Transcriptome analysis reveals significant difference in gene expression and pathways between two peanut cultivars under Al stress

Aluminum (Al) toxicity is an important factor in limiting peanut growth on acidic soil. The molecular mechanisms underlying peanut responses to Al stress are largely unknown. In this study, we performed transcriptome analysis of the root tips (0-1 cm) of peanut cultivar ZH2 (Al-sensitive) and 99-1507 (Al-tolerant) respectively. Root tips of peanuts that treated with 100 μM Al for 8 h and 24 h were analyzed by RNA-Seq, and a total of 8,587 differentially expressed genes (DEGs) were identified. GO and KEGG pathway analysis excavated a group of important Al-responsive genes related to organic acid transport, metal cation transport, transcription regulation and programmed cell death (PCD). These homologs were promising targets to modulate Al tolerance in peanuts. It was found that the rapid transcriptomic response to Al stress in 99-1507 helped to activate effective Al tolerance mechanisms. Protein and protein interaction analysis indicated that MAPK signal transduction played important roles in the early response to Al stress in peanuts. Moreover, weighted correlation network analysis (WGCNA) identified a predicted EIL (EIN3-like) gene with greatly increased expression as an Al-associated gene, and revealed a link between ethylene signaling transduction and Al resistance related genes in peanut, which suggested the enhanced signal transduction mediated the rapid transcriptomic responses. Our results revealed key pathways and genes associated with Al stress, and improved the understanding of Al response in peanut.

Genotyping tools and resources to assess peanut germplasm: smut-resistant landraces as a case study

Peanut smut caused by Thecaphora frezii is a severe fungal disease currently endemic to Argentina and Brazil. The identification of smut resistant germplasm is crucial in view of the potential risk of a global spread. In a recent study, we reported new sources of smut resistance and demonstrated its introgression into elite peanut cultivars. Here, we revisited one of these sources (line I0322) to verify its presence in the U.S. peanut germplasm collection and to identify single nucleotide polymorphisms (SNPs) potentially associated with resistance. Five accessions of Arachis hypogaea subsp. fastigiata from the U.S. peanut collection, along with the resistant source and derived inbred lines were genotyped with a 48K SNP peanut array. A recently developed SNP genotyping platform called RNase H2 enzyme-based amplification (rhAmp) was further applied to validate selected SNPs in a larger number of individuals per accession. More than 14,000 SNPs and nine rhAmp assays confirmed the presence of a germplasm in the U.S. peanut collection that is 98.6% identical (P < 0.01, bootstrap t-test) to the resistant line I0322. We report this germplasm with accompanying genetic information, genotyping data, and diagnostic SNP markers.

Integrated Transcriptomics and Metabolomics Analysis Reveal Key Metabolism Pathways Contributing to Cold Tolerance in Peanut

Low temperature (non-freezing) is one of the major limiting factors in peanut (Arachis hypogaea L.) growth, yield, and geographic distribution. Due to the complexity of cold-resistance trait in peanut, the molecular mechanism of cold tolerance and related gene networks were largely unknown. In this study, metabolomic analysis of two peanut cultivars subjected to chilling stress obtained a set of cold-responsive metabolites, including several carbohydrates and polyamines. These substances showed a higher accumulation pattern in cold-tolerant variety SLH than cold-susceptible variety ZH12 under cold stress, indicating their importance in protecting peanut from chilling injuries. In addition, 3,620 cold tolerance genes (CTGs) were identified by transcriptome sequencing, and the CTGs were most significantly enriched in the "phenylpropanoid biosynthesis" pathway. Two vital modules and several novel hub genes were obtained by weighted gene co-expression network analysis (WGCNA). Several key genes involved in soluble sugar, polyamine, and G-lignin biosynthetic pathways were substantially higher and/or responded more quickly in SLH (cold tolerant) than ZH12 (cold susceptible) under low temperature, suggesting they might be crucial contributors during the adaptation of peanut to low temperature. These findings will not only provide valuable resources for study of cold resistance in peanut but also lay a foundation for genetic modification of cold regulators to enhance stress tolerance in crops.

