186 research outputs found
Application of a non-invasive, non-destructive technique to quantify naphthalene emission rates from museum objects
For the last 30 years, the cultural heritage sector has undertaken research into pesticide residues in museum objects.
However, quantitative studies of volatile residues remain scarce. This research presents an active air sampling methâ
odology to obtain qualitative and quantitative data for naphthalene as the most common pesticide found in the
sampled objects. The sampling procedure comprises of placing contaminated objects inside a sampling chamber
ftted with a sorbent tube flled with TENAX, then connected via tubing to a calibrated sampling pump. The sample
is desorbed and analysed using automated thermal desorption (ATD) paired with gas chromatography-mass specâ
trometry (GCMS). The obtained information allows the calculation of emission rates and modelling of emissions in
common museum situations such as inside a box, cabinet or display case. This information informs decision-making
regarding ventilation in storage areas and health and safety implications for museum professionals and other stakeâ
holders coming in contact with objects
DiseĂąo de una nueva crepina para reducir la caida de presiĂłn en filtros de arena
La filtraciĂłn es necesaria para evitar la obturaciĂłn de los emisores, que es el principal problema del riego por goteo. Sin embargo, los filtros necesitan presiones elevadas que estĂĄn relacionadas con un mayor consumo energĂŠtico. Estudios anteriores han mostrado que la caĂda de presiĂłn en los filtros de arena, considerados como los estĂĄndares en riego por goteo, se localiza principalmente en el drenaje. El principal objetivo del trabajo fue diseĂąar un nuevo modelo de crepina que redujera la caĂda de presiĂłn en el filtro. Esta nueva crepina tiene mayores pasajes a la salida del drenaje, estĂĄ rodeada con un medio granular de mayor conductividad hidrĂĄulica y modifica la curvatura del flujo por encima de la crepina. La nueva crepina fue construida y ensayada en condiciones de filtrado y contralavado, con y sin medio filtrante, en un filtro de laboratorio escalado a partir de un filtro comercial. Esta nueva crepina redujo considerablemente la caĂda de presiĂłn con respecto el diseĂąo comercial. Se desarrollĂł tambiĂŠn un modelo CFD para analizar con detalle las zonas donde se consigue la reducciĂłn observada.Filtration is mandatory for preventing emitter clogging, which is the main drawback of microirrigation. However, microirrigation filters have high pressure requirements, which in turn are related to higher energy consumption. Previous studies have shown that pressure loss in sand media filters, which are usually considered the standard for microirrigation, are mainly located in the filter underdrain. The main objective was to design a new underdrain that could reduce sand media filter pressure drop. The new underdrain has wider passages to the underdrain outlet, is surrounded with a granular medium with higher hydraulic conductivity and it modifies the flow curvature above the underdrain. The new underdrain was built and tested under filtration and backwashing conditions and with and without filter bed using a laboratory filter which was scaled from a commercial filter. The new underdrain considerably reduced pressure loss compared with a commercial filter. A CFD model was developed for further study those filter areas where the underdrain achieved a higher reduction of pressure drop
Optimization of Pathogenicity Tests for Selection of Native Isolates of Entomopathogenic Fungi Isolated from Citrusgrowing Areas of MĂŠxico on Adults ofDiaphorina citriKuwayama (Hemiptera: Liviidae)
Huanglonbing (HLB), es considerado una de las mĂĄs letales enfermedades de los cĂtricos alrededor del mundo, y ha alcanzado las principales ĂĄreas de producciĂłn de limĂłn Mexicano (Citrus latifolia Tanaka) en la costa del pacifico de MĂŠxico. Los productores han iniciado el uso de insecticidas para controlar las poblaciones del psĂlido asiĂĄtico de los cĂtricos, Diaphorina citri Kuwayama (Hemiptera: Liviidae), el vector del patĂłgeno âCandidatus Liberibacter asiaticusâ asociado con el HLB. Actualmente los costos de los insecticidas y los efectos secundarios de su uso son las principales preocupaciones, ya que podrĂan perjudicar la estrategia de manejo contra el vector; y por lo tanto, alternativas ecolĂłgicas y econĂłmicamente viables a los insecticidas convencionales serian necesarias a corto plazo. Por tanto, el objetivo de este estudio fue evaluar la patogenicidad de 27 aislados nativos y 3 cepas de hongos entomopatĂłgenos para determinar su potencial como agentes de control biolĂłgico sobre Diaphorina citri usando 2 diferentes mĂŠtodos de bioensayo. Los bioensayos fueron realizados bajo condiciones de laboratorio (26 Âą 2 °C, 60 Âą 5% H.R y 16:8 h L:O) mediante la exposiciĂłn de insectos adultos a una concentraciĂłn de 1 Ă 108 conidios por mililitro utilizando 2 diferentes mĂŠtodos de aplicaciĂłn, es decir, por asperjado de esporas en las plĂĄntulas de cĂtricos y por asperjado directo a los psĂlidos adultos. Los resultados mostraron que para el asperjado directo a los adultos los aislados HIB-24 (B. bassiana) y HIB-32 (I. fumosorosea) mostraron el mayor porcentaje de mortalidad (60.66%). Respecto al asperjado de plĂĄntulas el aislado HIB-19 (I. fumosorosea) mostrĂł el mayor porcentaje de mortalidad (62.02%). Los resultados de este estudio demuestran el potencial para el uso de hongos entomopatĂłgenos en el manejo de D. citri en MĂŠxico.
