Peanut Rhizosphere Research Articles

Legacy of land use history determines reprogramming of plant physiology by soil microbiome

Microorganisms associated with roots are thought to be part of the so-called extended plant phenotypes with roles in the acquisition of nutrients, production of growth hormones, and defense against diseases. Since the crops selectively enrich most rhizosphere microbes out of the bulk soil, we hypothesized that changes in the composition of bulk soil communities caused by agricultural management affect the extended plant phenotype. In the current study, we performed shotgun metagenome sequencing of the rhizosphere microbiome of the peanut (Arachis hypogaea) and metatranscriptome analysis of the roots of peanut plants grown in the soil with different management histories, peanut monocropping and crop rotation. We found that the past planting record had a significant effect on the assembly of the microbial community in the peanut rhizosphere, indicating a soil memory effect. Monocropping resulted in a reduction of the rhizosphere microbial diversity, an enrichment of several rare species, and a reduced representation of traits related to plant performance, such as nutrients metabolism and phytohormone biosynthesis. Furthermore, peanut plants in monocropped soil exhibited a significant reduction in growth coinciding with a down-regulation of genes related to hormone production, mainly auxin and cytokinin, and up-regulation of genes related to the abscisic acid, salicylic acid, jasmonic acid, and ethylene pathways. These findings suggest that land use history affects crop rhizosphere microbiomes and plant physiology.

Streptomyces sp. strain SK68, isolated from peanut rhizosphere, promotes growth and alleviates salt stress in tomato (Solanum lycopersicum cv. Micro-Tom).

A novel actinobacterium, strain SK68, was isolated from the rhizosphere of peanut plant and its salinity stress alleviation ability was studied using tomato (Solanum lycopersicum cv. Micro-Tom) plants. Based on 16S rDNA based phylogenetic analysis, strain SK68 has been identified as a Streptomyces sp. Strain SK68 had branched substrate mycelium bearing smooth surfaced spores and the spore colour is brownish grey on ISP4 medium. It exhibited enzyme activities such as xylanase, cellulase, amylase, and pectinase and degraded hypoxanthine, casein, and L-tyrosine. The strain SK68 differed in its banding pattern in BOX-PCR and RAPD fingerprinting compared to the closely matching type strains Streptomyces erythrochromogenes NBRC 3304T (AB184746), S. flavotricini NBRC 12770T (AB184132), S. racemochromogenes NBRC 12906T (AB184235), and S. polychromogenes NBRC 13072T (NR041109). Strain SK68 was evaluated for its salinity stress-alleviating activity in tomato plants with 180 mmol/L NaCl under gnotobiotic condition. A significant increase in plant biomass was observed in strain SK68-inoculated tomato plants under salt stress compared to control and salt-stressed non-inoculated plants.

Resveratrol as a Growth Substrate for Bacteria from the Rhizosphere.

Resveratrol is among the best-known secondary plant metabolites because of its antioxidant, anti-inflammatory, and anticancer properties. It also is an important allelopathic chemical widely credited with the protection of plants from pathogens. The ecological role of resveratrol in natural habitats is difficult to establish rigorously, because it does not seem to accumulate outside plant tissue. It is likely that bacterial degradation plays a key role in determining the persistence, and thus the ecological role, of resveratrol in soil. Here, we report the isolation of an Acinetobacter species that can use resveratrol as a sole carbon source from the rhizosphere of peanut plants. Both molecular and biochemical techniques indicate that the pathway starts with the conversion of resveratrol to 3,5-dihydroxybenzaldehyde and 4-hydroxybenzaldehyde. The aldehydes are oxidized to substituted benzoates that subsequently enter central metabolism. The gene that encodes the enzyme responsible for the oxidative cleavage of resveratrol was cloned and expressed in Escherichia coli to establish its function. Its physiological role in the resveratrol catabolic pathway was established by knockouts and by the reverse transcription-quantitative PCR (RT-qPCR) demonstration of expression during growth on resveratrol. The results establish the presence and capabilities of resveratrol-degrading bacteria in the rhizosphere of the peanut plants and set the stage for studies to evaluate the role of the bacteria in plant allelopathy.IMPORTANCE In addition to its antioxidant properties, resveratrol is representative of a broad array of allelopathic chemicals produced by plants to inhibit competitors, herbivores, and pathogens. The bacterial degradation of such chemicals in the rhizosphere would reduce the effects of the chemicals. Therefore, it is important to understand the activity and ecological role of bacteria that biodegrade resveratrol near the plants that produce it. This study describes the isolation from the peanut rhizosphere of bacteria that can grow on resveratrol. The characterization of the initial steps in the biodegradation process sets the stage for the investigation of the evolution of the catabolic pathways responsible for the biodegradation of resveratrol and its homologs.

