Associative diazotrophic bacteria isolated from different biomes as potential plant growth promoters of common bean

In field tests we have observed year-to-year differences in the severity of the effects of soil compaction on nodulation and growth of common bean; these differences appeared to be related to the amount of rainfall during the growing season. We decided to use better controlled conditions in the greenhouse, and extend the scope of the study to another legume crop and a different soil type, in order to investigate the hypothesis that copious water supply alleviates the adverse effects of soil compaction on nodulation and plant growth.The effects of two levels of soil compaction and of high and low water supply on the growth and nodulation of common bean and soybean were investigated in separate pot tests using a Fox sandy loam and a Brookston clay loam soil.Root growth of both species was severely restricted by dry compacted conditions. Plant growth as a whole was clearly reduced by both increased compaction and by reduced water supply, presumably mediated by the effects on root growth. The effect of reduced water supply was more severe in the highly compacted pots, and more severe in the clay loam than in the sandy loam.In the sandy loam, low moisture reduced nodule numbers and weights in both species, while increased bulk density reduced the numbers of nodules but not the dry weights. In the clay loam, nodule weights and numbers were very low, presumably, owing to high levels of nitrate, which may have resulted from mineralization of soil organic matter during storage.A generous supply of water obviously alleviated some of the adverse effects of soil compaction on plant growth. This is in general agreement with results of earlier field trials, where severity of the effects of soil compaction varied with the quantity of rainfall. Key words: Soybean, common bean, soil compaction, soil moisture, nodulation, bulk density

Forty fluorescent pseudomonads were quantitatively evaluated for indole acetic acid (IAA) producing ability in the presence (trypt + ) or absence (trypt - ) of tryptophan and growth promotion in groundnut in response to seed treatment with high IAA producers was analyzed. There were significant differences in the amounts of IAA produced by the isolates and more amounts of IAA were released in trypt + . In trypt - increased IAA production was noticed for up to 144h and thereafter it stabilized or decreased. Analysis of plant growth promotion showed that the maximum root length (187.5mm) was exhibited by plants treated with BA16(A)2 which was a medium IAA producer whereas the highest IAA producer BA1(E)2 (32.2 μg/ml of IAA) showed a root length of 167.3mm. The isolate OTN7(E)2 which was a low IAA producer showed good root lengths of 148.3mm (sterile soil) and 133.3mm (unsterile soil). When the shoot lengths were compared, highest shoot length of 213.3mm (sterile soil) was by BA4(D) which is a medium to high IAA producer and in unsterile soil highest shoot length of 198.67mm was shown by the isolate ND1which is also a medium to high IAA producer. The highest IAA producer BA1(E)2 showed a low shoot length of 156.7mm (sterile soil) and 115mm (unsterile soil). The results in some way do establish that plant growth is not directly influenced by high IAA producers. Root growth seemed to be more affected by high IAA producers in unsterile soil and maximum vigour index of 32600 was exhibited by BA2(D)1 which is a medium IAA producer and the minimum of 15750 was by BA1(E)2 which is a high IAA producer. Hence IAA producers of the fluorescent Pseudomonas group showed significant plant growth when compared with control but plant growth was not greatly influenced by those organisms that produced high amounts of IAA. Antagonistic Pseudomonas spp. able to release moderate or even low amounts of IAA may be better growth promoters.

Common bean is one of the primary protein sources in third-world countries. They form nodules with nitrogen-fixing rhizobia, which have to be adapted to the local soils. Commercial rhizobial strains such as Rhizobium tropici CIAT899 are often used in agriculture. However, this strain failed to significantly increase the common bean yield in many places, including Kenya, due to the local soils’ low pH. We isolated two indigenous rhizobial strains from the nodules of common bean from two fields in Western Kenya that have never been exposed to commercial inocula. We then determined their ability to fix nitrogen in common beans, solubilize phosphorus, and produce indole acetic acid. In greenhouse experiments, common bean plants inoculated with two isolates, B3 and S2 in sterile vermiculite, performed better than those inoculated with CIAT899 or plants grown with nitrogen fertilizer alone. In contrast to CIAT899, both isolates grew in the media with pH 4.8. Furthermore, isolate B3 had higher phosphate solubilization ability and produced more indole acetic acid than the other two rhizobia. Genome analyses revealed that B3 and S2 are different strains of Rhizobium phaseoli. We recommend fieldwork studies in Kenyan soils to test the efficacy of the two isolates in the natural environment in an effort to produce inoculants specific for these soils.

