Peanut Root Research Articles

Comparative transcriptome analysis reveals key genes responsible for the homeostasis of iron and other divalent metals in peanut roots under iron deficiency

This study defines key genes involved in Fe homeostasis and reveals cultivar differences in Fe deficiency responses in peanuts. A comparative transcriptome analysis was conducted on two peanut cultivars, Silihong and Fenghua 1, under Fe-sufficient and -deficient conditions. Plant growth and metal contents were measured. Silihong is more tolerant to Fe-deficiency than Fenghua 1. Fe deficiency increased the uptake of Zn, Mn, Mg, Ca and Cu in peanut plants. A total of 56 and 19 transporter genes were identified to be differentially expressed genes in Silihong and Fenghua 1 respectively. Two cultivars shared twelve common differentially expressed genes encoding OPT3, FRO2, Nramp3, YSL3, IRT1, FER3 and FRO7. Silihong showed higher expressions of AHA4, COPT1, FRO2, IRT1, MTP4, MTP9, Nramp5, OPT3 and VITH4, while Fenghua 1 exhibited higher expressions of ATX1, HMA5, MPT1, OPT6, YSL3, YSL7, ZIP1, ZIP4, ZIP5 and ZIP11 under Fe deficiency. Peanuts overcome Fe deficiency by increasing Fe uptake and altering its transport pathway, in which FRO2, IRT1, Nramp3, YSL3 and OPT3 are involved. Higher expression of AHA4, FRO2, IRT1 and Nramp5 might be responsible for higher Fe-deficiency tolerance in Silihong. Induction of IRT1, Nramp5 and COPT1 by Fe deficiency contribute to increased metal uptake in peanut plants.

Phylogeography of the Bradyrhizobium spp. Associated With Peanut, Arachis hypogaea: Fellow Travelers or New Associations?

Legume plants have colonized almost all terrestrial biotopes. Their ecological success is partly due to the selective advantage provided by their symbiotic association with nitrogen-fixing bacteria called rhizobia, which allow legumes to thrive on marginal lands and nitrogen depleted soils where non-symbiotic plants cannot grow. Additionally, their symbiotic capacities result in a high protein content in their aerial parts and seeds. This interesting nutritional value has led to the domestication and agricultural exploitation of several legumes grown for seeds and/or fodder for human and domestic animal consumption. Several cultivated legume species are thus grown far beyond their natural geographic range. Other legume species have become invasives, spreading into new habitats. The cultivation and establishment of legume species outside of their original range requires either that they are introduced or cultivated along with their original symbiotic partner or that they find an efficient symbiotic partner in their introduced habitat. The peanut, Arachis hypogaea, a native of South America, is now cultivated throughout the world. This species forms root nodules with Bradyrhizobium, but it is unclear whether these came with the seeds from their native range or were acquired locally. Here we propose to investigate the phylogeography of Bradyrhizobium spp. associated with a number of different wild and cultivated legume species from a range of geographical areas, including numerous strains isolated from peanut roots across the areas of peanut cultivation. This will allow us to address the question of whether introduced/cultivated peanuts associate with bacteria from their original geographic range, i.e., were introduced together with their original bacterial symbionts, or whether they acquired their current associations de novo from the bacterial community within the area of introduction. We will base the phylogenetic analysis on sequence data from both housekeeping and core genes and a symbiotic gene (nif). Differences between the phylogenetic signal of symbiotic and non-symbiotic genes could result from horizontal transfer of symbiosis capacity. Thus this study will also allow us to elucidate the processes by which this symbiotic association has evolved within this group of Bradyrhizobium spp.

Restrictive water condition modifies the root exudates composition during peanut-PGPR interaction and conditions early events, reversing the negative effects on plant growth