Improved Genetic Map Identified Major QTLs for Drought Tolerance- and Iron Deficiency Tolerance-Related Traits in Groundnut

A deep understanding of the genetic control of drought tolerance and iron deficiency tolerance is essential to hasten the process of developing improved varieties with higher tolerance through genomics-assisted breeding. In this context, an improved genetic map with 1205 loci was developed spanning 2598.3 cM with an average 2.2 cM distance between loci in the recombinant inbred line (TAG 24 × ICGV 86031) population using high-density 58K single nucleotide polymorphism (SNP) “Axiom_Arachis” array. Quantitative trait locus (QTL) analysis was performed using extensive phenotyping data generated for 20 drought tolerance- and two iron deficiency tolerance-related traits from eight seasons (2004–2015) at two locations in India, one in Niger, and one in Senegal. The genome-wide QTL discovery analysis identified 19 major main-effect QTLs with 10.0–33.9% phenotypic variation explained (PVE) for drought tolerance- and iron deficiency tolerance- related traits. Major main-effect QTLs were detected for haulm weight (20.1% PVE), SCMR (soil plant analytical development (SPAD) chlorophyll meter reading, 22.4% PVE), and visual chlorosis rate (33.9% PVE). Several important candidate genes encoding glycosyl hydrolases; malate dehydrogenases; microtubule-associated proteins; and transcription factors such as MADS-box, basic helix-loop-helix (bHLH), NAM, ATAF, and CUC (NAC), and myeloblastosis (MYB) were identified underlying these QTL regions. The putative function of these genes indicated their possible involvement in plant growth, development of seed and pod, and photosynthesis under drought or iron deficiency conditions in groundnut. These genomic regions and candidate genes, after validation, may be useful to develop molecular markers for deploying genomics-assisted breeding for enhancing groundnut yield under drought stress and iron-deficient soil conditions.

Isolation, purification and characterization of cellulase produced by Aspergillus niger cultured on Arachis hypogaea shells

Cellulases are enzymes that hydrolyse cellulose and related cellu-oligosaccharides derivatives. Its applications are enormous but high cost of production is the bottle-neck against the utilization of cellulase in industries. Therefore, this study investigated the isolation, purification and characterization of cellulase produced by Aspergillus niger cultured on Arachis hypogaea shells. The crude cellulase enzyme was produced by A. niger through submerged fermentation process using A. hypogaea shells as a carbon source. The optima fermentation conditions were determined by varying different parameters. The crude cellulase was purified through ammonium sulphate precipitation, dialysis and gel-filtration chromatography. The molecular weight was estimated using sodium dodecyl sulphate polyacrylamide gel electrophoresis. The effects of pH and temperature on the activity of the purified cellulase were investigated. The study revealed that the: optimal production of crude cellulase was achieved at incubation period of 120 h, pH 4, temperature 40 °C, and inoculum size of 13 × 10⁵ CFU/ml. Cellulase was purified to 68.12-fold with a yield and specific activity of 3.87% and 484.3 U/mg respectively. The V_max for the cellulase was 9.26 U/ml while the K_m was 0.23 mg/ml. The molecular weight of the cellulase was approximately 13.5 kDa and the enzyme has higher specificity for CMC compared to other substrates. The optimum pH and temperature for the cellulase activity were 4 and 40 °C respectively. The present study has shown that A. hypogaea shells can be used as a carbon source by A. niger for the production of cellulase.

Effect of light and mechanical stress in combination with chemical elicitors on the production of stilbene compounds and defensive responses in peanut hairy root culture

Plants encounter diverse stressors simultaneously with changing environmental factors. The combined effect of different types of stresses can have a wide range of effects on plants. The present study demonstrated that various stress factors such as the combination of chemical elicitors, namely paraquat (PQ), methyl jasmonate (MeJA) and methyl-β-cyclodextrin (CD), light exposure versus darkness, and mechanical shearing stress affected the defence response in peanut hairy root culture. The antioxidant activities were dramatically increased at all time points after hairy roots were subjected to elicitation with PQ + MeJA + CD under root cutting in both light and dark conditions. The stilbene compounds were highly increased in the culture medium after elicitor treatment of uncut hairy roots under dark conditions. In contrast to the high stilbene contents detected in culture medium under dark conditions, the transcription of the stilbene biosynthesis genes PAL, RS and RS3 was enhanced by the effect of light in uncut hairy root tissues. The antioxidant enzyme genes APX, GPX and CuZn-SOD of uncut and cut hairy roots were more highly expressed in light conditions than in dark conditions. The pathogenesis-related protein (PR)-encoding genes chitinase, PR4A, PR5 and PR10 of uncut hairy roots were highly expressed in response to light conditions compared to dark conditions at all time points. Recent evidence of the production of antioxidant stilbene compounds and defence response genes has implicated plant protective functions through defence responses under different stress challenges. Plant responses might therefore be regulated by the coordination of different signal responses through dynamic pathways.

