Bacteria-inducing legume nodules involved in the improvement of plant growth, health and nutrition

Bacteria-inducing legume nodules are known as rhizobia and belong to the class Alphaproteobacteria and Betaproteobacteria. They promote the growth and nutrition of their respective legume hosts through atmospheric nitrogen fixation which takes place in the nodules induced in their roots or stems. In addition, rhizobia have other plant growth-promoting mechanisms, mainly solubilization of phosphate and production of indoleacetic acid, ACC deaminase and siderophores. Some of these mechanisms have been reported for strains of rhizobia which are also able to promote the growth of several nonlegumes, such as cereals, oilseeds and vegetables. Less studied are the mechanisms that have the rhizobia to promote the plant health; however, these bacteria are able to exert biocontrol of some phytopathogens and to induce the plant resistance. In this chapter, we revised the available data about the ability of the legume nodule-inducing bacteria for improving the plant growth, health and nutrition of both legumes and nonlegumes. These data showed that rhizobia meet all the requirements of sustainable agriculture to be used as bio-inoculants allowing the total or partial replacement of chemicals used for fertilization or protection of crops

Formulations of Plant Growth-Promoting Microbes for Field Applications

Development of a plant growth-promoting (PGP) microbe needs several steps starting with isolation of a pure culture, screening of its PGP or antagonistic traits by means of different efficacy bioassays performed in vitro, in vivo or in trials under greenhouse and/or field conditions. In order to maximize the potential of an efficient PGP microbe, it is essential to optimize mass multiplication protocols that promote product quality and quantity and a product formulation that enhances bioactivity, preserves shelf life and aids product delivery. Selection of formulation is very crucial as it can determine the success or failure of a PGP microbe. A good carrier material should be able to deliver the right number of viable cells in good physiological conditions, easy to use and economically affordable by the farmers. Several carrier materials have been used in formulation that include peat, talc, charcoal, cellulose powder, farm yard manure, vermicompost and compost, lignite, bagasse and press mud. Each formulation has its advantages and disadvantages but the peat based carrier material is widely used in different part of the world. This chapter gives a comprehensive analysis of different formulations and the quality of inoculants available in the market, with a case study conducted in five-states of India

Short-term recovery of Bradyrhizobium japonicum during an inoculation process using mineral microgranules

International audienc

Decomposition de corps microbiens dans des sols fumiges au chloroforme: Effets du type de sol et de microorganisme

International audienceve microbial species (Aspergillusflaous, Trichoderma viride, Streptomyces sp., Arthrobacter sp., Achromobacter liquefuciens) were cultivated in liquid media containing ‘Wabelled glucose. The decomposition of these microorganisms was recorded in four different soils after chloroform fumigation by a technique related to that proposed by Jenkinson and Powlson, to determine the mineralization rate of microbial organic matter (K, coefficient). Three treatments were used: untreated soil, fumigated soil alone and fumigated soil suuplied with “C-labelled cells. Total evolved CO, and WO, were measured after 7 and 14 days at 28”6.‘ The labelled microorganisms enabled the calculation of mineralization rate I& (K, = mineralized microbial carbon/supplied microbial carbon). The extent of mineralization of la.belled microbial carbon depended on the type-of soil and on the microbial species. Statistical analysis of results at 7 days showed that 58% of the variance is taken in account by the soil effect and 32% by the microorganism effect. Between 35 and 49% of the supplied microbial C was mineralized in 7 days according to the soil type and the species of microorganism. Our results confirmed that the average value for K, = 0.41 is acceptable, but K, variability according to soil type must be considered. The priming effect on organic C and native microbial biomass mineralization, due to microbial carbon addition was obtained by comparison between the amount of non-labelled CO,-C produced by fumigated soils with or without added labelled microorganisms: this priming effect was generally negligible. These results indicate that the major portion of the error of microbial biomass measurement comes from the K, estimation

Mineralisation dans le sol de materiaux microbiens marques au carbone 14 et a l'azote 15: Quantification de l'azote de la biomasse microbienne

