Trees harbouring ants are better defended than con-generic and sympatric ant-free trees.

Plant strategies against herbivores are classically divided into chemical, physical, biotic defences. However, little is known about the relative importance of each type of plant defence, especially in the same species. Using the myrmecophyte Triplaris americana (both with and without ants), and the congeneric non-myrmecophyte T. gardneriana, we tested whether ant defence is more effective than other defences of naturally ant-free myrmecophytes and the non-myrmecophyte congeneric species, all spatially co-occurring. In addition, we investigated how plant traits vary among plant groups, and how these traits modulate herbivory. We sampled data on leaf area loss and plant traits from these tree groups in the Brazilian Pantanal floodplain, and found that herbivory is sixfold lower in plants with ants than in ant-free plants, supporting a major role of biotic defences against herbivory. Whereas ant-free plants had more physical defences (sclerophylly and trichomes), they had little effect on herbivory-only sclerophylly modulated herbivory, but with opposite effects depending on ants' presence and species identity. Despite little variation in the chemicals among plant groups, tannin concentrations and δ13C signatures negatively affected herbivory in T. americana plants with ants and in T. gardneriana, respectively. We showed that ant defence in myrmecophytic systems is the most effective against herbivory, as the studied plants could not fully compensate the lack of this biotic defence. We highlight the importance of positive insect-plant interactions in limiting herbivory, and therefore potentially plant fitness.

Antifungal Potential of Capsaicinoids and Capsinoids from the Capsicum Genus for the Safeguarding of Agrifood Production: Advantages and Limitations for Environmental Health.

Opportunistic pathogenic fungi arise in agricultural crops as well as in surrounding human daily life. The recent increase in antifungal-resistant strains has created the need for new effective antifungals, particularly those based on plant secondary metabolites, such as capsaicinoids and capsinoids produced by Capsicum species. The use of such natural compounds is well-aligned with the One Health approach, which tries to find an equilibrium among people, animals, and the environment. Considering this, the main objective of the present work is to review the antifungal potential of capsaicinoids and capsinoids, and to evaluate the environmental and health impacts of biofungicides based on these compounds. Overall, capsaicinoids and their analogues can be used to control pathogenic fungi growth in plant crops, as eco-friendly alternatives to pest management, and assist in the conservation and long-term storage of agrifood products. Their application in different stages of the agricultural and food production chains improves food safety, nutritional value, and overcomes antimicrobial resistance, with a lower associated risk to humans, animals, and the environment than that of synthetic fungicides and pesticides. Nevertheless, research on the effect of these compounds on bee-like beneficial insects and the development of new preservatives and packaging materials is still necessary.

Genome size evolution is associated with climate seasonality and glucosinolates, but not life history, soil nutrients or range size, across a clade of mustards.

BACKGROUND AND AIMS: We investigate patterns of evolution of genome size across a morphologically and ecologically diverse clade of Brassicaceae, in relation to ecological and life history traits. While numerous hypotheses have been put forward regarding autecological and environmental factors that could favour small vs. large genomes, a challenge in understanding genome size evolution in plants is that many hypothesized selective agents are intercorrelated. METHODS: We contribute genome size estimates for 47 species of Streptanthus Nutt. and close relatives, and take advantage of many data collections for this group to assemble data on climate, life history, soil affinity and composition, geographic range and plant secondary chemistry to identify simultaneous correlates of variation in genome size in an evolutionary framework. We assess models of evolution across clades and use phylogenetically informed analyses as well as model selection and information criteria approaches to identify variables that can best explain genome size variation in this clade. KEY RESULTS: We find differences in genome size and heterogeneity in its rate of evolution across subclades of Streptanthus and close relatives. We show that clade-wide genome size is positively associated with climate seasonality and glucosinolate compounds. Model selection and information criteria approaches identify a best model that includes temperature seasonality and fraction of aliphatic glucosinolates, suggesting a possible role for genome size in climatic adaptation or a role for biotic interactions in shaping the evolution of genome size. We find no evidence supporting hypotheses of life history, range size or soil nutrients as forces shaping genome size in this system. CONCLUSIONS: Our findings suggest climate seasonality and biotic interactions as potential forces shaping the evolution of genome size and highlight the importance of evaluating multiple factors in the context of phylogeny to understand the effect of possible selective agents on genome size.

Inefficient weapon-the role of plant secondary metabolites in cotton defence against the boll weevil.

