MULTIFUNCTIONAL MUTANTS OF Azospirillum sp. WITH ENHANCED CAPABILITY OF SOLUBILIZING PHOSPHORUS, FIXING NITROGEN AND PRODUCING INDOLE ACETIC ACID

Azospirillum sp. have long been known as biofertilizer for plant growth because of its capability to produce phytohormones and fix nitrogen from the atmosphere. Multifunctional Azospirillum strain Aj Bandung 6.4.1.2 isolated in 2009 from cauliflower (Brassica oleracea) rhizosphere in Lembang, Bandung, West Java, was capable of fixing nitrogen, solubilizing tricalcium-phosphate, and producing phytohormone indole acetic acid (IAA). The study aimed to modify the multifunctions of Azos-pirillum sp. for better capability of fixing N2, solubilizing P, and producing IAA using ethyl methanesulfonate and 1-methyl-3-nitro-1-nitrosoguanidine (EMS) mutagen. The study was conducted at Indonesian Center for Agricultural Biotechnology and Genetic Resources Research and Development (ICABIOGRAD) in 2010. The results showed that this strain was genetically mutagenized using EMS for better performance in solubilizing P, fixing N2 (nitrogenase activity), and producing phytohormone (IAA). The optimum concentration and the length of incubation time for the process have been determined. Nine selected mutants with increasing capability to solubilize P (determined by clear-zone formation on Pikovskaya’s medium) have been characterized for nitrogenase activities and IAA production compared to wild type Aj Bandung 6.4.1.2. The effect of mutagenesis on IAA produc-tion and nitrogenase activities varied among the mutans. Two mutants, AzM 3.7.1.16 and AzM 1.7.2.12, showed superiority in the production of IAA, while two mutants, AzM 1.5.1.14 and AzM 3.7.1.15, were superior in nitrogenase activities. The EMS mutagenesis of Azospirillum sp. showed enhanced dissolving capa-bility of unsoluble phosphate (tricalciumphosphate) and increased IAA production and nitrogenase activity.

Effect of plant growth-promoting rhizobacteria on canola (Brassica napus L) and lentil (Lens culinaris Medik) plants

Plant growth-promoting rhizobacteria (PGPR) are free-living, soil-borne bacteria that colonize the rhizosphere and, when applied to crops, enhance the growth of plants. Plant growth-promoting rhizobacteria may enhance plant growth either by direct or indirect mechanisms. The direct mechanisms of action include nitrogen fixation,production of phytohormones and lowering of ethylene concentrations. The objective of this study was to determine whether Pseudomonas putida strain 6-8 isolated from the rhizosphere of legume crops grown in Saskatchewan fields was able to promote the growth of canola cv. Smart and lentil cv. Milestone plants by direct mechanisms. Initial studies determined the effect of strain 6-8 and other known phytohormoneproducing PGPR strains on the growth of canola and lentil plants both in gnotobiotic and growth chamber conditions. Variations in the results were observed, as there were significant differences among trials. Strain 6-8 enhanced the growth of canola cv. Smart in growth pouches but not in pots in growth chamber studies. In the case of lentil cv.Milestone, strain 6-8 had no significant effect in growth pouches, but it significantly increased root dry weight, shoot dry weight and root surface area in pots in growth chamber studies. A similar effect was observed with wild-type strains GR12-2 and G20- 18. Strain GR12-2 was consistent in promoting the growth of lentil cv. Milestone both in growth pouches and in pots in growth chambers when compared to other strains and the control. The ability of the PGPR strains to produce auxin and cytokinin phytohomones in pure culture and in the canola rhizosphere was tested using the enzyme linked immunosorbent assay (ELISA). All the PGPR strains produced indole compounds and the concentration of the indoles produced increased with increasing concentrations of the precursor tryptophan. There were no significant differences among PGPR strains in production of indole-3-acetic acid (IAA) when assayed using ELISA. The concentrations of IAA secreted by PGPR strains were extremely low (0.19 µg/ml – 9.80 µg/ml). Strain 6-8 produced the cytokinins, isopentenyl adenosine (IPA), zeatin riboside (ZR) and dihydroxyzeatin riboside (DHZR) in pure culture. Indole-3-acetic acid was detected in supernatants obtained from canola growth pouches inoculated with PGPR strains, but there were no significant differences in the concentrations of IAA secreted among PGPR strains. Significantly higher concentrations of IPA and ZR were observed in the rhizosphere of canola inoculated with strain 6-8 than in the non-inoculated control. Strain 6-8 produced siderophores, solubilized inorganic phosphate and used 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene, as sole nitrogen source. These traits are considered to be alternative mechanisms for direct plant growth promotion. A qualitative and quantitative study of root colonization by strain 6-8 was conducted by tagging the strain with green fluorescent protein in conjunction with confocal laser scanning microscopy and by conventional plating. The populations of strain 6-8 were higher on canola roots than on lentil roots by conventional plating. Similar results were also observed in confocal laser scanning microscopy (CLSM) studies after 5, 7 and 9 days for canola and 3, 6 and 9 days for lentil. Pseudomonas putida strain 6-8 produced cytokinins and also possessed other direct growth promoting characteristics. The ability of strain 6-8 to promote the growth of canola cv. Smart in growth pouches and lentil cv. Milestone in growth chamber studies may be related to these direct growth promoting characteristics. Strain 6-8 may have potential for development as a plant growth-promoting rhizobacterial inoculant