Water deficit is one of the most serious environmental factors that affect the productivity of crops in the world. Arachis hypogaea is a legume with a high nutritional value and 70% is cultivated in semi-arid regions. This research aimed to study the effect of water deficit on peanut root exudates composition, analyzing the importance of exudates on peanut-PGPR interaction under restrictive water condition.Peanut seedlings were subjected to six treatments: 0 and 15 mM PEG, in combination with non-inoculated, Bradyrhizobium sp. and Bradyrhizobium-Azospirillum brasilense inoculated treatments. We analyzed the 7-day peanut root exudate in response to a water restrictive condition and the presence of bacterial inocula. Molecular analysis was performed by HPLC, UPLC and GC. Bacteria motility, chemotaxis, bacterial adhesion to peanut roots and peanut growth parameters were analyzed.Restrictive water condition modified the pattern of molecules exuded by roots, increasing the exudation of Naringenin, oleic FA, citric and lactic acid, and stimulation the release of terpenes of known antioxidant and antimicrobial activity. The presence of microorganisms modified the composition of root exudates. Water deficit affected the first events of peanut-PGPR interaction and the root exudates favored bacterial mobility, the chemotaxis and attachment of bacteria to peanut roots.Changes in the profile of molecules exuded by roots allowed A. hypogaea-Bradyrhizobium and A.hypogaea–Bradyrhizobium-Azospirillum interaction thus reversing the negative effects of restrictive water condition on peanut growth. These findings have a future potential application to improve plant-PGPR interactions under water deficit by formulating inoculants containing key molecules exuded during stress.

Nitric oxide acts as an antioxidant and inhibits programmed cell death induced by aluminum in the root tips of peanut (Arachis hypogaea L.)

Aluminum (Al) causes programmed cell death (PCD) in plants. Our previous studies have confirmed that nitric oxide (NO) inhibits Al-induced PCD in the root tips of peanut. However, the mechanism by which NO inhibits Al-induced PCD is unclear. Here the effects of NO on mitochondrial reactive oxygen species (ROS), malondialdehyde (MDA), activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), expression of alternative oxidase (AhAOX) and cytochrome oxidase (AhCOX) were investigated in peanut (Arachis hypogaea L.) root tips treated with Al. The results showed that Al stress induced rapid accumulation of H2O2 and MDA and increased the ratio of SOD/APX. The up-regulation of AhAOX and AhCOX expressions was not enough to inhibit PCD occurrence. Sodium nitroprusside (SNP, a NO donor) decreased the ratio of SOD/APX and eliminated excess H2O2 and MDA, thereby inhibiting Al-induced PCD in the root tips of peanut. The expression of AhAOX and AhCOX was significantly enhanced in Al-induced PCD treated with SNP. But cPTIO (a NO specific scavenger) supply had the opposite effect. Taken together, these results suggested that lipid peroxidation induced by higher levels of H2O2 was an important cause of Al-induced PCD. NO-mediated inhibition of Al-induced PCD was related to a significant elimination of H2O2 accumulation by decreasing the ratio of SOD/APX and up-regulating the expression of AhAOX and AhCOX.

Priming With the Green Leaf Volatile (Z)-3-Hexeny-1-yl Acetate Enhances Salinity Stress Tolerance in Peanut (Arachis hypogaea L.) Seedlings.

Green leaf volatiles play vital roles in plant biotic stress; however, their functions in plant responses to abiotic stress have not been determined. The aim of this study was to investigate the possible role of (Z)-3-hexeny-1-yl acetate (Z-3-HAC), a kind of green leaf volatile, in alleviating the salinity stress of peanut (Arachis hypogaea L.) seedlings and the underlying physiological mechanisms governing this effect. One salt-sensitive and one salt-tolerant peanut genotype were primed with 200 μM Z-3-HAC at the 4-week-old stage before they were exposed to salinity stress. Physiological measurements showed that the primed seedlings possessed higher relative water content, net photosynthetic rate, maximal photochemical efficiency of photosystem II, activities of the antioxidant enzymes, and osmolyte accumulation under salinity conditions. Furthermore, the reactive oxygen species, electrolyte leakage, and malondialdehyde content in the third fully expanded leaves were significantly lower than in nonprimed plants. Additionally, we found that application of Z-3-HAC increased the total length, surface area, and volume of the peanut roots under salinity stress. These results indicated that the green leaf volatile Z-3-HAC protects peanut seedlings against damage from salinity stress through priming for modifications of photosynthetic apparatus, antioxidant systems, osmoregulation, and root morphology.

