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No description available.

Bruchid pests are of considerable economic importance, infesting legume seeds and pods in fields and stores, predominately in the semi-arid tropics. One of the foremost bruchid pests"Callosobruchus maculatus is a niche generalist in that it can infest seeds whilst within pods or when loose. It exhibits a much greater degree of polyphagy than its wild relatives, perhaps partly due to behavioural plasticity. As their larvae are restricted to a single seed, resources available for growth are directly related to egg distribution by the ovipositing female. Host selection is a complex process and involves host finding, recognition (which may occur before or after contact with the plant), and host acceptance which is manifested as contact inspection behaviour and culminates in oviposition. Numerous factors influence these processes including the nature of host chemistry and the presence of conspecific epideictic pheromones. The purpose of this study was to investigate the factors which modulate the tendency to oviposit and oviposition behaviour itself. 2 The oviposition behaviour of newly emerged beetles was recorded on several seeds that vary in their attractiveness as hosts. The behavioural repertoire and the stereotypical sequences that characterise the acceptance or rejection of a host were recorded on pristine and egg laden seeds. These sequences were used to construct flow charts of transitions between the most common behaviours. Several indicators of a host's acceptahility were identified and quantified, including the duration of selected key behaviours. The combination of behaviours exhibited, their position in the transitional matrix and their respective durations, indicated the relative acceptability of the host seeds studied, and provided information on how the different sense organs have complementary roles in the process of host acceptance. This demonstrated that the perception of primary host and conspecific stimuli which influence host acceptance is undertaken by the palps and., to a lesser extent, by the antennae. The study of oviposition behaviour in conjunction with studies on the course of oviposition over extended periods on real and artificial hosts provided the tools by which the chemical bases of host acceptance could be investigated. Host seed extracts were screened for their ability to influence behaviour, and some of the active components were identified as a number of commonly occurring fatty acids. These same fatty acids have been shown to stimulate egg laying, and in different proportions and concentrations, to deter oviposition both as components of a conspecific oviposition deterrent pheromone, and as components of vegetable oils added to stored seeds as a protectant

Thesis (M.Sc. (Agricultural Agronomy)) --University of Limpopo, 2015 / Refer to document / Department of Agriculture Forestry and Fisheries (DAFF)

Metapopulation ecology has developed to explain the population dynamics that occur in spatially structured landscapes. In this study, I combined an empirical laboratory approach, using metapopulation microcosms of Callosobruchus maculatus and its endospecific parasitoid Anisopteromalus calandrae, with mathematical population models in order to investigate several fundamental metapopulation processes. Population dynamics in these systems can be studied at two scales; the local patch-wise scale and the regional metapopulation scale. Here I demonstrate that in both homogeneous and heterogeneous landscapes knowledge of local scale demographic processes is necessary in order to understand regional metapopulation dynamics. The differences in the rate and net direction of dispersal between patches as a result of the permeability of the matrix in homogeneous systems and density-dependent dispersal in heterogeneous systems were also explored. Metapopulation dynamics rely on a balance between local extinctions and recolonisations. Therefore, increasing local mortality rates is likely to be detrimental to the persistence of the system. Here, the impact of several common harvesting strategies on the persistence of a host-parasitoid metapopulation was examined. Contrary to expectation I discovered that harvesting in these systems increased both local and regional population sizes. The increased population size as a result of increased mortality was explained in terms of a hydra effect, where harvesting relaxed density-dependence acting on local host populations. The results presented in this thesis are relevant for the monitoring, management and conservation of natural metapopulations and the development of sustainable harvesting strategies in structured landscapes.