Cloning and molecular characterization of new genes constitutes a useful approach in studying the symbiotic interactions between the model plant Medicago truncatula and Synorhizobium meliloti. Large numbers of expressed sequence tags (ESTs) available for Medicago truncatula, along with numerous cDNA, oligonucleotides, and Affimetrix DNA microarray chips, represent useful tools for gene discovery. In an attempt to identify a new gene that might be involved in the process of nodulation in Medicago truncatula, preliminary data reported by Fedorova et al. (2002), who identified 340 putative gene products or tentative consensus sequences (TCs) expressed only in nodules, was used. This research was focused on TC33166 (TC103185), which has 3 ESTs in the TC, and whose strongest BLASTX hit of TC103185 is the incomplete root hair elongation (IRE) protein kinase-like protein (NP_192429) from Arabidopsis thaliana. The Arabidopsis IRE gene is required for normal root hair growth, and a role in apical growth was suggested (Oyama et al., 2002). Infection thread growth can be looked at as an inward growth of the root hair. Thus, TC103185 was a good candidate for identifying a gene that may be involved in early events of nodulation. MtIRE (GenBank accession AC122727) is organized in 17 exons and 16 introns, similarly to the Arabidopsis IRE gene. MtIRE is a new member of the IRE family and it is a putative Ser/Thr protein kinase. MtIRE is a nodule- and flower-specific gene, suggesting that nodulation may have recruited it from other developmental processes. MtIRE is likely to be involved in the invasion process, or in the maturation of the symbiosome, or of the cells that contain rhizobia, rather than infection thread initiation and elongation or in nitrogen fixation. Nodule invasion precedes the onset of MtIRE expression and the expression pattern changes in time within the nodule. RNA interference results support MtIRE expression data and suggest a possible role in preventing extensive defense responses. Our study demonstrates the existence of an Arabidopsis IRE homolog in Medicago truncatula root nodules with an entirely new function and regulation.

The use of coated seed to establish crops is not a novel practice. Seed coatings have been used on small seeded crops to improve the handling ability by making the seed unit larger and heavier. Producers can therefore calibrate their sowing equipment more efficiently and wind will not cause as much drift at sowing. Seed coating can have an added benefit for leguminous crops if the symbiotic inoculant (Rhizobium) is added to the coating. This saves the producer time and allows peace of mind that inoculation was done by trained professionals. Other than the inoculation, there are some other constituents in the seed coating that can have benefits to the plant. It can, however, be theorized that added nutrients or pesticides will be beneficial to the plants only if these nutrients are deficient in the growth medium or when pests are present. This study evaluated the effect of seed coating on the life stages of germination, emergence and survival, seedling growth and ultimate yield of mature lucerne (Medicago sativa L.) plants, comparing the results with non-coated seed. Two cultivars were used in the evaluation, SA Standard and SuperCuf, to determine if the effects would be similar, or would genetic differences between the cultivar play a significant role. These life stages (germination, emergence and seedling growth) were chosen due to the importance of these stages to the success of establishment. Fast and uniform germination will result in a uniform stand with strong competition against weed infestation. The effect of growth medium on the emergence of seedlings and the interaction between the seed coating and the growth medium was important to determine to identify limitations in the use of seed coating. Changes in the growth of seedlings in terms of some physio-morphological characteristics will assist in identifying parameters influenced by the coating. It was, however, essential to not only do these trials under ideal agricultural conditions, but to identify if similar results would be obtained from stressed conditions, such as salinity, which is a growing concern for crop production areas. The question of whether seed coating will influence the ultimate production of the crop could then be answered. It was found that the method in which germination is tested can have a significant outcome for the results obtained. When the Jacobsen apparatus was compared with the use of petri dishes, using specification according to ISTA, it was found that the water movement in the Jacobsen apparatus overcomes concentrated nutrient conditions, especially for SuperCuf. Under saline conditions the coated SA Standard seed had higher germination than the non-coated seed, therefore overcoming inhibitions imposed by the salinity. It is clear that the coating influences germination of lucerne and the interaction with the seed environment is significant. It is also clear that the genetic differences between cultivars are significant and results should not be applied across all lucerne cultivars. When the emergence percentage had been determined in different growth media, namely a commercial growth media, a sandy