Changes in Root Anatomy of Peanut (Arachis hypogaea L.) under Different Durations of Early Season Drought

Changes in the anatomical structure of peanut roots due to early season drought will likely affect the water acquiring capacity of the root system. Yet, as important as these changes are likely to be in conferring drought resistance, they have not been thoroughly investigated. The objective of this study was to investigate the effects of different durations of drought on the root anatomy of peanut in response to early season drought. Plants of peanut genotype ICGV 98305 were grown in rhizoboxes with an internal dimension of 50 cm in width, 10 cm in thickness and 120 cm in height. Fourteen days after emergence, water was withheld for periods of 0, 7, 14 or 21 days. After these drought periods, the first and second order roots from 0–20 cm below soil surface were sampled for anatomical observation. The mean xylem vessel diameter of first- order lateral roots was higher than that of second- order lateral roots. Under early season drought stress root anatomy changes were more pronounced in the longer drought period treatments. Twenty-one days after imposing water stress, the drought treatment and irrigated treatment were clearly different in diameter, number and area of xylem vessels of first- and second-order lateral roots. Plants under drought conditions had a smaller diameter and area of xylem vessels than did the plants under irrigated control. The ability of plants to change root anatomy likely improves water uptake and transport and this may be an important mechanism for drought tolerance. The information will be useful for the selection of drought durations for evaluation of root anatomy related to drought resistance and the selection of key traits for drought resistance.

Comparative proteomics analysis of peanut roots reveals differential mechanisms of cadmium detoxification and translocation between two cultivars differing in cadmium accumulation

BackgroundPeanut is one of the most important oil and protein crops, and it exhibits wide cultivar variations in shoot Cd accumulation ability. However, the mechanism of Cd accumulation in peanut shoots has not been well understood. In this study, the root proteomics of two cultivars differing in seed Cd accumulation, Fenghua 1 (F, low Cd cultivar) and Silihong (S, high Cd cultivar), were investigated under 0 (CK) and 2 μM Cd conditions.ResultsA total of 4676 proteins were identified by proteomics screening. Of them, 375, 1762, 1276 and 771 proteins were identified to be differentially expressed proteins (DEPs) for comparison of FCd/FCK, SCd/SCK, FCK/SCK and FCd/SCd, respectively. Silihong is more sensitive to Cd exposure than Fenghua 1 in terms of root proteomics. A total of 30 and 86 DEPs were identified to be related with heavy metal transport and cell wall modification, respectively. The up-regulation of ABCB25, ABCC14, ABCC2, PDR1 and V-ATPases by Cd exposure in Silihong might enhance vacuolar sequestration of Cd and its efflux from symplast to apoplast. The higher Cd accumulation in the root CWs of Silihong might be resulted from its higher capability of CW modification, in which many proteins such as IRX10L, BGLU12-like, BGLU42, EXLB1, XTH30, XTH6, XYL7, PAL3, COMT, CAD1, and CCR1 were involved.ConclusionsThe vacuolar sequestration and efflux of Cd as well as its adsorption in CW might be the principal mechanism of cadmium detoxification in Silihong. The higher capacity of Cd accumulation and translocation of Silihong is an inherent characteristics in which ACA8 and ZIP1 might be involved.

Physiological and molecular mechanisms of improved iron nutrition of peanut intercropping with maize

