Population dynamics of P-solubilizers in the rhizosphere of major weed species from a tropical delta soil

  • ITFR - Indigenous and Frontier Technology Research Centre, Chennai, India
  • Professor of Botany and Microbiology (Retd.)
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Microbes are found ubiquitous in all environments and rhizosphere and weed rhizosphere is not an exception. In the present approach, rhizospheres of weeds found in Paddy, Sugarcane, Garden, Riverbed and Wasteland soils were screened for enumerating the P-solubilizer population. P-solubilizer population was found high in Paddy and Sugarcane soils and poor in the Riverbed soils. The total available population ranged from 0 to 74×103 /gm dry rhizosphere soils. The study throws light on knowledge of the occurrence of P-solubilizers in the weed rhizosphere environment, evidencing the sustenance of native populations through indirect means in the soil ecosystem during off-season periods and stresses the need for studying the weed rhizosphere microflora in future for better understanding.

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... The adaptation of many wild plants and crop genotypes to highly saline conditions has been ascribed to their close interaction with microbes associated with their roots. However, these omnipresent and omnipotent microbes are less explored and under-utilized option for alleviation of salinity stress [1]. In fact, plant growth-promoting rhizobacteria (PGPR) are an attractive eco-friendly alternative to chemicals in agriculture and so far, the most attempts have concentrated on their screening from the rhizosphere of crop plants. ...
... Y3 Y4 Y5 Y6 Y7 Y8 Y10 Y12 Y13 Y14 CB CW Seed germination in the culture filtrates with tryptophan (+TRP) and without tryptophan (−TRP).1 Values in the same data series represented by different letters are with significant difference (p = 0.05) in the Duncan's multiple range test ...
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Halotolerant bacteria associated with Psoralea corylifolia L., a luxuriantly growing annual weed in salinity-affected semi-arid regions of western Maharashtra, India were evaluated for their plant growth-promoting activity in wheat. A total of 79 bacteria associated with different parts viz., root, shoot and nodule endophytes, rhizosphere, rhizoplane, and leaf epiphytes, were isolated and grouped based on their habitat. Twelve bacteria isolated for their potential in plant growth promotion were further selected for in vitro studies. Molecular identification showed the presence of the genera Bacillus, Pantoea, Marinobacterium, Acinetobacter, Enterobacter, Pseudomonas, Rhizobium, and Sinorhizobium (LC027447-53; LC027455; LC027457, LC027459, and LC128410). The phylogenetic studies along with carbon source utilization profiles using the Biolog® indicated the presence of novel species and the in planta studies revealed promising results under salinity stress. Whereas the nodule endophytes had minute plant growth-promoting (PGP) activity, the cell free culture filtrates of these strains enhanced seed germination of wheat (Triticum aestivum L). The maximum vigor index was monitored in isolate Y7 (Enterobacter sp strain NIASMVII). Indole acetic acid (IAA) production by the isolates ranged between 0.22 and 25.58 μg mL−1. This signifies the need of exploration of their individual metabolites for developing next-generation bio-inoculants through co-inoculation with other compatible microbes. This study has potential in utilization of the weed-associated microbiome in terms of alleviation of salinity stress in crop plants.
... Studies when performed have targeted the deleterious rhizobacteria and their enhancement for control of weeds (Kremer et al. 1990;Li and Kremer 2000). Seshadri and Lakshminarasimhan (2007) made an extensive effort to enumerate P solubilizing population in rhizospheres of common agricultural weeds in India. ...
... Wide differences in ability to solubilise inorganic phosphates, and production of IAA among isolates from within and between the genera have been reported earlier (Kundu et al. 2002;Narsian and Patel 2006;Seshadri and Lakshminarasimhan 2007) and their varied ability can be ascribed to their genetic makeup. The values of IAA produced by isolates were in the same orders of magnitude as described earlier (Meunchang et al. 2006;Ali et al. 2009). ...
