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[Truncated abstract] In order to expand the gene pool of canola-quality rapeseed (Brassica napus) reciprocal interspecific crosses were made between B. napus cv. Mystic and near canola-quality B. juncea breeding line JN29. F1 progeny from these crosses were used to make backcrosses to both parents in all possible combinations and directions, and were selfed to form F2-derived lines. The highest frequencies of viable F2 and BC1 progeny were obtained when B. napus was the maternal parent of the interspecific hybrid. BC1 and F2 progeny (and subsequent generations) were grown under field conditions to identify agronomic improvements over the parents. Transgressive segregation was observed in F2 and BC1 and in subsequent generations for agronomic traits (seed yield under high or low rainfall conditions, plant biomass, harvest index, height, branching and days to anthesis) and seed quality traits (oil, protein, glucosinolates, oleic acid). The majority of progeny conformed to B. napus morphology, and a minority segregated to B. juncea morphology in subsequent generations. Some of the B. juncea morphotypes had lower glucosinolates and higher oleic acid than the parent JN29, with no detectable erucic acid, and thereby conformed to canola quality. Methods were developed for tracing B-genome in interspecific progeny. A repetitive DNA sequence pBNBH35 from B. nigra (genome BB, 2n = 16) was used to identify B-genome chromosomes and introgressions in interspecific progeny. Specific primers were designed for pBNBH35 in order to amplify the repetitive sequence by PCR. A cloned sub-fragment of 329 bp was confirmed by sequencing as part of pBNBH35. PCR and hybridisation techniques were used on an array of Brassica species to confirm that the pBNBH35 subfragment was Brassica B-genome specific. Fluorescence in situ hybridisation (FISH) in B nigra, B. juncea (AABB, 2n=36) and B. napus (AACC, 2n=38) showed that the pBNBH35 sub-fragment was present on all eight Brassica Bgenome chromosomes and absent from A- and C-genome chromosomes. The pBNBH35 repeat was localised to the centromeric region of each B-genome chromosome. FISH clearly distinguished the B-genome chromosomes from the A-genome chromosomes in the amphidiploid species B. juncea. This is the first known report of a B-genome repetitive marker that is present on all Brassica Bgenome chromosomes. ... The results suggest that novel B. napus genotypes have been generated containing introgressions of B-genome chromatin from B. juncea chromosomes. B. juncea morphology occurred in interspecific progeny with a chromosome complement similar to B. napus (2n = 38) and without the entire Bgenome present. It also is highly likely that recombination has occurred between the A-genome of the two Brassica species. This research has demonstrated that the secondary gene pool of B. napus may be accessed by selfing interspecific hybrids, and without sacrificing canola quality, if the B. juncea parent is near canola-quality. Interspecific progeny may be screened to enhance the proportion with B-genome positive signals. Some progeny with B. junceatype morphology had improved seed quality over the JN29 parent.

La phytoremédiation constitue une nouvelle technologie permettant de dépolluer les sols contaminés par l'utilisation de plantes. Parmi les différents aspects possibles de cette méthode, figure la phytoextraction basée sur l'absorption et l'accumulation du polluant dans les parties aériennes. Pour être efficace, il est nécessaire de disposer de plantes présentant une biomasse élevée. L'objectif de ce travail visait à sélectionner des variétés de moutarde indienne (Brassica juncea L.) tolérantes et accumulatrices de cadmium.<br />La première partie du travail a consisté à mettre au point et à optimiser une méthode de régénération in vitro de plantes de moutarde indienne, à partir de couches cellulaires minces transversales (CCMTs) (influence de l'organe utilisé, de AgNO3 et de la benzylaminopurine). La régénération a été réalisée en appliquant une pression de sélection par le cadmium pour modifier la tolérance au métal. <br />La deuxième partie aborde l'effet des traitements par le cadmium : in vitro et en serre, sur le développement des plants. Une analyse des perturbations physiologiques et biochimiques observées a permis d'évaluer la tolérance des plants vis à vis du cadmium et indiquent que les plantes néoformées en présence de cadmium mettent en place un système d'exclusion du métal.<br />Dans la troisième partie, pour compléter l'étude précédente sur des plantes néoformées, l'effet du cadmium a été testé sur des plantes de B. juncea directement issues de semis. Plusieurs paramètres physiologiques et biochimiques, caractéristiques des stress, ont été étudiés (activité gaïacol peroxydase, peroxydation des lipides, pigments, acides aminés libres, proline glucides, polyamines libres et conjuguées). En raison de leurs propriétés anti-oxydantes, une attention particulière a été portée aux polyamines dont l'application exogène permet d'envisager son utilisation pour améliorer la capacité d'accumulation du cadmium par les plantes.