Mechanisms by which organic fertilizer and effective microbes mitigate peanut continuous cropping yield constraints in a red soil of south China

Red soils are acid soils which occupy about one fifth of the total area of tropical and subtropical soils in China. Peanut (Arachis hypogaea L.) is regarded as the main oil and cash crop in the red soil region. However, yields of peanut have gradually but significantly declined under continuous cropping. We conducted a field experiment in Jiangxi province, south China from 1996 to investigate the mitigation of the peanut continuous cropping constraint. Three types of fertilizer (chemical, organic, and organic fertilizer with effective microbes) were applied in the field. After 20 years of cropping the continuous cropping constraint was found to be more severe where chemical fertilizers were applied and was mitigated where the fields were amended with organic fertilizer or organic fertilizer with effective microbes. Soil properties and the rhizosphere bacterial community structure were determined in 2016. Long-term application (20 years) of organic fertilizer increased the plant available phosphorus in the rhizosphere soil. Phosphorus is known to be one of the most limiting factors for peanut growth in red soils and peanut yield was promoted as the soil phosphorus status increased. Organic fertilizer and effective microbes also optimized the rhizobacteria of peanut to mitigate the continuous cropping obstacle. The bacterial wilt pathogen (Ralstonia) decreased in abundance in the rhizosphere and bacterial wilt disease of peanut declined significantly. Moreover, beneficial bacteria in the rhizosphere capable of promoting peanut growth increased in abundance.

Subterranean infestation by Holotrichia parallela larvae is associated with changes in the peanut (Arachis hypogaea L.) rhizosphere microbiome

Rhizosphere microorganisms contribute to the health and development of crops and these beneficial microbes are recruited to the root-zone when plants experience biotic/abiotic stress. The subterranean pests Holotrichia parallela cause severe crop loss in peanut (Arachis hypogaea L.) fields. Hypothesizing that infestation by H. parallela larva may influence the composition of rhizosphere microbial communities, deep sequencing of V3 and V4 hypervariable regions of 16S rRNA gene was used to characterize the rhizosphere bacteria of infested and uninfested peanuts. A total of 2,673,656 reads were generated and an average of 2558 OTUs were obtained for each sample. Comparisons of rhizosphere bacterial community structure of peanuts with those infested by H. parallela larva revealed that the relative abundance of Proteobacteria and Bacteroidetes increased, while that of Actinobacteria decreased in the rhizosphere with infestation. A significant shift in bacterial communities was observed within 24 h after infestation by principal coordinate analysis. For the 332 genera identified in 24 h treatment, infestation of white grubs led to the significant changes of abundance of 67 genera. An increase in the Pseudomonas genus of infested-samples for 24 h was verified by real-time qPCR. Our results indicate H. parallela larvae infestation can quickly leads to the change of peanut rhizosphere microbiome and enrichment of specific bacterial species. But the effects were not persistent. This study provides the insight into the function of rhizosphere microbiome in the interaction between subterranean pests and crops.

Belowground Interactions Impact the Soil Bacterial Community, Soil Fertility, and Crop Yield in Maize/Peanut Intercropping Systems.

