Peanut Root Research Articles

Cattle Grazing Affects Peanut Root Characteristics in a Bahiagrass-Based Crop Rotation System

ABSTRACT The critical aspect of production agriculture in the southeastern US with increasing associated costs is to improve economic and agronomic sustainability. A four yr sod-based rotation system consisting of two yr of bahiagrass (Paspalum notatum Flueggé) (grazed or non-grazed) followed by a yr of peanut (Arachis hypogaea L.) and a yr of cotton (Gossypium hirsutum L.), each with winter cover crop (grazed or non-grazed) was established in Marianna, FL. The effect of grazing on root parameters (length, volume, surface area, and diameter) of peanut was observed using a mini-rhizotron. There were differences in several root parameters between grazed and non-grazed plots including: peanut root length (307 mm in grazed vs 167 mm in non-grazed), volume (50 mm3 in grazed vs. 23 mm3 in non-grazed), surface area (399 mm2 in grazed vs. 197 mm2 in non-grazed), and diameter (2.4 mm in grazed vs. 1.7 mm in non-grazed). Roots at the 45-60 cm and 60-75 cm depths had significantly greater length in the grazed than the non-grazed plots. Likewise, surface area was significantly greater in the grazed plots at the 30-45 cm, 45-60 cm and 60-75 cm depths. Grazed plots at the 40-65 cm depths showed significant increase in root diameter. No significant difference in peanut yield was observed for the grazed or non-grazed treatments. A more developed root system associated with cattle grazing in the sod-based rotation system may enable peanuts to be more resilient in adverse environmental conditions such as drought stress, enhance nutrient cycling without affecting yield, thereby improving long-term sustainability.

Cattle grazing affects peanut root characteristics in a bahiagrass-based crop rotation system

Cattle grazing affects peanut root characteristics in a bahiagrass-based crop rotation system

Comparative transcriptomic analysis of the roots of intercropped peanut and maize reveals novel insights into peanut iron nutrition

Intercropping is a vital technology in resource-limited agricultural systems with low inputs. Peanut/maize intercropping enhances iron (Fe) nutrition in calcareous soil. In this study, the transcriptome of peanut and maize roots was analyzed by suppression subtractive hybridization (SSH) and microarray analysis separately. We constructed four SSH libraries using the cDNA of peanut roots based on two cropping patterns: monocropping and intercropping, and two growth stages: vegetative stage and reproductive stage. Lib M1, I1, M2 and I2 comprised 53, 51, 37 and 54 genes, respectively. Six and four transporters were found in the two intercropping-specific SSH libraries, which may facilitate Fe acquisition and protoplasmic homeostasis of metal ions and anions. Specifically, AhNARMP1 and MTP may play a role in boosting Fe nutrition during the vegetative stage. The expression of MYC2 was also upregulated by intercropping, while an ethylene-responsive transcription factor was downregulated during two growth periods. Microarrays indicated that homocysteine S-methyltransferase and serine acetyltransferase 1 upregulated in intercropped maize roots, which directly associated with methionine biosynthesis. It may account for the enhanced phytosiderophore released capacity in intercropping, which benefited the Fe nutrition of intercropped peanut in reproductive stage. Two aminocyclopropane-1-carboxylic acid synthase oxidase genes, which are related to ethylene biosynthesis, were downregulated in maize root by intercropping. Taken together with our previous proteomic work, the results indicated that intercropping enhances jasmonate signaling and weakens ethylene signaling in peanut and maize roots, which may improve ecological adaptation of the peanut plant to intercropping systems.