The phytopathogenic fungus <i>Leptosphaeria maculans</i> can cause blackleg disease on crucifers, which results in significant yield losses. Fungal diseases involve interactions between pathogenic fungi and host plants. One aspect of these interactions is mediated by secondary metabolites produced by both fungi and host plants. Phytotoxins and elicitors as well as phytoanticipins and phytoalexins are metabolites produced by fungi and plants, respectively. This thesis describes and discusses the isolation, structure, biological activity and biosynthesis of the secondary metabolites produced by L. maculans.<p> The elicitor-toxin activity bioassay guided isolation of elicitors and phytotoxins produced by <i>L. maculans</i> in a chemically defined medium lead to the isolation of general elicitors, <i>sirodesmin PL</i> (165) and <i>deacetylsirodesmin PL</i> (166), and specific elicitors, <i>cerebrosides C</i> (14) and D (31) from minimum medium (MM) culture under standard conditions. The known phytotoxins sirodesmin PL (165) and deacetylsirodesmin PL (166) induced the production of <i>phytoalexin spirobrassinin</i> (122) in both resistant plant species (brown mustard, <i>Brassica juncea</i> cv. Cutlass) and susceptible plant species (canola, B. napus cv. Westar). A mixture of cerebrosides C (14) and D (31) induced the production of the phytoalexin rutalexin (127) in resistant plant species (brown mustard, B. juncea cv. Cutlass) but not in susceptible plant species (canola, B. napus cv. Westar). New metabolites leptomaculins A-E (267-269, 272 and 274) and deacetylleptomaculins C-E (270, 273 and 275) were isolated from elicitor-phytotoxin active fractions but did not display detectable elicitor activity or phytotoxicity after purification.<p> New metabolites maculansins A (299) and B (300), which were not detected in cultures of L. maculans incubated in MM, were isolated from cultures of <i>L. maculans</i> incubated in potato dextrose broth (PDB). Maculansins A (299) and B (300) displayed higher phytotoxicity on brown mustard than on canola and white mustard (<i>Sinapis alba cv. Ochre</i>) but did not elicit detectable production of phytoalexins in either brown mustard or canola. Metabolite 2,4-dihydroxy-3,6-dimethylbenzaldehyde (212) was produced in higher amount in cultures of L. maculans incubated in PDB than in MM and displayed strong inhibition effect on the root growth of brown mustard and canola. <i>L. maculans</i> incubated in MM amended with high concentration of NaCl produced a new metabolite, 8-hydroxynaphthalene-1-sulfate (293), and a known metabolite, bulgarein (294), which are likely involved in the self-protection. The potential intermediates involved in the biosynthesis of sirodesmin PL (165) were investigated using deuterium labeled precursors: [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b), [5,5-2H2]phomamide (171a), [2,3,3-2H3]-L-serine (233d) and [5,5-2H2]cyclo-L-tyr-L-ser (252a). Intact incorporation of [5,5-2H2]phomamide (171a) into sirodesmin PL (165) suggested that leptomaculin D (272) and E (274), and deacetylleptomaculin D (273) and E (275) are not intermediates in the biosynthesis of sirodesmin PL (165). They are more likely the catabolic metabolites of sirodesmin PL (165). Phomamide (171), the intermediate in the biosynthetic pathway of sirodesmin PL (165), is likely biosynthesized by coupling of prenyl tyrosine (312) with serine (233) rather than prenylation of cyclo-L-tyr-L-ser (252). When [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), and E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b) were fed into cultures of L. maculans, a â proton exchange was detected by 1H NMR through intrinsic steric isotope effect, which occurs before the formation of phomamide (171). The biosynthesis and catabolism of sirodesmin PL (165) were proposed based on the results obtained in this work.

