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Bap: A family of surface proteins involved in biofilm formation
No full textA group of surface proteins sharing several structural and functional features is emerging as an important element in the biofilm formation process of diverse bacterial species. The first member of this group of proteins was identified in a Staphylococcus aureus mastitis isolate and was named Bap (biofilm-associated protein). As common structural features, Bap-related proteins: (i) are present on the bacterial surface; (ii) show a high molecular weight: (iii) contain a core domain of tandem repeats: (iv) confer upon bacteria the capacity to form a biofilm; (v) play a relevant role in bacterial infectious processes; and (vi) can occasionally be contained in mobile elements. This review summarizes recent studies that have identified and assigned roles to Bap-related proteins in biofilm biology and virulence. (c) 2005 Elsevier SAS. All rights reserved
Survival strategy of Erwinia amylovora against copper: Induction of the viable-but-nonculturable state
No full textCopper compounds, widely used to control plant-pathogenic bacteria, have traditionally been employed against fire blight, caused by Erwinia amylovora. However, recent studies have shown that some phytopathogenic bacteria enter into the viable-but-nonculturable (VBNC) state in the presence of copper. To determine whether copper kills E. amylovora or induces the VBNC state, a mineral medium without copper or supplemented with 0.005, 0.01, or 0.05 mM Cu2+ was inoculated with 107 CFU/ml of this bacterium and monitored over 9 months. Total and viable cell counts were determined by epifluorescence microscopy using the LIVE/DEAD kit and by flow cytometry with 5-cyano-2,3-ditolyl tetrazolium chloride and SYTO 13. Culturable cells were counted on King's B nonselective solid medium. Changes in the bacterial morphology in the presence of copper were observed by scanning electron microscopy. E. amylovora entered into the VBNC state at all three copper concentrations assayed, much faster when the copper concentration increased. The addition of different agents which complex copper allowed the resuscitation (restoration of culturability) of copper-induced VBNC cells. Finally, copper-induced VBNC cells were virulent only for the first 5 days, while resuscitated cells always regained their pathogenicity on immature fruits over 9 months. These results have shown, for the first time, the induction of the VBNC state in E. amylovora as a survival strategy against copper.
Fire blight, caused by the bacterium Erwinia amylovora (Burrill) Winslow et al. (39) and reported in more than 40 countries around the world, is a very serious and destructive disease of pome fruits and many ornamental plants from the Rosaceae family (34). Copper compounds, widely utilized against fire blight from the beginning of the last century (35), are still employed in many countries, especially in the European Union, where antibiotic utilization is restricted (2). Their use is one of the most common methods for controlling bacterial plant diseases, but it has led many bacteria to develop different strategies against copper ions (31). Until now, very little information on the interaction between E. amylovora and Cu2+ ions has been available (4, 15, 41).
Copper treatments have traditionally been considered as bactericides in agriculture (29, 34, 35), their effectiveness often being measured by the absence of bacterial growth on a solid medium (12, 13). However, recent studies have shown the induction of the viable-but-nonculturable (VBNC) state by copper in several plant-pathogenic bacteria, such as Agrobacterium tumefaciens (1), Xanthomonas campestris pv. campestris (16), and Ralstonia solanacearum (17). This state, in which cells progressively lose their culturability on nonselective solid medium but still remain viable, is considered to be a bacterial survival strategy under adverse environmental conditions (30). Therefore, the failure to produce a visible colony may not necessarily mean that the bacterial cell is dead. Furthermore, it has been reported that VBNC cells can maintain pathogenicity (17, 19). In this respect, it has been suggested that copper-induced VBNC cells of some phytopathogenic bacteria could be related to the persistent nature of infections in copper-treated fields (17). A similar situation could occur with E. amylovora, since fire blight remains difficult to control as a disease (26), which has been related to the ability of this bacterium to survive and spread in different ways (32). Moreover, some bacteria, under favorable environmental conditions, can revert from the VBNC state to a culturable one, in a process usually called resuscitation. This reversion is considered a confirmation that the VBNC state is a bacterial survival strategy (19, 28). The nature of the VBNC state, however, is still the topic of an intense debate in the literature, and some authors argue that this condition may be a physiological state prior to cell death (7, 23).