Intercropping has been widely used to control disease and improve yield in agriculture. In this study, maize and peanut were used for non-separation intercropping (NS), semi-separation intercropping (SS) using a nylon net, and complete separation intercropping (CS) using a plastic sheet. In field experiments, two-year land equivalent ratios (LERs) showed yield advantages due to belowground interactions when using NS and SS patterns as compared to monoculture. In contrast, intercropping without belowground interactions (CS) showed a yield disadvantage. Meanwhile, in pot experiments, belowground interactions (found in NS and SS) improved levels of soil-available nutrients (nitrogen (N) and phosphorus (P)) and enzymes (urease and acid phosphomonoesterase) as compared to intercropping without belowground interactions (CS). Soil bacterial community assay showed that soil bacterial communities in the NS and SS crops clustered together and were considerably different from the CS crops. The diversity of bacterial communities was significantly improved in soils with NS and SS. The abundance of beneficial bacteria, which have the functions of P-solubilization, pathogen suppression, and N-cycling, was improved in maize and peanut soils due to belowground interactions through intercropping. Among these bacteria, numbers of Bacillus, Brevibacillus brevis, and Paenibacillus were mainly increased in the maize rhizosphere. Burkholderia, Pseudomonas, and Rhizobium were mainly increased in the peanut rhizosphere. In conclusion, using maize and peanut intercropping, belowground interactions increased the numbers of beneficial bacteria in the soil and improved the diversity of the bacterial community, which was conducive to improving soil nutrient (N and P) supply capacity and soil microecosystem stability.

Organic amendments shift the phosphorus-correlated microbial co-occurrence pattern in the peanut rhizosphere network during long-term fertilization regimes

Root-associated microbial communities play important roles in driving the microbial transformation of soil carbon and nitrogen cycling, but evidence of how these communities shape microbial co-occurrence and change phosphorus (P) correlated microbial interactions is still lacking. In this study, a random matrix theory-based network analysis of 16S rRNA genes was used to identify bacterial networks associated with the peanut rhizosphere and bulk in four long-term fertilization schemes. High-throughput sequencing data revealed that with the decrease of rhizosphere bacterial diversity, its positive covariation in the network increased, indicating stronger commensal and mutual assemblage with less functional redundancy in the rhizosphere. P availability is the major variable modulating the peanut rhizosphere microbial community in acidic soil. Two strongly positive P-correlated rhizosphere OTUs (closely related to Chitinophaga pinensis and Nitrospira moscoviensis), which have the potential to promote carbon-phosphorus and nitrogen-phosphorus synergistic conversion, respectively, were used to investigate the advantages of manure amendment in promoting rhizosphere P cycling in peanut planting agrosystems.

Suppression of soil-borne Fusarium pathogens of peanut by intercropping with the medicinal herb Atractylodes lancea

Intercropping has historically been employed as an efficient management strategy to prevent disease outbreaks. Our previous studies indicated that intercropping of peanut with the Chinese medicinal herb, Atractylodes lancea effectively suppressed soil-borne peanut diseases, resulting in increased peanut yields. However, the underlying mechanism is unknown. In this study, the below ground effects of A. lancea on both fungal and bacterial communities in the peanut rhizosphere were investigated using pyrosequencing of the internal transcribed spacer (ITS1) and16S rRNA gene amplicons, respectively. Closed cultivation systems were constructed to investigate the role of volatiles and exudates originating from rhizomes and roots of A. lancea on fungal and bacterial communities. Intercropping with A. lancea significantly altered fungal community composition in the peanut rhizosphere, coinciding with decline of Fusarium root rot and improvement of peanut growth. Volatiles originating from A. lancea rhizome material had more effects on fungal communities than on bacterial communities, and significantly suppressed F. oxysporum growth. Root exudates of A. lancea had no apparent inhibitory effect on F. oxysporum. Gas chromatography–mass spectrometry (GC-MS) analysis revealed 21 volatiles originating from A. lancea rhizome material and terpenes and aromatic hydrocarbons were the most common types. Our results suggest that A. lancea suppressed pathogenic Fusarium populations by means of volatiles from the rhizome. Our results support the idea that intercropping with A. lancea or use of its effective components has a strong potential for managing soil-borne fungal diseases.