loam soil and silica medium, it was found that the emergence was influenced by the media. Even though the emergence of seedlings are mostly determined by the nutrients in the cotyledons, some growing conditions did cause lower emergence for non-coated SA Standard seeds and was overcome by the use of coated seed. When the growing conditions were manipulated with saline irrigation it was found that coated SuperCuf had a higher emergence % than the non-coated treatments when irrigated with the 750 μS.cm-1 water. From the data collected from this trial, it can be concluded that, even though the use of seed coating does not always influence the emergence of lucerne seedlings, seed coating does have an influence on the emergence, but it is dependent on the growth medium quality in terms of nutrient composition and salinity. Similar to the germination trial, the genetic influence of the different cultivars was noticeable. To determine the differences caused by seed coating to the physio-morphological characteristics (stem height, leaf area etc.) of lucerne, a pot trial was conducted using different irrigation treatments, municipal water (180 μS.cm-1), 500 and 750 μS.cm-1 water, created with NaCl. It was found that the physio-morphological characteristics were highly correlated, i.e. the stem height, leaf area, number of leaves and dry matter production changed in relation to each other. There were, however, differences in this correlation coated and non-coated seed treatments, when irrigated with 500 μS.cm-1 water. For the seedlings grown from coated seed, the correlation between shoot dry matter yield and the other parameters were low, while the seedlings growth from non-coated seed, leaf area was not correlated with the other parameters. It was concluded that the tolerance mechanism for salinity for plants irrigated with 500 μS.cm-1 water, caused more differences than the other water treatments. Taking into consideration that coating influences the germination and emergence of lucerne and that the two cultivars react differently to the seed coating, the yields obtained from field trials could then be interpreted if differences were observed. Three field trials were established, namely a trial established in autumn (established in 2009) and second trial established in spring (established in 2010) which were sown at 25 kg.ha-1, while a third trial established spring (established in 2010) was sown at 5 different sowing densities, namely 80%, 90%, 100%, 110% and 120% of recommended sowing density (25 kg.ha-1). It was found that the pasture stands established with SA Standard, did not show many differences between the coated and non-coated seed treatments and were mostly restricted to the second growing season, where the non-coated seed treatments had significantly higher dry matter yield than the coated seed treatments. Stands established with SuperCuf, displayed more variation between the seed treatments and the non-coated seed treatments had higher yields in the first season. It was, however, found that the stands established with coated SuperCuf seed had lower stem: leaf ratio’s, indicating that a better quality fodder can be produced from coated seed. The data from the sowing density trial showed very little difference between the yields of the stands established with coated and non-coated SA Standard seed. Differences were, however, observed between seed treatments at 90% and 120% of the recommended sowing density, where the stands established with non-coated seed had higher yields than the stands established with coated seed. It can be concluded that under these trial conditions, the use of coated seed had very little influence on the yield of the lucerne stands. The observed differences suggest that the lucerne growth under these few conditions, the stands established from non-coated seed had better yield, but the stands established from coated seed had better quality. It is, however, more likely that there will be no differences between the seed treatments. Data from the sowing density trial also led to the conclusion that stands established at 20% less seed will not result in lower yields if the stand establishment is successful. The similarity between the seed treatments and the sowing densities suggests that the number of plants per area were the same, caused by seedling mortality during the high growth rate in the early growing stage, or the morphological characteristics, such as number of stems per plant and number of leaves per stem, adapted to result in similar yields and quality. / Dissertation (MSc Agric)--University of Pretoria, 2013. / gm2014 / Plant Production and Soil Science / unrestricted

The aim of this diploma thesis is determination of alfalfa (Medicago sativa) infestation in Agricaltural company Kvasicko a. s. The monitoring of infestation was doing from 2013 to 2016 on land Odšenkovna, sawn on 29. 8. 2013, and on land Novina levá, sawn on 11. 4. 2014. Evaluation was made by counting method. The results of this evaluation were processed with DCA analysis and canonical corespondence analysis (CCA). It was found 11 species of weeds on observed lands during the monitoring. The most frequently weeds were: Capsella bursa-pastoris, Stellaria media, Taraxacum sec. Ruderalia and Veronica.

No description available.