In spite of previous work concerning the toxic effect of copper ions for E. amylovora (15), many questions on the survival of this bacterium in the presence of this metal remain unanswered. Thus, the aim of this work has been to determine whether copper kills or induces the VBNC state of E. amylovora cells and if such VBNC cells retain their pathogenicity. Furthermore, the possible reversion of this bacterium from the nonculturable state has been studied as well as whether resuscitated cells could regain their pathogenic potentia
Natural enemies of the spider mites, 'Tetranychus urticae' Koch and 'Panonychus citru' (McGregor) (Acari: Tetranychidae) in Spanish citrus orchards
No full textEffects of long-term ozone exposure on citrus: Chlorophyll a fluorescence and gas exchange
No full textThree-years-old trees of Satsuma mandarin (Citrus unshiu [Mak.] Marc.) cv. Okitsu were exposed to O-3 fumigation during long term (one year) in open-top chambers. As a result of the treatment, chlorophyll a fluorescence and gas exchange parameters were modified with respect to trees growing in O-3-free conditions. Net photosynthetic rate and stomatal conductance decreased and intercellular CO2 concentration increased according to a reduction of the non-cyclic electron flow and a lower capacity to reduce the quinone pool. O-3 also reduced the development of non-photochemical quenching preventing the dissipation of excess excitation energy and, therefore, generated several alterations in photosynthetic apparatus. All these effects were obtained in long-term exposure and higher O-3 concentration. In O-3 ambient conditions, the effects were minor
Estudio de un grupo de accesiones del banco de germoplasma de níspero del IVIA por análisis multivariante
Get PDFEl níspero (Eriobotrya japonica (Thunb) Lindl.) es originario de China (Zhang et al.,
1993), aunque existen vestigios de su introducción muy temprana en Japón (Zhang et al.,
1993; Ding et al.,1995). Sin embargo, la introducción en los países europeos del Mediterráneo
y América es mucho más tardía, data del siglo XIX y XX, respectivamente. A partir
del desarrollo del proyecto europeo “Conservación, evaluación y colección de frutales menores”
se realizó una prospección de material vegetal de níspero en los países europeos meridionales.
Como resultado de esta prospección se estableció en el IVIA la colección europea
de germoplasma de níspero. Esta colección se va ampliando con nuevas accesiones provenientes
de todo el mundo y en la actualidad cuenta con 123 entradas. La gestión del banco de
germoplasma exige en primer lugar una buena caracterización del material y en segundo lugar
se requieren estudios de diversidad que puedan definir patrones de variabilidad dentro de la
colección, grupos de accesiones con características comunes, variables más significativas etc,
que permitan ordenar la información obtenida y establecer las líneas de acción necesarias para
una conservación más eficaz y un mejor aprovechamiento de los recursos.
Para lograr este objetivo, las técnicas del análisis multivariante son una poderosa herramienta
ya que permite analizar una gran cantidad de datos (accesiones y variables) y simplificarlos
mediante la creación de nuevas variables ortogonales entre ellas que recogen gran
parte de la información contenida en las variables originales. Entre los distintos métodos de
análisis, el Análisis por Componentes Principales o PCA (Eriksson et al., 1999) es muy adecuado
para el objetivo y tipo de datos de esta colección
Genetic diversity of loquat germplasm (Eriobotrya japonica (Thunb) Lindl) assessed by SSR markers
No full textGenetic relationships among 40 loquat (Eriobotrya japonica (Thunb) Lindl) accessions that originated from different countries and that are part of the germplasm collection of the Instituto Valenciano de Investigaciones Agrarias (IVIA) (Valencia, Spain) were evaluated using microsatellites. Thirty primer pairs flanking microsatellites previously identified in Malus × domestica (Borkh.) were assayed. Thirteen of them amplified polymorphic products and unambiguously distinguished 34 genotypes from the 40 accessions analyzed. Six accessions showing identical marker patterns were Spanish local varieties thought to have been derived from 'Algerie' by a mutational process very common in loquat species. A total of 39 alleles were detected in the population studied, with a mean value of 2.4 alleles per locus. The expected and observed heterozygosities were 0.46 and 51% on average, respectively, leading to a negative value of the Wright's fixation index (–0.20). The values of these parameters indicate a smaller degree of genetic diversity in the set of loquat accessions analyzed than in other members of the Rosaceae family. Unweighted pair-group method (UPGMA) cluster analysis, based on Nei's genetic distance, generally grouped genotypes according to their geographic origins and pedigrees. The high number of alleles and the high expected heterozygosity detected with SSR markers developed in Malus × domestica (Borkh.) make them a suitable tool for loquat cultivar identification, confirming microsatellite marker transportability among genera in the Rosaceae family
Augmentative biological control of Bemisia tabaci biotype "Q" in Spanish greenhouse pepper production using Eretmocerus spp.