Intercropping is one of the most important farming practices for efficient use of farmland ecosystems and sustainable yield productions. Peanut intercropped with maize could significantly reduce peanut chlorosis symptom and increase the plant iron (Fe) content and crop yield in the North China Plain. The physiological and molecular mechanisms behind this phenomenon have been extensively studied for decades. Peanut and maize have evolved two distinct mechanisms in response to Fe deficiency, known as “the Strategy I” and “the Strategy II”, respectively. The Strategy I plants take up Fe2+ through soil acidification and Fe3+ reduction, while the Strategy II plants acquire Fe via secreting mugineic acid family phytosiderophores (MAs) to dissolve insoluble ferric Fe and to form absorbable Fe(III)–MAs complexes in the rhizosphere. At the molecular level, key genes involved in Fe acquisition have been well characterized. In the Strategy I plants, peanut ferric reductase oxidase2 (AhFRO2) and iron regulated transporter1 (AhIRT1) are responsible for the reduction of Fe(III)-chelate to Fe(II) and the uptake of Fe(II), respectively. In the Strategy II plants, MAs are synthesized from methionine and secreted by mugineic acid transporter1 (MA1). The secreted MAs solubilize Fe in the rhizosphere and the resultant Fe(III)-MAs complex is then absorbed by the yellow stripe1 (YS1) transporter in maize. As a result, the Strategy II maize is more effective at mobilizing precipitated Fe, less affected by high pH and bicarbonate levels, and having a much stronger ability to resist Fe-limitation stress in calcareous soils compared with Strategy I peanuts. However, the Fe-limitation stress in peanuts could be alleviated when intercropping with maize. At physiological and biochemical levels, the ecological advantages of rhizosphere interaction is to significantly enhance the absorption and transport of Fe by intercropped peanut roots and to validate the functions of genes involved. In particular, it has been demonstrated that the AhYSL1 gene which is expressed in the peanut root epidermal cells can specifically regulate the absorption of the Fe(III)–DMA compound. Peanuts could directly absorb Fe(III)-DMA from the rhizosphere of intercropped maize. The intercropping of maize and peanut with different Fe absorption mechanisms not only improves peanut Fe nutrition but also increases resistance of these two crops. In addition, higher accumulation of photosynthesis-related proteins in intercropped peanut leaves suggests that the intercropped peanuts have a higher photosynthetic efficiency. Moreover, stress-responsive proteins displayed elevated expression levels in both peanut and maize in a monocropping system. This suggests that intercropping contributes to resistance to stress conditions. Intercropping also enhances jasmonate signaling and weakens ethylene signaling in peanut and maize roots, which may improve ecological adaptation of the maize and peanut plants in the intercropping system. The advantage in ecology system makes maize/peanut intercropping as a typical model of “bio-fortification”. The nutrient benefit of the inter-rhizosphere regulatory measure can be an important technological measure for bio-fortification to improve human health and nutrition. The research on the mechanisms underlying the beneficial effects of maize/peanut intercropping could provide important theoretical and applied bases to understand and utilize the reciprocal effect of different plant biological characteristics and to improve rhizosphere ecological environments, crop iron nutrition and efficient utilization of resources.

A halotolerant growth promoting rhizobacteria triggers induced systemic resistance in plants and defends against fungal infection

A halotolerant rhizobacteria, Klebsiella species (referred to MBE02), was identified that had a growth stimulation effect on peanut. To gain mechanistic insights into how molecular components were reprogrammed during the interaction of MBE02 and peanut roots, we performed deep RNA-sequencing. In total, 1260 genes were differentially expressed: 979 genes were up-regulated, whereas 281 were down-regulated by MBE02 treatment as compared to uninoculated controls. A large component of the differentially regulated genes were related to phytohormone signalling. This included activation of a significant proportion of genes involved in jasmonic acid, ethylene and pathogen-defense signalling, which indicated a role of MBE02 in modulating plant immunity. In vivo and in vitro pathogenesis assays demonstrated that MBE02 treatment indeed provide fitness benefits to peanut against Aspergillus infection under controlled as well as field environment. Further, MBE02 directly reduced the growth of a wide range of fungal pathogens including Aspergillus. We also identified possible molecular components involved in rhizobacteria-mediated plant protection. Our results show the potential of MBE02 as a biocontrol agent in preventing infection against several fungal phytopathogens.

Performance of Bradyrhizobium and Bradyrhizobium–Azospirillum in Alleviating the Effects of Water-Restrictive Conditions During the Early Stages of Arachis hypogaea Growth

Fil: Cesari, Adriana Belen. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas, Fisicoquimicas y Naturales. Departamento de Biologia Molecular. Seccion Quimica Biologica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Estimates on nitrogen uptake in the subsequent wheat by above-ground and root residue and rhizodeposition of using peanut labeled with 15N isotope on the North China Plain

