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Light availability has a profound effect on plant growth and development. One of the ways to study the effects of light intensity on plant growth and development without the confounding problem of photosynthate availability is sucrose injection/supplementation. A greenhouse experiment was conducted to evaluate the effects of light levels (0% and 75% shade) and sucrose injection (distilled water or 150 g sucrose l(-1)) on three weed species: redroot pigweed (Amaranthus retroflexus L., C4), lambsquarters (Chenopodium album L., C3) and velvetleaf (Abutilon theophrasti Medic., C3). The average total sucrose uptake was 7.6 and 5.9 g per plant for 0% and 75% shading, respectively, representing 47% of the average total weed dry weight. Plants injected with sucrose had greater dry weights and shoot-to-root ratios under both light levels. In spite of sucrose supplementation the reduction in dry matter due to shading was greater for roots and reproductive structures than vegetative shoot tissues, indicating light level regulation of morphological changes resulting in changed C allocation that are independent of photosynthate availability. Dry weights of plants injected with sucrose under 75% shading were not different from distilled water-injected unshaded plants. However, both sucrose-injected and control plants, regardless of their photosynthetic pathways, underwent similar changes in allocation of dry matter and morphology due to shading, suggesting that these effects are strictly due to light intensity and not related to photosynthate availability.

International audience; The roles in replication and viral assembly of different beet western yellows luteovirus gene products were investigated in Chenopodium quinoa protoplasts using mutated transcripts. Of the six long open reading frames (ORFs) present on the viral RNA, only ORFs 2 and 3, which encode proteins containing conserved putative replicase domains, were essential for replication. Various deletions in the 3′ part of the genome within ORFs 4, 5, and 6 did not affect viral replication. Analysis of the progeny of those mutants capable of replication showed that virus particles were produced in protoplasts infected with transcripts modified in ORFs 1, 5, or 6 but not with transcripts unable to produce coat protein, encoded by ORF 4.

Les territoires de l’Intersalar, au Sud de l’Altiplano bolivien, sont emblématiques d’un système socio-écologique vulnérable où l’enjeu de durabilité est exacerbé par la fragilisation d’une agriculture paysanne parachutée dans le commerce mondial. La zone Intersalar constitue un espace convoité en dépit d’un milieu exigeant (froid, aridité, haute altitude, salinité, etc.). La forte augmentation des prix du quinoa et la mécanisation des pratiques agricoles, vécues comme des opportunités sans précédent par les agriculteurs aymaras, menacent l’équilibre fragile d’un système écologique et social aujourd’hui marqué par une crise de la fertilité (baisse de rendements, érosion des sols, exacerbation des conflits d’accès au foncier, etc.). La réduction significative de la complémentarité agriculture/élevage s’accompagne d’une individualisation et d’une monétarisation de certaines pratiques agricoles qui transforment les conditions du renouvellement de la fertilité. La capacité d’innovation dont font preuve les producteurs dans leurs modes de renouvellement de gestion individuelle et collective de la fertilité est donc au coeur des enjeux du maintien de l’activité agricole. Nous proposons une analyse critique du mouvement historique de la notion de fertilité, éminemment polysémique, pour ensuite en interroger le sens et les enjeux dans la zone Intersalar. Ce faisant nous proposons un regard renouvelé sur le concept de fertilité et montrons qu’il existe un fort hiatus entre les acceptions paysannes et le sens commun que lui confèrent les agronomes et les agents de développement. Ces résultats théoriques et empiriques invitent à de nouveaux paradigmes pour penser la fertilité et accompagner les agriculteurs aymaras de la zone Intersalar., At the south of Bolivian Altiplano, Intersalar territories represent a symbolic zone for the study of a vulnerable socio ecological system where durability is a stake heighten by the weakening of a rural agriculture dropped into world trade. Intersalar is a desired space despite the demanding environment (cold, aridity, high altitude, salinity, etc.). The great price increase of quinoa and the mechanization of agricultural practices, seen by Aymaras producers as a great opportunity, threaten the fragile stability of an ecological and social system which is influenced by a fertility crisis (yield decrease, soil erosion, increase of conflicts in access of land, etc.). The significant decrease of agriculture/livestock breeding cooperation comes along with an individualization and monetarization of some agricultural practices which transform the conditions of fertility renewal. The capacity of innovation shown by the producers in their modes of renewal of individual and collective fertility management is a core problem for the preservation of the agricultural activity. We propose a critical analysis of the historical movement of the notion of fertility, deeply polysemous, then to inquire the meaning and the stakes in the Intersalar zone. Furthermore, we suggest a critical review of fertility concept in order to show the deep gap between the meaning given by producers and the common sense conferred by the agronomists and the development agents. These theoretical and empirical results invite of new paradigms to think fertility and to support the Aymaras producers of the Intersalar area.