MAIN CONCLUSION: Cotton genotypes displayed similar volatile organic compound (VOC) profiles, but major differences in terpenoid aldehyde (TA) content. The differences in VOC production were minor among genotypes, but these differences are crucial for boll weevil attraction. Weevils did not display any preference in feeding behaviour towards cotton genotypes, suggesting physiological adaptation to cope with cotton chemical defence mechanisms. Plant cultivar selection for resistance to herbivore pests is an effective, environmentally safe and inexpensive method to implement in integrated pest management programmes. In this study, we evaluated seven cotton genotypes with respect to the production of volatile organic compounds (VOCs) and non-volatile compounds [terpenoid aldehydes (TAs)], and the attraction and feeding preference of adult boll weevils. Chemical analyses of VOCs from BRS-293, BRS-Rubi, CNPA TB-15, CNPA TB-85, CNPA TB-90, Delta Opal, and Empire Glandless showed that there were few qualitative and quantitative differences across the range of genotypes. In contrast, major differences in TA content were observed, with CNPA TB-15 and CNPA TB-85 producing higher levels of TAs compared to the other genotypes. Our results showed that boll weevil attraction to cotton genotypes varied, suggesting that the ratios and quantities of emitted cotton VOCs are important for host location. However, boll weevil feeding behaviour was neither positively nor negatively influenced by the terpenoid content (non-volatile compounds) of cotton genotypes. The results in this study suggest that boll weevils have adapted physiologically to cope with cotton chemical defence mechanisms.

The fungal subtilase AsES elicits a PTI-like defence response in Arabidopsis thaliana plants independently of its enzymatic activity.

Acremonium strictum elicitor subtilisin (AsES) is a 34-kDa serine-protease secreted by the strawberry fungal pathogen A. strictum. On AsES perception, a set of defence reactions is induced, both locally and systemically, in a wide variety of plant species and against pathogens of alternative lifestyles. However, it is not clear whether AsES proteolytic activity is required for triggering a defence response or if the protein itself acts as an elicitor. To investigate the necessity of the protease activity to activate the defence response, AsES coding sequences of the wild-type gene and a mutant on the active site (S226A) were cloned and expressed in Escherichia coli. Our data show that pretreatment of Arabidopsis plants with inactive proteins, i.e. inhibited with phenylmethylsulphonyl fluoride (PMSF) and mutant, resulted in an increased systemic resistance to Botrytis cinerea and expression of defence-related genes in a temporal manner that mimics the effect already reported for the native AsES protein. The data presented in this study indicate that the defence-eliciting property exhibited by AsES is not associated with its proteolytic activity. Moreover, the enhanced expression of some immune marker genes, seedling growth inhibition and the involvement of the co-receptor BAK1 observed in plants treated with AsES suggests that AsES is being recognized as a pathogen-associated molecular pattern by a leucine-rich repeat receptor. The understanding of the mechanism of action of AsES will contribute to the development of new breeding strategies to confer durable resistance in plants.

Potential and restrictions of Poincianella pyramidalis (Tul.) L. P. Queiroz as native forage in the Brazilian semi-arid region

Poincianella pyramidalis (catingueira) is a endemic plant of the Caatinga, selected by animals grazing on native pasture. With the aim of evaluating characteristics indicative of its nutritional quality, 10 plants were selected and identified, sampled at five different ages, were used to determine dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), mineral matter (MM), DM degradability (Deg DM), NDF degradability (Deg NDF) and in situ and in vitro leaf-tissue degradability. Phytochemical prospection was performed, and 1H and 13C nuclear magnetic resonance applied to detect the presence of secondary compounds. The data were submitted to analysis of variance and Tukey’s test at 5%, and correlation analysis was carried out on the variables for leaf maturity in days. The levels of CP, NDF and Deg NDF showed a negative correlation with the increases in leaf age. Leaf-tissue degradation was restricted due to a physical barrier developed in the leaf fragments, which can be attributed to plant defence mechanisms. The in situ degradability of the cell wall components decreased with the increase in leaf age. The high levels of tannins and lignin, and the strong presence of flavonoids, should be considered for their anti-nutritional and pharmacological potential.

