Injuries caused by citrus leafminer (Phyllocnistis citrella) exacerbate citrus canker (Xanthomonas axonopodis pv. citri) infection

After the introduction of citrus leafminer in São Paulo State, an increase in the number of new plants infected with citrus canker has been observed. The interaction between these two organisms is known, but there is no information about how the leafminer damage intensifies citrus canker incidence and severity. The objectives of this paper were to evaluate the effects of leafminer damage in citrus canker infection and its influence on the monocyclic components of the disease on Citrus limonia. Higher incidence of diseased plants, AUDPC (area under the disease progress curve), disease severity and shorter incubation periods were observed in plants inoculated after insect infestation. These factors explain the association found between the higher citrus canker intensity and the damage caused by the insect and show, albeit partially, the consequences of these changes in the spread of the pathogen under natural conditions of infection.

Insect feeding preferences on Piperaceae species observed in São Paulo city, Brazil

Piperaceae species have been placed among the basal angiosperm and are adapted to a variety of habitats including moist forests, secondary vegetation and dry high lands. The major anatomical/morphology features are of small trees, vines, and shrubs for Piper species, while the epiphytic and succulent characteristics are predominant forms among Peperomia species. Their secondary chemistry can be mostly represented by amides, phenylpropanoids/lignoids, and chromenes in addition to a phletoria of biosynthetically mixed-origin secondary compounds. Although several amides and lignans are known as insecticides, several phytophagous insects, among which some considered pests of economic importance, have been observed feeding vigorously on Piperaceae species. Herein we describe the feeding preferences of fourteen phytophagous species of Coleoptera, Lepidoptera and Hemiptera over approximately fifty Piperaceae species observed in São Paulo, SP, Brazil, in a long-term basis.

LARVICIDAL ACTIVITY OF Bacillus sphaericus 2362 AGAINST Anopheles nuneztovari, Anopheles darlingi AND Anopheles braziliensis (DIPTERA, CULICIDAE)

In this present study, preliminary data was obtained regarding the mortality rate of the Amazonian anophelines, Anopheles nuneztovari, Anopheles darlingi and Anopheles braziliensis when subjected to treatment with Bacillus sphaericus strain 2362, the WHO standard strain. Initially, experiments were conducted to test the mortality rate of the three species of anopheline larvae. The third larval instar of An. nuneztovari and the second and third larval instars of An. darlingi proved to be the least susceptible. In other experiments, the same three mosquito species were tested with the standard strain 2362, An. nuneztovari was the least susceptible to this insect pathogen, while An. braziliensis was the most susceptible. This latter species showed a difference in the level of LC50 concentration, when compared to the former, of 2.4, 2.5 and 1.8 in readings taken 24, 48 and 72 hours after exposure to the bacillus.

Phospholipase gene expression during Paracoccidioides brasiliensis morphological transition and infection

Phospholipase is an important virulence factor for pathogenic fungi. In this study, we demonstrate the following: (i) the Paracoccidioides brasiliensis pld gene is preferentially expressed in mycelium cells, (ii) the plb1 gene is mostly up-regulated by infection after 6 h of co-infection of MH-S cells or during BALB/c mice lung infection, (iii) during lung infection, plb1, plc and pld gene expression are significantly increased 6-48 h post-infection compared to 56 days after infection, strongly suggesting that phospholipases play a role in the early events of infection, but not during the chronic stages of pulmonary infection by P. brasiliensis.

Metabolomics in the fight against malaria

Metabolomics uses high-resolution mass spectrometry to provide a chemical fingerprint of thousands of metabolites present in cells, tissues or body fluids. Such metabolic phenotyping has been successfully used to study various biologic processes and disease states. High-resolution metabolomics can shed new light on the intricacies of host-parasite interactions in each stage of the Plasmodium life cycle and the downstream ramifications on the host’s metabolism, pathogenesis and disease. Such data can become integrated with other large datasets generated using top-down systems biology approaches and be utilised by computational biologists to develop and enhance models of malaria pathogenesis relevant for identifying new drug targets or intervention strategies. Here, we focus on the promise of metabolomics to complement systems biology approaches in the quest for novel interventions in the fight against malaria. We introduce the Malaria Host-Pathogen Interaction Center (MaHPIC), a new systems biology research coalition. A primary goal of the MaHPIC is to generate systems biology datasets relating to human and non-human primate (NHP) malaria parasites and their hosts making these openly available from an online relational database. Metabolomic data from NHP infections and clinical malaria infections from around the world will comprise a unique global resource.