Enhancement of adaptive response in peanut hairy root by exogenous signalling molecules under cadmium stress

Plants counteract Cd toxicity by activating cellular stress responses. The simultaneous exogenous application of methyl jasmonate (MeJA) and methyl-β-cyclodextrin (CD) before Cd exposure improved the response of Arachis hypogaea hairy root culture to the unfavourable effects of Cd toxicity. At 24 h after elicitation, genes that encode key enzymes in the phenylpropanoid biosynthesis pathway (i.e., PAL and RS3) were up-regulated to 3.2- and 5.4-fold changes respectively, thereby inducing stilbene production. The up-regulation of genes that encode transcription factors (i.e., ERF1 and ERF6) significantly increased the expression of several genes (PR4A, PR5, PR10, and chitinase) that encode the pathogenesis-related (PR) proteins to 25.8-, 45-, 5- and 12.6-fold changes, respectively. The more dramatic up-regulation of PR protein-encoding genes demonstrated the significant role of defence proteins in plant protective mechanisms. The prolonged (i.e., 72-h) treatment with MeJA + CD_Cd triggered adaptive responses by substantially increasing the levels of antioxidants, stilbenes, and other phenolic substances. These findings suggest that the interaction between signalling elicitors (MeJA and CD) and Cd modulates a complex signalling network for plant defence system.

Alternative splicing profiling provides insights into the molecular mechanisms of peanut peg development

BACKGROUND

The cultivated peanut (Arachis hypogaea) is one of the most important oilseed crops worldwide, and the generation of pegs and formation of subterranean pods are essential processes in peanut reproductive development. However, little information has been reported about alternative splicing (AS) in peanut peg formation and development.

RESULTS

Herein, we presented a comprehensive full-length (FL) transcriptome profiling of AS isoforms during peanut peg and early pod development. We identified 1448, 1102, 832, and 902 specific spliced transcripts in aerial pegs, subterranean pegs, subterranean unswollen pegs, and early swelling pods, respectively. A total of 184 spliced transcripts related to gravity stimulation, light and mechanical response, hormone mediated signaling pathways, and calcium-dependent proteins were identified as possibly involved in peanut peg development. For aerial pegs, spliced transcripts we got were mainly involved in gravity stimulation and cell wall morphogenetic processes. The genes undergoing AS in subterranean peg were possibly involved in gravity stimulation, cell wall morphogenetic processes, and abiotic response. For subterranean unswollen pegs, spliced transcripts were predominantly related to the embryo development and root formation. The genes undergoing splice in early swelling pods were mainly related to ovule development, root hair cells enlargement, root apex division, and seed germination.

CONCLUSION

This study provides evidence that multiple genes are related to gravity stimulation, light and mechanical response, hormone mediated signaling pathways, and calcium-dependent proteins undergoing AS express development-specific spliced isoforms or exhibit an obvious isoform switch during the peanut peg development. AS isoforms in subterranean pegs and pods provides valuable sources to further understand post-transcriptional regulatory mechanisms of AS in the generation of pegs and formation of subterranean pods.

Effect of Syzigium aromaticum and Allium sativum spice extract powders on the lipid quality of groundnuts (Arachis hypogaea) pudding during steam cooking

Groundnut seeds (Arachis hypogaea) contain higher concentrations of unsaturated lipids which are prone to oxidation in formulated foods. This study determined the antioxidant activities of water extract powders from two spices (Syzigium aromaticum and Allium sativum) and their ability to preserve the quality of lipids in groundnuts pudding during steam cooking with 0, 0.5, 1, 2 and 4% of spice extract powders. Total phenolic (TPC) and flavonoid (FC) contents of extracts from S. aromaticum were 140.23 mg GAE/100g extract and FC of 110.34 mg CAE/g extract compared to values of Allium sativum extracts (54.28 mg GAE/100g extract and 34.80 mg CAE/g extract). The showed DPPH free radical scavenging activities of the extract from S. aromaticum depending on the concentration ranged from 82.15% to 97.66% and this was higher than the activities of A. sativum but comparable to the values of buthylhydroxytoluene used as control. The chemical analysis of oil extracted revealed that the addition of the spice extract powders limited the appearance of oxidation products characterized by a reduction of up to 9-fold of peroxide value, 5-fold for anisidine and 2-fold for thiobarbituric acid reactive species. In many cases, the addition of S. aromaticum spice extract powder to the pudding better prevented lipid oxidation likely because of its superior ability to scavenge peroxyl radicals (ROO^., HO^., DPPH ^. ). In a nutshell, the addition S. aromaticum and A. sativum spice extract powders on grilled groundnuts paste for groundnuts pudding preparation in household can help preserve its lipid quality.