The phytopathogenic fungus <i>Leptosphaeria maculans</i> can cause blackleg disease on crucifers, which results in significant yield losses. Fungal diseases involve interactions between pathogenic fungi and host plants. One aspect of these interactions is mediated by secondary metabolites produced by both fungi and host plants. Phytotoxins and elicitors as well as phytoanticipins and phytoalexins are metabolites produced by fungi and plants, respectively. This thesis describes and discusses the isolation, structure, biological activity and biosynthesis of the secondary metabolites produced by L. maculans.<p> The elicitor-toxin activity bioassay guided isolation of elicitors and phytotoxins produced by <i>L. maculans</i> in a chemically defined medium lead to the isolation of general elicitors, <i>sirodesmin PL</i> (165) and <i>deacetylsirodesmin PL</i> (166), and specific elicitors, <i>cerebrosides C</i> (14) and D (31) from minimum medium (MM) culture under standard conditions. The known phytotoxins sirodesmin PL (165) and deacetylsirodesmin PL (166) induced the production of <i>phytoalexin spirobrassinin</i> (122) in both resistant plant species (brown mustard, <i>Brassica juncea</i> cv. Cutlass) and susceptible plant species (canola, B. napus cv. Westar). A mixture of cerebrosides C (14) and D (31) induced the production of the phytoalexin rutalexin (127) in resistant plant species (brown mustard, B. juncea cv. Cutlass) but not in susceptible plant species (canola, B. napus cv. Westar). New metabolites leptomaculins A-E (267-269, 272 and 274) and deacetylleptomaculins C-E (270, 273 and 275) were isolated from elicitor-phytotoxin active fractions but did not display detectable elicitor activity or phytotoxicity after purification.<p> New metabolites maculansins A (299) and B (300), which were not detected in cultures of L. maculans incubated in MM, were isolated from cultures of <i>L. maculans</i> incubated in potato dextrose broth (PDB). Maculansins A (299) and B (300) displayed higher phytotoxicity on brown mustard than on canola and white mustard (<i>Sinapis alba cv. Ochre</i>) but did not elicit detectable production of phytoalexins in either brown mustard or canola. Metabolite 2,4-dihydroxy-3,6-dimethylbenzaldehyde (212) was produced in higher amount in cultures of L. maculans incubated in PDB than in MM and displayed strong inhibition effect on the root growth of brown mustard and canola. <i>L. maculans</i> incubated in MM amended with high concentration of NaCl produced a new metabolite, 8-hydroxynaphthalene-1-sulfate (293), and a known metabolite, bulgarein (294), which are likely involved in the self-protection. The potential intermediates involved in the biosynthesis of sirodesmin PL (165) were investigated using deuterium labeled precursors: [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b), [5,5-2H2]phomamide (171a), [2,3,3-2H3]-L-serine (233d) and [5,5-2H2]cyclo-L-tyr-L-ser (252a). Intact incorporation of [5,5-2H2]phomamide (171a) into sirodesmin PL (165) suggested that leptomaculin D (272) and E (274), and deacetylleptomaculin D (273) and E (275) are not intermediates in the biosynthesis of sirodesmin PL (165). They are more likely the catabolic metabolites of sirodesmin PL (165). Phomamide (171), the intermediate in the biosynthetic pathway of sirodesmin PL (165), is likely biosynthesized by coupling of prenyl tyrosine (312) with serine (233) rather than prenylation of cyclo-L-tyr-L-ser (252). When [3,3-2H2]-L-tyrosine (251a), [3,3-2H2]O-prenyl-L-tyrosine (312a), and E-[3,3,5,5,5-2H5]O-prenyl-L-tyrosine (312b) were fed into cultures of L. maculans, a â proton exchange was detected by 1H NMR through intrinsic steric isotope effect, which occurs before the formation of phomamide (171). The biosynthesis and catabolism of sirodesmin PL (165) were proposed based on the results obtained in this work.