Gall midge attack intensity and host-plant response in a Neotropical coastal ecosystem

The gall inducer Clusiamyia nitida Maia, 1996 (Diptera, Cecidomyiidae) often infests the shrub Clusia lanceolata (Camb.) (Clusiaceae) in the Neotropical vegetation of restinga of Rio de Janeiro State, Brazil. Leaves of Clusia lanceolata host up to 20 spheroid galls and show variation in their shape. We aimed to evaluate the effect of gall's intensity on leaves of Clusia lanceolata, and the extension of gall's impact on adjacent non-galled leaves. We analyzed the effect of the number of galls on leaf area, biomass, specific area and leaf appearance from 509 leaves of 14 individual plants. The results showed that differences of individual plants, pairs of leaves, and gall presence were responsible for more then 90% of variation on infested leaves. Variation on parasitic intensity level created differences in leaf response. Under moderate gall attack characterized by scattered galls on a leaf, the increase of the number of galls caused an increase of leaf biomass and area, and a decrease of specific area. The specific area was smaller also under high attack intensity, characterized by coalescent galls on a leaf. In those cases of extremely high parasitic intensity, galled leaves became deformed and the surface area was severely reduced. Leaf deformation due to gall attack led to early leaf abscission, indicated by the 90% of deformed leaves found in the youngest leaf pair of the branch. There was insufficient evidence that the impact of galls on leaf morpho-physiological parameters extended beyond the attacked leaves, because ungalled leaves did not change significantly when their opposite leaf had been galled.

Natural variability in Arabidopsis thaliana germplasm response to Xanthomonas campestris pv. campestris

This work aimed to study the interaction between the model plant Arabidopsis thaliana and Xanthomonas campestris pv. campestris (Xcc), the pathogen responsible for black rot of crucifers. The response of 32 accessions of A. thaliana to the Brazilian isolate of Xcc CNPH 17 was evaluated. No immunity-like response was observed. "CS1308", "CS1566" and "CS1643" grown in continuous light were among the accessions that showed strongest resistance when inoculated with 5 x 10(6) CFU/mL. In contrast, "CS1194" and "CS1492" were among the most susceptible accessions. Similar results were obtained when plants were grown under short-day conditions. To quantify the differences in disease symptoms, total chlorophyll was extracted from contrasting accessions at different time points after inoculation. Chlorophyll levels from controls and Xcc inoculated plants showed a similar reduction in resistant accessions, whereas Xcc-inoculated susceptible accessions showed a greater reduction compared to controls. To test the specificity of resistance, accessions CS1308, CS1566, CS1643 and CS1438 (which showed partial resistance to CNPH 17), were inoculated with a more aggressive isolate of Xcc (CNPH 77) and Ralstonia solanacearum. Among the accessions tested, "CS1566" was the most resistant to Xcc CNPH 77 and also displayed resistance to R. solanacearum. Accessions CS1308, CS1566 and CS1643 were also inoculated with a high titer of Xcc CNPH 17 (5 x 10(8) CFU/mL). No collapse of tissue was observed up to 48 h after inoculation, indicating that a hypersensitive response is not involved in the resistance displayed by these accessions.

Inheritance of resistance to powdery mildew in pea and pathogenesis-related aspects

The inheritance of resistance to powdery mildew in the pea cultivar MK-10 and some histological aspects of infection were assessed. For the inheritance study, F1, F2, backcrosses and F3 generations of MK-10 crossed with two susceptible populations were evaluated. Histological evaluations included percentage of germinated conidia, percentage of conidia that formed appresoria, percentage of conidia that established colonies, and number of haustoria per colony. Segregation ratios obtained in the resistance inheritance study were compared by Chi-square (ײ) test and the histological data were analyzed by Tukey's test at 5% probability. It was concluded that resistance of MK-10 to powdery mildew is due to a pair of recessive alleles since it is expressed in the pre-penetration stage and completed by post-penetration localized cellular death, characteristic of the presence of the pair of recessive alleles er1er1.

Anatomical changes on coffee leaves infected by Pseudomonas syringae pv. garcae

ABSTRACTAlthough poorly studied, the bacterial halo blight is an important disease in the major coffee-producing states of Brazil. External damage and anatomical changes on leaves were measured in seedlings of Coffea arabica cv. Mundo Novo, susceptible to Pseudomonas syringae pv. garcae, by using histological sections obtained at 10 and 20 days after inoculation (DAI). The changes on the epidermis were smaller than the lesions measured in the mesophyll, irrespective of the evaluated colonization period, showing that the internal damage caused by the bacterium represent twice the damage observed externally. From the inoculation site, lysis occurred on the epidermal cells and on the palisade and spongy parenchyma cells, with strong staining of their cellular contents, as well as abnormal intercellular spaces in the palisade parenchyma, hypertrophy and hyperplasia of mesophyll cells and partial destruction of chloroplasts. Additionally, this study revealed the presence of inclusion bodies in epidermal and mesophyll cells. Bacterial masses were found in the apoplast between and within mesophyll cells. Bacteria were also observed in the bundle sheath and vascular bundles and were more pronounced at 20 DAI, not only near the inoculation site but also in distant areas, suggesting displacement through the vascular system. These results can be useful to understand this plant-pathogen interaction.