Nitric oxide suppresses aluminum-induced programmed cell death in peanut (Arachis hypoganea L.) root tips by improving mitochondrial physiological properties

Aluminum (Al) stress alters nitric oxide (NO) and induces programmed cell death (PCD) in plants. Recent study has shown that NO inhibits Al-induced PCD. However, the mechanism of NO inhibiting Al-induced PCD has not been revealed yet. Here, we investigated the behavior of mitochondria during Al-induced PCD suppressed by NO in peanut. Seedlings of peanut was grown hydroponically in a controllable growth room. The mitochondrial physiological parameters were determined spectrophotometrically. The expression of AhANT and AhHsp70 was determined by quantitative RT-PCR. Al-induced cell death rapidly in peanut root tips is mitochondria-dependent PCD. There was a significantly negative relationship between PCD and mitochondrial NO/H2O2 level. Compared with Al treatment alone, the addition of NO donor sodium nitroprusside (SNP) increased the ratio of NO/H2O2, down-regulated AhANT expression and inhibited the opening of mitochondrial permeability transition pore (MPTP), up-regulated AhHsp70 expression and increased mitochondrial inner membrane potential (ΔΨm), reduced cytochrome c (Cyt c) release from mitochondria and caspase 3-like protease activity, while the effect of NO specific scavenger cPTIO supplement was opposite. NO suppresses Al-induce PCD in peanut root tips by improving mitochondrial physiological properties.

Involvement of Root Hair during <i>Rhizobial</i> Invasion in Cultivated Peanut (<i>Arachis hypogaea</i> L.)

Peanut root invasion by Bradyrhizobia is through a crack entry, which is different from many other legumes applying an infection thread entry in root hair. Understanding the role of root hair in the crack entry of Bradyrhizobia invasion of peanut root and subsequent peanut nodulation would facilitate improvement of biological nitrogen fixation in cultivated peanut. The objective of this study was to investigate the involvement of root hair in Bradyrhizobial invasion of peanut. Seedling roots of a nodulating peanut cultivar were observed for root hair emergence, its life span, and nodule formation at the base of the lateral roots with and without rhizobia inoculation for 14 days after germination (DAG). Scanning electron microscopy (SEM) was utilized to observe rhizobia accumulation at lateral roots at 24 hours after inoculation (HAI) before the emergence of root hair. Root hair emerged at 7 DAG with or without rhizobia inoculation. Two variations of rosette hair (RoH) were observed, the transient-thin RoH had life span of 3 days after root hair emergence and the thick and densely distributed RoH type stayed till the time of nodule emergence (9 days after inoculation). The lateral root devoid of root hair at the top 2 cm region was found to produce nodules. The SEM observation of seedling roots at 24 HAI showed that Bradyrhizobia invaded the roots at epidermis, protoplasm of cortical cell, and cortical cells of the main root near the newly emerged lateral root in the absence of RoH. The observations validated that root hair is not required in the Bradyrhizobia invasion of peanut root in the crack entry mode. Results from this study provided important morphological information for the hypothesis of close relationship between RoH and peanut nodulation for further genetic study of crack entry mechanism and signaling pathway of symbiosis between Bradyrhizobia and peanut.

Nitric Oxide Inhibits Al-Induced Programmed Cell Death in Root Tips of Peanut (Arachis hypogaea L.) by Affecting Physiological Properties of Antioxidants Systems and Cell Wall.

It has been reported that nitric oxide (NO) is a negative regulator of aluminum (Al)-induced programmed cell death (PCD) in peanut root tips. However, the inhibiting mechanism of NO on Al-induced PCD is unclear. In order to investigate the mechanism by which NO inhibits Al-induced PCD, the effects of co-treatment Al with the exogenous NO donor or the NO-specific scavenger on peanut root tips, the physiological properties of antioxidants systems and cell wall (CW) in root tip cells of NO inhibiting Al-induced PCD were studied with two peanut cultivars. The results showed that Al exposure induced endogenous NO accumulation, and endogenous NO burst increased antioxidant enzyme activity in response to Al stress. The addition of NO donor sodium nitroprusside (SNP) relieved Al-induced root elongation inhibition, cell death and Al adsorption in CW, as well as oxidative damage and ROS accumulation. Furthermore, co-treatment with the exogenous NO donor decreased MDA content, LOX activity and pectin methylesterase (PME) activity, increased xyloglucan endotransglucosylase (XET) activity and relative expression of the xyloglucan endotransglucosylase/hydrolase (XTH-32) gene. Taken together, exogenous NO alleviated Al-induced PCD by inhibiting Al adsorption in CW, enhancing antioxidant defense and reducing peroxidation of membrane lipids, alleviating the inhibition of Al on root elongation by maintaining the extensibility of CW, decreasing PME activity, and increasing XET activity and relative XTH-32 expression of CW.