African leafy vegetables have been shown and suggested to have potential to contribute to human diets and alleviate malnutrition; however, their levels of utilisation are currently low especially in South Africa. This is because there is limited access to these crops due to low availability in the market. Limited access is attributed, in part, to the lack of commercialisation as a result of limited agronomic information describing optimum management options for these leafy vegetables. Availability of such information would contribute to successful commercialisation of these crops. The primary objective of this study was to establish optimum agronomic management factors for Amaranthus cruentus, Corchorus olitorius, Vigna unguiculata and Brassica juncea for irrigated commercial production in South Africa. Seeds of Amaranthus cruentus, Corchorus olitorius were obtained from the Agricultural Research Council seed bank; Vigna unguiculata were obtained from Hydrotech and Brassica juncea seeds were obtained from Stark Ayres. The project consisted of three field studies whose overall objective was to evaluate growth and yield responses of the selected African leafy vegetables to agronomic factors under irrigated commercial production. These field studies comprised of two single factors; summer trials (planting density and nitrogen on three selected crops) and a combined winter trial (nitrogen, irrigation, plant density and planting date on a winter crop). Chapter three (3) investigated the effect of plant density on growth, physiology and yield responses of Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata to three plant densities under drip irrigated commercial production. The plant density levels of 100 000, 66 666 and 50 000 plants/ha were used in the 2011/12 and 2012/13 summer seasons. Parameters measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number, leaf area index (LAI) and biomass. Amaranthus cruentus and Corchorus olitorius showed better leaf quality at lower plant density of 50 000 plants ha-1 than at 66 666 plants ha-1 and 100 000 plants ha-1. These results are based on bigger leaves expressed as leaf area index (LAI), better colour expressed as chlorophyll (CCI) and higher biomass per plant observed in these crops at 50 000 plants ha-1 in comparison to 66 666 plants ha-1 and 100 000 plants ha-1. In Vigna unguiculata there were no responses observed in LAI and CCI. In Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata fresh and dry mass yield of leaves were higher at 100 000 plants ha-1 compared to other treatments. In A. cruentus and C. olitorius, higher leaf quality parameters (CCI, plant height, leaf number, biomass per plant and LAI) indicated that these crops can perform better at lower densities of 50 000 than at 66 666 plants ha-1 and 100 000 plants ha-1 Therefore, using 50 000 plants ha- 1 is suitable for commercial production of A. cruentus and C. olitorius. In Vigna unguiculata, a plant density of 100 000 plants ha-1 produced the highest fresh and dry mass per unit area without compromising quality in terms of the leaf size (LAI) and colour (CCI). Therefore 100 000 plants ha-1 is a density recommended for commercial production in V. unguiculata.Chapter four (4) was conducted to investigate growth, physiology and yield responses of A. cruentus, C. olitorius and V unguiculata to nitrogen application under drip irrigated commercial production. Three nitrogen treatments levels were used viz. 0, 44 and 88 kg N ha- 1 in 2011/12 season and four nitrogen treatments levels viz. 0, 50, 100 and 125 kg N ha-1 were used in 2012/13 summer season. The nitrogen levels selected for each season were based on recommendations for Amaranthaceae species, Swiss chard (Beta vulgaris L.var cicla) derived from soil analysis of the trial (field) site. Parameters measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number, leaf area index (LAI) and biomass. Results showed that application of nitrogen at 44 kg N ha- 1 in 2011/12 summer season and 100 kg N ha-1 in 2012/13 summer season improved LAI, CCI, biomass per plants and yield in A. cruentus. A similar trend was observed in C. olitorius except that 44 kg N ha-1 improved stem fresh yield. Further increase in nitrogen fertiliser above 44 kg N ha-1 during the 2011/12 season and above 100 kg N ha-1 in 2012/13 summer season reduced leaf quality and yield in both crops. In V. unguiculata, nitrogen application showed a slight increase in yield values from 0 to 44 kg N ha-1 followed by decrease at 88 kg N ha-1 in 2011/12 summer season; however, this increase in yield was not significant. During the 2012/13 summer season, yield in terms of fresh weight was significantly (P<.001) reduced by applying nitrogen at various levels. However, leaf dry matter content increased significantly (P<.001) with increase in nitrogen from 0 kg up to 100 kg N ha-1, then remained unchanged at 125 kg N ha-1. Therefore, the current study recommends that C. olitorius and A. cruentus could be commercialised at 44 kg N ha-1 and 100 kg N ha-1 which were lower nitrogen application rates than those recommended for Amaranthaceae species. In V. unguiculata, 50 kg N ha-1 improved leaf number; however, this did not translate to any fresh yield advantage, implying that the optimum rate for nitrogen application might be lower than 50 kg N ha-1. Therefore, nitrogen rates less than the ones used in the current study are recommended for V. unguiculata. Chapter five (5) was conducted in winter and it was necessitated by observations made primarily in the previous studies which focused on the effects of single factors such as plant density, planting date and nitrogen deficits. Therefore, there was a need to address interactions between irrigation, nitrogen, spacing