Assessment of active bacteria metabolizing phenolic acids in the peanut (Arachis hypogaea L.) rhizosphere

Phenolic acids can enhance the mycotoxin production and activities of hydrolytic enzymes related to pathogenicity of soilborne fungus Fusarium oxysporum. However, characteristics of phenolic acid-degrading bacteria have not been investigated. The objectives of this study were to isolate and characterize bacteria capable of growth on benzoic and vanillic acids as the sole carbon source in the peanut rhizosphere. Twenty-four bacteria were isolated, and the identification based on 16S rRNA gene sequencing revealed that pre-exposure to phenolic acids before sowing shifted the dominant culturable bacterial degraders from Arthrobacter to Burkholderia stabilis-like isolates. Both Arthrobacter and B. stabilis-like isolates catalysed the aromatic ring cleavage via the ortho pathway, and Arthrobacter isolates did not exhibit higher C12O enzyme activity than B. stabilis-like isolates. The culture filtrate of Fusarium sp. ACCC36194 caused a strong inhibition of Arthrobacter growth but not B. stabilis-like isolates. Additionally, Arthrobacter isolates responded differently to the culture filtrates of B. stabilis-like isolates. The Arthrobacter isolates produced higher indole acetic acid (IAA) levels than B. stabilis-like isolates, but B. stabilis-like isolates were also able to produce siderophores, solubilize mineral phosphate, and exert an antagonistic activity against peanut root rot pathogen Fusarium sp. ACCC36194. Results indicate that phenolic acids can shift their dominant culturable bacterial degraders from Arthrobacter to Burkholderia species in the peanut rhizosphere, and microbial interactions might lead to the reduction of culturable Arthrobacter. Furthermore, increasing bacterial populations metabolizing phenolic acids in monoculture fields might be a control strategy for soilborne diseases caused by Fusarium spp.

Contribution of native phosphorous-solubilizing bacteria of acid soils on phosphorous acquisition in peanut (Arachis hypogaea L.).

The present investigation analyzes the in vitro P solubilization [Ca-P, Al-P, Fe(II)-P, and Fe(III)-P] efficiency of native PSB strains from acid soils of Odisha and exploitation of the same through biofertilization in peanut (Arachis hypogaea L.) growth and P acquisition. One hundred six numbers of soil samples with pH≤5.50 were collected from five districts of Odisha viz., Balasore, Cuttack, Khordha, Keonjhar, and Mayurbhanj. One bacterial isolate from each district were selected and analyzed for their P solubilization efficiency in National Botanical Research Institute Phosphate broths with Ca, Al, and Fe-complexed phosphates. CTC12 and KHD08 transformed more amount of soluble P from Ca-P (CTC12 393.30mg/L; KHD08 465.25mg/L), Al-P (CTC12 40.00mg/L; KHD08 34.50mg/L), Fe(III)-P (CTC12 175.50mg/L; KHD08 168.75mg/L), and Fe(II)-P (CTC12 47.40mg/L; KHD08 42.00mg/L) after 8days of incubation. The bioconversion of P by all the five strains in the broth medium followed the order Ca-P > Fe(III)-P > Fe(II)-P > Al-P. The identified five strains were Bacillus cereus BLS18 (KT582541), Bacillus amyloliquefaciens CTC12 (KT633845), Burkholderia cepacia KHD08 (KT717633), B. cepacia KJR03 (KT717634), and B. cepacia K1 (KM030037) and further studied for biofertilization effects on peanut. CTC12 and KHD08 enhanced the soil available P around 65 and 58% and reduced the amount of each Al3+ about 79 and 81%, respectively, over the uninoculated control pots in the peanut rhizosphere. Moreover, all tested PSB strains could be able to successfully mobilize P from inorganic P fractions (non-occluded Al-P and Fe-P). The strains CTC12 and KHD08 increased the pod yield (114 and 113%), shoot P (92 and 94%), and kernel P (100 and 101%), respectively, over the control. However, B. amyloliquefaciens CTC12 and B. cepacia KHD08 proved to be the potent P solubilizers in promoting peanut growth and yield.