Halotolerant PGPR Stenotrophomonas maltophilia BJ01 Induces Salt Tolerance by Modulating Physiology and Biochemical Activities of Arachis hypogaea

Arachis hypogaea (Peanut) is one of the most important cash crops grown for food and oil production. Salinity is a major constraint for loss of peanut productivity, and halotolerant plant growth promoting bacteria not only enhance plant-growth but also provide tolerance against salt stress. The potential of halotolerant bacterium Stenotrophomonas maltophilia BJ01 isolated from saline-soil was explored to enhance the growth of peanut plants under salt stress conditions. Interaction of S. maltophilia BJ01 enhances the growth of the peanut plants and protects photosynthetic pigments under salt stress. Lower electrolyte leakage (about 20%), lipid peroxidation (2.1 μmol g-1 Fw), proline (2.9 μg mg-1 Fw) content and H2O2 (55 μmol g-1 Fw) content were observed in plants, co-cultivated with PGPR compared to untreated plants under stress condition. The growth hormone auxin (0.4 mg g-1 Fw) and total amino acid content (0.3 mg g-1 Fw) were enhanced in plants co-cultivated with PGPR under stress conditions. Overall, these results indicate the beneficial effect of S. maltophilia BJ01 on peanut plants under salt (100 mM NaCl) stress conditions. In conclusion, bacterium S. maltophilia BJ01 could be explored further as an efficient PGPR for growing legumes especially peanuts under salt stress conditions. However, a detailed agronomic study would be needed to ascertain its commercial role.

Early Detection of Airborne Inoculum of Nothopassalora personata in Spore Trap Samples from Peanut Fields Using Quantitative PCR

A quantitative PCR (qPCR)-assay was developed to detect airborne inoculum of Nothopassalora personata, causal agent of late leaf spot (LLS) on peanut, collected with a modified impaction spore trap. The qPCR assay was able to consistently detect as few as 10 spores with purified DNA and 25 spores based on crude DNA extraction from rods. In 2019, two spore traps were placed in two peanut fields with a history of LLS. Sampling units were replaced every 2 to 4 days and tested with the developed qPCR assay, while plots were monitored for symptom development. The system detected inoculum 35 to 56 days before visual symptoms developed in the field, with detection related to environmental parameters affecting pathogen life-cycle and disease development. This study develops the framework of the qPCR spore trap system and represents the initial steps towards validation of the performance of the system for use as a decision support tool to complement integrated management of LLS.

Sixty-One Years Following Registration, Phorate Applied In-Furrow at Planting Suppresses Development of Late Leaf Spot on Peanut

Late and early leaf spot are caused by Nothopassalora personata and Passalora arachidicola, respectively, and are damaging diseases of peanut (Arachis hypogaea L.) capable of defoliation and yield loss. Management of these diseases is most effective through the integration of tactics that reduce starting inoculum and prevent infection. The insecticide phorate was first registered in 1959 and has been used in peanut production for decades in-furrow at planting to suppress thrips. Phorate further provides significant suppression of Tomato spotted wilt virus infection beyond suppression of its thrips vector alone by activating defense-related responses in the peanut plant. From six experiments conducted from 2017 to 2019 in Blackville, SC, Reddick, FL, and Quincy, FL, significantly less leaf spot defoliation was exhibited on peanuts treated with phorate in-furrow at planting (26%) compared with nontreated checks (48%). In-season fungicides were excluded from five of the experiments, whereas the 2018 Quincy, FL, experiment included eight applications on a 15-day interval. Across individual experiments, significant suppression of defoliation caused by late leaf spot was observed from 64 to 147 days after planting. Although more variable within location-years, pod yield following phorate treatment was overall significantly greater than for nontreated peanut (2,330 compared with 2,030 kg/ha; P = 0.0794). The consistent defoliation suppression potential was estimated to confer an average potential net economic yield savings of $90 to $120 per hectare under analogous leaf spot defoliation. To our knowledge, these are the first data in the 61 years since its registration demonstrating significant suppression of leaf spot on peanut following application of phorate in-furrow at planting. Results support phorate use in peanut as an effective and economical tactic to incorporate to manage late and early leaf spot infections and development of fungicide resistance.

Mineral nutrient homeostasis, photosynthetic performance, and modulations of antioxidative defense components in two contrasting genotypes of Arachis hypogaea L. (peanut) for mitigation of nitrogen and/or phosphorus starvation