and planting date. The objective of this study was to evaluate growth, physiology and yield responses of Brassica juncea to different agronomic and management factors in the 2012 and 2013 seasons. The treatments were as follows: two planting dates in main plot (1 June and 18 July, 2012); two irrigation frequency in sub main plot (once and three times a week); three nitrogen levels (0, 50, 100 kg N ha-1) and three plant densities (133 333, 80 000, 50 000 plants ha-1) as subplots. Parameters measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number, leaf area index (LAI) and biomass. Results from this study showed a significant interaction effect on plant height, LAI, CCI and CF. Crops irrigated thrice or once a week with 50 kg N ha-1 combined with 50 000 plants ha-1 produced tall plants and bigger leaves (LAI) in the early planting date (1 June) compared to other combinations. Irrigating three times a week combined with nitrogen application at 100 or 50 kg N ha-1 improved CF for late planting date (18 July) in comparison to other combinations. Irrigating once a week combined with nitrogen application at 100 kg N ha-1 increased CCI. There was no significant interaction effect on yield. Application of nitrogen at 50 and 100 kg N ha-1 significantly (P>0.05) increased yield in early and late planting dates compared to the control (0 kg N ha-1), in 2012 and 2013 winter season. Irrigating three times a week led to a significant (P<0.05) increase in yield in the late planting date (18th July) and early planting date (1st June) in 2013 season. Higher plant density of 133 333 plants ha-1 resulted in significantly (P<0.05) higher yield in terms of fresh mass and leaf number in the late planting date 18 July in 2012 and 2013 seasons. However, leaf quality parameters such as leaf size and colour was compromised at 133 333 plants ha-1 relative to 50 000 plants ha-1. Therefore, farmers are recommended to plant early, apply 50 kg N ha-1, irrigate thrice a week and utilise a spacing of 50 000 plants ha-1. The current study indicates that growth and yield of traditional leaf vegetables can be optimised through improved agronomic practise. / Agriculture and Life Sciences / D. Litt. et. Phil. (Agriculture)

Les conséquences des flux de gènes et de l'introgression entre les cultures transgéniques et leurs apparentés sauvages sont encore au cœur des débats associés à la commercialisation des plantes génétiquement modifiées. J'ai développé mon étude sur les conséquences écologiques et évolutives du flux de gènes entre le colza (Brassica napus) et ses apparentés, la moutarde brune sauvage (B. juncea) et la ravenelle (Raphanus raphanistrum), en réalisant une série d'expériences en serre, au jardin et au champ à Beijing et à Dijon. En premier, j'ai présenté une revue synthétique de la littérature publiée sur les flux de gènes et ses effets sur la fitness chez les Brassicées. En second, j'ai cherché à mettre en évidence le rôle de la taille des semences hybrides entre du colza transgénique Bt et la moutarde. La petite taille des semences a réduit les capacités de croissance et de reproduction, mais l'effet sur la fitness était variable en fonction des fonds génétiques ou spécifiques. Les rétrocroisements sur le colza étaient plus faciles et productifs que pour les autres types de descendants. La plupart de ces plantes avait une morphologie de colza. Liée à la résistance à l'herbicide, cette caractéristique pourrait permettre aux descendants de survivre dans les champs et de disséminer les transgènes aux repousses et aux autres colzas, ce qui serait peut être plus gênant que de voir l'introgression réelle dans le génome du parent sauvage. Troisièmement, j'ai simulé le phénomène d'herbivorie chez la moutarde pour étudier la compétition entre des plantes résistantes et des plantes sensibles indépendamment des problèmes de fitness des hybrides interspécifiques. Les plantes résistantes ont un avantage compétitif évident sous la pression d'herbivorie, et cet avantage est exacerbé sous des conditions difficiles telles que de faibles ressources du milieu et l'intensité de l'herbivorie. L'utilisation d'insectes pour attaquer des populations mixtes composées de rétrocroisements sensibles et Bt-résistants aux insectes a confirmé ce résultat et a montré que le transgène n'avait pas de coût en l'absence d'insectes. La productivité totale des populations a augmenté avec la proportion de plantes résistantes. Quatrièmement, des populations de ravenelles ont été échantillonnées dans quatre régions éloignées entre elles, dont une ayant une longue histoire de coexistence avec le colza et donc ayant plus de chance d'avoir été soumise à l'hybridation interspécifique avec le colza. J'ai interprété la divergence des traits et leur polymorphisme dans le cadre d'une hypothèse d'introgression stabilisée en opposition au simple hasard, bien que les différences avec les autres populations n'étaient pas assez marquées pour faire sortir ces populations du domaine de variation décrit pour les ravenelles. Ces études soulignent plusieurs facteurs qui peuvent accroître le risque des flux de transgènes et l'introgression entre les cultures génétiquement modifiées et leurs apparentés sauvages, et cela doit être pris en compte dans les procédures d'évaluation des risques de l'usage de ces plantes. A savoir : la morphologie cultivée qui rend confuse l'identification des introgressants dans le cadre de la bio-surveillance, les petites semences hybrides avec une dormance et une dispersion supérieures, et l'intensité de l'herbivorie et de la compétition qui exacerbe l'avantage adaptatif des plantes transgéniques résistantes aux insectes. Cependant, l'hypothèse de la formation de " super mauvaises herbes " ne semble pas justifiée.