Cette communication explore les tensions que les producteurs chiliens aymara de quinua affrontent entre la logique de leur culture ancestrale et celle des nouvelles formes d'action collectives à leur disposition : association et coopératives. Colchanes, commune perchée sur l’altiplano aymara est la principale zone de production de quinua chilienne. Sa population se consacre à l’agriculture, principalement quinua et productions maraichères, l’élevage de camélidés ainsi qu’au tourisme (accueil, hébergement, artisanat…). La quinua est partiellement auto-consommée et le surplus commercialisé dans les marchés locaux notamment en Bolivie. La situation économique difficile, l'absence de perspectives ont provoqué une migration temporaire ou définitive d’une grande partie de la population, principalement les jeunes partis s’installer en ville. Les agriculteurs de la commune, afin de bénéficier d'un marché porteur ont mis en place une coopérative, Quinacoop et une association Jura Marka, pour commercialiser la quinua et ses sous-produits et accompagner la production. Au sein de ces organisations se produisent des tensions entre « tradition » et « modernité ». Les travaux de B. Latour sur la modernité nous servent pour essayer de les comprendre et aussi pour saisir la façon dont les aymaras tentent de les résoudre. Nos observations montrent que les processus d’hybridation, modernité-tradition, se font autour de trois types d’articulations : i) organisationnel, entre les formes de travail : mutualisé (ayne) et individuel, i) spatial ou territorial, entre systèmes de culture à base de quinua (altiplano) et systèmes d’activités conduites pour la plupart en zone côtière iii) générationnel, entre les jeunes et les tatas., In this paper we explore the tensions that Aymara Quinoa producers must resolve between the logic of their ancestral culture and of new forms of collective action at their disposal: association and cooperatives. Colchanes county perched on the Aymara altiplano is the main Quinoa production area in Chile, The main activity is agriculture, mainly quinoa crop and vegetables, camelid livestock and tourism (accommodation, crafts ...). Much of the production is self-consumed and surplus is marketed in local markets especially in Bolivia. The difficult economic situation, lack of opportunities has led to a temporary or permanent migration of a large portion of the population; the younger generations move to town. To benefit from an advantageous market (high prices), local farmers have established a quinoa cooperative (Quinacoop) and an association (Jura Marka), to commercialize their production. Inside these organizations appear tensions between "tradition" and "modernity". We rely on the B. Latour's work on modernity to try to understand both the tension and the way that the Aymara, in cooperatives and association, are trying to solve them. Our observations show that the hybridization processes are around three types: i) linking labour organizational forms (shared (ayne) and individual), ii) linking quinoa cropping systems (in the altiplano) and systems of activities most of which are conducted in the coastal zone and iii) linking generations, young people and tata.

International audience

The first step in appearance of herbicide-resistant weed populations is the appearance of resistant plants or mutants. While efforts are underway to study and predict the spread of resistant plants within weed populations, knowledge of the conditions prevailing at the time of appearance of the first resistant plants is misunderstood. We try to shed some light on this phenomenon using the example of atrazine-resistant common lambsquarters. The population structure and variability, the presence of unusual genotypes that have a high mutation rate, the occurrence of a low-dose resistant phenotype that is the precursor of a high-dose resistant phenotype, and the potential for multiplication and spread are shown to be of major importance in the behavior of herbicide resistance.