English

China is an important global peanut producer and exporter. Nevertheless, excessive Cd in peanut kernels has become an important constraint of peanut exportation. Concerns over the heavy metal contamination in food crops have prompted scientists to find ways to solve these problems, including applications of microbiology. In the present research, a greenhouse pot culture experiment was conducted to investigate the effect of arbuscular mycorrhizal fungi (AMF) inoculation on cadmium (Cd) uptake and translocation in peanut plants at different Cd levels. The peanut seeds were sown in pots, where culture substrate was previously mixed with a given amount of Glomus intraradices and 0, 2 and 10 mg kg(-1) Cd. In the control plot, G. intraradices was inactivated before mixed into culture substrate. Symbiotic relationships were successfully established between AMF and peanut root at all Cd levels with an average colonization rate of 65.0%. Compared with control plants, AMF inoculation significantly improved phosphorus nutrition supply to peanut plants, increased chlorophyll by 7.5%, photosynthesis by 11.8%, transpiration by 13.9% and root dry weight by 27.0%. In AMF inoculated peanut plants, the concentration and accumulation of Cd were 45.9 and 87.4% higher, respectively, in root system but 31.1 and 31.8% lower, respectively in the aboveground part than in the control plants. At the Cd level of 10 mg kg(-1), the translocation rate of Cd in AMF inoculated peanut plants was 51.8% lower than in AMF non-inoculated plants. In summary, AMF inoculation could improve peanut plant growth, result in Cd immobilisation in the peanut root system and inhibit Cd translocation in peanut plants. In conclusion, AMF inoculation may be an effective way to reduce Cd accumulation in peanut kernels. (C) 2017 Friends Science Publishers

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.

Effects of P limitation and molecules from peanut root exudates on pqqE gene expression and pqq promoter activity in the phosphate-solubilizing strain Serratia sp. S119

The mineral phosphate-solubilizing phenotype in bacteria is attributed predominantly to secretion of gluconic acid produced by oxidation of glucose by the glucose dehydrogenase enzyme and its cofactor, pyrroloquinoline quinone. This study analyzes pqqE gene expression and pqq promoter activity in the native phosphate-solubilizing bacterium Serratia sp S119 growing under P-limitation, and in the presence of root exudates obtained from peanut plants, also growing under P-limitation. Results indicated that Serratia sp. S119 contains a pqq operon composed of six genes (pqqA,B,C,D,E,F) and two promoters, one upstream of pqqA and other between pqqA and pqqB. PqqE gene expression and pqq promoter activity increased under P-limiting growth conditions and not under N-deficient conditions. In the plant–bacteria interaction assay, the activity of the bacterial pqq promoter region varied depending on the concentration and type of root exudates and on the bacterial growth phase. Root exudates from peanut plants growing under P-available and P-limiting conditions showed differences in their composition. It is concluded from this study that the response of Serratia sp. S119 to phosphorus limitation involves an increase in expression of pqq genes, and that molecules exuded by peanut roots modify expression of these phosphate-solubilizing bacterial genes during plant–bacteria interactions.

Promotion of iron nutrition and growth on peanut by Paenibacillus illinoisensis and Bacillus sp. strains in calcareous soil.