Microscopic variability in mechanical defence and herbivory response in microphyllous leaves of tropical herb species from Serra do Cipó, Brazil

Tropical high altitude grasslands present several species with both microphyllous and highly sclerophyllous leaves, and co-occur in specific soil patches, thus exposed to identical environments. In this article we describe herbivory among co-occurring microphyllous species in a tropical high altitude grassland ecosystem of Serra do Cipó, Minas Gerais state, and we tested the effect of variable anatomic traits on leaf herbivory patterns. Leaf anatomical traits were investigated for Baccharis imbricata Heering , Lavoisiera imbricata DC. and L. subulata Triana (focal species). Herbivory was measured from branches and leaves of individual plants and compared among co-occurring species within one multispecific shrub patch and among L. subulata individuals from this patch and an adjacent monospecific patch. For all present plant species and individuals we estimated the proportion of leaves with different levels of area lost. For the focal species, six leaves were sorted and taken for histological sectioning, in order to allow precise measures of defensive structures. Relative mean leaf area lost differed significantly among the six species found in the multispecific patch. Lavoisiera subulata individuals were more attacked in the multispecific than in the monospecific patch. Leaf margin protection traits in both B. imbricata and L. imbricata showed significant effect against herbivory. Data suggest that some anatomic traits have direct effect against herbivory but their effect are not clearly perceptible among branches within individual plants or among plants within the same species.

Test of hypotheses about herbivory and chemical defences of Qualea parviflora (Vochysiaceae) in Brazilian Cerrado

(Test of hypotheses about herbivory and chemical defences of Qualea parviflora (Vochysiaceae) in Brazilian Cerrado). Qualea parviflora Mart. (Vochysiaceae), a widely distributed tree found in different habitats in Brazilian Cerrado (savanna), provides resources for a great variety of insects. In this study, we tested two hypotheses about plant investment in anti-herbivore defences along a fertility gradient in Cerrado: the carbon/nitrogen balance (CNBH) and resource availability (RAH). We also investigated how the pattern of herbivory varies through the year and among three types of vegetation in Brazilian Cerrado - campo sujo, cerrado sensu strictu and cerradão. Sampling was conducted in three types of vegetation and in rainy (January and November) and dry months (April and July). Damage on 20 completely expanded leaves, leaf nutrients, sclerophlylly, total phenols and tannins were recorded for each plant (n = 30). When leaves were young, less sclerophyllous, and with higher concentration of nutrients and tannins, damage by herbivores was about 7% in cerrado sensu stricto and 3% in campo sujo. Mature leaves did not show any significant difference on herbivory among habitats, that varied from 6 to 9%. Nutrient availability to plants is an important factor determining production of secondary metabolites in Q. parviflora, corroborating the CNBH. The absence of correlation between damaged leaf area and tannin concentration did not corroborate the RAH, suggesting that tannin production is not strongly influenced by herbivores on Q. parviflora.

Apoptosis in parasites and parasite-induced apoptosis in the host immune system: a new approach to parasitic diseases

Apoptosis, a form of programmed cell death (PCD), has been described as essential for normal organogenesis and tissue development, as well as for the proper function of cell-renewal systems in adult organisms. Apoptosis is also pivotal in the pathogenesis of several different diseases. In this paper we discuss, from two different points of view, the role of apoptosis in parasitic diseases. The description of apoptotic death in three different species of heteroxenic trypanosomatids is reviewed, and considerations on the phylogenesis of apoptosis and on the eventual role of PCD on their mechanism of pathogenesis are made. From a different perspective, an increasing body of evidence is making clear that regulation of host cell apoptosis is an important factor on the definition of a host-pathogen interaction. As an example, the molecular mechanisms by which Trypanosoma cruzi is able to induce apoptosis in immunocompetent cells, in a murine model of Chagas' disease, and the consequences of this phenomenon on the outcome of the experimental disease are discussed.