Quinoa (Chenopodium quinoa Willd) is an Andean pseudo-cereal, of the Chenopodiaceae family, which is currently being studied for introduction in Northern Europe as an alternative to industrial crops. The aim of this work was to verify existence in quinoa of the distinctive cell wall features identified in other Chenopodiaceae, ie presence of pectin-bound ferulic acid and dehydrodiferulic acids. Alcohol-insoluble solids (AIS) were prepared from leaves, stems and roots of mature quinoa plants, representing 0.10, 0.20 and 0.47 g g−1 respectively of the fresh weight. Ferulic acid and dehydrodiferulic acid derivatives were present in all the organs, with the highest concentrations in the leaves with 2.1 and 0.5 mg g−1 AIS respectively. The ratio of dehydrodiferulic acid to ferulic acid was highest in the roots. Pectins extracted by hot HCl from AIS of leaves were rich in ferulic acid (3.4 mg g−1), but also highly acetylated (DAc 20), and rich in rhamnose, two characteristics encountered in other Chenopodiaceae. © 1999 Society of Chemical Industry

International audience

The role of three weed management strategies on weed populations and community dynamics was investigated from 1989 to 1994. These were chemical weed control (CH), integrated weed control (IN) and mechanical weed control (ME). Weed populations and communities were analysed by univariate (species richness, rank: frequency diagrams) and multivariate (correspondence analysis) methods. Species richness of the soil seedbank differed with weed management strategies and over time, with an observed annual number of species that ranged from 18 to 32. The seedbank was dominated by the same pool of species in all cases, but these species responded differently among years and management strategies ; their rank (relative abundance) and densities changed between strategy and within a strategy among the years. In the last 2 years of the study, the soil seedbank was characterized mainly by Capsella bursa-pastoris (L.) Medik on the ME strategy and Chenopodium album L. on the IN strategy. The CH strategy contrasted with the other two by the presence of a high density of Amaranthus retroflexus L.

By definition, weeds are wild species adapted to agroecosystems. Moreover genetic variations are almost always present within wild populations and frequently at high rates. This leads to the fact that, given sufficient duration, evolutionary responses are inevitable within weed populations according to intensity of the selection. If there is some polymorphism for almost all the characteristics of the species we may expect polymorphism for herbicide susceptibility. As this is the highest selective pressure against weed species, this will lead to resistance i.e. the fact that some plants will survive and produce seeds despite a treatment which should have killed all the plants of the species in the field. At least a part of their progeny must survive the same treatment. Resistance can be defined either as being the inherited ability of a plant to not be controlled by (at least) the normal doses of a herbicide or as a peculiar physiological characteristic occurring in some plants.