Plant growth promoting rhizobacteria (PGPR) are an attractive eco-friendly alternative to chemicals in agriculture. While the rhizospheres of crop plants have been well studied with the objective of screening PGPR, weeds, which play an important role in maintaining ecological balance, have largely been ignored. The rhizosphere of a luxuriantly growing, medicinal weed, Cassia occidentalis was analysed by enumerating PGPR on N free media from the most diverse stage of plant (determined by profiles obtained on denaturing gradient gel electrophoresis). Each isolate was tested for other plant growth promotion assays including production of cellulase, indole acetic acid (IAA), ammonia, HCN, siderophore and chitinase to select for ones possessing multi-trait plant growth promoting (PGP) properties. Selected isolates were used for bacterization of Vigna radiata and Vigna mungo to evaluate their efficacy in promoting plant's growth in seedling germination and axenic pot conditions. Thirty five isolates were analysed further for the array of PGP properties they exhibit. A total of 6 isolates were shortlisted on the basis of maximum traits positive, amount of phosphate solubilized and IAA produced. V. radiata responded well to seed bacterization during seedling germination. A maximum increase of approximately 36 and 60 % was observed for shoot and root length, respectively in V. radiata in axenic pot culture over control plants. Extensive branching of roots was also observed with isolate NL, which produced the maximum amount of IAA. Present study investigated the plant growth promoting isolates obtained on N free media in the rhizosphere of C. occidentalis, which have the potential to be used as inoculants for other crops. This provides a new dimension to the significance of weeds in agricultural ecosystems. The study opens up possibilities for utilization of this property of weeds in plant growth promotion, and subsequent enhancement of yield for agricultural crops.
... Lower CFU counts of PSBs in rhizospheric soils was reported earlier ranging from 0 to 74 x 10 3 g -1 dry rhizosphere of weeds found in paddy, sugarcane, garden, riverbed and wasteland soils (Seshadri and Lakshminarasimhan, 2007), 32 to 95 x 10 3 g -1 soil (Vikram et al., 2007) to 9 to 67 x 10 5 CFU g -1 soil in chickpea (Kundu et al., 2009). The difference in population of PSB by 2 orders of magnitude is probably because most studies consider only colonies producing a distinct halo on medium used for enumeration of phosphate solubilizers. ...
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Analysis of diversity of phosphate solubilizers in agricultural soil is essential to understand their ecological role and their utilization in sustainable agriculture. One of the factors contributing to the success of weeds, even in nutrient limiting conditions, is the microbial community they select in their vicinity. Phosphate solubilizers from the rhizosphere of a widely growing weed, Parthenium hysterophorus, were enumerated on Pikovskaya’s medium, with an aim to screen for their plant growth promoting abilities for crops. The isolates were further assayed for multi-trait plant growth promoting properties. Two potential isolates, P1 and P2, were employed in seed germination and pot experiments with crop species. While bacterization led to an increase of 70 and 200% in shoot length in both seedling germination and pot experiments with Cajanus cajan (red gram), Vigna radiata (green gram) displayed an increase in shoot length by about 20% in pot assay using isolates P1 and P2, respectively. The present study reveals the presence of phosphate solubilizers in the rhizosphere of P. hysterophorus with plant growth promoting effect on other crop species. Due to their potential in exhibiting plant growth promoting properties, these phosphate solubilizing isolates provide a new dimension to the significance of weeds in agricultural ecosystems. The study opens up possibilities of utilization of this property of weeds in plant growth promotion, disease suppression and subsequent enhancement of yield in agriculture.