A field experiment was conducted at the Experimental farm of the University of Peradeniya, Sri Lanka, over 2 dry seasons (May-August 1999 and 2000) to evaluate the impact of tillage and soil moisture on growth, yield and nodulation of common bean (Phaseolus vulgaris L.) and mungbean (Phaseolus radiatus L). The legumes were grown in tilled or compacted soils, under rainfed or irrigated conditions, which corresponded to low or high soil- moisture regimes. Germination of the small-seeded mungbean was reduced by soil compaction and low moisture. Crop growth of mungbean was also reduced to a greater extent by soil compaction and moisture stress. In contrast, the adverse impact of soil compaction and moisture stress was greater on pod yields of com- mon bean than on seed yields of mungbean. Tillage promoted root branching to a greater extent than root dry weights of both species, especially in the low soil-moisture regime. Nodulation was reduced to a greater extent by soil-moisture stress especially in common bean, the poor nodulating species.

Rhizosphere actinobacteria for combating Phytophthora capsici and Sclerotium rolfsii, the major soil borne pathogens of black pepper (Piper nigrum L.)

Nodulation and growth of common bean ( Phaseolus vulgaris) under water deficiency

Yeasts are an interesting group of microorganisms, which occur naturally in soil and on plant surfaces. Few studies have analysed their potential as plant growth promoters. Thus, the aim of this study was to evaluate the indole acetic acid (IAA) production and phosphate solubilization by the yeasts Torulaspora globosa (CCA5S51 and CCA5S55), Meyerozyma guilliermondii (CCA3C98), and Rhodotorula mucilaginosa (CCA2F32), and the influence of T. globosa (CCA5S55) in the development of tomato seedlings. The results showed that T. globosa strains present both plant growth promotion traits (IAA production and phosphate solubilization). The strains of T. globosa (5S51 and 5S55) showed high IAA production (641 and 669 µg.ml-1, respectively) after 48 h of incubation, while Rh. mucilaginosa produced 406 µg.ml-1 of IAA after 120 h. The strains CCA5S55 and CCA5S51 could also solubilize 47 and 35% of tricalcium phosphate in the medium, respectively, after 12 days of incubation; whereas M. guilliermondii (CCA3C98) solubilized only 10% of the tricalcium phosphate after 12 days. The inoculation of tomato seedlings with T. globosa stimulates the plant growth; root height was statistically superior when the higher cell concentration was inoculated. The root dry weight was enhanced with addition of glucose and tryptophan. The conclusion is the yeast species T. globosa is able to produce IAA in the presence of tryptophan and also solubilize phosphate in vitro. The inoculation of tomato seedlings promoted its development. The cell concentration and the addition of glucose and tryptophan must be evaluated in details to attain optimized yields. Key words: indole acetic acid (IAA) production, phosphate solubilisation, yeast as plant growth promoter.

Soil acidity is among the major limiting factors for common bean nodulation and productivity. Therefore, field experiments were conducted to investigate the effects of the application of phosphorus (P), lime, and compost on nodulation and dry-matter accumulation of common bean under field conditions at Areka during the long rainy season (belg) and short rainy season (meher). Three rates of compost (0, 5 and 10 t ha-1), three rates of lime (0, 0.64 and 1.28 t ha-1) and three rates of phosphorus (0, 23 and 46 kg P2O5 ha-1) were laid out as a randomized complete block design in a factorial arrangement and replicated three times. All data on nodulation and aboveground drymatter were collected. Results showed that the combined application of P at rates of 46 kg P2O5 ha-1 and lime at rates of 1.28 t ha-1 resulted in the maximum number of total and effective nodules during the long rainy season. Similarly, application of the highest rates of compost along with the highest rates of lime increased the aboveground dry biomass yield significantly over the control during both seasons. Finally, it can be concluded that the application of compost, lime and phosphorus can boost biomass accumulation and nodulation of common bean in acid soils.