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National audience; Since the beginning of the 1980s, a disease has been observed on Danae racemosa Moench (Alexander Laurel), a plant of horticultural interest. In the south of France, as in Italy, D racemosa is commonly cultivated for its ornamental foliage, like Asparagus plumosus L. This monocot from the Liliaceae family shows typical damage on its foliage: first a mottle appears on the young phylloclades which turn yellow with time. This disease is rarely widespread in a plantation. Only single plant or small areas are usually affected but the regular extension of the disease is responsible for important economic consequences. In the present paper we show that these symptoms are due to the propagation of a virus in the plant. The use of general virological tests, host range inoculation and retroinoculation, purification and EM, demonstrated the systematic presence of isometric virus particles (26 nm) in the diseased D racemosa collected from various geographic areas. The study of the serological properties of the virus (immunodiffusion, immunoelectrophoresis and DAS-ELISA) with the MW determination of the capsid-subunit and the RNA, led to its identification as a Sowbane mosaic virus strain. When healthy D racemosa were inoculated with the virus, the typical symptoms of the disease could only be identified after a long delay (9 months after the inoculation) on the young neoformed boughs, from which the virus was isolated. We therefore consider the Sowbane mosaic virus as the single pathogen inducing the mottle and the yellowing of the D racemosa foliage. In the diseased tissues, the virus was present in very low amounts and could not be detected by classical immunoenzymatic assay (DAS-ELISA). Retroinoculation and rare direct inoculations from crude extracts, on a sensitive host (ie Chenopodium quinoa) were necessary to propagate the virus. Disease diagnostic is discussed, especially as the virus seemed to be latent with no external symptoms during a certain growing period of the plant under special conditions (shadowing, high nitrogen fertilization). A rapid and efficient method for detection of the virus is absolutely necessary to carry out a phytosanitary programme and to obtain virus-free plants for vegetative propagation. Evidence was found that the virus could be transmitted by several aphids; this is an important parameter for the control of the disease.; Depuis plusieurs années, on observe l’extension importante d’une maladie sur Danae racemosa, liliacée cultivée dans le sud-est de la France pour son feuillage d’ornement. Les symptômes observés sont une marbrure et un jaunissement caractéristiques du feuillage rendant ce dernier impropre à la commercialisation. L’utilisation de techniques virologiques classiques - inoculation d’une gamme d’hôtes, rétro-inoculation systématique, purification, microscopie électronique - ont permis de mettre en évidence la présence régulière d’un virus isométrique (26 nm) à partir des plantes malades de différentes provenances géographiques. À partir de ces premiers résultats, une étude sérologique - immunodiffusion et immunoélectrophorèse en milieu gélosé, technique immunoenzymatique, couplée à une analyse biochimique (détermination des poids moléculaires de la sous-unité capsidiale et de l’acide ribonucléique) - a permis de démontrer qu’il s’agit du virus de la mosaïque du chénopode (Sowbane mosaic virus). L’inoculation du virus sur D racemosa sain a permis de reproduire les symptômes typiques de la maladie et on a réisolé le virus. Le virus de la mosaïque du chénopode est donc le seul agent causal de la marbrure et du jaunissement du feuillage de D racemosa et il est, à notre connaissance, le premier virus signalé sur cette liliacée. Dans la plante malade, le virus est présent à des concentrations très faibles car non détectables par la méthode immunoenzymatique DAS-ELISA et il est nécessaire, pour le mettre en évidence, d’avoir recours à des rétro-inoculations systématiques sur plante hôte sensible (Chenopodium quinoa Wild). La transmission du virus par pucerons a été confirmée (mode non-persistant). Elle doit contribuer, avec la multiplication végétative des plants, à la propagation de la maladie.

Depuis plusieurs années, on observe l’extension importante d’une maladie sur Danae racemosa, liliacée cultivée dans le sud-est de la France pour son feuillage d’ornement. Les symptômes observés sont une marbrure et un jaunissement caractéristiques du feuillage rendant ce dernier impropre à la commercialisation. L’utilisation de techniques virologiques classiques - inoculation d’une gamme d’hôtes, rétro-inoculation systématique, purification, microscopie électronique - ont permis de mettre en évidence la présence régulière d’un virus isométrique (26 nm) à partir des plantes malades de différentes provenances géographiques. À partir de ces premiers résultats, une étude sérologique - immunodiffusion et immunoélectrophorèse en milieu gélosé, technique immunoenzymatique, couplée à une analyse biochimique (détermination des poids moléculaires de la sous-unité capsidiale et de l’acide ribonucléique) - a permis de démontrer qu’il s’agit du virus de la mosaïque du chénopode (Sowbane mosaic virus). L’inoculation du virus sur D racemosa sain a permis de reproduire les symptômes typiques de la maladie et on a réisolé le virus. Le virus de la mosaïque du chénopode est donc le seul agent causal de la marbrure et du jaunissement du feuillage de D racemosa et il est, à notre connaissance, le premier virus signalé sur cette liliacée. Dans la plante malade, le virus est présent à des concentrations très faibles car non détectables par la méthode immunoenzymatique DAS-ELISA et il est nécessaire, pour le mettre en évidence, d’avoir recours à des rétro-inoculations systématiques sur plante hôte sensible (Chenopodium quinoa Wild). La transmission du virus par pucerons a été confirmée (mode non-persistant). Elle doit contribuer, avec la multiplication végétative des plants, à la propagation de la maladie., Since the beginning of the 1980s, a disease has been observed on Danae racemosa Moench (Alexander Laurel), a plant of horticultural interest. In the south of France, as in Italy, D racemosa is commonly cultivated for its ornamental foliage, like Asparagus plumosus L. This monocot from the Liliaceae family shows typical damage on its foliage: first a mottle appears on the young phylloclades which turn yellow with time. This disease is rarely widespread in a plantation. Only single plant or small areas are usually affected but the regular extension of the disease is responsible for important economic consequences. In the present paper we show that these symptoms are due to the propagation of a virus in the plant. The use of general virological tests, host range inoculation and retroinoculation, purification and EM, demonstrated the systematic presence of isometric virus particles (26 nm) in the diseased D racemosa collected from various geographic areas. The study of the serological properties of the virus (immunodiffusion, immunoelectrophoresis and DAS-ELISA) with the MW determination of the capsid-subunit and the RNA, led to its identification as a Sowbane mosaic virus strain. When healthy D racemosa were inoculated with the virus, the typical symptoms of the disease could only be identified after a long delay (9 months after the inoculation) on the young neoformed boughs, from which the virus was isolated. We therefore consider the Sowbane mosaic virus as the single pathogen inducing the mottle and the yellowing of the D racemosa foliage. In the diseased tissues, the virus was present in very low amounts and could not be detected by classical immunoenzymatic assay (DAS-ELISA). Retroinoculation and rare direct inoculations from crude extracts, on a sensitive host (ie Chenopodium quinoa) were necessary to propagate the virus. Disease diagnostic is discussed, especially as the virus seemed to be latent with no external symptoms during a certain growing period of the plant under special conditions (shadowing, high nitrogen fertilization). A rapid and efficient method for detection of the virus is absolutely necessary to carry out a phytosanitary programme and to obtain virus-free plants for vegetative propagation. Evidence was found that the virus could be transmitted by several aphids; this is an important parameter for the control of the disease.