The Role of Soil Beneficial Bacteria in Wheat Production: A Review

Free-living plant growth-promoting rhizobacteria (PGPR) have favourable effect on plant growth, tolerance against stresses and are considered as a promising alternative to inorganic fertilizer for promoting plant growth, yield and quality. PGPR colonize at the plant root, increase germination rates, promote root growth, yield, leaf area, chlorophyll content, nitrogen content, protein content, tolerance to drought, shoot and root weight, and delayed leaf senescence. Several important bacterial characteristics, such as biological nitrogen fixation, solubilization of inorganic phosphate and mineralization of organic phosphate, nutrient uptake, 1-aminocydopropane-1-carboxylic acid (ACC) deaminase activity and production of siderophores and phytohormones, can be assessed as plant growth promotion traits. By efficient use, PGPR is expected to contribute to agronomic efficiency, chiefly by decreasing costs and environmental pollution, by eliminating harmful chemicals. This review discusses various bacteria acting as PGPR, their genetic diversity, screening strategies, working principles, applications for wheat and future aspects in terms of efficiency, mechanisms and the desirable properties. The elucidation of the diverse mechanisms will enable microorganisms developing agriculture further

Plant growth promoting rhizobacteria: Beneficial effects for healthy and sustainable agriculture

It is unanimously admitted that the chemical fertilizers and pesticides used in modern agriculture create a real environmental and public health problems. One of the promising solutions to substitute these agrochemicals products is the use of bio-resources, including plant growth promoting rhizobacteria (PGPR). The PGPR focused more and more scientific attention in recent decades. These rhizospheric bacteria colonize actively the root system of plants and improve their growth and yield. The PGPR use different mechanisms of action to promote plant growth. These mechanisms were grouped into three clusters according to the PGPR effects on plant physiology. These groups are as follow: (i) biofertilization including biological fixation of atmospheric nitrogen, phosphate solubilization, siderophores production and exopolysaccharides production; (ii) phytostimulation including production of indole acetic acid, gibberellins, cytokinins and ethylene; and (ii) biocontrol including induction of systemic resistance, competition for iron, nutrient and space, production of antibiotics, lytic enzymes, hydrogen cyanide and volatile compounds. In view of the latest advances in PGPR biotechnology, this paper proposes to do the review on PGPR in rhizosphere and describes the different mechanisms used by PGPR to promote the plants growth and health. In prospect to a healthy and sustainable agriculture, respectful of environment, the PGPR approach revealed as one of the best alternatives.Keywords: Rhizosphere, plant growth promoting rhizobacteria (PGPR), root colonization, biofertilization, biocontrol, biostimulation, interaction plant-microorganisms, sustainable agricultur

Effect of plant growth promoting rhizobacterial (PGPR) inoculation on growth in tomato (Solanum Lycopersicum L.) and characterization for direct PGP abilities in Morocco

Plant Growth promoting rhizobacteria are a heterogeneous group of bacteria that can be found in the rhizosphere, at root surfaces and in association with roots. They benefit plants through Production of plant hormones, such as auxins, asymbiotic N2 fixation, solubilization of mineral phosphates, antagonism against phytopathogenic microorganisms by production of antibiotics, siderophroes, Chitinase and other nutrients ability to effectively colonize roots are responsible for plant growth promotion. An experiment was conducted in the field of National Institute of Agronomic Research of Meknes. Morocco. The experiment was a completely randomized design with six replicates. There were four treatments viz. T1: (control; N0 -PGPR), T2: (N0 +2027-2), T3: (N0 +2066-7) and T4: (N0+2025-1). The results indicated that a remarkable increase in root growth, namely length, the diameter of the rod and the total chlorophyll. A total of three different bacteria colonies were isolated and proceed with in vitro screening for plant growth promoting activities; phosphate solubilization, nitrogen fixation, indole acetic acid (IAA), ammonia production and antimicrobial enzymes (cellulose, chitinase and protease) activity. Among the three bacterial strains, all bacterial strains are able to produce ammonia, IAA production and nitrogen fixation activity, one strain phosphate solubilizing activity, two strain are able to produce cellulase syntheses, Protease activity and Chitinase activity

Potency of Rhizosphere Bacteria to Promote Rice Growth Under Saline Condition

Saline soil is a common problem in coastal paddy field, especially in Indonesia. Salinity affects rice growth and the activities of soil functional microbes, including functional bacteria, which play roles in plant growth. Some of these microbes are associated with rice plants and are able to survive under saline condition. The presence of functional microbes is also important to improve soil quality. Nitrogen and phosphate are essential soil nutrients and is available in soil due to the activities of nitrogen-fixing bacteria and free-living plant-associated bacteria. The objective of the present study was to obtain nitrogen-fixing, phosphate solubilizing and Indole Acetic Acid (IAA)-producing bacteria that are able to survive and promote the growth of rice under saline conditions. From rice and peanut rhizosphere, Ca-phosphate (Ca-P) solubilizing and nitrogen-fixing bacteria were isolated separately using specific media. Then, the Ca-P solubilizing ability, phosphomonoesterase activity and IAA-producing ability were quantitatively examined. Based on the abilities, 20 strains were selected and identified as Burkholderia cepacia-complex, Burkholderia anthina, Burkholderia cenocepacia, Bacillus cereus-complex (three strains), Achromobacter spanius, Azospirillum sp. (four strains), Azotobacter sp. (three strains), Rhizobium leguminosarum, Rhizobium sp. (two strains), and Pseudomonas sp. (three strains). The inoculation of several single strains or the mixture of the selected strains promoted the growth of rice under saline conditions. These inoculants could be potential as biofertilizer in saline paddy fields