Sinorhizobium meliloti est une bactérie du sol Gram- capable d'induire la formation denodosités fixatrices d'azote lors d'une interaction symbiotique avec les plantes de la familledes légumineuses. L'importance de la balance redox au cours de cette interaction a été miseen évidence. Ainsi, des mutants bactériens déficients dans la production du glutathion (GSH),présentent un phénotype altéré d'infection et de fixation de l'azote atmosphérique.Le premier objectif a donc été de déterminer si les phénotypes observés chez les mutants de lavoie de biosynthèse du GSH étaient liés à l'activité des glutarédoxines (GRX). Une analysebioinformatique a révélé la présence de trois gènes codant des GRX chez S. meliloti. Lesmutants, Smgrx1, Smgrx2 et Smgrx3, déficients pour chacune des GRX, ne produisent pasdes phénotypes similaires à ceux observés avec les mutants GSH. Si Smgrx2 présente unphénotype moins marqué, Smgrx1 est plus sévèrement affecté puisqu'il n'est plus capable dese différencier en bactéroïde. L'implication de SmGrx2 dans la régulation du métabolisme dufer et la mise en place des centres Fe-S a, par ailleurs, été mise en évidence.Le second objectif a été de définir s'il existait, chez S. meliloti, une redondance fonctionnelleentre les GRX et les thiorédoxines (TRX). Ainsi, le mutant SmtrxB, dépourvu de thiorédoxineréductase, présente la particularité d'induire la formation d'un plus grand nombre de nodulesque la souche sauvage. Le système TRX de S. meliloti apparaît donc comme un régulateurnégatif de la nodulation. D'autre part, les nodosités formées par ce mutant SmtrxB, ont uneactivité fixatrice d'azote significativement diminuée. Les rôles des TRX et des GRXapparaissent donc, au moins partiellement, distincts.Les résultats obtenus ici apportent des éléments nouveaux sur l'implication du GSH, des GRXet des TRX dans la mise en place d'une nodosité fonctionnelle, et ouvrent de nouvellesperspectives d'études sur les rôles de ces molécules dans le processus de fixation d'azote. / Sinorhizobium meliloti is a soil bacterium Gram- able to induce the formation of nitrogenfixingnodules during a symbiotic interaction with plants of the legume family. Theimportance of redox balance during this interaction has been demonstrated. In this way,bacterial mutants deficient in the production of glutathione (GSH), exhibit an alteredphenotype of infection and fixation of atmospheric nitrogen.The first objective was therefore to determine whether the phenotypes observed in mutants ofthe GSH biosynthesis pathway were related to the activity of glutaredoxins (GRX). Abioinformatic analysis revealed the presence of three genes encoding GRX in S. meliloti. Themutants, Smgrx1, Smgrx2 and Smgrx3, deficient for each of the GRX, do not producephenotypes similar to those observed with the GSH mutants. If Smgrx2 presents a less severephenotype, Smgrx1 is more severely affected since it is incapable of differentiating intobacteroïd. The involvement of SmGrx2 in the regulation of iron metabolism and theestablishment of Fe-S cluster has also been demonstrated.The second objective was to determine if there was, in S. meliloti, a functional redundancybetween GRX and thioredoxin (TRX). Thus, the SmtrxB mutant, devoid of thioredoxinreductase, has the distinctive feature of inducing the formation of more nodules than the wildtype strain. The TRX system of S. meliloti appears to be a negative regulator of nodulation.On the other hand, the nodules formed by this SmtrxB mutant have a significantly decreasednitrogen-fixing activity. Hence, the roles of TRX and GRX appear to be at least partiallydistinct.The results obtained here provide new evidence on the involvement of GSH, the GRX andTRX in the establishment of a functional nodule, and open new perspectives for studying onthe roles of these molecules in the process of nitrogen fixation.