Arachis hypogaea L. (peanut) is a major oil yielding crop and its productivity is largely affected by the availability of nitrogen and phosphorus. The present study aims to elucidate the differential physiological and biochemical mechanisms involved in two contrasting genotypes of peanut for mitigation of N and/or P deficiency. The plants of two contrasting genotypes of peanut (GG7 and TG26) were subjected to N and/or P deficiency under hydroponic culture condition. After 15 d of N and/or P deficiency, various growth parameters, mineral nutrient status, nutrient use efficiency, photosynthesis, transpiration, water use efficiency, chlorophyll fluorescence, ROS level, and changes in enzymatic and non-enzymatic antioxidative components were measured in control and nutrient deficient plants. Our results showed that GG7 is fast-growing genotype than TG26 under control condition, whereas under N and/or P deficiency growth performance of GG7 was significantly declined as compared to TG26. The levels of photosynthetic pigments, net photosynthesis activity (P_N), and stomatal conductance (g_s) declined in N and/or P deficient plants of both the genotypes. However, quantum efficiency of photosystem II (Fv/Fm) did not change significantly under N and/or P starvation in both the genotypes. In the present investigation, most of the antioxidative enzymes either remained in steady state or downregulated in both the genotypes of peanut under N and/or P deficiency condition. N and/or P deficiency did not influence the levels of ROS and oxidative stress indicators such as O₂^·-, H₂O₂, and MDA in both the genotypes. In the present investigation, the decline in growth in both the genotypes under N and/or P deficiency might be due to the reduced photosynthetic performance. Our results suggest that TG26 is more resistant to N and P deficiency than GG7 genotype. Higher NUE value of GG7 as compared to TG26 suggests that GG7 can utilize N more efficiently to promote biomass production than TG26 under sufficient nutrient condition. On the other hand, mineral resource allocation to leaf and higher PUE are key adaptive features of the TG26 genotype under N, and P deficiency conditions. The differential regulations of various enzymatic and non-enzymatic antioxidative components in peanut genotypes maintain the cellular redox homeostasis under mineral deficiency conditions and prevent the peanut plants from oxidative stress, thereby maintaining PSII efficiency. The information from the present study can be useful for the improvement of traits in peanut that can maintain the productivity under N and P deficient environment with minimum input of fertilizers.

Aspergillus and Fusarium control in the early stages of Arachis hypogaea (groundnut crop) by plant growth-promoting rhizobacteria (PGPR) consortium

In this study, we have attempted to develop a plant growth promoting rhizobacteria (PGPR) consortia against early-stage diseases in Arachis hypogaea (Groundnut crop) plantation of Andhra Pradesh, India. The dominant PGPRs were selected by considering the various plant growth and protection qualities, followed by characterisation and grouping based on compatibility to form a consortium of PGPRs [Group-1 includes EX-1 (Acinetobacter baumannii stain HAMBI 1846); EX-3 (Pseudomonas aeruginosa strain A1K319); EX-5 (Bacillus subterraneus strain CF1.9); KNL-1 (Bacillus subtilis strain JMP-B); CTR-4 (Enterobacter cloacae strain VITKJ1); ANT-4 (Bacillus subtilis strain SBMP4) and Group-2 includes EX-4 (Pseudomonas otitidis strain SLC8); KDP-4 (Pseudomonas aeruginosa strain Kasamber 11); NLR-4 (Bacillus species ADMK68); ANT-6 (Bacillus subtilis subsp. inaquosorum strain KCTC 13429)]. In addition to resistance to early stage pathogens, in both in vitro and pot experiments the PGPR consortium showed significantly higher germination rate and root induction (Aspergillus niger; A. flavus; Fusarium oxysporum) when compared to control and fertilizer treated groups. In addition, Group 2 was more successful in stimulating and protecting plant growth among the two groups of PGPRs developed. The PGPR consortia developed showed multiple plant growth characteristics, including phosphate solubilization, production of HCN and Indole acetic acid along with broad antagonism against the tested phytopathogens.

Melatonin Regulatory Mechanisms and Phylogenetic Analyses of Melatonin Biosynthesis Related Genes Extracted from Peanut under Salinity Stress

Melatonin improves the tolerance of plants to various environmental stresses by protecting plant cells against oxidative stress damage. The objective of the current study was to determine whether exogenous melatonin (MT) treatments could help protecting peanut (Arachis hypogaea) seedlings against salinity stress. This was achieved by investigating enzymatic and non-enzymatic antioxidant systems and the expression of melatonin biosynthesis related genes in response to salinity stress with or without exogenous MT. The results showed a significant increase in the concentrations of reactive oxygen species (ROS) in peanut seedlings under salinity stress. The exogenous application of melatonin decreased the levels of ROS through the activation of antioxidant enzymes in peanut seedlings under salinity stress. Transcription levels of melatonin biosynthesis related genes such as N-acetylserotonin methyltransferase (ASMT1, ASMT2, ASMT3), tryptophan decarboxylase (TDC), and tryptamine 5-hydroxylase (T5H) were up-regulated with a 150 µM melatonin treatment under salinity stress. The results indicated that melatonin regulated the redox homeostasis by its ability to induce either enzymatic or non-enzymatic antioxidant systems. In addition, phylogenetic analysis of melatonin biosynthesis genes (ASMT1, ASMT2, ASMT3, TDC, T5H) were performed on a total of 56 sequences belonging to various plant species including five new sequences extracted from Arachis hypogaea (A. hypogaea). This was based on pairwise comparison among aligned nucleotides and predicted amino acids as well as on substitution rates, and phylogenetic inference. The analyzed sequences were heterogeneous and the A. hypogaea accessions were primarily closest to those of Manihot esculenta, but this needs further clarification.