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / mRNA sequences coding for two cystatins were isolated from leaves of hydroponically growing cowpea plants. The sequences were ligated in the expression vector pET302NT-HIS, which was introduced into Escherichia coli, ArcticExpress (DE3) cells. The expression was induced by addition of 0.5 mM IPTG and the recombinant proteins VuCys1 (Vigna unguiculata one-domain cystatin) and VuCys2 (Vigna unguiculata two-domain cystatin), both fused to an N-terminal 6x-His tag, were purified by homogeneity using an affinity matrix containing Ni2+ immobilized to Sepharose. The apparent molecular masses for VuCys1 (yield of 10 mgP.L-1 culture) and VuCys2 (yield of 22 mgP.mL-1 culture) were 14 and 26 kDa, respectively. Both inhibitors were strongly active against the proteinases papain and chymopapain, while bromelain and particularly cathepsin B were less susceptible to in vitro inhibition. No inhibition was detected against the serine proteinase trypsin. Thermal stability tests revealed that both cystatins are thermostable proteins able to achieve a minimum residual proteolytic inhibition activity against papain of 95% (VuCys1) and 85% (VuCys2) when incubated at 100 C for 60 minutes. Similar stability results were also obtained when the proteins were tested to the ability of to inhibit papain activity after incubation in pH values ranging from 2.0 to 11.0. Circular dichroism spectroscopy measurements demonstrated that the secondary structure arrangement of both cystatins undergoes only fewer alterations when both proteins were incubated in temperatures varying from 10 to 90 C and pH values varying from 2.0 to 11.0, as well. These data are in agreement with the thermal and pH stability results previously obtained on papain inhibition assays. Biological assays conducted with different phytopathogenic fungi didnât show any negative impact on spore germination as well as on mycelial growth of the tested fungi. Different human pathogens, including the pathogenic yeast Candida albicans were shown to be insensible to VuCys1 and VuCys2. Some scientific reports have proposed the use of cystatins as potential molecules in the control and inhibition of the activity of cysteine proteinases related to carcinogenic process. However, cytotoxicity assays performed on three tumor cell lineages revealed no toxic effects of VuCys1 and VuCys2. Inhibitor activities were also tested against digestive enzymes isolated from third instar larvae of the bruchid insects Callosobruchus maculatus and Zabrotes subfasciatus, two major cowpea plagues. Both cystatins were able to cause high inhibition of C. maculatus enzymes; however they were poorly active against Z. subfasciatus counterpart. Feeding tests were conducted in which both cystatins were added to artificial seeds at final concentrations of 0.025, 0.05 and 0.1% and supplied to C. maculatus. Despite the in vitro inhibition of C. maculatus larvae enzymes, the bioassay data suggest that larvae and adult insects appear to develop adaptive mechanisms which can make them insensible to the ingestion of the inhibitors. Crystallographic studies were carried out in order to solve the tridimensional structure of cystatins. 576 different crystallization conditions were tested in which three were favorable to the formation and growth of diffractable crystals of VuCys1 protein. These crystals belong to the orthorhombic space group P212121 and the unit cell dimension was a = 41.48 Ã; b = 64.68 à and c = 87.91 Ã, α = β = γ = 90. V. unguiculata one-domain cystatin presents a typical 3D domain swapped dimmer molecular structure, which was solved at 1.95 à resolution. No crystals were obtained for VuCys2. The physiological importance of this structure to the plant, the structural stability of both inhibitors and the results raised from biological assays are all discussed in