Genotypic variation in nodule conductance to the oxygen diffusion in common bean (Phaseolus vulgaris)

Nodule conductance to O$_2$ diffusion in Phaseolus vulgaris was calculated from the in situ measurement of the response of nodulated-root O$_2$ uptake to variations of rhizospheric partial pressure of O$_2$ at the flowering stage for nodulated-plants grown hydroaeroponically in a glasshouse. Comparing common bean lines BAT477, CocoT, DOR364, Flamingo and NAG310, the nodule O$_2$ uptake at ambient pO$_2$ was the highest (372 $\mu$mol O$_2$ $\cdot$h$^{-1}$ $\cdot$pl$^{-1}$) for BAT477 in symbiosis with the reference strain Rhizobium tropici CIAT899. The maximal value (2800 $\mu$mol O$_2$ $\cdot$h$^{-1}$ $\cdot$pl$^{-1}$) was observed at 50 kPa O$_2$. This was associated with the lowest nodule conductance (4.5 $\mu$m$\cdot$s$^{-1}$), though the latter was higher with the native strain Sinorhizobium fredii 1a6. The highest nodule conductance (7.5 $\mu$m$\cdot$s$^{-1}$) was observed for the less efficient symbiosis CocoT-CIAT899. It is argued that nodule conductance is an adaptation mechanism to respond to plant N demand in compensation for low nodulation or the high respiratory cost for nitrogen fixation in some symbioses.Variabilité génotypique de la conductance nodulaire à la diffusion de l'oxygène chez le haricot (Phaseolus vulgaris). La conductance nodulaire à la diffusion d'oxygène chez Phaseolus vulgaris a été calculée par la mesure in situ à la floraison de la réponse de la consommation d'O$_2$ à des variations de pO$_2$ rhizosphérique sur des racines nodulées de plantes en culture hydroaéroponique sous serre vitrée. Comparant les lignées de haricot BAT477, CocoT, DOR364, Flamingo et NAG310, la consommation nodulaire d'O$_2$ a été la plus élevée à la pO$_2$ ambiante (372 $\mu$mol O$_2$ $\cdot$h$^{-1}$ $\cdot$pl$^{-1}$) pour la symbiose de BAT477 avec la souche de référence Rhizobium tropici CIAT899. Elle a atteint la valeur maximale de 2800 $\mu$mol O$_2$ $\cdot$h$^{-1}$ $\cdot$pl$^{-1}$ à 50 kPa O$_2$. Elle est associée à la plus faible conductance nodulaire (4.5 $\mu$m O$_2$ $\cdot$s$^{-1}$) alors que cette dernière est plus élevée avec la souche native Sinorhizobium fredii 1a6. La conductance la plus élevée (7.5 $\mu$m O$_2$ $\cdot$s$^{-1}$) est observée chez la symbiose CocoT-CIAT899. Il est suggéré que l'augmentation de conductance nodulaire observée chez certaines symbioses est un mécanisme d'adaptation pour répondre à la demande en azote de la plante en compensation d'une faible masse nodulaire ou d'un fort coût respiratoire lié à l'activité nitrogénase

Effects of hydroponic culture system and NaCl on interactions between common bean lines and native rhizobia from Tunisian soils