International audienceThe mineralization of microbial material of different C-to-N ratios (5.2, 7.9, 10.2, 12.7) was followed in fumigated soil. The microbial materials used were from Aspergillus,flavus cultures, grown in liquid media and labelled with [‘4C]glucose and (‘5NH,)2S0,. Three contrasting soils were used and the microbial materials incubated with the fumigated soils for 28 days at 28°C. The evolution of the added organic microbial C was fast: 80% of the [‘4C]C02 produced during the whole 28 days incubation was evolved in the first week. Microbial C mineralization was mainly related to soil type; the C-to-N ratio had small effect on the ratio (mineralized microbial carbon-to-added microbial carbon). Calculation of the KC coefficient (the fraction of the added microbial C mineralized in 7 days) shows that KC values lie between 0.38 and 0.43 in the 3 soils. Organic N in the added microbial material also breaks down quickly: between 60 and 100% of the organic nitrogen mineralized was evolved during the first week of incubation. Mineralization kinetics are related to soil type and to the C-to-N ratio of the microbial material. The proportion of N mineralized in 7 days was lower in an acid soil than in near neutral soils and lower with high C-to-N ratio material than with low C-to-N ratio material. The ratio (mineralized microbial N-to-added microbial N) depends on soil type and is negatively correlated with the C-to-N ratio of the microbial material. The KN value (the fraction of the added microbial N mineralized in 7 days) lies between 0.22 and 0.47 for the three soils and four materials investigated. The added microbial material induced a priming effect on soil native N: materials with C-to-N ratios of 10.2 and 12.7 produced negative priming effects whereas materials with C-to-N ratios of 5.2 and 7.9 sometimes produced a positive priming action. From the relationship between the C-to-N ratio of the added material and the (mineralized microbial C-to-mineralized microbial N) ratio, the soil native microbial biomass was estimated using the flush-C-to-flush-N ratio. Biomass nitrogen was then calculated from the formula biomass-N = biomass- C/(biomass C-to-N ratio). Calculated in this way, 24% of the total nitrogen in the three soils was in microbial biomass

Increase of Bradyrhizobium japonicum numbers in soils and enhanced nodulation of soybean (Glycine max L.merr) using granular inoculants amended with nutrients

40 ref.International audienc

Mineralisation dans le sol de materiaux microbiens marques au carbone 14 et a l'azote 15 : Quantification de l'azote de la biomasse microbienne

National audienc

Prise en compte de la reorganisation d'azote lors de l'estimation de l'azote de la biomasse microbienne avec la methode de fumigation au chloroforme

International audienceImmobilization of nitrogen was measured in three soils that had been amended with 15N-labelled NH4+ and fumigated with chloroform. After removal of the chloroform, each soil was then incubated for I4 days at 28°C. Little immobilization of labelled N occurred during incubation of unfumigated control soils. Immobilization was greater in fumigated soils, particularly during the first 7 days. However, even in fumigated soils, immobilization was relatively small. The gross flush of mineralization in fumigated soil was related to the net flush by the relationship: gross N-flush = 1.04-net N-Flush. In a supplementary experiment, four preparations of Aspergillus flavus mycelium of varying C/N ratio were added to one of the soils, which was amended with 15N-labelled NH4+ and then fumigated. The soil was incubated as before. The wider the C/N ratio of the mycelium. the more labelled K immobilized. Thus, for cell material of C/N ratio 5.8 the gross N-flush/net N-Rush ratio was 1.09. For cell material of C/N ratio 11.9, the ratio was 1.54. In another supplementary experiment, 15N-labelled A. flavus mycelium was added to soil, fumigated and then incubated in the presence of increasinrg quantities of unlabelled NH4+. The addition of unlabelled NH4+ increased the-amount of labelled NH4+ present in the soil, presumably as a result of pool substitution. The relationship N-biomass = N-flush/0.37 is proposed for calculating microbial biomass N in soils that have not recently received decomposable organic matter