This study aimed to explore the effects of two siderophore-producing bacterial strains on iron absorption and plant growth of peanut in calcareous soil. Two siderophore-producing bacterial strains, namely, YZ29 and DZ13, isolated from the rhizosphere soil of peanut, were identified as Paenibacillus illinoisensis and Bacillus sp., respectively. In potted experiments, YZ29 and DZ13 enhanced root activity, chlorophyll and active iron content in leaves, total nitrogen, phosphorus and potassium accumulation of plants and increased the quality of peanut kernels and plant biomass over control. In the field trial, the inoculated treatments performed better than the controls, and the pod yields of the three treatments inoculated with YZ29, DZ13, and YZ29 + DZ13 (1:1) increased by 37.05%, 13.80% and 13.57%, respectively, compared with the control. Based on terminal restriction fragment length polymorphism analysis, YZ29 and DZ13 improved the bacterial community richness and species diversity of soil surrounding the peanut roots. Therefore, YZ29 and DZ13 can be used as candidate bacterial strains to relieve chlorosis of peanut and promote peanut growth. The present study is the first to explore the effect of siderophores produced by P. illinoisensis on iron absorption.

Control of peanut root-rot using some chemical substances

PEANUT (Arachis hypogaea L.) is an important leguminous crop in Egypt. Root rot caused by Rhizoctonia solani is the most common disease of peanuts. In this study, six isolates of R. solani were isolated from peanut roots in El-Behera governorate during 2014 and 2015 growing seasons. Humic acid (H), sulfur (S) and gypsum (G) alone or in combinations were used as a seed dressing or a soil application to control root-rot disease in two peanut cultivars (Gregory and Ismailia1). Results indicated that peanut cv. Gregory appeared to be more susceptible to the fungus than cv. Ismailia1. Under greenhouse conditions, the combination of the three substances (H+S+G) caused the highest reduction in the incidence of R. solani damping-off on peanut cv. Gregory. Similar results were also obtained in the field experiment during 2015 and 2016 growing seasons. Furthermore, the results also indicated that each chemical substances and their combinations improved the growth characters in terms of the root and shoot weight as well as the yield of peanut plants.

Antioxidant responses of peanut roots exposed to realistic groundwater doses of arsenate: Identification of glutathione S-transferase as a suitable biomarker for metalloid toxicity

Arsenic (As)-polluted groundwater constitutes a serious problem for peanut plants, as roots can accumulate the metalloid in their edible parts. Characterization of stress responses to As may help to detect potential risks and identify mechanisms of tolerance, being the induction of oxidative stress a key feature. Fifteen-day old peanut plants were treated with arsenate in order to characterize the oxidative stress indexes and antioxidant response of the legume under realistic groundwater doses of the metalloid. Superoxide anion (O2−) and hydrogen peroxide (H2O2) histochemical staining along with the activities of NADPH oxidase, superoxide dismutase (SOD), catalase (CAT) and thiol (glutathione and thioredoxins) metabolism were determined in roots. Results showed that at 20 μM H2AsO4−, peanut growth was reduced and the root architecture was altered. O2− and H2O2 accumulated at the root epidermis, while lipid peroxidation, NADPH oxidase, SOD, CAT and glutathione S-transferase (GST) activities augmented. These variables increased with increasing As concentration (100 μM) while glutathione reductase (GR) and glutathione peroxidase/peroxiredoxin (GPX/PRX) were significantly decreased. These findings demonstrated that the metalloid induced physiological and biochemical alterations, being the NADPH oxidase enzyme implicated in the oxidative burst. Additionally, the strong induction of GST activity, even at the lowest H2AsO4− doses studied, can be exploited as suitable biomarker of As toxicity in peanut plants, which may help to detect risks of As accumulation and select tolerant cultivars.