ABSTRACT
Huanglongbing (HLB), considered one of the most lethal diseases of citrus worldwide, has reached the main areas of Mexican lime (Citrus latifolia Tanaka) fruit production on the Pacific coast of MĂŠxico. Growers have initiated intensive use of insecticides in order to control populations of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), the vector of the pathogen, âCandidatus Liberibacter asiaticusâ associated with huanglongbing. Presently, costs of insecticides and the side effects of their use are major concerns, because they could impair the management strategy against the vector; and thus, ecologically and economically viable alternatives to conventional insecticides are required in the short term. Therefore the goal of this study was to evaluate the pathogenicity of 27 native isolates and 3 strains of entomopathogenic fungi and determine their potential as biological control agents of D. citri by using 2 different bioassay methods. Bioassays were performed under laboratory conditions (26 Âą 2 °C, 60 Âą 5% RH and 16:8 h L:D) by exposing adult insects to a concentration of 1 Ă 108 conidia per milliliter using 2 different application methods, i.e., spraying the spores onto the citrus seedlings and spraying the spores directly onto the adult psyllids. The results showed that by direct spraying the adults, HIB-24 (B. bassiana) and HIB-32 (I. fumosorosea) isolates showed the highest mortality (60.66%). Regarding spraying of the seedlings, HIB-19 (I. fumosorosea) showed the highest percentage of mortality (62.02%). The results from this study demonstrate potential for using entomopathogenic fungi in the management of D. citri in MĂŠxico
An effector from the Huanglongbing-associated pathogen targets citrus proteases
The citrus industry is facing an unprecedented challenge from Huanglongbing (HLB). All cultivars can be affected by the HLB-associated bacterium âCandidatus Liberibacter asiaticusâ (CLas) and there is no known resistance. Insight into HLB pathogenesis is urgently needed in order to develop effective management strategies. Here, we use Sec-delivered effector 1 (SDE1), which is conserved in all CLas isolates, as a molecular probe to understand CLas virulence. We show that SDE1 directly interacts with citrus papain-like cysteine proteases (PLCPs) and inhibits protease activity. PLCPs are defense-inducible and exhibit increased protein accumulation in CLas-infected trees, suggesting a role in citrus defense responses. We analyzed PLCP activity in field samples, revealing specific members that increase in abundance but remain unchanged in activity during infection. SDE1-expressing transgenic citrus also exhibit reduced PLCP activity. These data demonstrate that SDE1 inhibits citrus PLCPs, which are immune-related proteases that enhance defense responses in plants
Sexual Transmission of a Plant Pathogenic Bacterium, Candidatus Liberibacter asiaticus, between Conspecific Insect Vectors during Mating
Candidatus Liberibacter asiaticus is a fastidious, phloem-inhabiting, gram-negative bacterium transmitted by Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae). The bacterium is the presumed causal agent of huanglongbing (HLB), one of the most destructive and economically important diseases of citrus. We investigated whether Las is transmitted between infected and uninfected D. citri adults during courtship. Our results indicate that Las was sexually transmitted from Las-infected male D. citri to uninfected females at a low rate (<4%) during mating. Sexual transmission was not observed following mating of infected females and uninfected males or among adult pairs of the same sex. Las was detected in genitalia of both sexes and also in eggs of infected females. A latent period of 7 days or more was required to detect the bacterium in recipient females. Rod shaped as well as spherical structures resembling Las were observed in ovaries of Las-infected females with transmission electron microscopy, but were absent in ovaries from uninfected D. citri females. The size of the rod shaped structures varied from 0.39 to 0.67 Âľm in length and 0.19 to 0.39 Âľm in width. The spherical structures measured from 0.61 to 0.80 Âľm in diameter. This investigation provides convincing evidence that a plant pathogenic bacterium is sexually transmitted from male to female insects during courtship and established evidence that bacteria persist in reproductive organs. Moreover, these findings provide an alternative sexually horizontal mechanism for the spread of Las within populations of D. citri, even in the absence of infected host trees