Le monoxyde d'azote (NO) est une molécule gazeuse impliquée dans de nombreux processus biologiques chez les plantes, de la germination de la graine à la mise en place de réponses à des stress abiotiques et biotiques. Dans les interactions plante/ pathogène, le NO fait partie de l'arsenal de défenses de l'hôte. En réponse, les pathogènes ont développé des mécanismes pour contrer les effets du NO. Dans la symbiose fixatrice d'azote entre la légumineuse modèle Medicago truncatula et la bactérie Sinorhizobium meliloti, du NO a été détecté durant toutes les phases de l'interaction. L'équipe avait précédemment montré que la réponse de S. meliloti au NO est nécessaire au maintien de la symbiose puisque des nodules formés par une souche mutée dans le gène hmp (le gène hmp est induit par le NO et code pour une protéine qui dégrade le NO) sénescent prématurément. Au cours de cette thèse, nous avons étudié 3 nouveaux gènes de S. meliloti induits par le NO : nnrS1, nnrS2 et norB. nnrS1 et nnrS2 codent pour deux protéines de fonction inconnue et norB code pour une NO réductase qui dégrade le NO. Nous avons montré que ces 3 protéines participent d'une part à la résistance des bactéries au NO en culture et d'autre part, au maintien de l'interaction symbiotique. Par ailleurs, nous avons montré que ces 3 protéines sont impliquées directement ou indirectement dans la dégradation du NO et des résultats préliminaires suggèrent que NnrS1 présente une activité NO réductase. De plus, nous avons montré que NnrS1 et Hmp n'agissent pas seulement sur les bactéries mais aussi sur les protéines végétales. Il était connu que dans les nodules de M. truncatula, la glutamine synthétase (GS) végétale, une enzyme clé de la symbiose, est inhibée par tyrosine nitration, une modification post-traductionnelle dépendante du NO. Nous avons montré que NnrS1 et Hmp, en modulant le niveau de NO dans les nodules, contrôlent l'activité de la GS. Enfin des expériences préliminaires montrent que d'autres protéines (bactériennes et/ou végétales) pourraient être tyrosine nitratées. / Nitric oxide (NO) is a gaseous molecule involved in a large range of biological processes in plants from the seed germination to abiotic and biotic stress responses. In plant-pathogen interactions, NO is part of the defense systems. In response, pathogens have developed mechanisms in order to counteract the NO effects. In the nitrogen fixing symbiosis between the model leguminous plant Medicago truncatula and the bacterium Sinorhizobium meliloti, NO has been detected at all stages of the symbiosis. The team had previously shown that the S. meliloti response to NO is necessary to maintain the symbiotic interaction since nodules elicited by a strain mutated in the hmp gene (hmp is induced by NO and codes for a flavohemoglobine that degrades NO) senesce prematurely. During this thesis, we have studied 3 new genes of S. meliloti whose expression is induced by NO: nnrS1, nnrS2 and norB. nnrS1 and nnrS2 encode two proteins of unknown function and norB codes for a NO reductase which degrades NO. We have shown that these 3 proteins participate on one hand in bacterial NO resistance in culture and on the other hand in maintaining the symbiotic interaction. Furthermore, we have shown that these 3 proteins are involved, directly or indirectly, in NO degradation and preliminary results suggest that NnrS1 displays a NO reductase activity. Moreover, we have shown that NnrS1 and Hmp are not only dedicated to protect bacteria against NO but also play a role on plant proteins. It was already known that, in M. truncatula nodules, the plant glutamine synthétase (GS), a key enzyme of the symbiosis is inhibited by tyrosine nitration, a NO post-translational modification. We have shown that NnrS1 and Hmp, by modulating NO levels in nodules, control the GS activity. Finally, preliminary experiments suggest that other proteins (from bacterial and/or plant origin), could be tyrosine nitrated.

Bibliography: leaves 300-321. / xiii, 321 leaves [11] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis aims to extend knowledge and understanding of the seed-seedling dynamics and productivity of annual Medicago pastures. In particular this study concentrates on the impact of grazing by sheep on Medicago pasture herbage and seed production and sheep body weight gains. / Thesis (Ph.D.)--University of Adelaide, Depts. of Agronomy and Farming Systems and Plant Science, 1997