Common bean (Phaseolus vulgaris L.) lines, namely BAT477, CocoT, Flamingo, DOR364 and NAG310, were inoculated with reference strain Rhizobium tropici CIAT899 or native rhizobia, namely Sinorhizobium fredii 1a6 and R. etli 12a3 and then grown in two hydroponic semi-sterile systems: (i) gravel in pots, (ii) aerated nutrient solution in bottles. In the aerated solution system, shoot plant growth was 5 to 9 times higher, depending on the symbiosis, than on gravel. A strain $\times$ line interaction was observed in the gravel system. However, such an interaction was not significant in the aerated system because of large intra-treatment variability. In the aerated system and under NaCl treatment, BAT477 inoculated with local strains (1a6 and 12a3) appeared to be a highly tolerant line. In contrast, NAG310 was the least tolerant line when inoculated by CIAT899. However, the tolerance of NAG310 to NaCl increased when it was inoculated with 12a3, although this strain conferred low nodule growth to Flamingo under NaCl. It is concluded that strain $\times$ line interactions are important and should be considered for selecting the legume most adapted to such an environmental constraint as salinity, and that the aerated solution system is efficient for selecting highly efficient rhizobial symbioses.Effets du système de culture hydroponique et de NaCl sur les interactions entre lignées de haricot et des rhizobia natifs des sols de Tunisie. Les lignées de haricot (Phaseolus vulgaris L.) BAT477, CocoT, Flamingo, DOR364 et NAG310 ont été inoculées avec la souche de référence CIAT899 (Rhizobium tropici) et celles locales 1a6 (R. fredii) et 12a3 (R. etli), et cultivées sur deux systèmes hydroponiques semi-stériles : (i) en pots sur gravier et (ii) en flacons sur solution nutritive aérée. La croissance des parties aériennes est 5 à 9 fois supérieure dans le milieu hydroponique aéré par rapport à celui utilisant le gravier comme support. Une interaction souche $\times$ lignée a été observée sur gravier mais non sur milieu aéré où elle semble être masquée par une importante variabilité. Sous traitement salin en milieu aéré, la lignée BAT477 inoculée avec les souches locales (1a6 et 12a3) se montre particulièrement tolérante. La lignée NAG310 est la moins tolérante quand elle est inoculée avec la souche CIAT899. Par contre, la souche 12a3 lui confère une tolérance au sel pour la production de la biomasse nodulaire contrairement à sa symbiose avec la lignée Flamingo. Il est conclu qu'il est important de prendre en considération les interactions souche $\times$ lignées pour la sélection d'une légumineuse adaptée à une contrainte comme la salinité, et que la culture sur solution aérée est une bonne méthode pour la sélection de symbioses rhizobiennes à fort potentiel de fixation d'azote

Characterization of rhizobia nodulating chickpea in Tunisia

One hundred and fifty rhizobia nodulating chickpea (Cicer arietinum L.) were isolated from soils sampled in different regions of Tunisia. Variability in the time at which nodules appeared after plant inoculation was observed among these isolates. Five isolates induced nodules two weeks after inoculation, whereas, with the remaining 145 isolates, nodules were observed after more than four weeks. On the basis of PCR/RFLP analysis of 16S rDNA, isolates from the first group were classified as Mesorhizobium mediterraneum, and isolates from the second group as Sinorhizobium medicae. The respective taxonomic position of both types of isolates was confirmed by their symbiotic properties. M. mediterraneum isolates did not nodulate Medicago sativa and formed effective nodules on C. arietinum while S. medicae isolates were able to form effective nodules on M. sativa but formed ineffective nodules on C. arietinum, as did reference strains of the species.Caractérisation des rhizobia nodulant le pois chiche en Tunisie. Cent cinquante rhizobia nodulant le pois chiche (Cicer arietinum L.) ont été isolés à partir de sols échantillonnés dans différentes régions de Tunisie. L'inoculation de la plante hôte avec ces isolats montre une variabilité dans le temps d'apparition des premières nodosités. Cinq isolats induisent des nodosités deux semaines après inoculation alors que pour les 145 isolats restants les nodosités ne sont observées qu'après au moins quatre semaines. L'étude par PCR/RFLP de l'ADNr 16S a permis de rattacher les isolats du premier groupe à l'espèce Mesorhizobium mediterraneum et ceux du second groupe à l'espèce Sinorhizobium medicae. La position taxonomique des isolats a été confirmée par leurs propriétés symbiotiques. Les isolats de M. mediterraneum ne nodulent pas Medicago sativa mais forment une symbiose fixatrice avec C. arietinum, ceux de S. medicae, comme les souches références de l'espèce, forment des nodosités efficientes avec M. sativa et inefficientes avec C. arietinum

Nodule conductance varied among common bean (Phaseolus vulgaris) genotypes under phosphorus deficiency

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699International audienceCommon bean genotypes BAT477, COCOT, DOR364, Flamingo, and NAG310 were inoculated with Rhizobium tropici CIAT899 and grown under phosphorus deficiency. This treatment induced a significant decrease in shoot and nodule growth that varied among genotypes from 35% to 57% and from 45% to 61%, respectively, whereas root biomass was less affected. Phosphorus deficiency affected differently the genotypes for nodule number and size, and the responses of nodulated-root O2 uptake (Conr) to raising rhizospheric pO2. From the later data, nodule conductance could be computed by dividing the slope of the regression of Conr as a function of external pO2 by nodule surface area. It is concluded that differences in nodule conductance are related to genotypic tolerance to P deficiency