Potential and restrictions of Poincianella pyramidalis (Tul.) L. P. Queiroz as native forage in the Brazilian semi-arid region

Poincianella pyramidalis (catingueira) is a endemic plant of the Caatinga, selected by animals grazing on native pasture. With the aim of evaluating characteristics indicative of its nutritional quality, 10 plants were selected and identified, sampled at five different ages, were used to determine dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), mineral matter (MM), DM degradability (Deg DM), NDF degradability (Deg NDF) and in situ and in vitro leaf-tissue degradability. Phytochemical prospection was performed, and 1H and 13C nuclear magnetic resonance applied to detect the presence of secondary compounds. The data were submitted to analysis of variance and Tukeys test at 5%, and correlation analysis was carried out on the variables for leaf maturity in days. The levels of CP, NDF and Deg NDF showed a negative correlation with the increases in leaf age. Leaf-tissue degradation was restricted due to a physical barrier developed in the leaf fragments, which can be attributed to plant defence mechanisms. The in situ degradability of the cell wall components decreased with the increase in leaf age. The high levels of tannins and lignin, and the strong presence of flavonoids, should be considered for their anti-nutritional and pharmacological potential.(AU)

Mechanisms of plant protection against two oxalate-producing fungal pathogens by oxalotrophic strains of Stenotrophomonas spp.

KEY MESSAGE: Oxalotrophic Stenotrophomonas isolated from tomato rhizosphere are able to protect plants against oxalate-producing pathogens by a combination of actions including induction of plant defence signalling callose deposition and the strengthening of plant cell walls and probably the degradation of oxalic acid. Oxalic acid plays a pivotal role in the virulence of the necrotrophic fungi Botrytis cinerea and Sclerotinia sclerotiorum. In this work, we isolated two oxalotrophic strains (OxA and OxB) belonging to the bacterial genus Stenotrophomonas from the rhizosphere of tomato plants. Both strains were capable to colonise endophytically Arabidopsis plants and protect them from the damage caused by high doses of oxalic acid. Furthermore, OxA and OxB protected Arabidopsis from S. sclerotiorum and B. cinerea infections. Bacterial inoculation induced the production of phenolic compounds and the expression of PR-1. Besides, both isolates exerted a protective effect against fungal pathogens in Arabidopsis mutants affected in the synthesis pathway of salicylic acid (sid2-2) and jasmonate perception (coi1). Callose deposition induced by OxA and OxB was required for protection against phytopathogens. Moreover, B. cinerea and S. sclerotiorum mycelial growth was reduced in culture media containing cell wall polysaccharides from leaves inoculated with each bacterial strain. These findings suggest that cell walls from Arabidopsis leaves colonised by these bacteria would be less susceptible to pathogen attack. Our results indicate that these oxalotrophic bacteria can protect plants against oxalate-producing pathogens by a combination of actions and show their potential for use as biological control agents against fungal diseases.

Compensation to simulated insect leaf herbivory in wild cotton (Gossypium hirsutum): responses to multiple levels of damage and associated traits.

Identifying the mechanisms of compensation to insect herbivory remains a major challenge in plant biology and evolutionary ecology. Most previous studies have addressed plant compensatory responses to one or two levels of insect herbivory, and the underlying traits mediating such responses remain elusive in many cases. We evaluated responses associated with compensation to multiple intensities of leaf damage (0% control, 10%, 25%, 50%, 75% of leaf area removed) by means of mechanical removal of foliar tissue and application of a caterpillar (Spodoptera exigua) oral secretions in 3-month-old wild cotton plants (Gossypium hirsutum). Four weeks post-treatment, we measured plant growth and multiple traits associated with compensation, namely: changes in above- and belowground, biomass and the concentration of nutrients (nitrogen and phosphorus) and non-structural carbon reserves (starch and soluble sugars) in roots, stems and leaves. We found that wild cotton fully compensated in terms of growth and biomass allocation when leaf damage was low (10%), whereas moderate (25%) to high leaf damage in some cases led to under-compensation. Nonetheless, high levels of leaf removal (50% and 75%) in most cases did not cause further reductions in height and allocation to leaf and stem biomass relative to low and moderate damage. There were significant positive effects of leaf damage on P concentration in leaves and stems, but not roots, as well as a negative effect on soluble sugars in roots. These results indicate that wild cotton fully compensated for a low level of leaf damage but under-compensated under moderate to high leaf damage, but can nonetheless sustain growth despite increasing losses to herbivory. Such responses were possibly mediated by a re-allocation of carbohydrate reserves from roots to shoots.

Anthonomus grandis aggregation pheromone induces cotton indirect defence and attracts the parasitic wasp Bracon vulgaris.