this work. / SequÃncias de mRNA que codificam para duas cistatinas foram isoladas de folhas de plantas de feijÃo-caupi cultivadas em sistema hidropÃnico. As sequÃncias foram ligadas no vetor de expressÃo pET302NT-His, o qual foi introduzido em cÃlulas de Escherichia coli, ArcticExpress (DE3). A induÃÃo da expressÃo foi realizada por meio de adiÃÃo de IPTG (0,5 mM) e as proteÃnas recombinantes VuCys1 â (cistatina de um domÃnio de Vigna unguiculata) e VuCys2 â (cistatina de dois domÃnios de V. unguiculata) ambas fusionadas a uma cauda de histidina N-terminal, foram purificadas por homogeneidade em matriz de afinidade constituÃda de Ni2+ imobilizado à Sepharose. VuCys1 apresentou uma massa molecular aparente de 14 kDa e um rendimento de 10 mgP.L-1 de meio de cultura, jà a proteÃna VuCys2 mostrou uma massa molecular aparente de 26 kDa e um rendimento de 22 mgP.L-1 de meio de cultura. As duas proteÃnas foram fortemente ativas contra as proteinases papaÃna e quimopapaÃna, moderadamente ativas contra bromelaÃna e apenas fracamente ativas contra catepsina B, enquanto que nenhuma atividade inibitÃria foi detectada contra a proteinase serÃnica tripsina. Ensaios de estabilidade tÃrmica mostraram que as duas cistatinas sÃo proteÃnas termoestÃveis, uma vez que, mesmo apÃs incubaÃÃo a 100 C por 60 minutos apresentam atividade inibitÃria residual contra papaÃna superior a 95% (VuCys1) e superior a 85% (VuCys2). Resultados similares de estabilidade tambÃm foram obtidos quando as proteÃnas foram testadas quanto à capacidade de inibir a atividade de papaÃna, apÃs incubaÃÃo em valores de pH variando de 2,0 a 11,0. AnÃlises espectroscÃpicas de dicroÃsmo circular revelaram que o padrÃo de estruturas secundÃrias de ambos inibidores sofre pouca alteraÃÃo apÃs incubaÃÃo em temperaturas variando de 10 a 90 C e em valores de pH variando de 2,0 a 11,0. Estes dados estÃo de acordo com os resultados de elevada estabilidade tÃrmica e a extremos de pH previamente obtidos nos ensaios de inibiÃÃo in vitro de papaÃna. Ensaios biolÃgicos realizados com diferentes espÃcies de fungos fitopatogÃnicos nÃo mostraram nenhum efeito negativo das proteÃnas sobre a germinaÃÃo de esporos ou crescimento micelial dos fungos testados. Os inibidores tambÃm nÃo se mostraram ativos contra diferentes patÃgenos humanos, incluindo a levedura patogÃnica Candida albicans. Alguns relatos cientÃficos propÃem o uso de cistatinas como agentes em potencial no controle e inibiÃÃo da atividade de proteinases cisteÃnicas relacionados a processos carcinogÃnicos. Contudo, testes de citotoxicidade dos inibidores para trÃs diferentes linhagens de cÃlulas tumorais nÃo mostraram potencial citotÃxico. Os inibidores tambÃm foram testados quanto à capacidade de inibir a atividade de enzimas digestivas isoladas do intestino de larvas de terceiro instar dos insetos bruquÃdeos Callosobruchus maculatus e Zabrotes subfasciatus, duas importantes pragas do feijÃo-caupi. Ambas as cistatinas apresentaram elevado potencial inibitÃrio contra as enzimas de C. maculatus sendo, porÃm, fracamente ativas contra as de Z. subfasciatus. Bioensaios foram realizados nos quais as cistatinas foram inseridas em sementes artificiais nas concentraÃÃes finais de 0,025; 0,05 e 0,1% e administradas a C. maculatus. A despeito da inibiÃÃo in vitro das enzimas digestivas das larvas de C. maculatus, os resultados do bioensaio sugerem que, tanto larvas como insetos adultos, parecem desenvolver mecanismos adaptativos à administraÃÃo dos inibidores que os tornam insensÃveis à sua ingestÃo. Estudos cristalogrÃficos foram realizados na tentativa de solucionar a estrutura tridimensional das cistatinas. 576 condiÃÃes de cristalizaÃÃo foram testadas das quais trÃs levaram à formaÃÃo e crescimento de cristais difratÃveis de VuCys1. Os cristais pertencem ao grupo espacial ortorrÃmbico, P212121, e a cÃlula unitÃria apresentou dimensÃes de a = 41,48; b = 64,68 e c = 87,91 Ã, α = β = γ = 90. VuCys1 apresenta uma estrutura molecular de dÃmero de domÃnios trocados a qual foi resolvida a uma resoluÃÃo de 1,95 Ã. Cristais de VuCys2 nÃo foram obtidos nas condiÃÃes testadas. O significado fisiolÃgico desta estrutura para a planta, a estabilidade estrutural de ambos inibidores e os resultados referentes aos diferentes bioensaios sÃo discutidos no presente trabalho.