International audience

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A seed lot of pea cv. Belinda was shown to transmit with high frequency a latent strain of Pea seed-borne mosaic virus, weakly detectable in ELISA only 5 weeks after plant growth. This strain did not induce apparent symptoms on plants, was no more detectable in 9 week old plants and showed a reduced multiplication even on retro-inoculating healthy pea plants; contrarily, the common strain could be easily detected in the seed and young seedlings on which it induced clearcut symptoms. ZusammenfassungSamenubertragung des Pea Seed-borne Mosaic Virus in Erbsen: friihe und spate Wirkung des Virus in den Nachkommen Es konnte gezeigt werden, dafi Samen der Erbsensorte Belinda einen latenten Stamm des Pea Seed-borne Mosaic Virus mit hoher Haufigkeit iibertragen konnten. Das Virus konnte schon 5 Wochen nach der Samenkeimung in den Pflanzen mit ELISA schwach nachgewiesen werden, in 9 Wochen alten Pflanzen war die Nachweisbarkeit nicht besser, und es zeigte sich eine vertninderte Vermehrung auch nach einer Retroinokulation gesunder Erbsenpflanzen. Der Wildstamm dagegen konnte iehr leicht in den Samen und in |ungen Samlingen nachgewiesen werden, eindeutige Sytnptotne wurden in den Samlingen verursacht.

Summary Electrophoretic variations within four enzyme systems (α-esterase, acid phosphatase, malate dehydrogenase and leucine amino peptidase), were studied for various garden and field populations of Chenopodium album. A correlation was found between the degree of polymorphism for the electrophoretic traits and environmental conditions. The amount of phenotypic polymorphism is very high in gardens, intermediate in an untreated and, low in herbicide-treated fields and nil for a triazine resistant population in a maize (Zea mats L.) monoculture. Furthermore, the tetraploid versus hexaploid ratio is higher within garden populations. Higher variability in garden populations is due, in part, to a high proportion of polymorphic phenotypes, and in part to a low effect of selection pressure in such types of habitat. Although there is a difference between phenotypes of populations from acid soils and those from more basic ones, we cannot be sure that the variation of polymorphism is due only to selection.