No full textEretmocerus mundus Mercet is indigenous to the Mediterranean basin and the most abundant parasitoid attacking Bemisia tabaci Gennadius on the southern coast of Spain. However, E. mundus was not available commercially until 2002 and the North American Eretmocerus eremicus Rose and Zolnerowich had been used instead to control whiteflies in greenhouse vegetables, including sweet pepper in Campo de Cartagena (Murcia). The ability of these two Eretmocerus species to control B. tabaci on pepper by augmentation was compared with weekly releases of E. mundus and E. eremicus, alone, and in 1:1 combination (three treatments) initiated early in the winter crop cycle in 12 commercial greenhouses. E. mundus rapidly displaced E. eremicus in greenhouses where both were released, and eventually, even where only E. eremicus was released, indicating that a significant portion of the E. mundus population entered the greenhouses from outside. Nevertheless, parasitism rates were greater in greenhouses where E. mundus was released, especially early in the trial. Whitefly populations were lower compared to where E. eremicus was released alone, presumably in response to parasitism. Thus, higher incidence of parasitism and superior control of B. tabaci with E. mundus confirmed the value of early season augmentation with this parasitoid as opposed to E. eremicus under conditions of this test. © 2005 Elsevier Ltd. All rights reserved
Release rates for control of Bemisia tabaci (Homoptera: Aleyrodidae) biotype "Q" with Eretmocerus mundus (Hymenoptera: Aphelinidae) in greenhouse tomato and pepper
No full textTomato and sweet pepper are the principal crops grown in protected culture on the southern coast of Spain. Augmentative biological control based on the parasitoid Eretmocerus mundus Mercet promises to be a useful component to manage Bemisia tabaci, the key pest of these and other horticultural crops. The present studies were undertaken with the objective of evaluating control obtained with different release rates under simulated commercial conditions. Experiments were conducted in an air-conditioned plastic greenhouse located on the southern Spanish coast during the two main horticultural cropping seasons of the region (fall-winter and spring). Host plant (tomato and sweet pepper) constituted the main plots and release rate of E. mundus (0, 1.5 and 6 m -2) the subplots in split plot design with four replicates. No other management practices were used against whitefly. Whitefly populations in fall reached over 80 nymphs/100 cm2 leaf surface in pepper and twice this in tomato. Nevertheless, control using the high release rate in fall exceeded 90% in both crops, with no differences between rates in pepper, although the high rate was significantly better in tomato. Whitefly populations on pepper in spring reached densities five times greater than in fall, and yet control equalled or exceeded 95% with the high rate. Adult whiteflies on tomato were reduced by 92% in response to the high rate in spring, but nymphs were only reduced 69%. These experiments suggested that, although higher rates may be required in tomato to achieve the same level of control as in pepper, good suppression of B. tabaci could be achieved in both crops under most conditions using E. mundus without recourse to insecticides
Morphology and development of immature stages of Galeopsomyia fausta (Hymenoptera: Eulophidae: Tetrastichinae)
Get PDFGaleopsomyia fausta LaSalle (Hymenoptera: Eulophidae) is a Neotropical eulophid solitary ectoparasitoid of the immature stages of Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae). In Central and South America, the activity of this wasp has resulted in good biological control of P. citrella. Characterization of the immature morphology of parasitoids is important for the identification to the species level before adult emergence and for the quantification of the impact of these natural enemies in biological control programs. This article reports our study of the immature stages of G. fausta from a laboratory colony maintained on P. citrella that were examined using scanning electron microscopy (SEM). The wasp has a typical hymenopteriform egg attached to the leaf chamber where P. citrella pupates. The parasitoid has three instars, very similar to each other, holopneustic, hymenopteriform, and 13-segmented. Its cuticle has multiple spines. The cranium is conspicuous and has a mandibulate suctorial mouth. On completion of its larval development an exarate pupa is produced. The distinctive attachment of the egg to the leaf and typical pupal morphology allow the identification of this parasitoid by using a binocular microscope, but identification of the larvae requires SEM. © 2005 Entomological Society of America
La eficiencia de uso de los fertilizantes nitrogenados como estrategia para el establecimiento de normas de fertilización en cítricos
Get PDFEl objetivo del presente trabajo es cuantificar la eficiencia de la absorción por la
planta y retención en el suelo del N aportado con los fertilizantes en cítricos, en
función de diversas variables que, a priori, pueden influir de forma decisiva sobre
estos parámetros; tales como tipo de suelo, sistema de riego, forma del N utilizado, uso
de inhibidores de la nitrificación, época y frecuencia de aplicación y tiempo de
marcado. En el suelo arenoso se obtuvo una mayor absorción de N por las plantas
jóvenes de cítricos que en el franco. Por el contrario, este último retuvo una mayor
proporción del N aplicado que el arenoso. Los árboles fertilizados en primavera con
nitrato potásico mostraron una eficiencia inferior a los abonados en verano. El
aumento de la frecuencia de aplicación y la adición del DMPP incrementaron la
eficiencia de absorción de N por los plantones. Así mismo, en el suelo se retuvieron
menores concentraciones de N como nitrato y mayores en forma amoniacal y
orgánica. Al aplicar una dosis de N excesiva, la eficiencia decreció considerablemente
y aumentó en gran medida el riesgo potencial de lixiviación del ion nitrato. En riego a
goteo y alta frecuencia de aplicación se lograron eficiencias más altas en la planta que
en riego por inundación; además, se recuperaron porcentaje inferiores de N como
nitrato en todo el perfil del suelo. Entre las diferentes formas del N aportado, la
amoniacal adicionada con el inhibidor nitrificación resultó ser la más eficiente