Endophytes are colonizers of healthy plants and they normally exhibit biocontrol activities, such as reducing the occurrence of plant diseases and promoting plant growth. The endophytic bacterium Bacillus halotolerans Q2H2 (Q2H2) was isolated from the roots of potato plants and was found to have an antagonistic effect on pathogenic fungi. Q2H2 was identified by morphological observations, physiological and biochemical identification, and 16S rRNA gene sequence analysis. Genes related to the anti-fungal and growth-promoting effects were analyzed using whole-genome sequencing and comparative genomic analysis. Finally, we analyzed the growth-promoting and biocontrol activities of Q2H2 in potato plants using pot experiments. Antagonism and non-volatile substance plate tests showed that Q2H2 had strong antagonism against Fusarium oxysporum, Fusarium commune, Fusarium graminearum, Fusarium brachygibbosum, Rhizoctonia solani and Stemphylium solani. The plate test showed that Q2H2 had the ability to produce proteases, cellulases, β-1,3-glucanase, dissolved organic phosphate, siderophores, indole-3-acetic acid (IAA), ammonia and fix nitrogen. The suitable growth ranges of Q2H2 under different forms of abiotic stress were pH 5-9, a temperature of 15-30°C, and a salt concentration of 1-5%. Though whole-genome sequencing, we obtained sequencing data of approximately 4.16 MB encompassed 4,102 coding sequences. We predicted 10 secondary metabolite gene clusters related to antagonism and growth promotion, including five known products surfactin, bacillaene, fengycin, bacilysin, bacillibactin, and subtilosin A. Average nucleotide identity and comparative genomic analyses revealed that Q2H2 was Bacillus halotolerans. Through gene function annotation, we analyzed genes related to antagonism and plant growth promotion in the Q2H2 genome. These included genes involved in phosphate metabolism (pstB, pstA, pstC, and pstS), nitrogen fixation (nifS, nifU, salA, and sufU), ammonia production (gudB, rocG, nasD, and nasE), siderophore production (fhuC, fhuG, fhuB, and fhuD), IAA production (trpABFCDE), biofilm formation (tasA, bslA, and bslB), and volatile compound production (alsD, ilvABCDEHKY, metH, and ispE), and genes encoding hydrolases (eglS, amyE, gmuD, ganB, sleL, and ydhD). The potato pot test showed that Q2H2 had an obvious growth-promoting effect on potato roots and better control of Fusarium wilt than carbendazim. These findings suggest that the strain-specific genes identified in bacterial endophytes may reveal important antagonistic and plant growth-promoting mechanisms.

Recently, public concerns regarding the use of agrochemicals have increased due to the environmental impacts and potential risks to human health. The application of beneficial microorganisms is a novel technology to improve plant health and productivity and has therefore been extensively studied as an alternative strategy for biocontrol. In our study, 122 microbial isolates were obtained from the rhizosphere of Panax ginseng and subsequently tested in vitro for phosphate solubilization and indole acetic acid (IAA) production. Pikovskaya’s medium was used to estimate rhizomicrobial isolates to solubilize tricalcium phosphate [Ca3 (PO4)2]. Among all the investigated strains, 82 % of rhizospheric fungi showed phosphate solubilization activity; however, only 57.1 % of the rhizobacteria isolates showed phosphate solubilization ability. For IAA production, 64.7 % of the tested rhizofungi isolates were able to produce the phytohormone; however, only 47.62 % of the rhizobacteria isolates exhibited IAA production. Among all investigated species, Pseudomonas fluorescence and Azotobacter chroococcum showed the highest phosphate solubility demonstrating 885.4 and 863.4 μg mL−1, respectively. Mucor sp. produced 42.3 μg mL−1 of IAA in Czapek’s tryptophan medium, and the highest fungal species to solubilize the inorganic phosphate (237.5 μg mL−1) was estimated by Penicillium sp. Rhizobacteria were more effective than rhizofungi in phosphate solubilization and IAA production. This study introduces some potent species in terms of phosphate solubilization and IAA production which could be likely to improve soils’ quality and promote plant growth.