The effect of monoculture peanut and cassava/peanut intercropping on physical and chemical properties in peanut rhizosphere soil under the biochar application and straw mulching

Cassava/peanut intercropping is a popular cultivation method in the south China, with the advantage of apparent yield increase. In order to analyze the effect of cassava/peanut intercropping on physical and chemical properties in peanut rhizosphere soil, the physical and chemical properties were investigated under the biochar application and straw mulching. The result showed that the Ph, organic materials content, available phosphorus content, available potassium content in peanut rhizosphere under the biochar application increased by 7.06%, 94.52%, 17.53%, 25.08% (monoculture peanut) and 8.47%, 89.94%, 17.93%, 22.87% (cassava/peanut intercropping) compared with Ck in the same planting patterns. In addition, the available nitrogen content, organic materials content, available phosphorus content, and available potassium content in peanut rhizosphere under the straw mulching increased by 89.80%, 60.92%, 5.95%, 9.98% (monoculture peanut) and 67.09%, 52.34%, 6.96%, 11.94% (cassava/peanut intercropping) compared with Ck in the same planting patterns. In the same treatment conditions, bulk density in peanut rhizosphere soil decreased and porosity and saturated permeability coefficient increased slightly. But there was no significant difference between the two. At the same time, cassava/peanut intercropping could increase soil nutrients. Therefore, it is beneficial to apply biochar and straw mulching, and the suitable intercropping row spacing is more beneficial to increase soil nutrient contents.

Multifunctional Pseudomonasputida strain FBKV2 from arid rhizosphere soil and its growth promotional effects on maize under drought stress

In the present study, rhizobacteria were isolated from the rhizosphere of maize, okra, eggplant, tomato, green gram, peanut and red gram grown in arid and semi-arid regions in India and were screened for drought tolerance in Trypticase soy broth (TSB) supplemented with different concentrations of polyethylene glycol 6000 (PEG 6000). Out of 23 isolates, three could tolerate minimal negative water potential of −1.03MPa and were evaluated for plant growth promoting (PGP) traits under control and drought stress (−1.03MPa) conditions. Pseudomonas spp. strain FBKV2 isolated from eggplant (Solanum melongeana L.) rhizosphere, showed multiple PGP traits under both control and drought stress conditions. The strain was identified as Pseudomonas putida by 16S rRNA sequence analysis and the sequence was submitted to GenBank under the accession number KT311002.1. The strain was evaluated for growth promotion of maize (Zea mays L.) under drought stress. Seedlings inoculated with P. putida strain FBKV2 showed better growth in terms of shoot, root length, and dry biomass. Furthermore, inoculation improved cellular metabolites and stomatal conductance in maize seedlings. Scanning electron microscopy confirmed the colonization of P. putida strain FBKV2 on the root surface of maize seedlings. The present study demonstrates that the isolation of indigenous drought tolerant P. putida strain FBKV2 from stressed ecosystems can be a very useful approach for the development of bio-inoculants for drought stress management in crops.

Isolation and identification of IAA-producing strains from peanut rhizosphere and its promoting effects on peanut growth

Isolation and identification of IAA-producing strains from peanut rhizosphere and its promoting effects on peanut growth

Prevention of collar rot disease in germinating peanut seedlings by Azotobacter sp. RA2

Use of plant growth promoting rhizobacteria (PGPR) to increase the production and decrease disease occurrence is a useful, ecofriendly method in agriculture. A rhizospheric bacterial culture named RA2 was isolated from peanut rhizosphere from Junagadh region of Gujarat, India and showed different direct and indirect plant growth promoting activity like indole acetic acid, gibberellic acid, siderophore, hydrogen cyanide, Ammonia and (1‐Aminocyclopropane‐1‐Carboxylate) deaminase production, N2 fixation, phosphate and potassium solubilization in vitro. RA2 was able to protect peanut germinating seedling from A. niger infection and reduce collar rot disease incidence from 72–60% to 41–35% and increase germination percentage from 75–70% to 97–82% in two varieties GG20 and GG2 of peanut. RA2 was found to induce resistance in A. hypogaea L. seedlings via induction of different defense related enzyme like phenylalanine ammonia lyase, peroxidase, polyphenol oxidase, lipoxygenase and pathogenesis related protein like chitinase and β– 1, 3‐ glucanase. Jasmonic acid, one of the major signaling molecules during induce systemic resistance, was also found to induce due to RA2 treatments. RA2 bacterium also promoted peanut growth and reduced A. niger infection in pot studies. 16S rDNA sequence of RA2 showed 99 % homology to Azotobacter species.Support or Funding InformationAuthors are thankful to BRD School of Biosciences, Sardar Patel University for providing infrastructure and all necessary facilities. Authors are also grateful to University Grant commission (UGC Major Research Project F.No. 39‐247/ 2012 (SR)) for providing financial aid.