DATE PALM WASTE COMPOST IMPROVES THE PRODUCTION OF ORGANIC BARLEY IN AN OASIS ENVIRONMENT

In Tunisia, date palm cultivation generates huge quantities of waste that can be recycled by composting. Composting is a simple, ecological and inexpensive way of recovering and transforming this waste into an organic amendment in organic oases. Renewable biomass waste reincorporates organic matter into the soil and improves soil fertility, promoting plant growth and increasing crop productivity. In the present study, we investigate the performance of compost on the growth and yield of organic barley in a Tunisian oasis

Alternative oxidase 1 (Aox1) gene expression in roots of Medicago truncatula is a genotype-specific component of salt stress tolerance

Alternative oxidase (AOX) is the central component of the non-phosphorylating alternative respiratory pathway in plants and may be important for mitochondrial function during environmental stresses. Recently it has been proposed that Aox can be used as a functional marker for breeding stress tolerant plant varieties. This requires characterization of Aox alleles in plants with different degree of tolerance in a certain stress, affecting plant phenotype in a recognizable way. In this study we examined Aox1 gene expression levels in Medicago truncatula genotypes differing in salt stress tolerance, in order to uncover any correlation between Aox expression and tolerance to salt stress. Results demonstrated a specific induction of Aox1 gene expression in roots of the tolerant genotype that presented the lowest modulation in phenotypic and biochemical stress indices such as morphologic changes, protein level, lipid peroxidation and ROS generation. Similarly, in a previous study we reported that induction of antioxidant gene expression in the tolerant genotype contributed to the support of the antioxidant cellular machinery and stress tolerance. Correlation between expression patterns of the two groups of genes was revealed mainly in 48 h treated roots. Taken together, results from both experiments suggest that M. truncatula tolerance to salt stress may in part due to an efficient control of oxidative balance thanks to (i) induction of antioxidant systems and (ii) involvement of the AOX pathway. This reinforces the conclusion that differences in antioxidant mechanisms can be essential for salt stress tolerance in M. truncatula and possibly the corresponding genes, especially Aox, could be utilized as functional marker

Genetic variabilitly in Tunisian populations of faba bean (Vicia faba L. var. major) assessed by morphological and SSR markers

peer reviewe

Comportement agro-physiologique et biochimique de différents génotypes de féverole (Vicia fava L. var. 'minor') soumis au déficit hydrique

Drought is one of the major abiotic factors affecting growth and productivity of plants by imposing certain morphological, physiological and biochemical changes at different growth stages. The objective of this work is to study key morphological, physiological and biochemical response of faba bean (Vicia faba L. var. 'minor') to soil water deficit stress and to assess the contribution of genetic factors in improving faba bean tolerance to water deficit. Plant of 11 faba bean cultivars were grown in the greenhouse and subjected to three levels of water deficit (90, 50 and 30% of field capacity (FC)) in a simple randomized design for 20 days. Water deficit effects on plant growth, relative water content (RWC), gaz exchange, chlorophyll a (Chla) and Chlorophyll b (Chlb) content, osmoprotectant accumulations (such as proline and soluble sugars), antioxydant enzyme activities and grain yield were determined. Soil water deficit stress reduced growth and affected physiological parameters, especially antioxidant enzyme activities. Water deficit also increased proline, soluble sugars and protein contents. The studied cultivars significantly differed in their responses to water deficit stress. Photosynthetic parameters were less affected in the 'Hara' cultivar. Furthermore, this cultivar produced the highest value of grain yield at 30% FC, and showed higher antioxidant enzyme activities (CAT, GPX and APX), osmoprotectant accumulations, Chlb and RWC. The 'Hara' cultivar was found to be more tolerant to water deficit stress than the other cultivars. Our methodology can be used for assessing the response of faba bean genetic resources to soil water deficit. The identified tolerant cultivar can be utilized as a source for water stress tolerance in faba bean breeding programs aimed at improving drought tolerance