As part of a study of triazine resistance in weed species, the authors have collected several resistant populations of Chenopodium album in different areas in France. A study of intra- and inter-population variability between different susceptible and resistant populations has been made using polyacrylamide gel electrophoresis of foliar isoenzymes. The separation of esterases and malate dehydrogenase isoenzymes was carried out in a modified vertical apparatus. Within each resistant population, all individuals have the same pattern of esterase and populations collected in the same area have the same zymogram. However, populations from different areas have distinct zymograms. These data suggest that the resistant populations originated in the region where they now occur, and that there is a high rate of self-pollination in each resistant population. After treating a susceptible population with a low dose of atrazine, about 1% of plants survived and these have a high frequency of the esterase zymogram typical of resistant individuals. The offspring of these plants are completely resistant. The resistant and susceptible populations grew near each other so that they may have a common origin. The pattern of occurrence of resistance in relation to its inheritance and the level of inbreeding in populations is discussed.

National audience

Resume The authors checked resistance of different populations of Chenopodium album L. to heavy doses of atrazine. In the presence of different triazines, diazine and urea, they compared the behaviour of susceptible and resistant populations. Measured by whole leaves fluorescence, electron transfer of susceptible and resistant plants is respectively stopped or not by the different herbicides. Furthermore, with low doses of herbicides, about 1 % of tolerant plants have been selected from susceptible plants. In the presence of the same herbicides, leaves of tolerant plants present intermediate and variable reactions.

International audience

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La résistance chloroplastique aux triazines a été observée en France chez 13 espèces, dont les auteurs précisent l’importance agronomique et la distribution géographique ; les 3 espèces qui présentent la plus grande dispersion sont Amaranthus retroflexus L., Chenopodium album L. et Solanum nigrum L., Triazine-resistant populations have been reported within 13 species in France. Their agronomic importance and geographical distribution is given. The 3 most widen distributed species are Amaranthus retroflexus L., Chenopodium album L. and Solanum nigrum L.

National audience

National audience; Triazine-resistant populations have been reported within 13 species in France. Their agronomic importance and geographical distribution is given. The 3 most widen distributed species are Amaranthus retroflexus L., Chenopodium album L. and Solanum nigrum L.; La résistance chloroplastique aux triazines a été observée en France chez 13 espèces, dont les auteurs précisent l’importance agronomique et la distribution géographique ; les 3 espèces qui présentent la plus grande dispersion sont Amaranthus retroflexus L., Chenopodium album L. et Solanum nigrum L.

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Within two plant species, Chenopodium album L. generally susceptible to atrazine, and Poa annua L. always reported as susceptible, atrazine tolerant populations were observed. This resistance is due to lower atrazine susceptibility of chloroplastic electron transfert. Oxygen evolution in isolated chloroplasts was mesured to determine the concentrations required for 50 % inhibition. They are similar in the two species for the susceptible and the tolerant chloroplasts 2 × 10−7 M and 10−4 M respectively. Differential chlorophyll fluorescence observed on whole leaf was used as a simple mean for detection of chloroplastic resistance.