MONTEIRO JUNIOR, José Edvar. Caracterização bioquímica, funcional e estrutural de duas cistatinas recombinantes de feijão-caupi. 2012. 179 f.Tese (Doutorado em Bioquímica)-Universidade Federal do Ceará, Fortaleza-CE, 2012. / Submitted by Eric Santiago (erichhcl@gmail.com) on 2016-07-20T14:56:24Z No. of bitstreams: 1 2012_tese_jemonteirojunior.pdf: 22956458 bytes, checksum: 4912cb5f52b152df0d6dcc912bb7ccef (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-08-02T20:37:33Z (GMT) No. of bitstreams: 1 2012_tese_jemonteirojunior.pdf: 22956458 bytes, checksum: 4912cb5f52b152df0d6dcc912bb7ccef (MD5) / Made available in DSpace on 2016-08-02T20:37:33Z (GMT). No. of bitstreams: 1 2012_tese_jemonteirojunior.pdf: 22956458 bytes, checksum: 4912cb5f52b152df0d6dcc912bb7ccef (MD5) Previous issue date: 2012 / mRNA sequences coding for two cystatins were isolated from leaves of hydroponically growing cowpea plants. The sequences were ligated in the expression vector pET302NT-HIS, which was introduced into Escherichia coli, ArcticExpress (DE3) cells. The expression was induced by addition of 0.5 mM IPTG and the recombinant proteins VuCys1 (Vigna unguiculata one-domain cystatin) and VuCys2 (Vigna unguiculata two-domain cystatin), both fused to an N-terminal 6x-His tag, were purified by homogeneity using an affinity matrix containing Ni2+ immobilized to Sepharose. The apparent molecular masses for VuCys1 (yield of 10 mgP.L-1 culture) and VuCys2 (yield of 22 mgP.mL-1 culture) were 14 and 26 kDa, respectively. Both inhibitors were strongly active against the proteinases papain and chymopapain, while bromelain and particularly cathepsin B were less susceptible to in vitro inhibition. No inhibition was detected against the serine proteinase trypsin. Thermal stability tests revealed that both cystatins are thermostable proteins able to achieve a minimum residual proteolytic inhibition activity against papain of 95% (VuCys1) and 85% (VuCys2) when incubated at 100 C for 60 minutes. Similar stability results were also obtained when the proteins were tested to the ability of to inhibit papain activity after incubation in pH values ranging from 2.0 to 11.0. Circular dichroism spectroscopy measurements demonstrated that the secondary structure arrangement of both cystatins undergoes only fewer alterations when both proteins were incubated in temperatures varying from 10 to 90 C and pH values varying from 2.0 to 11.0, as well. These data are in agreement with the thermal and pH stability results previously obtained on papain inhibition assays. Biological assays conducted with different phytopathogenic fungi didn’t show any negative impact on spore germination as well as on mycelial growth of the tested fungi. Different human pathogens, including the pathogenic yeast Candida albicans were shown to be insensible to VuCys1 and VuCys2. Some scientific reports have proposed the use of cystatins as potential molecules in the control and inhibition of the activity of cysteine proteinases related to carcinogenic process. However, cytotoxicity assays performed on three tumor cell lineages revealed no toxic effects of VuCys1 and VuCys2. Inhibitor activities were also tested against digestive enzymes isolated from third instar larvae of the bruchid insects Callosobruchus maculatus and Zabrotes subfasciatus, two major cowpea plagues. Both cystatins were able to cause high inhibition of C. maculatus enzymes; however they were poorly active against Z. subfasciatus counterpart. Feeding tests were conducted in which both cystatins were added to artificial seeds at final concentrations of 0.025, 0.05 and 0.1% and supplied to C. maculatus. Despite the in vitro inhibition of C. maculatus larvae enzymes, the bioassay data suggest that larvae and adult insects appear to develop adaptive mechanisms which can make them insensible to the ingestion of the inhibitors. Crystallographic studies were carried out in order to solve the tridimensional structure of cystatins. 