Molecular battles between plant and pathogenic bacteria in the phyllosphere

The phyllosphere, i.e., the aerial parts of the plant, provides one of the most important niches for microbial colonization. This niche supports the survival and, often, proliferation of microbes such as fungi and bacteria with diverse lifestyles including epiphytes, saprophytes, and pathogens. Although most microbes may complete the life cycle on the leaf surface, pathogens must enter the leaf and multiply aggressively in the leaf interior. Natural surface openings, such as stomata, are important entry sites for bacteria. Stomata are known for their vital role in water transpiration and gas exchange between the plant and the environment that is essential for plant growth. Recent studies have shown that stomata can also play an active role in limiting bacterial invasion of both human and plant pathogenic bacteria as part of the plant innate immune system. As counter-defense, plant pathogens such as Pseudomonas syringae pv tomato (Pst) DC3000 use the virulence factor coronatine to suppress stomate-based defense. A novel and crucial early battleground in host-pathogen interaction in the phyllosphere has been discovered with broad implications in the study of bacterial pathogenesis, host immunity, and molecular ecology of bacterial diseases.

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease: 3 - On the interaction of vector species and parasite strain in the reaction of bugs to infection by Trypanosoma cruzi

The reaction of nine vector species of Chagas' disease to infection by seven different Trypanosoma cruzi strains; Berenice, Y, FL, CL, S. Felipe, Colombiana and Gávea, are examined and compared. On the basis of the insects' ability to establish and maintain the infection, vector species could be divided into two distinct groups which differ in their reaction to an acute infection by T. cruzi. While the proportion of positive bugs was found to be low in Triatoma infestans and Triatoma dimidiata it was high, ranging from 96.9% to 100% in the group of wild (Rhodnius neglectus, Triatoma rubrovaria)and essentially sylvatic vectors in process of adaptation to human dwellings, maintained under control following successful insecticidal elimination of Triatoma infestans (Panstrongylus megistus, Triatoma sordida and Triatoma pseudomaculata). An intermediate position is held by Triatoma brasiliensis and Rhodnius prolixus. This latter has been found to interchange between domestic and sylvatic environments. The most important finding is the strikingly good reaction between each species of the sylvatic bugs and practically all T. cruzi strains herein studied, thus indicating that the factors responsible for the excellent reaction of P.megistus to infection by Y strain, as previously reported also come into operation in the reaction of the same vector species to acute infections by five of the remaining T.cruzi strains. Comparison or data reported by other investigators with those herein described form the basis of the discussion of Dipetalogaster maximus as regards its superiority as a xenodiagnostic agent.

Studies in search of a suitable experimental insect model for xenodiagnosis of hosts with Chagas' disease: 4 - The reflection of parasite stock in the responsiveness of different vector species to chronic infection with different Trypanosoma cruzi stocks

Previous studies (1982,1987) have emphasized the superiority of sylvatic vector species over domestic species as xenodiagnostic agents in testing hosts with acute or chronic infections by T. cruzi "Y" stock. The present study, which is unique in that it contains data on both infectivity rates produced by the same stock in 11 different vector species and also the reaction of the same vector species to seven different parasite stocks, establishes the general validity of linking efficiency of xenodiagnosis to the biotope of its agent. For example, infectivity rates produced by "São Felipe" stock varied from 82.5% to 98.3% in sylvatic vectors but decreased to 42.5% to 71.3% in domestic species. "Colombiana" stock produced in the same sylvatic vectors infectivity rates ranging from 12.5% to 45%. These shrank to 5%-22.5% in domestic bugs. The functional role of the biotope in the vector-parasite interaction has not been eluddated. But since this phenomenon has been observed to be stable and easy to reproduce, it leads us to believe that the results obtained are valid. Data presented also provide increasing evidence that the infectivity rates exhibited by bugs from xenodiagnosis in chronic hosts, are parasite stock specific. For example, infectivity rates produced by "Berenice", "Y", "FL" and "CL" varied in R. neglectus from 26.3% to 75%; in P. megistus from 56.3% to 83.8%; in T. sordida from 28.8% to 58.8% in T. pseudomaculata from 41.3% to 66.3% and in T. rubrovaria from 48.8% to 85%. Data from xenodiagnosis in the same hosts, carrying acute infections by the same parasite stocks, gave the five sylvatic vectors a positive rating of approximately 100%, thus suggesting that the heavy loads of parasites circulating in the acute hosts obscured the characteristic interspecific differences for the parasite stock. Nonetheless these latter were revealed in the same hosts with chronic infections stimulated by very low numbers of the same parasite stocks. Certain observations here described lead us to speculate as to the possibility of further results from other parasite stocks, allowing the association of the infectivity rates produced in bugs by different parasite stocks with the isoenzymic patterns revealed by these stocks.