Insect-derived volatiles seem to provide reliable chemical cues that plants could employ to defend themselves. Here we investigated the effect of pheromone emission from a closely associated (Anthonomus grandis; boll weevil) and an unassociated (Tibraca limbativentris) herbivore on cotton volatile emission. Exposure to A. grandis aggregation pheromone induced cotton defence response by enhancing the emission of volatiles attractive to the natural enemy of A. grandis, the parasitic wasp Bracon vulgaris, but only when the pheromonal blend was complete (all four components). Individual components of A. grandis aggregation pheromone were not able to induce cotton plants to increase the release of volatiles. On the other hand, T. limbativentris sex pheromone did not induce any change in the cotton constitutive volatile profile. Our results support the hypothesis that plants are able to detect pheromones of tightly co-evolved herbivores. Moreover, A. grandis pheromone exposure induced similar volatile compounds to herbivore-induced cotton, such as linalool, (E)-ocimene, (E)-4,8-dimethylnona-1,3,7-triene (DMNT), and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT). We also showed that the larval ectoparasitoid B. vulgaris relies on boll weevil's aggregation pheromone and pheromone-induced plant volatiles as kairomones to locate suitable hosts.

Bacterial and plant natriuretic peptides improve plant defence responses against pathogens.

Plant natriuretic peptides (PNPs) have been implicated in the regulation of ions and water homeostasis, and their participation in the plant immune response has also been proposed. Xanthomonas citri ssp. citri contains a gene encoding a PNP-like protein (XacPNP) which has no homologues in other bacteria. XacPNP mimics its Arabidopsis thaliana homologue AtPNP-A by modifying host responses to create favourable conditions for pathogen survival. However, the ability of XacPNP to induce plant defence responses has not been investigated. In order to study further the role of XacPNP in vivo, A. thaliana lines over-expressing XacPNP, lines over-expressing AtPNP-A and AtPNP-A-deficient plants were generated. Plants over-expressing XacPNP or AtPNP-A showed larger stomatal aperture and were more resistant to saline or oxidative stress than were PNP-deficient lines. In order to study further the role of PNP in biotic stress responses, A. thaliana leaves were infiltrated with pure recombinant XacPNP, and showed enhanced expression of genes related to the defence response and a higher resistance to pathogen infections. Moreover, AtPNP-A expression increased in A. thaliana on Pseudomonas syringae pv. tomato (Pst) infection. This evidence led us to analyse the responses of the transgenic plants to pathogens. Plants over-expressing XacPNP or AtPNP-A were more resistant to Pst infection than control plants, whereas PNP-deficient plants were more susceptible and showed a stronger hypersensitive response when challenged with non-host bacteria. Therefore, XacPNP, acquired by horizontal gene transfer, is able to mimic PNP functions, even with an increase in plant defence responses.

A few sequence polymorphisms among isolates of Maize bushy stunt phytoplasma associate with organ proliferation symptoms of infected maize plants.

Background and Aims: Maize bushy stunt phytoplasma (MBSP) is a bacterial pathogen of maize ( Zea mays L.) across Latin America. MBSP belongs to the 16SrI-B sub-group within the genus ' Candidatus Phytoplasma'. MBSP and its insect vector Dalbulus maidis (Hemiptera: Cicadellidae) are restricted to maize; both are thought to have coevolved with maize during its domestication from a teosinte-like ancestor. MBSP-infected maize plants show a diversity of symptoms. and it is likely that MBSP is under strong selection for increased virulence and insect transmission on maize hybrids that are widely grown in Brazil. In this study it was investigated whether the differences in genome sequences of MBSP isolates from two maize-growing regions in South-east Brazil explain variations in symptom severity of the MBSP isolates on various maize genotypes. Methods: MBSP isolates were collected from maize production fields in Guaíra and Piracicaba in South-east Brazil for infection assays. One representative isolate was chosen for de novo whole-genome assembly and for the alignment of sequence reads from the genomes of other phytoplasma isolates to detect polymorphisms. Statistical methods were applied to investigate the correlation between variations in disease symptoms of infected maize plants and MBSP sequence polymorphisms. Key Results: MBSP isolates contributed consistently to organ proliferation symptoms and maize genotype to leaf necrosis, reddening and yellowing of infected maize plants. The symptom differences are associated with polymorphisms in a phase-variable lipoprotein, which is a candidate effector, and an ATP-dependent lipoprotein ABC export protein, whereas no polymorphisms were observed in other candidate effector genes. Lipoproteins and ABC export proteins activate host defence responses, regulate pathogen attachment to host cells and activate effector secretion systems in other pathogens. Conclusions: Polymorphisms in two putative virulence genes among MBSP isolates from maize-growing regions in South-east Brazil are associated with variations in organ proliferation symptoms of MBSP-infected maize plants.