576 different crystallization conditions were tested in which three were favorable to the formation and growth of diffractable crystals of VuCys1 protein. These crystals belong to the orthorhombic space group P212121 and the unit cell dimension was a = 41.48 Å; b = 64.68 Å and c = 87.91 Å, α = β = γ = 90. V. unguiculata one-domain cystatin presents a typical 3D domain swapped dimmer molecular structure, which was solved at 1.95 Å resolution. No crystals were obtained for VuCys2. The physiological importance of this structure to the plant, the structural stability of both inhibitors and the results raised from biological assays are all discussed in this work. / Sequências de mRNA que codificam para duas cistatinas foram isoladas de folhas de plantas de feijão-caupi cultivadas em sistema hidropônico. As sequências foram ligadas no vetor de expressão pET302NT-His, o qual foi introduzido em células de Escherichia coli, ArcticExpress (DE3). A indução da expressão foi realizada por meio de adição de IPTG (0,5 mM) e as proteínas recombinantes VuCys1 – (cistatina de um domínio de Vigna unguiculata) e VuCys2 – (cistatina de dois domínios de V. unguiculata) ambas fusionadas a uma cauda de histidina N-terminal, foram purificadas por homogeneidade em matriz de afinidade constituída de Ni2+ imobilizado à Sepharose. VuCys1 apresentou uma massa molecular aparente de 14 kDa e um rendimento de 10 mgP.L-1 de meio de cultura, já a proteína VuCys2 mostrou uma massa molecular aparente de 26 kDa e um rendimento de 22 mgP.L-1 de meio de cultura. As duas proteínas foram fortemente ativas contra as proteinases papaína e quimopapaína, moderadamente ativas contra bromelaína e apenas fracamente ativas contra catepsina B, enquanto que nenhuma atividade inibitória foi detectada contra a proteinase serínica tripsina. Ensaios de estabilidade térmica mostraram que as duas cistatinas são proteínas termoestáveis, uma vez que, mesmo após incubação a 100 C por 60 minutos apresentam atividade inibitória residual contra papaína superior a 95% (VuCys1) e superior a 85% (VuCys2). Resultados similares de estabilidade também foram obtidos quando as proteínas foram testadas quanto à capacidade de inibir a atividade de papaína, após incubação em valores de pH variando de 2,0 a 11,0. Análises espectroscópicas de dicroísmo circular revelaram que o padrão de estruturas secundárias de ambos inibidores sofre pouca alteração após incubação em temperaturas variando de 10 a 90 C e em valores de pH variando de 2,0 a 11,0. Estes dados estão de acordo com os resultados de elevada estabilidade térmica e a extremos de pH previamente obtidos nos ensaios de inibição in vitro de papaína. Ensaios biológicos realizados com diferentes espécies de fungos fitopatogênicos não mostraram nenhum efeito negativo das proteínas sobre a germinação de esporos ou crescimento micelial dos fungos testados. Os inibidores também não se mostraram ativos contra diferentes patógenos humanos, incluindo a levedura patogênica Candida albicans. Alguns relatos científicos propõem o uso de cistatinas como agentes em potencial no controle e inibição da atividade de proteinases cisteínicas relacionados a processos carcinogênicos. Contudo, testes de citotoxicidade dos inibidores para três diferentes linhagens de células tumorais não mostraram potencial citotóxico. Os inibidores também foram testados quanto à capacidade de inibir a atividade de enzimas digestivas isoladas do intestino de larvas