Thirteen pink-pigmented facultative methylotrophic (PPFM) strains isolated from Adyar and Cooum rivers in Chennai and forest soil samples in Tamil Nadu, India, along with Methylobacterium extorquens, M. organophilum, M. gregans, and M. komagatae were screened for phosphate solubilization in plates. P-solubilization index of the PPFMs grown on NBRIP—BPB plates for 7 days ranged from 1.1 to 2.7. The growth of PPFMs in tricalcium phosphate amended media was found directly proportional to the glucose concentration. Higher phosphate solubilization was observed in four strains MSF 32 (415 mg l−l), MDW 80 (301 mg l−l), M. komagatae (279 mg l−l), and MSF 34 (202 mg l−l), after 7 days of incubation. A drop in the media pH from 6.6 to 3.4 was associated with an increase in titratable acidity. Acid phosphatase activity was more pronounced in the culture filtrate than alkaline phosphatase activity. Adherence of phosphate to densely grown bacterial surface was observed under scanning electron microscope after 7-day-old cultures. Biochemical characterization and screening for methanol dehydrogenase gene (mxaF) confirmed the strains as methylotrophs. The mxaF gene sequence from MSF 32 clustered towards M. lusitanum sp. with 99% similarity. This study forms the first detailed report on phosphate solubilization by the PPFMs.
Von 20 phosphatlösenden Mikroorganismen, die aus einem repräsentativen indischen Laterit (typischer Ochraguali) isoliert worden waren, waren 9 Bazillen, 6 Aktinomyzeten (Streptomyces) und 5 Pilze, darunter 4 Aspergillen und ein Penicillium-Stamm. Am besten wurde Ca3(PO4)2-gelöst, gefolgt von AlPO4 und FePO4. Fýr die P-lösende Wirkung der Mikroorganismen ergab sich folgende Reihung: Bacillus > Penicillium > Aspergillus > Streptomyces. Die von diesen Organismen in einem flýssigen Saccharose-Kalziumphosphat-Medium erzeugten organischen Säuren waren 2-Ketoglukon-, Oxal-, Bernstein- und Malonsäure sowie eine nicht identifizierte. Obgleich keine Beziehung zwischen Säurebildung und Löslichmachung von Phosphat bestand, zeigten die Isolate, die 2-Ketoglukon- und Bernsteinsäure produzierten, eine ausgeprägtere Fähigkeit zur Lösung unlöslicher anorganischer Phosphate.
A number of microorganisms capable of solubilizing apatite mere isolated from soil and from the rhizosphere of plants. Many genera of common soil fungi and bacteria were represented. The organis~ns solubilizing apatite were consistently present in higher proportions in rhizosphere isolates than in those from nearby soil. The zone of solution of apatite surrounding colonies on agar plates was usually characteristic of organisms producing acid in liquid culture; however, the degree of solubilization was not proportional to the fall in pH. On subculturing, many isolates rapidly and irreversibly lost their ability to dissolve apatite. Soil isolates lost their ability to solubilize apatite more readily than isolates from the rhizosphere.
The effect of applications of γ-benzene hexachloride (γ-BHC) to two submerged tropical soils at rates equivalent to recommended field practice (5 kg/ha) and 10 times this level upon the mineralization of native soil nitrogen was studied. No inhibitory effect on nitrogen mineralization was detected. A significant increase in the amount of nitrogen mineralized was detected in one of the soils over a period of 16 weeks of submergence. Additions of γ-BHC at 6 kg/ha resulted in significant increases in nitrogen fixation in both soils. Populations of anaerobic, phosphate-dissolving bacteria were found to be higher in the two soils when they were treated with γ-BHC at 6 kg/ha.
Bacterial isolates from the roots of wheat (rhizoplane) were more active in oxidizing glucose and alanine than cultures isolated from rhizosphere and non-rhizosphcre soils. In general, metabolic activity was greater with alanine than with glucose. Over one third of the cultures tested were capable of dissolving insoluble phosphorus in the form of CaHPO4 but the roots did not appear to exert a selective effect on these forms. However, the phosphate-solubilizing organisms from the rhizoplane were also the most active in oxidizing glucose and alanine. Those from the rhizosphere soil were intermediate in this respect. By far the majority of these phosphate-dissolving bacteria were in the nutritional group requiring unknown substances in yeast and soil extracts for optimal growth. It was suggested that although these bacteria were not preferentially stimulated in the root zone, their large numbers and their greater metabolic activity may contribute significantly to the phosphate economy of the plant.
Phosphate solubilizing fungi from Thanjavur Delta
  • S Seshadri