Background: Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae is a major disease and a threat to rice production worldwide. Several biological, chemical and genetic control approaches has resulted the improved management of BLB of rice. Recently, biological control using plant growth-promoting bacteria is emerging as potential alternative to chemicals. Therefore, identification and evaluation of new PGP bacteria from native sources is an essential step to determine their plant growth promoting activities. Objectives The aim of this work was to isolate and identify the plant growth promoting bacteria from rice phylloplane and rhizosphere that antagonistic to X. oryzae pv.oryzae, the causal agent of BLB of rice for eco-friendly management of the disease. Methodology Rice phylloplane and rhizosphere bacteria were isolated from the surface of rice leaves and stem as well as from the soil attached to the roots of rice plants, respectively, by dilution plate technique. The antagonistic activity of these isolated bacteria was determined by dual culture method. The antagonistic bacterial isolates were identified by sequencing of 16SrDNA.Plant growth promoting activities were determined by the production of indole acetic Acid (IAA), siderophore and phosphate solubilization assay. Plant growth promotion was assessed by the determination of root length, shoot length and vigor index. Key findings Sixteen bacterial isolates were identified as antagonist to X. oryzae pv. oryzae out of 300 bacterial isolates by dual culture method. The results revealed that the maximum growth inhibition of X. oryzae pv.oryzae was recorded in plate inoculated with BDISOB05P while the minimum growth inhibition was recorded by BDISOB98P and BDISOB272R. The moderate growth inhibition was recorded in BDISOB241P, BDISOB16P, BDISOB306R, BDISOB242P, BDISOB220R, BDISOB04P, BDISOB258R, BDISOB219R, BDISOB221R, BDISOB275R, BDISOB283R and BDISOB61R. The antagonistic bacterial isolates were identified by sequencing of 16SrDNA. The bacterial isolates were identified BDISOB04P as Pseudomonas putida, BDISOB05P as Pseudomonas putida, BDISOB16P as Bacillus sp., BDISOB98P as Stenotrophomonas maltophilia, BDISOB241P as Burkholderia sp., BDISOB242P as Burkholderia gladioli, BDISOB219R as Pseudomonas taiwanensis, BDISOB220R as Serratia sp., BDISOB221R as Pseudomonas sp., BDISOB222R as Pseudomonas plecoglossicida, BDISOB258R as Pseudomonas putida, BDISOB272R as Stenotrophomonas maltophilia, BDISOB275R as Pseudomonas putida , BDISOB283R as Pseudomonas fluorescens and BDISOB306R as Pseudomonas putida. The results of growth promoting determinants revealed that eight antagonistic bacterial isolates were observed to produce Indole acetic acid (IAA), sixteen bacterial isolates were able to produce siderophore and nine bacterial isolates were found to show phosphate solubilizing capability. The results of plant growth promotion showed that these bacterial isolates can increase the root growth, shoot growth and vigor index. Conclusion The results conceded some of the PGP bacterial isolates seem potential in both growth inhibition of X. oryzae pv. oryzae and growth promotion of rice plants. [Fundam Appl Agric 2019; 4(4.000): 1068-1080]

IntroductionWheat is one of the three major cereal crops in the world and is susceptible to the effects of drought stress. Rhizosphere microorganisms can affect plant growth by altering nutrient absorption and resistance to stress. Studying the plant–microbe interaction under drought stress to reveal the impact of soil microorganisms on plant growth in dry land has important scientific significance.MethodsIn this study, seven plant growth-promoting bacteria were isolated from the rhizosphere soil of winter wheat, and their growth-promoting ability was compared and analyzed.ResultsThe results indicate that these strains are capable of hydrolyzing organic and inorganic phosphorus, fixing nitrogen, producing IAA (indole-3-acetic acid), ACC deaminase, and iron siderophore. Combined with pot experiment data, Microbacterium sp. I2, Arthrobacter sp. R4, and Microbacterium sp. K2 can significantly promote wheat growth. Under normal conditions, the wheat plant height increased by 5.17%, 13.02%, and 12.14% compared to the control group after one month of treatment with I2, R4, and K2, respectively. Under drought stress, the plant height increased by 6.41%, 2.56%, and -3.46%, respectively. However, under drought stress, only K2 significantly increased wheat root length by 11.94% compared to the control group. Therefore, K2 has stronger drought resistance than I2 and R4. Genome sequencing and comparative genome analysis of I2, R4, and K2 strains revealed that the strains contain functional gene clusters related to phosphorus solubilization (pstABCS, phoUR), ACC deamination (accABD), iron transport (fepCDG), IAA production (trpABC), nitrogen fixation (nifUHJ), drought resistance (ostAB, treXYZ), but with different gene types and copy numbers. Compared to I2, the R4 genome lacks one copy of the phoUR gene cluster, ACC deaminase, and iron transport related functional gene clusters. The K2 genome contains both treXYZ and ostAB gene clusters, which may be associated with its significant improvement in plant drought resistance.DiscussionThis study indicates that PGPB may promote plant growth by affecting nutrient absorption and hormone synthesis, while also affecting plant drought resistance by regulating osmotic pressure and trehalose biosynthesis, providing a theoretical basis for regulation of plant growth in a sustainable way.