Biochemical and microbial properties of rhizospheres under maize/peanut intercropping

Maize/peanut intercropping system shows the significant yield advantage. Soil microbes play major roles in soil nutrient cycling and were affected by intercropping plants. This experiment was carried out to evaluate the changing of rhizosphere microbial community composition, and the relationship between microbial community and soil enzymatic activities, soil nutrients in maize/peanut intercropping system under the following three treatments: maize (Zea mays L.) and peanut (Arachis hypogaea L.) were intercropped without any separation (NS), by half separation (HS) using a nylon net (50 µm) and complete separation (CS) by using a plastic sheet, respectively. The soil microbial communities were assessed by phospholipid fatty acid (PLFA). We found that soil available nutrients (available nitrogen (Avail N) and available phosphorus (Avail P)) and enzymatic activities (soil urase and phosphomonoesterase) in both crops were improved in NS and HS treatments as compared to CS. Both bacterial and fungal biomasses in both crops were increased in NS followed by HS. Furthermore, Gram-positive bacteria (G+) in maize soils were significant higher in NS and HS than CS, while the Gram-negative (G–) was significant higher in peanut soil. The ratio of normal saturated to monounsaturated PLFAs was significantly higher in rhizosphere of peanut under CS treatment than in any other treatments, which is an indicator of nutrient stress. Redundancy analysis and cluster analysis of PLFA showed rhizospheric microbial community of NS and HS of both plants tended to be consistent. The urase and Avail N were higher in NS and HS of both plants and positively correlated with bacteria, fungi (F) and total PLFAs, while negatively correlated with G+/G– and NS/MS. The findings suggest that belowground interactions in maize/peanut intercropping system play important roles in changing the soil microbial composition and the dominant microbial species, which was closely related with the improving of soil available nutrients (N and P) and enzymatic activities.

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.

Actividad de las fosfatasas ácidas y alcalinas (extracelulares e intracelulares) en hongos de la rizosfera de <i>Arachis hypogaea</i> (Papiloneaceae

The potential role of the fungi, isolated from the peanut rhizosphere, in the production of extracellular and intracellular acid and alkaline phosphatase, was evaluated in vitro. Acid and alkaline extracellular phosphatases showed the highest activities, and the Penicillium species were the most efficient in their production. The correlation analysis showed that extracellular acid and intracellular acid phosphatase produced by Aspergillus niger A. terreus, Penicillium sp. y P. brevicompactum were negatively correlated; while the extracellular and intracellular phosphatase activities, were positively correlated. The extracellular acid phosphatase activities produced in vitro by majority of fungi assayed, were not correlated with the acid phosphatase activity present in the peanut soil rhizosphere. Nevertheless, the extracellular alkaline phosphatase activities produced in vitro, were negatively correlated with the extracellular alkaline phosphatase activities present in the rhizosphere. The ability of phosphatase production by fungi isolated from peanut rhizosphere suggests they have great potential to contribute to the P mineralization in this zone.