African leafy vegetables have been shown and suggested to have potential to contribute to human diets and alleviate malnutrition; however, their levels of utilisation are currently low especially in South Africa. This is because there is limited access to these crops due to low availability in the market. Limited access is attributed, in part, to the lack of commercialisation as a result of limited agronomic information describing optimum management options for these leafy vegetables. Availability of such information would contribute to successful commercialisation of these crops. The primary objective of this study was to establish optimum agronomic management factors for Amaranthus cruentus, Corchorus olitorius, Vigna unguiculata and Brassica juncea for irrigated commercial production in South Africa. Seeds of Amaranthus cruentus, Corchorus olitorius were obtained from the Agricultural Research Council seed bank; Vigna unguiculata were obtained from Hydrotech and Brassica juncea seeds were obtained from Stark Ayres. The project consisted of three field studies whose overall objective was to evaluate growth and yield responses of the selected African leafy vegetables to agronomic factors under irrigated commercial production. These field studies comprised of two single factors; summer trials (planting density and nitrogen on three selected crops) and a combined winter trial (nitrogen, irrigation, plant density and planting date on a winter crop). Chapter three (3) investigated the effect of plant density on growth, physiology and yield responses of Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata to three plant densities under drip irrigated commercial production. The plant density levels of 100 000, 66 666 and 50 000 plants/ha were used in the 2011/12 and 2012/13 summer seasons. Parameters measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number, leaf area index (LAI) and biomass. Amaranthus cruentus and Corchorus olitorius showed better leaf quality at lower plant density of 50 000 plants ha-1 than at 66 666 plants ha-1 and 100 000 plants ha-1. These results are based on bigger leaves expressed as leaf area index (LAI), better colour expressed as chlorophyll (CCI) and higher biomass per plant observed in these crops at 50 000 plants ha-1 in comparison to 66 666 plants ha-1 and 100 000 plants ha-1. In Vigna unguiculata there were no responses observed in LAI and CCI. In Amaranthus cruentus, Corchorus olitorius and Vigna unguiculata fresh and dry mass yield of leaves were higher at 100 000 plants ha-1 compared to other treatments. In A. cruentus and C. olitorius, higher leaf quality parameters (CCI, plant height, leaf number, biomass per plant and LAI) indicated that these crops can perform better at lower densities of 50 000 than at 66 666 plants ha-1 and 100 000 plants ha-1 Therefore, using 50 000 plants ha- 1 is suitable for commercial production of A. cruentus and C. olitorius. In Vigna unguiculata, a plant density of 100 000 plants ha-1 produced the highest fresh and dry mass per unit area without compromising quality in terms of the leaf size (LAI) and colour (CCI). Therefore 100 000 plants ha-1 is a density recommended for commercial production in V. unguiculata.Chapter four (4) was conducted to investigate growth, physiology and yield responses of A. cruentus, C. olitorius and V unguiculata to nitrogen application under drip irrigated commercial production. Three nitrogen treatments levels were used viz. 0, 44 and 88 kg N ha- 1 in 2011/12 season and four nitrogen treatments levels viz. 0, 50, 100 and 125 kg N ha-1 were used in 2012/13 summer season. The nitrogen levels selected for each season were based on recommendations for Amaranthaceae species, Swiss chard (Beta vulgaris L.var cicla) derived from soil analysis of the trial (field) site. Parameters measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number, leaf area index (LAI) and biomass. Results showed that application of nitrogen at 44 kg N ha- 1 in 2011/12 summer season and 100 kg N ha-1 in 2012/13 summer season improved LAI, CCI, biomass per plants and yield in A. cruentus. A similar trend was observed in C. olitorius except that 44 kg N ha-1 improved stem fresh yield. Further increase in nitrogen fertiliser above 44 kg N ha-1 during the 2011/12 season and above 100 kg N ha-1 in 2012/13 summer season reduced leaf quality and yield in both crops. In V. unguiculata, nitrogen application showed a slight increase in yield values from 0 to 44 kg N ha-1 followed by decrease at 88 kg N ha-1 in 2011/12 summer season; however, this increase in yield was not significant. During the 2012/13 summer season, yield in terms of fresh weight was significantly (P<.001) reduced by applying nitrogen at various levels. However, leaf dry matter content increased significantly (P<.001) with increase in nitrogen from 0 kg up to 100 kg