de terceiro instar dos insetos bruquídeos Callosobruchus maculatus e Zabrotes subfasciatus, duas importantes pragas do feijão-caupi. Ambas as cistatinas apresentaram elevado potencial inibitório contra as enzimas de C. maculatus sendo, porém, fracamente ativas contra as de Z. subfasciatus. Bioensaios foram realizados nos quais as cistatinas foram inseridas em sementes artificiais nas concentrações finais de 0,025; 0,05 e 0,1% e administradas a C. maculatus. A despeito da inibição in vitro das enzimas digestivas das larvas de C. maculatus, os resultados do bioensaio sugerem que, tanto larvas como insetos adultos, parecem desenvolver mecanismos adaptativos à administração dos inibidores que os tornam insensíveis à sua ingestão. Estudos cristalográficos foram realizados na tentativa de solucionar a estrutura tridimensional das cistatinas. 576 condições de cristalização foram testadas das quais três levaram à formação e crescimento de cristais difratáveis de VuCys1. Os cristais pertencem ao grupo espacial ortorrômbico, P212121, e a célula unitária apresentou dimensões de a = 41,48; b = 64,68 e c = 87,91 Å, α = β = γ = 90. VuCys1 apresenta uma estrutura molecular de dímero de domínios trocados a qual foi resolvida a uma resolução de 1,95 Å. Cristais de VuCys2 não foram obtidos nas condições testadas. O significado fisiológico desta estrutura para a planta, a estabilidade estrutural de ambos inibidores e os resultados referentes aos diferentes bioensaios são discutidos no presente trabalho.

Lentil (Lens culinaris Med.) is an important component of the human diet in the world, but in the meantime, Europe produces only 26% of the lentils it consumes. This is partly due to strong agronomic weaknesses that reduce yield such as lodging, bruchid beetles and weeds, especially in organic farming. Intercropping, the simultaneous growing of two or more species in the same field is tested here as an option to reduce these drawbacks and develop organic lentil production. The aims of this thesis were to (1) assess the potential of lentil-spring wheat intercrops to produce organic lentil, (2) understand the mechanisms that explain their performances, and (3) evaluate the profitability of such intercrops. A two-year field experiment was carried out in southwestern France in 2015 and 2016 under organic farming rules. Four lentil and two wheat cultivars were grown as sole crops and intercrops in multiple additive and substitutive designs. Our results showed that the total intercrop attainable grain yield was higher than the mean of sole crops. Yet, lentil yield in intercrop was lower than in sole crop as the result of a strong competition for resources from wheat in early lentil growth stages reducing the number of branches per plant of lentil. This led to lower gross margins of intercrops. However, lentil lodging was strongly reduced in intercrops thus its mechanical harvest efficiency increased. This led to similar mechanically harvested yields of lentil in intercrop and sole crop. Consequently, after mechanical harvest and grain cleaning, the marketable gross margin of intercrops was higher than that of sole crops. Our results suggest that (1) intercrop had no effect on bruchids, (2) the most effective intercrop is when lentil is at sole crop density and wheat at 15-20%, (3) intercrop performance is due to complementary use of N pools through legume N2 fixation and (4) the intensity of interspecific interactions depends on year, wheat density and genotypes. Our work indicates that lentil-spring wheat intercrop can develop organic lentil production but a better understanding of Genotype x Environment x Cropping system interactions may be useful to design optimized managements.