Leguminous crops play a vital role in enhancing crop yield and improving soil fertility. Therefore, it can be used as an organic N source for improving soil fertility. The purpose of this study was to (i) quantify the amounts of N derived from rhizodeposition, root and above-ground biomass of peanut residue in comparison with wheat and (ii) estimate the effect of the residual N on the wheat-growing season in the subsequent year. The plants of peanut and wheat were stem fed with 15N urea using the cotton-wick method at the Wuqiao Station of China Agricultural University in 2014. The experiment consisted of four residue-returning strategies in a randomized complete-block design: (i) no return of crop residue (CR0); (ii) return of above-ground biomass of peanut crop (CR1); (iii) return of peanut root biomass (CR2); and (iv) return of all residue of the whole peanut plant (CR3). The 31.5 and 21% of the labeled 15N isotope were accumulated in the above-ground tissues (leaves and stems) of peanuts and wheat, respectively. N rhizodeposition of peanuts and wheat accounted for 14.91 and 3.61% of the BG15N, respectively. The 15N from the below-ground 15N-labeled of peanuts were supplied 11.3, 5.9, 13.5, and 6.1% of in the CR0, CR1, CR2, and CR3 treatments, respectively. Peanut straw contributes a significant proportion of N to the soil through the decomposition of plant residues and N rhizodeposition. With the current production level on the NCP, it is estimated that peanut straw can potentially replace 104 500 tons of synthetic N fertilizer per year. The inclusion of peanut in rotation with cereal can significantly reduce the use of N fertilizer and enhance the system sustainability.

Comparative transcriptome analysis reveals gene network regulating cadmium uptake and translocation in peanut roots under iron deficiency

BackgroundIron (Fe) is an essential element for plant growth and development, whereas cadmium (Cd) is non-essential and highly toxic. Previous studies showed that Fe deficiency enhanced Cd uptake and accumulation in peanuts. However, the molecular mechanism underlying the increased Cd accumulation in Fe-deficient peanut plants is poorly understood.ResultsWe employed a comparative transcriptome analysis approach to identify differentially expressed genes (DEGs) in peanut roots exposed to Fe-sufficient without Cd, Fe-deficient without Cd, Fe-sufficient with Cd and Fe-deficient with Cd. Compared with the control, Fe deficiency induced 465 up-regulated and 211 down-regulated DEGs, whereas the up- and down-regulated DEGs in Cd exposed plants were 329 and 189, respectively. Under Fe-deficient conditions, Cd exposure resulted in 907 up-regulated DEGs and 953 down-regulated DEGs. In the presence of Cd, Fe deficiency induced 1042 up-regulated and 847 down-regulated genes, respectively. Based on our array data, we found that metal transporter genes such as CAX4, COPT1, IRT1, NRAMP5, OPT3, YSL3, VIT3 and VIT4 might be involved in iron homeostasis. Moreover, combined with quantitative real-time PCR, IRT1, NRAMP3, NRAMP5, OPT3, YSL3, ABCC3, ZIP1, and ZIP5 were verified to be responsible for Cd uptake and translocation in peanut plants under iron deficiency. Additionally, a larger amount of ABC transporter genes was induced or suppressed by iron deficiency under Cd exposure, indicating that this family may play important roles in Fe/Cd uptake and transport.ConclusionsThe up-regulated expression of NRAMP5 and IRT1 genes induced by iron deficiency may enhance Cd uptake in peanut roots. The decrease of Cd translocation from roots to shoots may be resulted from the down-regulation of ZIP1, ZIP5 and YSL3 under iron deficiency.

The Yellow Stripe-Like (YSL) Gene Functions in Internal Copper Transport in Peanut

Copper (Cu) is involved in fundamental biological processes for plant growth and development. However, Cu excess is harmful to plants. Thus, Cu in plant tissues must be tightly regulated. In this study, we found that the peanut Yellow Stripe-Like family gene AhYSL3.1 is involved in Cu transport. Among five AhYSL genes, AhYSL3.1 and AhYSL3.2 were upregulated by Cu deficiency in peanut roots and expressed mainly in young leaves. A yeast complementation assay suggested that the plasma membrane-localized AhYSL3.1 was a Cu-nicotianamine complex transporter. High expression of AhYSL3.1 in tobacco and rice plants with excess Cu resulted in a low concentration of Cu in young leaves. These transgenic plants were resistant to excess Cu. The above results suggest that AhYSL3.1 is responsible for the internal transport of Cu in peanut.