Plant growth promoting rhizobacteria (PGPR) are beneficial bacteria that colonize plant roots and enhance plant growth with a wide variety of mechanisms. The use of PGPR is steadily increasing in agriculture and offers an attractive way to replace chemical fertilizers, pesticides and supplements. Here, we have isolated, enumerated and characterized the PGPR from the rhizosphere soil of pigeon pea for the enhancement of growth of pigeon pea. Rhizosphere soils were collected from different areas of Samalkot, Pithapuram, Peddapuram and Kakinada. Sixty five (65) isolates were identified and characterized for their morphological, cultural, staining and biochemical characteristics, of which 35 was selected for the screening of PGPR isolates. Sixteen isolates were successfully characterized for the PGPR traits like indole acetic acid (IAA) production, phosphorus solubilization, and production of enzymes like urease, chitinase, amylase, cellulase, protease and β-1,3 glucanase and were assayed. The antagonistic nature of these strains towards fungi and bacteria were estimated by siderophore estimation, 1-amino-cyclopropane-1-carboxylate (ACC) deaminase characterization, dual plate culture method and HCN production technique, and the best one was selected. These were further investigated to show the PGPR traits in pigeon pea seedling emergence, increase of shoot length, root length, dry matter production of shoot, nodule number and nodule mass. Furthermore, PGPR isolates remarkably increased seed germination of pigeon pea. Among the sixteen isolates, seven were found to be high IAA producing. Six were found to be efficient phosphate solubilizers, five isolates were found to be good antagonistic towards pathogen soil fungi and eight isolates were found to be better in enzyme productions, and thus, may enhance the mineralization efficiency of soils. Three isolates were shown to be promising in IAA production, phosphate solubilization, antagonism towards fungi, and mineralizing capacity. Thus, this study suggests the use of these isolates as inoculant biofertilizers which might be beneficial for pigeon pea cultivation as they enhanced the growth and other growth parameters. Keywords: Indole acetic acid (IAA), plant growth promoting rhizobacteria (PGPR), phosphorus solubilization, enzyme productions, seed germination

The physiochemical mechanism of nitrate nitrogen stress on root nodulation was compared in common bean and soybean seedlings. Rhizobium- inoculated common bean and soybean were grown in vermiculite with a mineral nutrient solution containing 5, 30 or 60 mg L-1 15NO3-nitrogen in a growth chamber. Nodulation of common bean was strongly suppressed by 30 mg L-1 nitrate, while 60 mg L-1 nitrate caused distinct suppression in soybean. Common bean absorbed and assimilated larger amounts of medium-derived nitrogen (MDN) than soybean with the same nitrate treatment. Substantial activities of nitrate reduction and assimilation were detected in common bean earlier than in soybean. The percentage of MDN in root amino-nitrogen was closely correlated with the inhibition of nodulation in both common bean and soybean. In conclusion, nitrate stress on nodulation in seedlings of common bean and soybean arose through assimilation of MDN in roots, and the MDN assimilation process proceeded earlier and more actively in roots of common bean than in soybean.

In the present study, sixteen bacterial isolates were collected and identified from the rhizosphere soil of the bean plant (Phaseolus vulgaris), named BB-1 to BB-16. Out of the sixteen bacterial isolates, six isolates showed positive activity of phosphate solubilization ability, three bacterial isolates were found positive for ammonia production, six were positive for Indole acetic acid (IAA) production, three could solubilize potash, three bacterial isolates produced cellulase, six exhibited positive for chitinase, five were tested positive for amylase and four bacterial isolates were positive for protease activity. Hydrogen Cyanide (HCN) production was noticed by the bacterial isolates BB-7only. The fungal pathogen such as Aspergillus terreus, and Penicillium rubidurum was resistant to most bacterial isolates, whereas bacterial isolate BB-3 showed sensitivity against Penicillium rubidurum. Their quantitative phosphate solubilization ability was 47.5-77.8 µg/ml, ammonia production was between 2.45 - 3.45 mg/l, and IAA production was 22.5 -29.5 µg/ml. Of the sixteen bacterial isolates, one bacterial isolate, BB-7, was positive for most of the tests and identified as Pantoea agglomerans. Plant growth-promoting activity of the isolate showed that in comparison to the control rice plant, higher root and shoot growth was achieved in rice pot inoculated with P. agglomerans culture