Ex vitro hairy root induction in detached peanut leaves for plant\u2013nematode interaction studies

BackgroundPeanut (Arachis hypogaea) production is largely affected by a variety of abiotic and biotic stresses, including the root-knot nematode (RKN) Meloidogyne arenaria that causes yield losses worldwide. Transcriptome studies of wild Arachis species, which harbor resistance to a number of pests and diseases, disclosed several candidate genes for M. arenaria resistance. Peanut is recalcitrant to genetic transformation, so the use of Agrobacterium rhizogenes-derived hairy roots emerged as an alternative for in-root functional characterization of these candidate genes.ResultsThe present report describes an ex vitro methodology for hairy root induction in detached leaves based on the well-known ability of peanut to produce roots spontaneously from its petiole, which can be maintained for extended periods under high-humidity conditions. Thirty days after infection with the A. rhizogenes ‘K599’ strain, 90% of the detached leaves developed transgenic hairy roots with 5 cm of length in average, which were then inoculated with M. arenaria. For improved results, plant transformation, and nematode inoculation parameters were adjusted, such as bacterial cell density and growth stage; moist chamber conditions and nematode inoculum concentration. Using this methodology, a candidate gene for nematode resistance, AdEXLB8, was successfully overexpressed in hairy roots of the nematode-susceptible peanut cultivar ‘Runner’, resulting in 98% reduction in the number of galls and egg masses compared to the control, 60 days after M. arenaria infection.ConclusionsThis methodology proved to be more practical and cost-effective for functional validation of peanut candidate genes than in vitro and composite plant approaches, as it requires less space, reduces analysis costs and displays high transformation efficiency. The reduction in the number of RKN galls and egg masses in peanut hairy roots overexpressing AdEXLB8 corroborated the use of this strategy for functional characterization of root expressing candidate genes. This approach could be applicable not only for peanut–nematode interaction studies but also to other peanut root diseases, such as those caused by fungi and bacteria, being also potentially extended to other crop species displaying similar petiole-rooting competence.

Nitric oxide inhibits aluminum-induced programmed cell death in peanut (Arachis hypoganea L.) root tips

It had been reported that Aluminum (Al) stress altered nitric oxide (NO) concentration and induced programmed cell death (PCD) in plants. However, the relationship between NO and PCD occurrence under Al stress is unclear. The results showed that cell death induced by Al was significant negative correlation with the inhibition of Al on root elongation growth in peanut. AlCl3 at 100μmolL−1 induced DNA ladder, chromatin condensation, typical apoptotic chromatin condensation staining with DAPI, apoptosis related gene Hrs203j expression and caspase3-like protease activation in peanut root tip cells, and showed that Al-induced cell death in peanut root tip cells was a typical PCD. Exogenous NO donor sodium nitroprusside (SNP) at 200μmolL−1 inhibited Al-induced PCD occurrence, but NO specific scavenger cPTIO aggravated PCD production. It suggests that NO is a negative regulator of Al-induced PCD in peanut root tips.

The Diversity of Arbuscular Mycorrhiza Fungus (AMF) Indigenous in Peanuts (Arachis Hypogea L) Rhizosphere under Different Elevation

Arbuscular Mycorrhiza Fungus (AMF) is a type of soil microorganisms with obligate symbiotic characteristic. It can associate with high-level plants at the rate of 90%. Its association level highly depends on the type of AMF and the host plant. The lack of information about the AMF diversity in an ecosystem, and the insufficient number and types of isolates available, are limiting factors for the widespread use of AMF. It was a survey and observation research. In this research AMF indigenous potentials were observed in soil and roots of peanuts. Samples were taken from area with different elevation: low, medium, and high in West Sumatra. The study reveals that the highest number of AMF indigenous spores in peanuts rhizosphere from area with different elevation: low, medium, and high are dominated by Glomus sp 1 (159 spores), Acaulospora sp1 (110 spora) and Glomus sp2 (82 spores), however AMF indigenous with the highest percentage of existence is Glomus sp1 and Acaulospora sp1 (100%). In addition, the infectious level of AMF indigenous on roots of peanuts are 81.1%, 64,4% and 78,9% on low, medium and high elevation, respectively. The highest number of population and infectious level are on low elevation whereas the lowest number is on high elevation. Thus, the elevation level correlates with the type of infection, the size of population, and the percentage of infection.

