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Dassou A.G.,CIRAD - Agricultural Research for Development | Dassou A.G.,African Research Center on Bananas and Plantains | Dassou A.G.,University of Benin | Tixier P.,CIRAD - Agricultural Research for Development | Tixier P.,Tropical Agriculture Research and Higher Education Center
Ecology and Evolution | Year: 2016

Disentangling the effects of plant diversity on the control of herbivores is important for understanding agricultural sustainability. Recent studies have investigated the relationships between plant diversity and arthropod communities at the landscape scale, but few have done so at the local scale. We conducted a meta-analysis of 32 papers containing 175 independent measures of the relationship between plant diversity and arthropod communities. We found that generalist predators had a strong positive response to plant diversity, that is, their abundance increased as plant diversity increased. Herbivores, in contrast, had an overall weak and negative response to plant diversity. However, specialist and generalist herbivores differed in their response to plant diversity, that is, the response was negative for specialists and not significant for generalists. While the effects of scale remain unclear, the response to plant diversity tended to increase for specialist herbivores, but decrease for generalist herbivores as the scale increased. There was no clear effect of scale on the response of generalist predators to plant diversity. Our results suggest that the response of herbivores to plant diversity at the local scale is a balance between habitat and trophic effects that vary according to arthropod specialization and habitat type. Synthesis and applications. Positive effects of plant diversity on generalist predators confirm that, at the local scale, plant diversification of agroecosystems is a credible and promising option for increasing pest regulation. Results from our meta-analysis suggest that natural control in plant-diversified systems is more likely to occur for specialist than for generalist herbivores. In terms of pest management, our results indicate that small-scale plant diversification (via the planting of cover crops or intercrops and reduced weed management) is likely to increase the control of specialist herbivores by generalist predators. © 2016 Published by John Wiley & Sons Ltd. Source


Ewane C.A.,University of Liege | Ewane C.A.,African Research Center on Bananas and Plantains | Ewane C.A.,University of Yaounde I | Lepoivre P.,University of Liege | And 2 more authors.
Biotechnology, Agronomy and Society and Environment | Year: 2012

Crown rot of bananas, caused by a fungal parasitic complex, is one of the main quality defects of exported bananas. Major variations in the susceptibility of bananas to crown rot have been observed in different production zones. The physiological state of the banana fruit at harvest is said to influence its response to pathogenic attack and thus to modulate its susceptibility to crown rot. The susceptibility of bananas to this disease, however, appears to be influenced by many pre-harvest factors, although the underlying defense mechanisms have not been clearly identified. A recent report based on molecular analyses suggests that phenolic compounds might be involved in the different variations in the susceptibility of bananas to crown rot. Results of other earlier studies point to an involvement of phenolic compounds in the defensive reactions of banana plants against various pathogens. The present paper reviews the current state of knowledge on the variations in the susceptibility of bananas to crown rot and takes stock of what is known about phenolic compounds in relation to their potential involvement in the defense mechanisms of the banana plant. Source


Duyck P.-F.,CIRAD | Dortel E.,CIRAD | Tixier P.,CIRAD | Vinatier F.,CIRAD | And 3 more authors.
Soil Biology and Biochemistry | Year: 2012

Understanding how environmental factors structure communities is important in conservation biology and ecosystem management. The aim of this study was to test the hypothesis that a plant-feeding nematode community composed of six species is structured by soil type and climate at the landscape scale, and that niche partitioning via these factors is consistent with the coexistence of the species. Martinique has an impressive diversity of abiotic factors (climate and soil type) over a relatively small land area, which facilitates the study of how soil type and climate affect the nematode community.We conducted this study by building an extensive data set containing the abundance of each nematode species on banana (3708 samples and 5,673,705 nematodes) in a wide range of sites in Martinique. The data set also contained environmental data (soil, climate) and plantation age. We analyzed the response of each nematode species to climate and soil type with a generalized linear model in order to understand whether niche partitioning of factors could contribute to the coexistence of the nematode species.Temperature, rainfall, soil type, and plantation age significantly affected the abundance of the six nematode species. While some pairs of species shared the same environmental niches, other showed clear niche partitioning along climatic axes. The two dominant species, Radopholus similis and Helicotylenchus multicinctus, have similar convergent ecological niches regarding climate, soil type, plantation age, and host range. These two species, which often co-occur, probably have different resources at the root scale. Soil type and climate structure plant-feeding nematode species community at the island scale. Further studies need to evaluate coexistence at the root scale among dominant species. © 2011 Elsevier Ltd. Source


Duyck P.-F.,CIRAD | Lavigne A.,CIRAD | Vinatier F.,CIRAD | Achard R.,CIRAD | And 2 more authors.
Basic and Applied Ecology | Year: 2011

Generalist predators can play an important role in agroecosystems by controlling herbivores via top-down effects. As cover crops are increasingly used in agroecosystems, the effects of this resource on generalist predator diet need to be evaluated. We studied the effect of adding a cover crop, Brachiaria decumbens, on trophic niches of generalist predators in a banana agroecosystem by analysing stable isotope variation in C and N for Cosmopolites sordidus, a major banana pest, and its potential predators (spiders, ants, centipedes, and earwigs). While addition of the new resource did not change the trophic niche of the banana pest C. sordidus, the trophic position of the generalist predators was changed as indicated by δ13C signature. Cover crop provided resources that are likely to support a community of insect herbivores, which are alternative preys for generalist predators. The failure of the cover crop to increase δ15N signature is inconsistent with the hypothesis that the cover crop would increase intraguild predation. By providing alternative preys, the addition of a new resource in agroecosystems has the potential to increase populations of generalist predators and therefore pest control. Source


Emaga T.H.,University of Liege | Emaga T.H.,African Research Center on Bananas and Plantains | Rabetafka N.,University of Liege | Blecker C.S.,University of Liege | Paquot M.,University of Liege
Biotechnology, Agronomy and Society and Environment | Year: 2012

Different hydrolysis procedures of flaxseed polysaccharides (chemical and enzymatic) were carried out with H 2SO 4, HCl andTFA at different acid concentrations (0.2,1 and 2 M) and temperatures (80 and 100°C). Enzymatic and combined chemical and enzymatic hydrolyses of polysaccharide from flaxseed mucilage were also studied. Acid hydrolysis conditions (2 M H 2S 4, 4 h, 100°C) are required to quantify total monosaccharide content of flaxseed mucilage. The enzymatic pathway (Pectinex™ Ultra SP) limits sugar destruction during hydrolysis, but it is also insufficient for complete depolymerization. The combination of the two treatments, i.e. moderate chemical hydrolysis (0.2 M H 2SO 4, 80°C, 48 h) combined with enzymatic hydrolysis is not more effective compared to chemical hydrolysis in drastic conditions (2 M H 2SO 4 at 100°C). The strong interaction between the neutral and acid fractions of flaxseed mucilage may hinder total release of sugar residues. Physical treatment prior to the hydrolysis could be necessary to achieve complete depolymerisation of flaxseed mucilage. Source

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