Genome-wide identification of potato long intergenic noncoding RNAs responsive to Pectobacterium carotovorum subspecies brasiliense infection.

BACKGROUND: Long noncoding RNAs (lncRNAs) represent a class of RNA molecules that are implicated in regulation of gene expression in both mammals and plants. While much progress has been made in determining the biological functions of lncRNAs in mammals, the functional roles of lncRNAs in plants are still poorly understood. Specifically, the roles of long intergenic nocoding RNAs (lincRNAs) in plant defence responses are yet to be fully explored. RESULTS: In this study, we used strand-specific RNA sequencing to identify 1113 lincRNAs in potato (Solanum tuberosum) from stem tissues. The lincRNAs are expressed from all 12 potato chromosomes and generally smaller in size compared to protein-coding genes. Like in other plants, most potato lincRNAs possess single exons. A time-course RNA-seq analysis between a tolerant and a susceptible potato cultivar showed that 559 lincRNAs are responsive to Pectobacterium carotovorum subsp. brasiliense challenge compared to mock-inoculated controls. Moreover, coexpression analysis revealed that 17 of these lincRNAs are highly associated with 12 potato defence-related genes. CONCLUSIONS: Together, these results suggest that lincRNAs have potential functional roles in potato defence responses. Furthermore, this work provides the first library of potato lincRNAs and a set of novel lincRNAs implicated in potato defences against P. carotovorum subsp. brasiliense, a member of the soft rot Enterobacteriaceae phytopathogens.

Plant defence as a complex and changing phenotype throughout ontogeny.

BACKGROUND AND AIMS: Ontogenetic changes in anti-herbivore defences are common and result from variation in resource availability and herbivore damage throughout plant development. However, little is known about the simultaneous changes of multiple defences across the entire development of plants, and how such changes affect plant damage in the field. The aim of this study was to assess if changes in the major types of plant resistance and tolerance can explain natural herbivore damage throughout plant ontogeny. METHODS: An assessment was made of how six defensive traits, including physical, chemical and biotic resistance, simultaneously change across the major transitions of plant development, from seedlings to reproductive stages of Turnera velutina growing in the greenhouse. In addition, an experiment was performed to assess how plant tolerance to artificial damage to leaves changed throughout ontogeny. Finally, leaf damage by herbivores was evaluated in a natural population. KEY RESULTS: The observed ontogenetic trajectories of all defences were significantly different, sometimes showing opposite directions of change. Whereas trichome density, leaf toughness, extrafloral nectary abundance and nectar production increased, hydrogen cyanide and compensatory responses decreased throughout plant development, from seedlings to reproductive plants. Only water content was higher at the intermediate juvenile ontogenetic stages. Surveys in a natural population over 3 years showed that herbivores consumed more tissue from juvenile plants than from younger seedlings or older reproductive plants. This is consistent with the fact that juvenile plants were the least defended stage. CONCLUSIONS: The results suggest that defensive trajectories are a mixed result of predictions by the Optimal Defence Theory and the Growth-Differentiation Balance Hypothesis. The study emphasizes the importance of incorporating multiple defences and plant ontogeny into further studies for a more comprehensive understanding of plant defence evolution.

Role of Arginine decarboxylase (ADC) in Arabidopsis thaliana defence against the pathogenic bacterium Pseudomonas viridiflava.

Polyamine biosynthesis starts with putrescine production through the decarboxylation of arginine or ornithine. In Arabidopsis thaliana, putrescine is synthesised exclusively by arginine decarboxylase (ADC), which exists as two isoforms (ADC1 and 2) that are differentially regulated by abiotic stimuli, but their role in defence against pathogens has not been studied in depth. This work analysed the participation of ADC in Arabidopsis defence against Pseudomonas viridiflava. ADC activity and expression, polyamine levels and bacterial resistance were analysed in null mutants of each ADC isoform. In non-infected wild-type (WT) plants, ADC2 expression was much higher than ADC1. Analysis of adc mutants demonstrated that ADC2 contributes to a much higher extent than ADC1 to basal ADC activity and putrescine biosynthesis. In addition, adc2 mutants showed increased basal expression of salicylic acid- and jasmonic acid-dependent PR genes. Bacterial infection induced putrescine accumulation and ADC1 expression in WT plants, but pathogen-induced putrescine accumulation was blocked in adc1 mutants. Results suggest a specific participation of ADC1 in defence, although basal resistance was not decreased by dysfunction of either of the two ADC genes. In addition, and as opposed to WT plants, bacterial infection increased ADC2 expression and ADC activity in adc1 mutants, which could counterbalance the lack of ADC1. Results demonstrate a major contribution of ADC2 to total ADC activity and the specific induction of ADC1 in response to infection. A certain degree of functional redundancy between the two isoforms in relation to their contribution to basal resistance is also evident.