The Endophytic Fungus Phomopsis liquidambari Increases Nodulation and N2 Fixation in Arachis hypogaea by Enhancing Hydrogen Peroxide and Nitric Oxide Signalling

The continuous cropping obstacles in monoculture fields are a major production constraint for peanuts. Application of the endophytic fungus Phomopsis liquidambari has increased peanut yields, and nodulation and N2 fixation increases have been considered as important factors for P. liquidambari infection-improved peanut yield. However, the mechanisms involved in this process remain unknown. This work showed that compared with only Bradyrhizobium inoculation, co-inoculation with P. liquidambari significantly elevated endogenous H2O2 and NO levels in peanut roots. Pre-treatment of seedlings with specific scavengers of H2O2 (CAT) and NO (cPTIO) blocked P. liquidambari-induced nodulation and N2 fixation. CAT not only suppressed the P. liquidambari-induced nodulation and N2 fixation, but also suppressed the enhanced H2O2 and NO generation. Nevertheless, the cPTIO did not significantly inhibit the induced H2O2 biosynthesis, implying that H2O2 acted upstream of NO production. These results were confirmed by observations that exogenous H2O2 and sodium nitroprusside (SNP) reversed the inhibition of P. liquidambari-increased nodulation and N2 fixation by the specific scavengers. The transcriptional activities of the symbiosis-related genes SymRK and CCaMK of peanut-Bradyrhizobium interactions also increased significantly in response to P. liquidambari, H2O2 and SNP treatments. The pot experiment further confirmed that the P. liquidambari infection-enhanced H2O2 and NO signalling pathways were significantly related to the increase in peanut nodulation and N2 fixation. This is the first report that endophytic fungus P. liquidambari can increase peanut-Bradyrhizobium interactions via enhanced H2O2/NO-dependent signalling crosstalk, which is conducive to the alleviation of continuous cropping obstacles via an increase in nodulation and N2 fixation.

Entomopathogen Metarhizium anisopliae promotes the early development of peanut root

The benefit of the entomopathogen Metarhizium anisopliae to early root development was evaluated. Two inoculating methods, conidia-suspension-drenching (T<sub>1</sub>) and conidia-coating (T<sub>2</sub>), were used when sowing peanut. The results showed that taproot length and lateral root number in T<sub>1</sub> significantly increased compared to the control (T<sub>0</sub>) in days 4–10 after treatment, whereas no significant difference was found between T<sub>2</sub> and T<sub>0</sub>. The fungal density by T<sub>1</sub> and T<sub>2</sub> fluctuated in the first 8 days, followed by a gradual decline. The ratio of the taproot length or lateral root number in T<sub>1 </sub>and T<sub>0</sub> was significant relative to the fungal persistence. It suggested that M. anisopliae promotes peanut root development and should be considered as important factor in plant protection besides pest controls.

Effect of benzoic acid on soil microbial communities associated with soilborne peanut diseases

As potent allelochemicals, phenolic acids are believed to be associated with soilborne diseases, and can influence plant-microbe interactions. Benzoic acid (BA) is one major phenolic acid found in peanut (Arachis hypogaea) root exudates. The objectives of this study were to estimate the BA degradation in the soil and its effects on soil bacterial and fungal communities and to detect the specific taxa responding to BA amendment. BA degradation was investigated by monitoring the BA retained in the soil using high-performance liquid chromatography (HPLC) and the CO2 production rate using gas chromatography (GC). The abundance and diversity of the bacterial and fungal communities were investigated by quantitative real-time PCR (qPCR) and Illumina MiSeq sequencing. The results showed that the BA concentration decreased significantly with an increased rate of CO2 production during the first 36h after amendment, implying that the BA in the soil was quickly metabolized by the microbes. Quantitative PCR analysis further detected a significant increase in soil bacterial and fungal abundances in response to BA addition, but a reduced bacteria-to-fungi ratio. As a result of BA amendment, the relative abundance of Fusarium, Bionectria and Trichoderma was markedly increased, whereas Metarhizium was reduced. Moreover, BA (0.1mmolL−1) promoted the mycelial growth, sporulation capacity and conidial germination of the peanut root rot pathogen Fusarium sp. in vitro. Among bacteria, the relative abundance of Betaproteobacteria was significantly increased in response to BA treatment, whereas the relative abundances of AD3 and Actinobacteria were reduced. A deeper taxonomic analysis of the Betaproteobacteria taxa showed a great increase in the abundance of the genus Burkholderia, from 0.71% to 10.12%, in response to BA amendment. Constructing clone libraries with the partial 16S rRNA genes of Burkholderia further demonstrated that BA amendment had modified the Burkholderia species composition. Our results highlight that the effects of BA in the soil are reflected by changes in populations of soil microbes and suggest that the response of specific microbes such as Fusarium and Burkholderia to BA might be associated with the development of soilborne diseases in monocultures.

