerobic degradation of different types of organic matter waste and can be used as substrates or substrate/soil amendments for plant cultivation. There is a small but increasing number of reports that suggest that foliar diseases may be reduced when using compost, rather than standard substrates, as growing medium. The purpose of this study was to examine the gene expression alteration produced by the compost to gain knowledge of the mechanisms involved in compost-induced systemic resistance. A compost from olive marc and olive tree leaves was able to induce resistance against Botrytis cinerea in Arabidopsis, unlike the standard substrate, perlite. Microarray analyses revealed that 178 genes were differently expressed, with a fold change cut-off of 1, of which 155 were up-regulated and 23 were down-regulated in compost-grown, as against perlite-grown plants. A functional enrichment study of up-regulated genes revealed that 38 Gene Ontology terms were significantly enriched. Response to stress, biotic stimulus, other organism, bacterium, fungus, chemical and abiotic stimulus, SA and ABA stimulus, oxidative stress, water, temperature and cold were significantly enriched, as were immune and defense responses, systemic acquired resistance, secondary metabolic process and oxireductase activity. Interestingly, PR1 expression, which was equally enhanced by growing the plants in compost and by B. cinerea inoculation, was further boosted in compost-grown pathogen-inoculated plants. Compost triggered a plant response that shares similarities with both systemic acquired resistance and ABA-dependent/independent abiotic stress responses

Diversity, Pathogenicity, and Management of Verticillium Species

The genus Verticillium encompasses phytopathogenic species that cause vascular wilts of plants. In this review, we focus on Verticillium dahliae, placing emphasis on the controversy surrounding the elevation of a long-spored variant as a new species, recent advances in the analysis of compatible and incompatible interactions, highlighted by the use of strains expressing fluorescent proteins, and the genetic diversity among Verticillium spp. A synthesis of the approaches to explore genetic diversity, gene flow, and the potential for cryptic recombination is provided. Control of Verticillium wilt has relied on a panoply of chemical and nonchemical strategies, but is beset with environmental or site-specific efficacy problems. Host resistance remains the most logical choice, but is unavailable in most crops. The genetic basis of resistance to Verticillium wilt is unknown in most crops, as are the subcellular signaling mechanisms associated with Ve-mediated, race-specific resistance. Increased understanding in each of these areas promises to facilitate management of Verticillium wilts across a broad range of crops

Translating cropland and trade connectivity for mitigation of emerging pathogens: Priority locations globally and focusing on the Americas

Analyses of crop-specific cropland and trade network structures provide a first step for guiding strategies to manage emerging crop pathogens, for iterative improvement as more detailed data become available. We analyzed global to regional cropland and trade networks for the potential spread of emerging pathogens in twelve crops key to food sustainability. We identified which locations have high cropland connectivity globally, and in a more detailed analysis for Central America. A location with high cropland connectivity is more likely to have an important role in epidemics, and so is a candidate for prioritizing mitigation. In epidemic scenario analyses to evaluate relative risk for each crop, we identified countries in the Americas with cropland patterns more likely to result in high levels of pathogen establishment, and so more likely to need focused attention to manage invasions. Country-specific trade networks indicate how invasion risk varies among crops and pathogens, and which components of the network merit particular phytosanitary attention. Using these maps of risk for planning in advance can inform phytosanitary strategies globally, regionally, and within countries, for an efficient response to epidemic invasion. Integrating cropland and trade connectivity with other geographic factors - such as weather conduciveness, management landscapes, regional transportation, local trade, and international phytosanitary networks, will strengthen pest risk assessment and mitigation

Elementos traço e parasitismo em tilápia do nilo cultivada no sul do Brasil

This study evaluated the trace elements and parasitological indices in Nile tilapia examined from two different facilities, named as swine-consorted, using pig manure, and monoculture. For trace element analysis, the fish muscle tissue was collected individually in each facility. Each portion was weighed, dried in a stove at 60°C for 48 h and analyzed by Energy Dispersive X-ray Fluorescence Spectrometry (EDXRF). Parasitological analysis followed the routine method for parasites collection, quantification and identification. The predominant element was zinc (Zn) followed by iron (Fe) and arsenic (As) in fish from both facilities. Fish from swine-consorted system had greater values of abundance and mean intensity of trichodinids and fish from monoculture showed higher abundance and mean intensity of monogeneans. Nevertheless, no signs of damage to fish production was observed. The contents of the elements Zn, Fe, As, cooper (Cu) and mercury (Hg) were above of the maximum permitted limits recommended by the Brazilian legislation. © 2016, Instytut Technologii Drewna. All rights reserved