N ha-1, then remained unchanged at 125 kg N ha-1. Therefore, the current study recommends that C. olitorius and A. cruentus could be commercialised at 44 kg N ha-1 and 100 kg N ha-1 which were lower nitrogen application rates than those recommended for Amaranthaceae species. In V. unguiculata, 50 kg N ha-1 improved leaf number; however, this did not translate to any fresh yield advantage, implying that the optimum rate for nitrogen application might be lower than 50 kg N ha-1. Therefore, nitrogen rates less than the ones used in the current study are recommended for V. unguiculata. Chapter five (5) was conducted in winter and it was necessitated by observations made primarily in the previous studies which focused on the effects of single factors such as plant density, planting date and nitrogen deficits. Therefore, there was a need to address interactions between irrigation, nitrogen, spacing and planting date. The objective of this study was to evaluate growth, physiology and yield responses of Brassica juncea to different agronomic and management factors in the 2012 and 2013 seasons. The treatments were as follows: two planting dates in main plot (1 June and 18 July, 2012); two irrigation frequency in sub main plot (once and three times a week); three nitrogen levels (0, 50, 100 kg N ha-1) and three plant densities (133 333, 80 000, 50 000 plants ha-1) as subplots. Parameters measured included chlorophyll content index (CCI), chlorophyll fluorescence (CF), stomatal conductance (SC), leaf number, leaf area index (LAI) and biomass. Results from this study showed a significant interaction effect on plant height, LAI, CCI and CF. Crops irrigated thrice or once a week with 50 kg N ha-1 combined with 50 000 plants ha-1 produced tall plants and bigger leaves (LAI) in the early planting date (1 June) compared to other combinations. Irrigating three times a week combined with nitrogen application at 100 or 50 kg N ha-1 improved CF for late planting date (18 July) in comparison to other combinations. Irrigating once a week combined with nitrogen application at 100 kg N ha-1 increased CCI. There was no significant interaction effect on yield. Application of nitrogen at 50 and 100 kg N ha-1 significantly (P>0.05) increased yield in early and late planting dates compared to the control (0 kg N ha-1), in 2012 and 2013 winter season. Irrigating three times a week led to a significant (P<0.05) increase in yield in the late planting date (18th July) and early planting date (1st June) in 2013 season. Higher plant density of 133 333 plants ha-1 resulted in significantly (P<0.05) higher yield in terms of fresh mass and leaf number in the late planting date 18 July in 2012 and 2013 seasons. However, leaf quality parameters such as leaf size and colour was compromised at 133 333 plants ha-1 relative to 50 000 plants ha-1. Therefore, farmers are recommended to plant early, apply 50 kg N ha-1, irrigate thrice a week and utilise a spacing of 50 000 plants ha-1. The current study indicates that growth and yield of traditional leaf vegetables can be optimised through improved agronomic practise. / Agriculture and Life Sciences / D. Litt. et. Phil. (Agriculture)

Les conséquences des flux de gènes et de l’introgression entre les cultures transgéniques et leurs apparentés sauvages sont encore au cœur des débats associés à la commercialisation des plantes génétiquement modifiées. J’ai développé mon étude sur les conséquences écologiques et évolutives du flux de gènes entre le colza (Brassica napus) et ses apparentés, la moutarde brune sauvage (B. juncea) et la ravenelle (Raphanus raphanistrum), en réalisant une série d’expériences en serre, au jardin et au champ à Beijing et à Dijon. En premier, j’ai présenté une revue synthétique de la littérature publiée sur les flux de gènes et ses effets sur la fitness chez les Brassicées. En second, j’ai cherché à mettre en évidence le rôle de la taille des semences hybrides entre du colza transgénique Bt et la moutarde. La petite taille des semences a réduit les capacités de croissance et de reproduction, mais l’effet sur la fitness était variable en fonction des fonds génétiques ou spécifiques. Les rétrocroisements sur le colza étaient plus faciles et productifs que pour les autres types de descendants. La plupart de ces plantes avait une morphologie de colza. Liée à la résistance à l’herbicide, cette caractéristique pourrait permettre aux descendants de survivre dans les champs et de disséminer les transgènes aux repousses et aux autres colzas, ce qui serait peut être plus gênant que de voir l’introgression réelle dans le génome du parent sauvage. Troisièmement, j’ai simulé le phénomène d’herbivorie chez la moutarde pour étudier la compétition entre des plantes résistantes et des plantes sensibles indépendamment des problèmes de fitness des hybrides interspécifiques. Les plantes résistantes