Halotolerant Rhizobacteria Promote Growth and Enhance Salinity Tolerance in Peanut.

Use of Plant growth promoting rhizobacteria (PGPR) is a promising strategy to improve the crop production under optimal or sub-optimal conditions. In the present study, five diazotrophic salt tolerant bacteria were isolated from the roots of a halophyte, Arthrocnemum indicum. The isolates were partially characterized in vitro for plant growth promoting traits and evaluated for their potential to promote growth and enhanced salt tolerance in peanut. The 16S rRNA gene sequence homology indicated that these bacterial isolates belong to the genera, Klebsiella, Pseudomonas, Agrobacterium, and Ochrobactrum. All isolates were nifH positive and able to produce indole -3-acetic acid (ranging from 11.5 to 19.1 μg ml−1). The isolates showed phosphate solubilisation activity (ranging from 1.4 to 55.6 μg phosphate /mg dry weight), 1-aminocyclopropane-1-carboxylate deaminase activity (0.1 to 0.31 μmol α-kB/μg protein/h) and were capable of reducing acetylene in acetylene reduction assay (ranging from 0.95 to 1.8 μmol C2H4 mg protein/h). These isolates successfully colonized the peanut roots and were capable of promoting the growth under non-stress condition. A significant increase in total nitrogen (N) content (up to 76%) was observed over the non-inoculated control. All isolates showed tolerance to NaCl ranging from 4 to 8% in nutrient broth medium. Under salt stress, inoculated peanut seedlings maintained ion homeostasis, accumulated less reactive oxygen species (ROS) and showed enhanced growth compared to non-inoculated seedlings. Overall, the present study has characterized several potential bacterial strains that showed an enhanced growth promotion effect on peanut under control as well as saline conditions. The results show the possibility to reduce chemical fertilizer inputs and may promote the use of bio-inoculants.

Distribution patterns of peanut roots under different durations of early season drought stress

The distribution patterns of peanut roots in response to different durations of drought events might affect water acquiring capacity of peanut and this information has not been clearly investigated. In this study, the response to different durations of drought in root distribution was evaluated in peanut genotype ICGV 98305 for three seasons in rhizoboxes in a rainout shelter at Khon Kaen University. Two seasons of this study were in 2013 and one in 2014. The first and the second trials were conducted in the rainy season and the third trial was carried out in the dry season. A completely randomized design with three replications was used. Drought treatments were imposed at 14days after emergence. The durations of drought imposition were 7, 14 and 21days after the irrigation withholding. Root samples were divided into 11 soil layers at 10cm intervals from the top to the bottom of the rhizobox. Drought imposed to peanut at early growth stages could change root distribution patterns of peanut, and the change in root distribution patterns was more pronounced with long duration of drought. In this study, imposing of drought for 21days caused a clear difference of root distribution patterns between peanut grown under well-watered (WW) and under drought stress (DS) treatments. The peanut adaptation to severe drought appears to be through enhanced root length and the root system growing deeper. The knowledge obtained is useful to decide the duration of drought that causes discernible modification in root system and can help identification of genetic variation for such adaptation. As water stress can mean excess water stress too, generally the expression drought stress is adopted.