Dynamics in the rhizosphere and iron-uptake gene expression in peanut induced by intercropping with maize: Role in improving iron nutrition in peanut

The intercropping of maize with peanuts is an effective cropping practice. Indeed, peanut/maize intercropping reportedly improves the iron nutrition of peanuts in calcareous soils. The limited evidence available suggests that the improved Fe nutrition in intercropping is largely attributable to a rhizosphere effect of maize. In this study, the effects of peanut/maize intercropping on the Fe nutritional status of peanut associated with the dynamics of the rhizosphere processes and Fe uptake gene expression induced by the interaction of the two species at various growth days were investigated. The results suggest that an interspecific rhizosphere effect improves Fe nutrition in peanut, as shown by changes in the rhizosphere available Fe concentration, pH, and Olsen-P concentration, based on time-course changes in peanut–maize interaction. The increase in available Fe in the rhizosphere of peanut ranged from 0.2 to 2.64 mg kg−1. The transition from the vegetative to reproductive stage was a key turning point in the time-course of changes in the rhizosphere processes in intercropping. There was more consistently positive effect of intercropping on peanut Fe nutrition after 53 days. Moreover, the expression of AhFRO1 and AhYSL1 was expressed at significantly higher level in intercropped peanuts compared to monocropped peanut at the vegetative stage, indicating a role for these genes in Fe improvement in intercropped peanuts. We conclude that the enhanced time-course changes in the rhizosphere processes and iron uptake gene expression with a consistent positive interspecific effect appear to be one of the mechanisms underlying the improved Fe nutrition in intercropped peanut plants.

The composition of root exudates from two different resistant peanut cultivars and their effects on the growth of soil-borne pathogen.

The high incidence of various soil-borne diseases in the monoculture field of peanut is a major production constraint in the red soil regions of southern China. The peanut root exudates are generally thought to play an important role in regulating soil-borne pathogens. The responses of the soil-borne pathogens, Fusarium oxysporum and F. solani to the peanut root exudates were studied using one susceptible cultivar Ganhua-5 (GH) and one mid-resistant cultivar Quanhua-7 (QH) as the test materials. The components and contents of the amino acids, sugars and phenolic acids in the peanut root exudates were determined. The results demonstrated that the root exudates from both susceptible and mid-resistant cultivars significantly promoted the spore germination, sporulation and mycelial growth of soil-borne pathogens, F. oxysporum, F. solani compared with the control. The extent of the stimulation was depended on the strains of the Fusarium tested, and gradually increased with the increased concentrations of peanut root exudates. HPLC analysis showed that the contents of sugars, alanine, total amino acids in the root exudates of GH were significantly higher than that in QH, whereas the contents of p-hydroxybenzoic acid, benzoic acid, p-coumaric acid and total phenolic acids were significantly lower than that in QH. Results of the study suggested that the differences in the root exudates from the different peanut cultivars were considered to regulate the wilt-resistance mechanism in the rhizosphere of peanut. The results are therefore crucial important to illustrate the mechanism of peanut replanted obstacle, and to develop its control techniques in the red soil regions of southern China.

Effects of single and co-inoculation with native phosphate solubilising strain Pantoea sp J49 and the symbiotic nitrogen fixing bacterium Bradyrhizobium sp SEMIA 6144 on peanut (Arachis hypogaea L.) growth

In the present study, attempts were made to analyze the effect of co-inoculation with an efficient phosphate solubilising native isolate Pantoea sp J49 and the symbiotic nitrogen fixing Bradyrhizobium sp SEMIA 6144 strain on Arachis hypogaea L. plants growth. Single and co-inoculation of peanut plants growing in plastic pots containing soil with low P content were developed. Plants were harvested at R1 and R4 growth stages and were analyzed in different growth parameters. Survival of strain Pantoea sp J49 was analyzed in soil samples and in root tissues. Plants inoculated only with Pantoea sp J49 showed the highest shoot and root weight in both reproductive growth stages evaluated. Plants co-inoculated with this strain and Bradyrhizobium sp SEMIA 6144 showed increase in aerial dry weight at R1 stage. Survival assays demonstrated that Pantoea sp J49 survives not only in the peanut rhizosphere but also inside plant tissues, including nodules formed when it was co-inoculated with Bradyrhizobium sp SEMIA 6144. Results obtained in this study confirm the great potential of the native Pantoea sp J49 isolate in the promotion of peanut plant growth, probably related with its capacity to solubilise phosphate.