La lentille (Lens culinaris Med.) est une composante importante des régimes alimentaires de nombreuses populations à travers le monde mais sa consommation en Europe est relativement faible. L’Europe produit seulement 26% de sa consommation de lentille et ce déficit est en partie causé par d’importants verrous agronomiques comme la verse, les bruches et la compétition des adventices qui réduisent ses rendements, notamment en agriculture biologique. Les associations de cultures, définies comme la culture simultanée d’au moins deux espèces différentes sur une même surface pendant une durée significative, sont considérées comme une option pour lever ces verrous agronomiques et ainsi développer la production de lentille en agriculture biologique. Les objectifs de cette thèse étaient de (1) évaluer le potentiel des associations de lentille et de blé de printemps pour produire de la lentille en conditions d’agriculture biologique et (2) comprendre les principaux mécanismes sous-jacents à la performance des associations. Des essais agronomiques ont été mis en place en 2015 et 2016 en conditions d’agriculture biologique. Quatre variétés de lentille et de blé de printemps ont été conduites en culture pures et en plusieurs associations de type substitutif et additif. Nos résultats montrent que le rendement moyen des associations avant récolte mécanique était plus élevé que le rendement moyen des cultures pures. Néanmoins, le rendement de lentille en association était inférieur à celui de la lentille en culture pure en raison d’une compétition forte et précoce du blé pour les ressources qui a causé la diminution nombre de ramifications par plante de la lentille. Le prix de la lentille étant environ quatre fois plus élevé que celui du blé, la marge brute des associations avant récolte était inférieure à celle de la lentille en culture pure. Cependant, la verse de la lentille a été fortement réduite en association, entrainant une augmentation de l’efficacité de sa récolte mécanique. En conséquence les rendements de lentille issus de la récolte mécanique se sont avérés similaires en association et en culture pure. Enfin, après tri et nettoyage des graines, la marge brute des associations sur le rendement commercialisable était supérieure à celle des cultures pures. Nos résultats montrent que (1) les associations n’ont pas eu d’effet sur le taux de bruchage des lentilles, (2) l’association la plus performante est constituée de lentille à densité équivalente à la culture pure dans laquelle on ajoute 15-20% de blé, (3) la performance des associations est due à une utilisation complémentaire de l’azote rendue possible par la fixation symbiotique de l’azote par la lentille et (4) l’intensité des compétitions entre espèces dépendent de l’année, de la densité de blé et des génotypes. En conclusion, nos travaux indiquent que les associations de lentille et de blé de printemps peuvent permettre de développer la production de lentille en agriculture biologique mais qu’une meilleure compréhension des interactions de type génotype x environnement x conduite pourrait permettre de mettre au point des couverts encore plus performants. / Lentil (Lens culinaris Med.) is an important component of the human diet in the world, but in the meantime, Europe produces only 26% of the lentils it consumes. This is partly due to strong agronomic weaknesses that reduce yield such as lodging, bruchid beetles and weeds, especially in organic farming. Intercropping, the simultaneous growing of two or more species in the same field is tested here as an option to reduce these drawbacks and develop organic lentil production. The aims of this thesis were to (1) assess the potential of lentil-spring wheat intercrops to produce organic lentil, (2) understand the mechanisms that explain their performances, and (3) evaluate the profitability of such intercrops. A two-year field experiment was carried out in southwestern France in 2015 and 2016 under organic farming rules. Four lentil and two wheat cultivars were grown as sole crops and intercrops in multiple additive and substitutive designs. Our results showed that the total intercrop attainable grain yield was higher than the mean of sole crops. Yet, lentil yield in intercrop was lower than in sole crop as the result of a strong competition for resources from wheat in early lentil growth stages reducing the number of branches per plant of lentil. This led to lower gross margins of intercrops. However, lentil lodging was strongly reduced in intercrops thus its mechanical harvest efficiency increased. This led to similar mechanically harvested yields of lentil in intercrop and sole crop. Consequently, after mechanical harvest and grain cleaning, the marketable gross margin of intercrops was higher than that of sole crops. Our results suggest that (1) intercrop had no effect on bruchids, (2) the most effective intercrop is when lentil is at sole crop density and wheat at 15-20%, (3) intercrop performance is due to complementary use of N pools through legume N2 fixation and (4) the intensity of interspecific interactions depends on year, wheat density and genotypes. Our work indicates that lentil-spring wheat intercrop can develop organic lentil production but a better understanding of Genotype x Environment x Cropping system interactions may be useful to design optimized managements.