[Effects of salt and drought stresses on rhizosphere soil bacterial community structure and peanut yield]

A pot experiment with Huayu 25 as experimental material was conducted, with treatments of drought and salt stresses. The effects of drought and salt stresses at the flowering stage on the plant morphology, pod yield, and soil bacterial community structure in the rhizosphere were examined. The results showed that Proteobacteria, Actinobacteria, Saccharibacteria, Chloroflexi, Cyanobacteria, and Acidobacteria were the dominant phyla in the rhizosphere soil of peanut. Compared with that under normal conditions, the relative abundance of Proteobacteria and Actinobacteria dramatically decreased, while that of Cyanobacteria evidently increased in drought-treated and salt-treated soil. Moreover, the variation of Cyanobacteria abundance caused by combined drought and salt stresses was stronger than that caused by single drought or salt stress. Functional meta-genomic profiling indicated that a series of sequences related to signaling transduction, defense mechanism and post-translational modification, protein turnover, chaperones were enriched in rhizosphere soil under stressed conditions, which might have implications for plant survival and stress tolerance. Drought and salt stress affectedpeanut growth and reduced pod yield. Results from this study would present reference on the future improvement of stress tolerance of peanuts via modifying soil microbial community.

Adding Epidemiologically Important Meteorological Data to Peanut Rx, the Risk Assessment Framework for Spotted Wilt of Peanut

Management of disease affecting peanut in the southeastern United States has benefited from extensive field research identifying disease-associated risk factors since the 1990s. An assessment of risk factors associated with tomato spotted wilt (TSW), caused by tomato spotted wilt virus and spread exclusively by thrips, is available to growers through Peanut Rx, a tool developed to inform peanut management decisions. Peanut Rx provides an assessment of relative TSW risk as an index. The assessment provides information about the relative degree to which a field characterized by a specified suite of practices is at risk of crop loss caused by TSW. Loss results when infection occurs, and infection rates are determined, in part, by factors outside a grower's control, primarily the abundance of dispersing, viruliferous thrips. In this study, we incorporated meteorological variables useful for predicting thrips dispersal, increasing the robustness of the Peanut Rx framework in relation to variation in the weather. We used data from field experiments and a large grower survey to estimate the relationships between weather and TSW risk mediated by thrips vectors, and developed an addition to Peanut Rx that proved informative and easy to implement. The expected temporal occurrence of major thrips flights, as a function of heat and precipitation, was translated into the existing risk-point system of Peanut Rx. Results from the grower survey further demonstrated the validity of Peanut Rx for guiding growers' decisions to minimize risk of TSW.

Peanut Yield Loss in the Presence of Defoliation Caused by Late or Early Leaf Spot

Late and early leaf spot, respectively caused by Nothopassalora personata and Passalora arachidicola, are damaging diseases of peanut (Arachis hypogaea) capable of defoliating canopies and reducing yield. Although one of these diseases may be more predominant in a given area, both are important on a global scale. To assist informed management decisions and quantify relationships between end-of-season defoliation and yield loss, meta-analyses were conducted over 140 datasets meeting established criteria. Slopes of proportion yield loss with increasing defoliation were estimated separately for Virginia and runner market type cultivars. Yield loss for Virginia types was described by an exponential function over the range of defoliation levels, with a loss increase of 1.2 to 2.2% relative to current loss levels per additional percent defoliation. Results for runner market type cultivars showed yield loss to linearly increase 2.2 to 2.8% per 10% increase in defoliation for levels up to approximately 95% defoliation, after which the rate of yield loss was exponential. Defoliation thresholds to prevent economic yield loss for Virginia and runner types were estimated at 40 and 50%, respectively. Although numerous factors remain important in mitigating overall yield losses, the integration of these findings should aid recommendations about digging under varying defoliation intensities and peanut maturities to assist in minimizing yield losses.

Using mathematical models to describe aerial dispersal and silk ball formation of peanut red spider mite, Tetranychus ogmophallos (Acari: Tetranychidae)