Extrafloral nectar fuels ant life in deserts.

Interactions mediated by extrafloral nectary (EFN)-bearing plants that reward ants with a sweet liquid secretion are well documented in temperate and tropical habitats. However, their distribution and abundance in deserts are poorly known. In this study, we test the predictions that biotic interactions between EFN plants and ants are abundant and common also in arid communities and that EFNs are only functional when new vegetative and reproductive structures are developing. In a seasonal desert of northwestern Argentina, we surveyed the richness and phenology of EFN plants and their associated ants and examined the patterns in ant-plant interaction networks. We found that 25 ant species and 11 EFN-bearing plant species were linked together through 96 pairs of associations. Plants bearing EFNs were abundant, representing ca. 19 % of the species encountered in transects and 24 % of the plant cover. Most ant species sampled (ca. 77 %) fed on EF nectar. Interactions showed a marked seasonal pattern: EFN secretion was directly related to plant phenology and correlated with the time of highest ant ground activity. Our results reveal that EFN-mediated interactions are ecologically relevant components of deserts, and that EFN-bearing plants are crucial for the survival of desert ant communities.

A novel antifungal protein from seeds of Sesbania virgata (Cav.) Pers. (Leguminosae-Faboideae) / Uma nova proteína antifúngica obtida de sementes de Sesbania virgata (Cav.) Pers. (Leguminosae-Faboideae)

A novel antifungal protein with a molecular mass around 50 kDa was purified from seeds of Sesbania virgata (Cav.) Pers. using ammonium sulfate fractionation followed by gel filtration on a Sephadex G-75 Superfine (Sigma) column and reverse-phase high performance liquid chromatography on a C8 column. The protein, designated FP1-A, with a novel N-terminal sequence AMVHSPGG(S)FS(P), showed growth inhibitory activity of filamentous fungi Aspergillus niger, Cladosporium cladosporioides, Colletotrichum gloeosporioides and Fusarium solani.

Uma nova proteína com atividade antifúngica, com massa molar de cerca de 50 kDa, foi purificada de sementes de Sesbania virgata (Cav.) Pers. utilizando precipitação com sulfato de amônia, filtração em gel em coluna de Sephadex G-75 Superfine (Sigma) e cromatografia líquida de alta eficiência em fase reversa (coluna C8). A proteína purificada foi designada FP1-A, com a sequência N-terminal AMVHSPGG(S)FS(P), apresentando atividade inibitória do crescimento dos fungos filamentosos Aspergillus niger, Cladosporium cladosporioides, Colletotrichum gloeosporioides e Fusarium solani.

A novel antifungal protein from seeds of Sesbania virgata (Cav.) Pers. (Leguminosae-Faboideae) / Uma nova proteína antifúngica obtida de sementes de Sesbania virgata (Cav.) Pers. (Leguminosae-Faboideae)

A novel antifungal protein with a molecular mass around 50 kDa was purified from seeds of Sesbania virgata (Cav.) Pers. using ammonium sulfate fractionation followed by gel filtration on a Sephadex G-75 Superfine (Sigma) column and reverse-phase high performance liquid chromatography on a C8 column. The protein, designated FP1-A, with a novel N-terminal sequence AMVHSPGG(S)FS(P), showed growth inhibitory activity of filamentous fungi Aspergillus niger, Cladosporium cladosporioides, Colletotrichum gloeosporioides and Fusarium solani.(AU)

Uma nova proteína com atividade antifúngica, com massa molar de cerca de 50 kDa, foi purificada de sementes de Sesbania virgata (Cav.) Pers. utilizando precipitação com sulfato de amônia, filtração em gel em coluna de Sephadex G-75 Superfine (Sigma) e cromatografia líquida de alta eficiência em fase reversa (coluna C8). A proteína purificada foi designada FP1-A, com a sequência N-terminal AMVHSPGG(S)FS(P), apresentando atividade inibitória do crescimento dos fungos filamentosos Aspergillus niger, Cladosporium cladosporioides, Colletotrichum gloeosporioides e Fusarium solani.(AU)