Green and Efficient Extraction of Resveratrol from Peanut Roots Using Deep Eutectic Solvents

Deep eutectic solvents (DESs), a new group of ecofriendly solvent combined with the ultrasonic-assisted extraction (UAE) technique, were first successfully used for extraction of resveratrol from peanut roots. Resveratrol in the extract was analyzed and quantified using a HPLC-UV method. A series of DESs consisting of choline chloride (ChCl) and 1,4-butanediol, citric acid, and ethylene glycol were formulated, finding ChCl/1,4-butanediol was a most proper extraction system. The optimal extraction parameters were obtained using a Box–Behnken design (BBD) test combined with response surface methodology as follows: 40% of water in ChCl/1,4-butanediol (1/3, g/g) at 55°C for 40 min and solid/liquid ratio of 1:30 g/mL. The total extraction content and extraction yield of resveratrol from peanut roots could reach 38.91 mg/kg and 88.19%, respectively, under such optimal conditions. The present study will provide a typical example for using DESs to extract natural bioactive compounds from plants.

Behavioral responses of Holotrichia oblita larvae to root exudates from three host plants

The larva of Holotrichia oblita is a serious soil pest that feed with plant roots in north China. To explore the effects of host root exudates on the larva could provide theoretical basis for the development of green prevention and control methods. In order to elucidate the behavioral responses of Holotrichia oblita larva to the roots of peanut, soybean and maize, an experiment was conducted using the Y-olfactometers with the air as control. The constituents of the root exudates from the three host plants were identified by the gas chromatography-mass spectrometer (GC-MS). The olfactory responses of H. oblita larvae to the main components were tested. The results showed that H. oblita larvae had a significant behavioral preference toward the roots of peanut, soybean and maize than the control. The GC-MS analysis showed that the main components of volatile compounds in the three plants had more than twenty compounds, with only three shared ones, which was glycerol, dodecanol, ethyl benzene. The results of the Y-olfactometers showed that at low concentrations (40 to 80 μg·mL-1), the number of insects attracted by compound 2-butenoic acid, methylsuccinic acid, myristic acid, acetic acid and phthalate was significantly higher than that of control. At the concentrations of 100 μg·mL-1, 200 μg·mL-1, compound tetradecane and hexadecane were more attractive to the larvae than the control. The compounds p-xylene, o-xylene, and palmitic acid glycerol were found to significantly induce the larva at the concentration of 300 μg·mL-1 and 500 μg·mL-1. In summary, the main components of plant root exudates had a significant luring effect on H. oblita larvae.

Interspecific facilitation between intercropped millets and peanuts: insights from root proteomics analysis

ABSTRACTIntercropping is practised globally because of its advantages in terms of productivity and resource use efficiency. However, our knowledge on the molecular mechanisms underlying belowground interspecific interactions in intercropping systems is still very limited. Pot experiments involving both intercropped millet and peanut were conducted to quantify the differentially expressed proteins in each component crop under conditions of complete, partial and no interspecific interactions based on tandem mass tag (TMT) labelling. The results showed that the yields of both crops in the intercropping system increased in response to complete root interactions due to increases in nutrient acquisition as well as increases in root length and surface area. There were 73 differentially expressed proteins in the millet roots and 41 in the peanut roots, most of which were involved in C metabolism, N metabolism, transport and signal transduction. Additional bioinformatic analyses revealed that root interactions improved N and P assimilation via relatively high amounts of proteins such as urease and inorganic phosphate transporter in the millet roots and malate dehydrogenase increased P assimilation related proteins in the peanut roots. These results would contribute to a comprehensive understanding at molecular level in cereal/legume intercropping systems in response to interspecific root interactions.

Antimicrobial, plant growth-promoting and genomic properties of the peanut endophyte Bacillus velezensis LDO2

Peanut suffer from a number of fungal and bacterial pathogens, while plant endophytes were considered excellent candidates as biocontrol agents. In this study, the peanut endophytic bacterium LDO2 was evaluated for the potential of peanut pathogens inhibition and growth-promotion, and the genetic mechanisms were explored by genome mining. Strain LDO2 significantly inhibited the growth of peanut pathogenic fungi and pathogenic bacteria, and specifically, it showed pronounced inhibition on mycelia growth of Aspergillus flavus mycelia and caused mycelial deformity. Gene clusters responsible for antifungal metabolites (fengycin, surfactin, bacilysin) and antibacterial metabolites (butirosin, bacillaene, difficidin, macrolactin, surfactin, bacilysin) were identified. Strain LDO2 also exhibited several growth-promoting related features including phosphate solubilization, siderophore production and growth promotion of peanut root. Genes associated with plant growth promotion were also identified and analyzed, as well as genes related to secreted proteins. These findings suggested that this peanut endophyte could be a potential biocontrol agent in peanut production and a source of antimicrobial compounds for further exploitation.