Peanut red spider mite, Tetranychus ogmophallos, exhibits a peculiar dispersal behavior using silk balls, which involves clustering of mites and spinning of webs at the top of plants. Such a dispersal mechanism has not been studied for this species yet. Therefore, this study aimed at using mathematical models to describe aerial dispersal and silk ball formation of peanut red spider mite on peanut plants. The influence of wind speed, generated by a wind tunnel, on the dispersal of mites was studied in two experiments, one with 500 mites per plant and one with 1000 mites per plant, and six wind speeds (5, 10, 15, 20, 25, and 30 km h^-1) for each mite density. The proportion of displaced mites and the distance they were blown were measured. Another series of experiments considered the formation of silk balls to assess how fast balls were formed as a function of time and the number of mites present on a peanut plant. Data from the wind tunnel experiments were analyzed by logistic regression and multiple regression to assess the proportion of displaced mites and the distance moved, respectively, as functions of wind speed and the initial density of mites on the donor plant. The distribution of dispersal distances from the donor plant was fitted by a mathematical model proposed by Ricker (J Fish Res Board Can 11:559-623, 1954). The number of mites moving upwards on a plant to be involved in silk ball formation was modeled as a function of time based on the initial number of spider mites and their estimated birth, death and movement rates per capita. Logistic regression was used to analyze the presence of balls as a function of time elapsed since a plant was infested with spider mites. Finally, non-linear regression was applied to link ball size to the total number of mites occupying the ball. The data analyses revealed that wind speed had a significant positive effect on take-off probability and distance moved by individual mites, whereas mite density had little influence. Ricker's model adequately described the distribution of dispersal distances. The models describing silk ball formation also described data very well. Ball size was found to increase almost linearly with the number of mites found in the ball. We expect that the knowledge provided by the present study will help to develop efficient management strategies against T. ogmophallos in peanut crops as dispersal seems to be a key factor in the species' capability to become a serious pest.

Efficacy and Profitability of Insecticide Treatments for Tomato Spotted Wilt Management on Peanut in South Carolina

Tomato spotted wilt (TSW) is a common and serious disease of peanut (Arachis hypogaea L.) caused by Tomato spotted wilt virus (TSWV; family Tospoviridae, genus Orthotospovirus). Management frequently uses an integrated approach, with cultivar resistance and application of in-furrow insecticide as two critical components. In-furrow insecticides help suppress thrips, which can injure and stunt young growing plants and transmit TSWV, with postemergent application of acephate capable of providing additional thrips control. To examine effects of systemic insecticides (imidacloprid, imidacloprid plus fluopyram, phorate, and acephate) on TSW management, yield, and economic return across cultivar susceptibilities (susceptible, moderately susceptible, and resistant) in South Carolina, a meta-analysis was used to synthesize results from 32 studies conducted between 2009 and 2018. Although efficacy and magnitude of individual treatments varied with susceptibility, imidacloprid increased, whereas phorate generally decreased TSW incidence relative to nontreated controls. In-furrow treatments followed by acephate further reduced TSW incidence and increased profitability. All examined treatments improved yield compared with untreated peanuts except for susceptible cultivars treated with imidacloprid. Imidacloprid plus fluopyram increased yield more than imidacloprid alone for the susceptible group, although there was little difference between these treatments in association with moderately susceptible cultivars. When comparing individual applications, phorate was overall the most profitable option across susceptibilities, although imidacloprid plus fluopyram exhibited analogous profitability for susceptible cultivars. Results from this study can be used to assist producer selection of management options for TSW in peanut.

Identification of the key genes involved in the regulation of symbiotic pathways induced by Metarhizium anisopliae in peanut (Arachis hypogaea) roots

We detected and compared the mRNA and protein expression levels of immunity-associated and symbiosis-associated genes in peanut (Arachis hypogaea) roots inoculated with entomopathogenic fungus M. anisopliae or the phytopathogenic fungus Fusarium oxysporum, by RT-qPCR and parallel reaction monitoring (PRM). The selected genes were mainly associated with plant-fungus interactions, signal transduction, regulation of cell death, nitrogen or iron metabolism, nutrient acquisition or transport, and compound synthesis based on previous transcriptome analysis. The results showed that the host basal defense responses were significantly inhibited by both M. anisopliae and F. oxysporum, which suggests that both fungi actively suppress the host immunity for successful colonization and infection. However, only F. oxysporum induced a strong host hypersensitivity, which indicates that the host is strongly resisting F. oxysporum but potentially allowing M. anisopliae. Additionally, the genes (SYMRK, CaM, CCaMK, FRI2, ABCC2, F6H1, SCT, NRT24 and LTP1) related to symbiosis and growth were distinctively observed with an up-regulated expression following M. anisopliae treatment, which implies that the host was actively initiating the establishment of symbiosis with the fungus. This study revealed a synergistic relationship between host immunosuppression and the promotion of symbiosis during interactions with M. anisopliae. It suggested that M. anisopliae benefited plant for symbiotic relationship, in addition to controlling herbivorous insects as an entomopathogen.

Advances in Crop Improvement and Delivery Research for Nutritional Quality and Health Benefits of Groundnut (Arachis hypogaea L.)