INDUCCIÓN DE ACTIVIDAD PEROXIDASA Y DE FENOLES TOTALES COMO RESPUESTA DEL FRUTO DE LULO (Solatium quitoense L.) AL PATÓGENO CAUSAL DE LA ANTRACNOSIS / INDUCTION OF PEROXIDASE AND TOTAL PHENOLS AS A RESPONSE OF LULO (Solanum quitoense L.) FRUIT TO PATHOGEN CAUSING ANTHRACNOSE / INDUÇÃO DA ACTMDADE PEROXIDASA E FENÓIS TOTAIS COMO RESPOSTA DO FRUTO DE LULO (Solanum quitoense L.) AO PATÓGENO QUE CAUSA ANTRACNOSE

Se evaluó la inducción de peroxidasa en frutos de lulo con el fin de determinar su participación en las respuestas bioquímicas hacia el patógeno Colletotrichum acutatum, causante de la antracnosis. Se establecieron como mejores condiciones para su extracción y para determinación de la actividad: buffer fosfatos 100 mM pH 7, 1% SDS y 1 % PVPP; sustrato guayacol 15 mM, peróxido de hidrógeno 10 mM, pH 6,5, 55 °C y 30 µL de extracto. Se realizó un ensayo in vivo usando frutos verdes, pintones y maduros, inoculados con el hongo o con agua estéril. Se determinó la actividad peroxidasa a diferentes horas a partir de la inoculación, encontrándose una respuesta diferencial con el tiempo por efecto de la presencia del patógeno, y según el estado de madurez de los frutos. En lulos verdes inoculados con el hongo se observó aumento en la actividad al cabo de 6 y 144 horas. En lulos pintones no se observó efecto notable, mientras que en maduros el aumento en actividad fue prácticamente a todos los tiempos. Los resultados del contenido de fenoles totales mostraron que hubo acumulación a 96 y 144 horas por efecto del patógeno, para lulos en estado verde y maduro, mientras que para pintones, en los que se presentaron más rápido y con mayor severidad los síntomas de la antracnosis, no se observó aumento a ninguno de los tiempos. En los frutos más enfermos, el cambio en actividad peroxidasa y en contenido total de fenoles fue menos evidente, por lo que se sugiere una relación inversa de estos con el desarrollo de la antracnosis.

The induction of peroxidase in lulo fruits was evaluated in order to determine its participation in the biochemical responses towards the pathogen Colletotrichum acutatum, which causes the antrachnosis disease. For extraction and activity determination, these conditions were established as the best: buffer phosphates 100 mM pH 7, 1% SDS y 1 % PVPP; substrate guaiacol 15 mM, hydrogen peroxide 10 mM, pH 6,5, 55 °C and 30 µL of the extract. An in vivo test was developed using unripe, semi-ripe and ripe fruits, inoculated with the fungus or sterile water. The peroxidase activity was measured at different hours starting from the inoculation, finding a time differential response caused by the pathogen presence and according to the maturity state of fruits; in unripe lulo fruits inoculated with the fungus, an increase of the activity was observed after 6 and 144 hours. In semi-ripe fruits no considerable effect was seen, while in ripe fruits the increase of the activity was found practically at all times. The results of the measured total phenol content, showed accumulation at 96 and 144 hours as a result of the pathogen presence in unripe and ripe fruits, while for semi-ripe fruits, in which the antrachnosis symptoms were noticed faster and more severely, no phenol increase was found at any time. The less evident changes seen in peroxidase and phenol content, using severely affected fruits by the disease, suggest an inverse relationship between these parameters and the development of the antrachnosis.