La phase de maturation des graines est caractérisée par l’ac-quisition successive de composantes qui constituent la qua-lité physiologique d’un lot de semences, à savoir la toléranceà la dessiccation (capacité à survivre au retrait total de l’eaucellulaire), la longévité (capacité de survivre à l'état sec pen-dant le stockage), la dormance ainsi que la vigueur germina-tive (capacité à germer de façon rapide et homogène quelquessoient les conditions de l’environnement). La production desemences à haute qualité germinative représente un enjeumajeur pour les semenciers car elle constitue un levier clefpour augmenter les rendements agricoles. Cependant, lesmécanismes régulant l’acquisition de la qualité germinativeet en particulier la longévité restent peu connus. Une étudepréalable d’un réseau de co-expression génique de facteursde transcription avait identifi é trois gènes candidats associésà la longévité chez Medicago truncatula :MtABL (ABA INSEN-SITIVE4-LIKE), MtABI5 (ABA INSENSITIVE5) et MtHSFA2.2(HEAT SHOCK FACTOR A2.2). L'objectif de cette thèse était devalider ces gènes et d’en comprendre leur fonction chez Medicagotruncatula et le pois par la caractérisation de mutantsd’insertion et EMS. ABL et ABI5 jouent un rôle dans la matu-ration en régulant positivement la longévité alors que celle-ci n’est pas affectée dans les mutants hsfa2.2. Des étudestranscriptomiques et biochimiques montrent que ABL et ABI5régulent de manière complexe la photosynthèse, la dégrada-tion de la chlorophylle et l’accumulation des oligosaccharide / Seed maturation is characterized by the acquisition ofthe various components that collectively constitute thephysiological quality or vigor of the seed: desiccation tolerance(DT, i.e. the capacity to survive complete drying), seedstorability or longevity (the capacity to remain alive duringstorage), dormancy, as well as fast and uniform germinationand seedling emergence under stressful conditions. Thesetraits are pivotal to ensure rapid and homogenous seedlingestablishment required for stable yield and are a majoreconomic challenge for the seed industry. Despite theiragronomic importance, the mechanisms regulating theiracquisition, including longevity, are still poorly understood. InMedicago truncatula, a gene co-expression network inferredthat transcription factors such asMtABL (ABA INSENSITIVE4-LIKE), MtABI5 (ABA INSENSITIVE5) and MtHSFA2.2 (HEATSHOCK FACTOR A2.2) are putative regulators of seedlongevity. The aim of this thesis was to characterize theirroles in Medicago truncatula and Pisum sativum using Tnt1insertion and EMS mutants. ABL and ABI5 are positiveregulators of longevity while defects in hsfa2.2 do not affectit. Transcriptomic and biochemical analyses show that ABLand ABI5 are involved in the regulation of photosynthesisassociated genes, chlorophyll loss and accumulation ofraffi nose family oligosaccharides (RFO). ABI5 is also involvedin the accumulation of stress proteins such as LEA proteins.By establishing a link between degreening, RFO contents andlongevity, our work offers new opportunities to tackle a

La symbiose légumineuse/rhizobium résulte en la formation d’un nouvel organe racinaire, le nodule, au sein duquel une induction coordonnée et massive de milliers de gènes a lieu. Plusieurs gènes contrôlant la méthylation de l’ADN sont régulés de façon spatiale au sein des nodules de Medicago truncatula, dont notamment un gène codant pour une déméthylase, DEMETER (DME), fortement exprimé dans la zone de différenciation. Ici, nous montrons que MtDME est essentiel pour le développement du nodule et qu’il régule l’expression de 1425 gènes, dont certains essentiels pour la différenciation des cellules de plantes et des bactéries. Une approche de séquençage bisulfite couplée à une capture génomique nous a permis d’identifier 474 régions qui sont différentiellement méthylées au cours du développement nodulaire, comportant notamment des gènes codant pour des peptides NCRs (Nodule-specific Cysteine-Rich). La diminution de l’expression de MtDME par ARN interférant mène à l’hyperméthylation et à la down-régulation de 400 gènes, la plupart d’entre eux étant associés à la différenciation du nodule. Une reprogrammation massive de l’expression génique via la déméthylation de l’ADN représente donc un nouveau mécanisme épigénétique qui contrôle une étape clé de l’organogenèse des nodules indéterminés durant l’interaction symbiotique. / The legume-Rhizobium symbiosis leads to the formation a new organ, the root nodule, involving coordinated and massive induction of specific genes. Several genes controlling DNA methylation are spatially regulated within the Medicago truncatula nodule, with notably a demethylase gene, DEMETER (DME), mostly expressed in the differentiation zone. Here, we show that MtDME is essential for nodule development and regulates the expression of 1425 genes, certain critical for plant and bacterial cell differentiation. Bisulphite sequencing coupled to genomic capture enabled the identification of 474 regions that are differentially methylated during nodule development, including notably Nodule-specific Cysteine-Rich peptide genes. Decreasing DME expression by RNA interference led to hypermethylation and concomitant downregulation of 400 genes, most of them associated with nodule differentiation. Massive reprogramming of gene expression through DNA de-methylation is a new epigenetic mechanism controlling a key stage of indeterminate nodule organogenesis during symbiotic interactions.

