Assessing hydroaeroponic culture for the tripartite symbiosis of mungbean (Vigna radiata L.) with arbuscular mycorrhizal fungi and rhizobia

Mungbean (Vigna radiata L.) has the potential to establish symbiosis with rhizobia that fix atmospheric dinitrogen (N2), and arbuscular mycorrhizal fungi (AMF) that improve the uptake of low mobile soil nutrients such as phosphorus. Both rhizobial and mycorrhizal symbioses can benefit plants synergistically. The tripartite symbiosis of mungbean with rhizobia and AMF was assessed in hydroaeroponic culture under sufficient versus deficient P supplies (250 versus 75 μmol P plant-1 week-1) by comparing the effects of three AMF species on the mycorrhizal root colonization, rhizobial nodulation, and plant growth. Although, Glomus intraradices colonized well the roots of mungbean in sand and hydroaeroponic cultures, Gigaspora rosea only established well under sand culture conditions, and Acaulospora mellea weakly colonized roots under both culture conditions. Though significant differences of mungbean growth were found with different AMF species in sand, only few differences were observed in hydroaeroponic cultures. It is argued that the later will probably be a valuable tool for scrutinizing the interactions among the three symbionts, as well as plant  physiology, and nutrient partitioning within the symbiotic system.Key words: Acaulospora mellea, arbuscular mycorrhizal, Bradyrhizobium, Gigaspora rosea, Glomus intraradices, mungbean, phosphorus, symbiotic nitrogen fixation

Competitiveness and symbiotic effectiveness of a R. gallicum strain isolated from root nodules of Phaseolus vulgaris

The rhizobia strain R. gallicum bv. gallicum 8a3 was isolated from root nodules of Phaseolus vulgaris cultivated in Tunisian soils. This strain was selected on the basis of its high symbiotic effectiveness in laboratory conditions. In order to assess its ability to compete indigenous rhizobia, this strain was labelled with gusA gene. Conservation of initial effectiveness and competitiveness by transconjugants was tested. A transconjugant was introduced in three soil-core microcosms originating from different geographical and agronomic regions. Nodulation monitoring showed that the labelled transconjugant was able to occupy more than 90% of nodules at 30 days after inoculation. The nodule occupancy by the introduced strain was high even in the soil sample of Mateur which showed an MPN value of 103 rhizobia/g of dry soil. A significant improvement of plant productivity by inoculation was observed with the three soil samples in green house. Field inoculation with the parental strain showed a significant increase in nodule number, pod number and seed dry weight. The improvement of plant productivity in green house or in field conditions was equal or better than nitrogen fertilisation

Response of common bean lines to inoculation: comparison between the Rhizobium tropici CIAT899 and the native Rhizobium etli 12a3 and their persistence in Tunisian soils

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 audienceSince Phaseolus vulgaris (L) is poorly nodulated in all regions of Tunisia where this crop is grown, the response of common-bean lines CocoT and Flamingo to inoculation with reference Rhizobium tropici CIAT 899 or native rhizobia, namely Sinorhizobium fredii 1a6, Rhizobium etli 12a3, and Rhizobium gallicum 8a3, was studied in a field station. Since R. etli 12a3 was found to be the most effective native rhizobium, it was subsequently compared with R. tropici CIAT 899 in a broader study in two stations over 3 years. A significant interaction between bean and rhizobia was observed for nodule number, shoot dry weight, grain yield, and contents of nitrogen and chlorophyll. The native rhizobia was more efficient than CIAT899 for Flamingo, though not for CocoT. The Enzyme-linked immunosorbent assay technique was used with polyclonal antibody to assess the occupancy in nodule and persistence in soil of the inoculated rhizobia. For both stations the nodule occupancy was 100% during the first year for each rhizobium, but during the next 2 years, between 7 and 15% of nodules were formed by the rhizobia inoculated in the neighboring plot. It is concluded that the first-year inoculation is sufficient to maintain an adequate rate of nodulation during three growth cycles, and that the native R etli can be recommended for the common-bean inoculation in similar soils of Tunisia

Methods for large-scale production of AM fungi: past, present, and future.

Many different cultivation techniques and inoculum products of the plant-beneficial arbuscular mycorrhizal (AM) fungi have been developed in the last decades. Soil- and substrate-based production techniques as well as substrate-free culture techniques (hydroponics and aeroponics) and in vitro cultivation methods have all been attempted for the large-scale production of AM fungi. In this review, we describe the principal in vivo and in vitro production methods that have been developed so far. We present the parameters that are critical for optimal production, discuss the advantages and disadvantages of the methods, and highlight their most probable sectors of application