Silicon effect on growth, nutrient uptake, and yield of peanut (Arachis hypogaea L.) under aluminum stress

The objective of this study was to investigate the effect of silicon (Si) on growth, nutrient uptake, and yield of peanut under aluminum (Al) stress. Peanut (Arachis hypogaea L. cv. Zhonghua 4) raised with or without Si (1.5 mM) in the growth chamber under 0 and toxic Al (0.3 mM) levels. Aluminum stress significantly decreased the biomass and root dry weight by 12.9% and 10.7%, and the pod yield, number of mature pod per plant and seed number of per pod by 16.7%, 10.7%, and 13.9%. The content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) was significantly decreased, but that of Al increased markedly in shoots and roots of peanut after Al exposure at seedling, flower-needle and pod-setting stage. Under Al stress condition, Si application protected peanut by improving nutrient uptake at different growth stages and favoring the partitioning of dry mass to pod and the allocation of tissue N, P, K, Ca, and Mg to shoots and pod and decreasing Al uptake and accumulation.

Assessment of nematicidal properties of fluorescent pseudomonads using peanut root-knot nematode, Meloidogyne arenaria

The primary objective of this study was to identify natural isolates of fluorescent pseudomonads with superior antagonistic activity towards plant parasitic nematodes. Nematicidal potential of eighteen isolates of fluorescent pseudomonads were compared against peanut root-knot nematode, Meloidogyne arenaria . Cell-free culture filtrate of DAPG-producing isolates of Pseudomonas putida caused significantly higher mortality of M. arenaria (J2) with highest in isolate DAPG3 (87.36%), followed by DAPG1 (84.16%) compared to other isolates of fluorescent pseudomonads, i.e., P. gessardii BHU1 and P. aeruginosa BM6 after exposure period of 72h at 100% concentration. The selected DAPG-producing isolates of P. putida caused significant inhibition in egg hatching. The lowest cumulative per cent hatch of M. arenaria was observed in the isolate DAPG3 (17.84%) followed by DAPG1 (18.10%). The isolates DAPG1 and DAPG3 also inhibited the nematode invasion in the roots of peanut by 41.30% and 36.34%, respectively. Significant reduction in number of galls/plant in peanut roots was recorded. The maximum reduction (51.30%) in root galling was recorded with combination of seed treatment and soil application of P. putida DAPG1 followed by 41.73% in combined treatment of seed treatment and soil application of P. putida DAPG3. The levels of Peroxidase (POD), Catalase (CAT) and Polyphenol Oxidase (PPO) were non-significant in the leaves of peanut in the treatment that received P. putida DAPG1 and DAPG3, either as seed treatment and/or soil application, compared to inoculated and un-inoculated control. However, significantly enhanced phenol content was recorded in the leaves of peanut in the treatment that received combination of seed treatment and soil application of P. putida DAPG1 and seed treatment alone.

Impact of different pineapple mealybug densities in a peanut crop

The pineapple mealybug Dysmicoccus brevipes (Hemiptera: Pseudococcidae) is a cosmopolitan and polyphagous species that causes severe damage to peanut crops in many countries around the world. This work was conducted in Campina Grande, Paraíba Sate, Brazil, aiming to assess losses in productivity caused by D. brevipes in a peanut crop. A completely randomized design with five treatments and four replicates was used. Treatments consisted of five mealybug population densities (nymphs and adults) on peanut roots and pods, described as follows: T1 = 0 mealybugs per plant; T2 = 1 to 20 mealybugs per plant; T3 = 21 to 40 mealybugs per plant; T4 = 41 to 80 mealybugs per plant and T5 = more than 80 mealybugs per plant. Roots and pods infested with the pest were observed on 84 % of the peanut plants sampled, ranging from zero to 147.1 individuals per plant. The higher the number of mealybugs per plant, the lower the weight of pod. The mean pod productivities of BR1 peanut cultivars, with the highest and lowest densities of mealybugs per plant were 1,695 and 3,290 kg per ha, respectively. Fields heavily infested with D. brevipes risk significant losses due to the enormous capacity of this organism for causing damage.