La verticilliose est une maladie vasculaire des plantes dont les symptômes typiques sont un flétrissement des parties aériennes, des feuilles chlorosées puis séchées, et dans les cas de maladie grave la mort de la plante. Au niveau des racines on observe une coloration brune du tissu conducteur. Cette maladie est causée par un champignon du sol du genre Verticillium. Les espèces majeures V. dahliae et V. albo-atrum sont responsables de pertes importantes de rendement sur de nombreuses cultures. Le champignon entre dans la racine par des blessures ou par des fissures au niveau de sites d’émergence de racines latérales, puis il avance vers le cylindre central et envahit les vaisseaux du xylème. Sa croissance reste pendant longtemps limitée aux vaisseaux qu’il colonise en avançant vers les parties aériennes de la plante. Aux stades tardifs, le champignon sort du cylindre central et colonise les autres tissus. En Europe, V. albo-atrum constitue l’une des principales causes de maladies chez la luzerne pérenne et est à l’origine de pertes économiques très importantes. La capacité de V. albo-atrum de survivre dans le sol ainsi que sa localisation protégée dans le cylindre centrale des plantes infectées en font un pathogène difficile à combattre, la lutte génétique par sélection de variétés tolérantes apparaissant comme une approche prometteuse. Cependant, la capacité des microorganismes pathogènes de s’adapter rapidement à des nouvelles plantes hôtes est une menace bien connue de la durabilité des variétés résistantes. Au laboratoire, des travaux ultérieurs ont établi que la plante modèle des légumineuses Medicago truncatula, une espèce sauvage proche de la luzerne cultivée, peut être utilisée pour étudier les mécanismes de résistance et sensibilité vis-à-vis de V. alboatrum. Une lignée résistant et une lignée sensible ont été identifiées et l’étude de la descendance d’un croisement entre ces deux lignées a permis d’identifier un locus majeur (Quantitative trait locus, QTL) contrôlant la résistance à une souche de V. albo-atrum isolée de la Luzerne (Ben et al., 2013 ; Negahi en 6e co-auteur). Ce travail a également montré qu’il existait une grande biodiversité au sein de l’espèce M. truncatula par rapport à la réponse à cette souche de V. albo-atrum. / Verticillium wilt, caused by Verticillium albo-atrum (Vaa) and Verticillium dahliae (Vd), is responsible for yield losses in many economically important crops. The capacity of pathogenic fungi to adapt to new hosts is a well-known threat to the durability of resistant crop varieties. Medicago truncatula is a good model for studying resistance and susceptibility to Verticillium wilt in legume plants. Phenotyping a population of inbred lines from a cross between resistant parent line A17 and susceptible parent F83005.5 contributed to the identification of a first QTL controlling resistance to an alfalfa strain of Vaa in M. truncatula. Then, 25 M. truncatula genotypes from a core collection and six Vaa and Vd strains were used to study the potential of non-host Verticillium strains isolated from different plant species to infect this legume plant, and the plant’s susceptibility to the pathogens. The experiment was arranged as factorial based on a randomized complete block design with three replications. The wilt symptoms caused by Vaa and Vd were scored on a disease index scale from 0 to 4, during 30 days after inoculation of ten day-old plantlets. Disease severity was quantified by the parameters Maximum Symptom Scores (MSS) and Areas Under the Disease Progress Curves (AUDPC). Highly significant differences were observed among plant genotypes and fungal strains, and their interaction was also significant. The correlation between MSS and AUDPC was 0.86 and highly significant. The most severe symptoms were caused by the alfalfa strain Vaa-V31-2 and the least severe by Vd-JR2, as shown by mean values obtained on the 25 genotypes. M. truncatula genotype TN8.3 was identified as the most susceptible genotype by mean values obtained with the 6 fungal strains, whereas F11013-3, F83005.9 and DZA45.6 were highly resistant to all strains studied. The results were used to choose parents for studying the genetics of resistance in M. truncatula to a nonalfalfa Verticillium strain. So, in the second part of this work, genotype A17 which was susceptible and genotype F83005.5 which was resistant to the potato strain Vaa-LPP0323 and recombinant inbred lines (RILs) from a cross between these genotypes were selected in order to study the genetic control of resistance to this strain of the pathogen. Our experimental design was a randomized complete blocks with 116 RILs and three replications. High genetic variability and transgressive segregation for resistance to Vaa-LPP0323 were observed among RILs. A total of four QTLs controlling resistance to Vaa-LPP0323 were detected for the parameters MSS and AUDPC. The phenotypic variance explained by each QTL (R2) was moderate, ranging from 3 to 21%. A negative sign of additive gene effects showed that favourable alleles for resistance come from the resistant parent.