Groundnut is an important global food and oil crop that underpins agriculture-dependent livelihood strategies meeting food, nutrition, and income security. Aflatoxins, pose a major challenge to increased competitiveness of groundnut limiting access to lucrative markets and affecting populations that consume it. Other drivers of low competitiveness include allergens and limited shelf life occasioned by low oleic acid profile in the oil. Thus grain off-takers such as consumers, domestic, and export markets as well as processors need solutions to increase profitability of the grain. There are some technological solutions to these challenges and this review paper highlights advances in crop improvement to enhance groundnut grain quality and nutrient profile for food, nutrition, and economic benefits. Significant advances have been made in setting the stage for marker-assisted allele pyramiding for different aflatoxin resistance mechanisms-in vitro seed colonization, pre-harvest aflatoxin contamination, and aflatoxin production-which, together with pre- and post-harvest management practices, will go a long way in mitigating the aflatoxin menace. A breakthrough in aflatoxin control is in sight with overexpression of antifungal plant defensins, and through host-induced gene silencing in the aflatoxin biosynthetic pathway. Similarly, genomic and biochemical approaches to allergen control are in good progress, with the identification of homologs of the allergen encoding genes and development of monoclonal antibody based ELISA protocol to screen for and quantify major allergens. Double mutation of the allotetraploid homeologous genes, FAD2A and FAD2B, has shown potential for achieving >75% oleic acid as demonstrated among introgression lines. Significant advances have been made in seed systems research to bridge the gap between trait discovery, deployment, and delivery through innovative partnerships and action learning.

Molecular Basis of Root Nodule Symbiosis between Bradyrhizobium and 'Crack-Entry' Legume Groundnut (Arachis hypogaea L.)

Nitrogen is one of the essential plant nutrients and a major factor limiting crop productivity. To meet the requirements of sustainable agriculture, there is a need to maximize biological nitrogen fixation in different crop species. Legumes are able to establish root nodule symbiosis (RNS) with nitrogen-fixing soil bacteria which are collectively called rhizobia. This mutualistic association is highly specific, and each rhizobia species/strain interacts with only a specific group of legumes, and vice versa. Nodulation involves multiple phases of interactions ranging from initial bacterial attachment and infection establishment to late nodule development, characterized by a complex molecular signalling between plants and rhizobia. Characteristically, legumes like groundnut display a bacterial invasion strategy popularly known as "crack-entry'' mechanism, which is reported approximately in 25% of all legumes. This article accommodates critical discussions on the bacterial infection mode, dynamics of nodulation, components of symbiotic signalling pathway, and also the effects of abiotic stresses and phytohormone homeostasis related to the root nodule symbiosis of groundnut and Bradyrhizobium. These parameters can help to understand how groundnut RNS is programmed to recognize and establish symbiotic relationships with rhizobia, adjusting gene expression in response to various regulations. This review further attempts to emphasize the current understanding of advancements regarding RNS research in the groundnut and speculates on prospective improvement possibilities in addition to ways for expanding it to other crops towards achieving sustainable agriculture and overcoming environmental challenges.

Protein purification from Arachis hypogaea in one step: stability studies and anticarcinogenic analysis

The study involved purification of trypsin inhibitor from the seeds of Indian peanuts (Arachis hypogaea), a member of leguminosae family. The inhibitor was purified to homogeneity via three sequential step procedure i.e., salt precipitation to anion-exchange chromatography. The purity and molecular mass was detected using SDS PAGE analysis i.e. ~ 16 kDa. The purified inhibitor termed as Peanut Trypsin Inhibitor (PTI) which inhibits trypsin belonging to serpins family. Anti- neoplastic potential on breast cancer cells (MCF-7) and normal Human Embryonic Kidney cells (HEK) was determined using MTT assay. PTI exhibited IC50 value of ~ 18.412 µg/mL in HEK cells compared to ~ 9.635 µg/mL in MCF-7 cells. The values were quite comparable to curcumin, the standard anticancer drug demonstrating IC50 values of ~ 21.581 µg/mL and ~ 7.135 µg/mL in HEK and MCF-7 respectively. Therefore, we conclude that PTI may be used as supplement along with the conventional drugs for increased efficacy in the treatment of cancer.

Thermal processing of peanut impacts detection by current analytical techniques

Recalls of spice containing products due to undeclared peanut have highlighted the importance of analytical methods in these foods. We examined the performance of peanut detection methods in cumin and garlic, focusing on quantitative ELISA. Although suitable for qualitative detection, accurate quantitation proved difficult. Roasting of peanut contaminants influenced ELISA results, with raw peanut over-detected (3.9-fold) and roasted peanut under-detected (3.5-fold). Further investigation demonstrated the importance of protein targets for ELISA. The kit which gave the least variable results was based on detection of 2S albumin proteins. Additionally, we show that these proteins are more efficiently extracted from roasted peanut. We conclude that current methods are largely suitable for the qualitative detection of peanut in cumin and garlic. Quantitation relies on assumptions as to the state of thermal processing of peanut. We suggest that analytical method providers address robust detection by target selection, including identifying targets by MS.