A indução da peroxidasa foi avaliada na casca de frutos de lulo com a finalidade de determinar a sua possível participação em reacções de defesa contra o patógeno Colletotrichum acutatum, causador da doença antracnose. Foram estabelecidas as melhores condições para a sua extracção e para medir a actividade da enzima extraída, encontrando-se que com tampão fosfato 100 mM pH 7, 1% SDS y 1% PVPP, substrato guaicol 15 mM, peróxido de hidrogeno 10 mM, pH 6,5, 55 °C y 30 µL de extracto enzimático se conseguiram as actividades enzimáticas mais elevadas. Foi realizado um ensaio in vivo usando frutos verdes, em processo de maduração e maduros, inoculados com o fungo ou com água estéril. A actividade peroxidasa foi determinada a diferentes horas a partir da inoculação encontrando-se uma resposta diferencial com o tempo pelo efeito da presença ao patógeno e de acordo ao estado de madurez dos frutos. Em lulos verdes observou-se um aumento da actividade nos frutos inoculados com o fungo ao fim de 6 e 144 horas. Em lulos em processo de maduração, o patógeno não teve maior efeito, enquanto que em lulos maduros o aumento na actividade da enzima, como resposta à presença do patógeno, foi praticamente a todos os tempos avaliados. Os resultados do conteúdo de fenóis totais mostraram que ouve uma acumulação significativa a 96 e 144 horas por efeito da inoculação com o patógeno para lulos em estado verde e maduro, enquanto que para os lulos em processo de maduração, nos quais se apresentaram mais rápido e com maior severidade os sintomas de antracnose, não se observou aumento em nenhum dos tempo avaliados. Nos frutos mais afectados pelos sintomas, a mudança na actividade POD e no conteúdo total de fenóis foi menos evidente, motivo pelo qual se sugere uma relação inversa de estes com o desenvolvimento de antracnose.

Interactions mediated by predators in arthropod food webs / Interações mediadas por predadores em teias alimentares de artrópodes

Studies on interactions among plants, herbivores and natural enemies are important for understanding population dynamics of species in food webs, but they are also important for the practice of pest control with natural enemies. Biological control programs heavily rely on the occurrence of trophic cascades, where the addition of one natural enemy causes a decrease of pest densities and an increase of plant biomass. However, when more that one natural enemy is used to control various pests in the same system, artificial food webs are created and simple tritrophic interactions change to more complicated ones. The occurrence of complex interactions and omnivory in these food webs may modify the sign and the strength of direct effects of natural enemies on pests. In this paper, we show and discuss the experimental results on interactions mediated by predators in an artificial food web that occurs on cucumber plants in greenhouses where biological control is applied. The two pests in this food web are the two-spotted spider mite Tetranychus urticae Koch, and the western flower thrips Frankliniella occidentalis (Pergande). The predatory mites Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor) are used to control spider mites, and the generalist predatory bug Orius laevigatus (Fieber) and a specialist predatory mite Neoseiulus cucumeris (Oudemans) are predators of thrips. Results from behavioural studies showed that some of these species are attracted to the same patch and do not avoid each other's presence. We show some complex interactions arising from the meeting of these species: (a) the intraguild predation by O. laevigatus on P. persimilis, (b) the use of spider-mite web as a refuge by thrips larvae against their predators. The consequences of such interactions for population dynamics of predators and prey and their implications for success of biological control are discussed.

Estudos sobre interações entre plantas, herbívoros e inimigos naturais são importantes para o entendimento da dinâmica populacional das espécies em teias alimentares, bem como para o sucesso do controle de pragas por inimigos naturais. Os programas de controle biológico fundamentam-se na ocorrência de sucessões tróficas, onde a adição de um inimigo natural causa o decréscimo na densidade da presa/hospedeiro e o aumento da biomassa da planta. Entretanto, quando mais de uma espécie de inimigo natural é usada para controlar várias pragas no mesmo sistema, teias alimentares artificiais são criadas e as interações tritróficas simples transformam-se em outras mais complicadas. A ocorrência de interações complexas e de onivoria nestas teias alimentares pode modificar a direção e a intensidade dos efeitos diretos dos inimigos naturais sobre as pragas. Neste artigo, são apresentados e discutidos os resultados experimentais sobre interações mediadas por predadores em uma teia alimentar artificial. Esta teia é formada em plantas de pepino em casa de vegetação onde o controle biológico é aplicado. A teia constitui-se de duas pragas, o ácaro rajado Tetranychus urticae Koch e o tripes Frankliniella occidentalis (Pergande). Para o controle dos ácaros rajados são liberados os ácaros predadores Phytoseiulus persimilis Athias-Henriot e Neoseiulus californicus (McGregor). O controle dos tripes é feito através de liberações do percevejo generalista Orius laevigatus (Fieber) e do ácaro predador especialista Neoseiulus cucumeris (Oudemans). Resultados de estudos comportamentais mostraram que algumas destas espécies são atraídas para o mesma planta e não evitam plantas ocupados por outras espécies. Quando estas espécies são encontradas na mesma planta, interações complexas ocorrem: (a) predação intraguilda de O. laevigatus sobre P. persimilis, (b) uso da teia produzida pelo ácaro rajado pelas larvas de tripes como refúgio contra seus predadores. As conseqüências ...