Comparison of the âCa. Liberibacter asiaticusâ Genome Adapted for an Intracellular Lifestyle with Other Members of the Rhizobiales
An intracellular plant pathogen âCandidatus Liberibacter asiaticus,â a member of the Rhizobiales, is related to Sinorhizobium meliloti, Bradyrhizobium japonicum, nitrogen fixing endosymbionts, Agrobacterium tumefaciens, a plant pathogen, and Bartonella henselae, an intracellular mammalian pathogen. Whole chromosome comparisons identified at least 50 clusters of conserved orthologous genes found on the chromosomes of all five metabolically diverse species. The intracellular pathogens âCa. Liberibacter asiaticusâ and Bartonella henselae have genomes drastically reduced in gene content and size as well as a relatively low content of guanine and cytosine. Codon and amino acid preferences that emphasize low guanosine and cytosine usage are globally employed in these genomes, including within regions of microsynteny and within signature sequences of orthologous proteins. The length of orthologous proteins is generally conserved, but not their isoelectric points, consistent with extensive amino acid substitutions to accommodate selection for low GC content. The âCa. Liberibacter asiaticusâ genome apparently has all of the genes required for DNA replication present in Sinorhizobium meliloti except it has only two, rather than three RNaseH genes. The gene set required for DNA repair has only one rather than ten DNA ligases found in Sinorhizobium meliloti, and the DNA PolI of âCa. Liberibacter asiaticusâ lacks domains needed for excision repair. Thus the ability of âCa. Liberibacter asiaticusâ to repair mutations in its genome may be impaired. Both âCa. Liberibacter asiaticus and Bartonella henselae lack enzymes needed for the metabolism of purines and pyrimidines, which must therefore be obtained from the host. The âCa. Liberibacter asiaticusâ genome also has a greatly reduced set of sigma factors used to control transcription, and lacks sigma factors 24, 28 and 38. The âCa. Liberibacter asiaticusâ genome has all of the hallmarks of a reduced genome of a pathogen adapted to an intracellular lifestyle
The Complete Genome Sequence of âCandidatus Liberibacter solanacearumâ, the Bacterium Associated with Potato Zebra Chip Disease
Zebra Chip (ZC) is an emerging plant disease that causes aboveground decline of
potato shoots and generally results in unusable tubers. This disease has led to
multi-million dollar losses for growers in the central and western United States
over the past decade and impacts the livelihood of potato farmers in Mexico and
New Zealand. ZC is associated with âCandidatus
Liberibacter solanacearumâ, a fastidious alpha-proteobacterium that is
transmitted by a phloem-feeding psyllid vector, Bactericera
cockerelli Sulc. Research on this disease has been hampered by a
lack of robust culture methods and paucity of genome sequence information for
âCa. L. solanacearumâ. Here we present the
sequence of the 1.26 Mbp metagenome of âCa. L.
solanacearumâ, based on DNA isolated from potato psyllids. The coding
inventory of the âCa. L. solanacearumâ genome was
analyzed and compared to related Rhizobiaceae to better
understand âCa. L. solanacearumâ physiology and
identify potential targets to develop improved treatment strategies. This
analysis revealed a number of unique transporters and pathways, all potentially
contributing to ZC pathogenesis. Some of these factors may have been acquired
through horizontal gene transfer. Taxonomically, âCa. L.
solanacearumâ is related to âCa. L.
asiaticusâ, a suspected causative agent of citrus huanglongbing, yet many
genome rearrangements and several gene gains/losses are evident when comparing
these two Liberibacter. species. Relative to âCa. L.
asiaticusâ, âCa. L. solanacearumâ probably
has reduced capacity for nucleic acid modification, increased amino acid and
vitamin biosynthesis functionalities, and gained a high-affinity iron transport
system characteristic of several pathogenic microbes
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