40 ref.; International audience

Resume: Par des observations sur la germination dans differentes conditions et sur le developpement vegetatif en conditions non competitives, les auteurs comparent des biotypes sensibles et resistants de quatre especes chez lesquelles on a decouvert des populations resistantes: Chenopodium album, Amaranthus retroflexus, Solanum nigrum et Polygonum lapathifolium. Malgre des niveaux de signification differents les resultats indiquent un meilleur developpement vegetatif des plantes sensibles, Cependant, ces donnees peuvent etre modulees selon les conditions de croissance. Par ailleurs, les valeurs elevees des variances des caracteres mesures traduisent une heterogeneite tres importante, au moins dans les lots sensibles. En revanche, les semences des plantes resistantes de Polygonum lapathifolium et, dans une moindre mesure, d'Amaranthus retroflexus germent plus facilement aux basses temperatures. A la lumiere de ces donnees les auteurs discutent les avantages que peuvent conferer ces caracteristiques aux differents lots, mais surtout soulignent la necessite de considerer chaque espece separement et de prendre en compte la nature des genotypes compares. Enfin, il est difficile, a partir de telles donnes et tant que l'on ignore precisement le determinisme de la resistance, d'en deduire dans les stations d'origine et en l'absence de traitement, une moindre valeur adaptative des resistants par rapport aux sensibles. Summary: Comparison of germination and growth of biotypes sensitive and resistant to triazines in four weed species. By observing germination under various conditions and plant development in non-competitive conditions, a comparison was made between sensitive and resistant biotypes of four species in which resistant populations have been discovered: Chenopodium album, Amaranthus retroflexus. Solanum nigrum and Polygonum lapathifolium. In spite of different levels of significance, results indicate that the sensitive plants develop better. However, these findings may be modified according to the growth conditions. Moreover, high variance values in the characteristics measured reflect considerable heterogeneity at least in the sensitive lots. Nevertheless, seed from resistant plants of P. lapathifolium and, to a lesser extent, of Amaranthus, germinate more readily at low temperatures. In the light of these findings the authors discuss the possible advantages conferred on different lots by these characteristics, stressing the need to consider each species separately and to take into account the nature of the genotypes being compared. From such findings, while the exact factor determining resistance is not known, it is difficult to deduce a lower level of adaptability in resistant, as opposed to sensitive individuals, based on their place of origin and in the absence of herbicide treatments. Zusammenfassung Vergleich der Keimung und des Wachstums von Triazin-empfindlichen und -resistenten Biotypen von vier Unkrautarten Die Autoren vergleichen empfindliche und resistente Biotypen von vier Unkraularten, bei denen man resistente Populationen gefunden hat: Chenopodium album. Amaranthus retroflexus. Solanum nigrum und Polygonum lapathifolium. Es wurden die Keimung bei unterschiedlichen Be-dingungen und das vegetative Wachstum ohne Konkurrenzeinfluss beobachtet. Die sensiblen Pflanzen zeigten eine signifikant bessere vegeta-tive Entwicklung. Jedoch konnen diese Unter-schiede gemass den Wachst umsbedingungen vari-ieren. Diese Unterschiede bei den gemessenen Parametern zeigen eine sehr wichtige Heterogeni-tat auf, wenigstens bei den emptindlichen Pflanzen. Dagegen keimen die Samen resistenter Pflanzen von Polygonum lapathifolium und, im geringeren Ausmass von Amaranthus retrqfiexus. leichter bei niedrigen Temperaturen, In Anbe-tracht dieser Ergebnisse diskutieren die Autoren de Vorteile, die sich aus diesen Unterschieden fur die einzelnen Biotypen ergeben; unterstreichen aber vor allem die Notwendigkeit. jede Art einzeln zu untersuchen und die unterschiedlichen Genotypen in Betracht zu ziehen, Solange man die eigentlichen Ursachen der Resistenz nicht beriicksichtigt und keine Herbizidbehandlungen durchfuhrt, ist es schwierig. anhand solcher Ergebnisse an den Herkunftsorten auf ein ge-ringeres Adaptionsvermdgen der resistenten–im Vergleich zu den sensiblen Typen zu schliessen.

In vitro culture Symposium, Hambourg, DEU, 1982/08/29-31-1982/09/04; International audience; Eight cultivars have been micropropagated. The critical stage of micropropagation was rooting : keeping tubes in darkness for a maximum time of 21 days on a medium with NAA 0.5 mg/l and kinetin 0.05 mg/l, has given about 70% in vitro rooting in 40 days. 285 micropropagated plants were observed until harvest. They were true to their varietal types. Micropropagated plants showed a rapid growth in the fields and a slightly larger size. The increase of the yield reached 30% in the second year of production (mean for 5 varieties). This increase was sometimes partly due to an increase of productive stalks per plant. In all the cultivars, Artichoke Latent (Poty) Virus (ALV) was identified. In some of them, an icosahedric virus, not yet identified, was found. Rarely, Cucumber Mosaic Virus (CMV) was observed. Virus-free clones were obtained. The preliminary observations have showed that their advantage is more or less pronounced depending on the initial health status of the cultivars.

* INRA URD BP 86510 21065 Dijon cedex (FRA); International audience