ont un avantage compétitif évident sous la pression d’herbivorie, et cet avantage est exacerbé sous des conditions difficiles telles que de faibles ressources du milieu et l’intensité de l’herbivorie. L’utilisation d’insectes pour attaquer des populations mixtes composées de rétrocroisements sensibles et Bt-résistants aux insectes a confirmé ce résultat et a montré que le transgène n’avait pas de coût en l’absence d’insectes. La productivité totale des populations a augmenté avec la proportion de plantes résistantes. Quatrièmement, des populations de ravenelles ont été échantillonnées dans quatre régions éloignées entre elles, dont une ayant une longue histoire de coexistence avec le colza et donc ayant plus de chance d’avoir été soumise à l’hybridation interspécifique avec le colza. J’ai interprété la divergence des traits et leur polymorphisme dans le cadre d’une hypothèse d’introgression stabilisée en opposition au simple hasard, bien que les différences avec les autres populations n’étaient pas assez marquées pour faire sortir ces populations du domaine de variation décrit pour les ravenelles. Ces études soulignent plusieurs facteurs qui peuvent accroître le risque des flux de transgènes et l’introgression entre les cultures génétiquement modifiées et leurs apparentés sauvages, et cela doit être pris en compte dans les procédures d’évaluation des risques de l’usage de ces plantes. A savoir : la morphologie cultivée qui rend confuse l’identification des introgressants dans le cadre de la bio-surveillance, les petites semences hybrides avec une dormance et une dispersion supérieures, et l’intensité de l’herbivorie et de la compétition qui exacerbe l’avantage adaptatif des plantes transgéniques résistantes aux insectes. Cependant, l’hypothèse de la formation de « super mauvaises herbes » ne semble pas justifiée. / In the framework of commercial release for transgenic crops with novel traits, consequences of gene flow and introgression are still one main concern. I explored the ecological and evolutionary consequences of gene flow between oilseed rape (Brassica napus) and its wild relatives, brown mustard (B. juncea) and wild radish (Raphanus raphanistrum), through several experiments carried out in greenhouse, common garden and field in Beijing and Dijon. First, I revised a comprehensive review of the literature about gene flow and its effect on plant fitness in the Brassiceae. Second, I investigated the effects on gene flow of seed size of hybrids between Bt-transgenic oilseed rape and mustard. Small seed size significantly reduced plant growth and reproduction, but its influence on plant fitness varied among genetic backgrounds. Backcrosses to oilseed rape were easier and more productive than other types of progeny of hybrids. Most of these plants exhibited oilseed rape morphology. Together with herbicide-resistance, this trait could help the progeny to survive in the field and disseminate the transgene to volunteers and feral populations, which could be more troublesome than completing introgression into the genome of the wild parent species. Third, I simulated herbivory on mustard to study the competition between insect-resistant and susceptible plants independently to the fitness of the interspecific hybrid. Resistant plants held a competitive advantage under herbivory pressure, and this advantage was magnified in harsh conditions, such as low resources and high simulated herbivory pressure. The use of insects to attack mixed populations composed of transgenic Bt-resistant and susceptible backcrosses confirmed the same conclusion and provided evidence of no cost due to the transgene in the absence of insect. The overall population production increased with the increasing proportion of insect-resistant plants in the presence of insects. Fourth, wild radish populations were sampled from four geographically distant regions, of which one region had a long history of oilseed rape cultivation, and, therefore, higher chance to have been submitted to interspecific hybridization with the crop. Traits divergence and polymorphism in the putative introgressed populations could be supported as alternate hypothesis to random variation, although the differences were not marked enough to place these populations out of the range of variation described in wild radish. These studies pointed out different factors that could enhance the risk of transgenic flow and introgression from transgenic crops to wild relatives, and they must be taken into account in the risk assessment of the use of GM crops: crop traits to identify the hybrid progeny and perform monitoring, small seed size to account for seed dispersal and dormancy, and intensity of herbivory and competition that magnify the fitness advantage of insect-resistant transgenic plants. However, the impact of introgression to create super-weeds was not supported.