Impacts of cobalt and zinc on improving peanuts nutrient uptake, yield and irrigation water use efficiency under different irrigation levels.

The knowledge of proper fertigation across various irrigation levels is necessary for maximizing peanut yield and irrigation use efficiency in arid areas, and it also can effectively alleviate the risk of nutrient deficiency induced by water stress. This study evaluated the effectiveness of cobalt combined with two zinc application methods on peanut nutrient uptake, yield, and irrigation water use efficiency across varying irrigation levels. A split-split plot experiment was carried out in 2021 and 2022. Three peanut gross water requirement (GWR) levels (100%, 80%, and 60%) were designated for main plots. Subplots featured plants treated with either 0 or 7.5 mg L-1 of cobalt. The sub-sub plots assessed chelated zinc effects at rates of 0 and 2 g L-1 via foliar and soil applications. In comparison to the control (100% GWR), nutrient uptake decreased, with sodium being the exception, and there was an increase in soil pH at 60% GWR. The results showed also significant reductions in yield and water use by approximately 60.3% and 38.1%, respectively. At this irrigation level, applying zinc via soil, either alone or combined with cobalt, led to significant yield increases of 89.7% and 191.3% relative to the control. Also, it's crucial to note that cobalt application negatively affected iron and copper at 60% GWR, but this impact was lessened with soil-applied zinc. Hence, under a similar circumstance, treating stressed peanut plants with additional foliar applications of iron + copper and applying zinc via soil, could enhance nutrient uptake and improve yield. On the other hand, at 80% GWR, a combination of foliar-applied zinc and cobalt, had a tremendous impact on the absorption of (nitrogen, phosphorus, magnesium, and zinc), resulting in enhanced agronomic traits and decreased water losses. Additionally, at this irrigation level, foliar zinc application alone yielded a 32.4% increase compared to the 80% GWR control. When combined with cobalt, there was a 70.0% surge in water use. Based on this knowledge, the study suggests using 80% GWR and treating peanut plants with a combination of foliar-applied zinc and cobalt. This strategy aids plants in countering the adverse effects of water stress, ultimately leading to enhanced yield and irrigation water use efficiency.

Enhanced dosage delivery of pesticide under unmanned aerial vehicle condition for peanut plant protection: tank-mix adjuvants and formulation improvement.

BACKGROUND: Suspension concentrate (SC) is one of the most widely used formulations for agricultural plant protection. With the rapid development of unmanned aerial vehicle (UAV) plant protection, the problems of spray drift, droplet rebound and poor wettability in the application of SC from UAVs have attracted wide attention. Although some tank-mix adjuvants have been used to enhance dosage delivery for UAV, their effects and mechanisms are not fully clear, and few formulations are specifically designed for UAV. RESULTS: The type and concentration of tank-mix adjuvant affect the dosage delivery of SC. MO501 can significantly reduce DV<100µm , and inhibit droplet rebound on peanut leaves at concentrations ≥0.5%. Silwet 408 can achieve complete wetting and superspreading after adding ≥0.2% concentrations, but only ≥0.5% can inhibit rebound. XL-70 shows excellent regulation ability even at low concentration, and 0.2% concentration can simultaneously suppress impact and promote spreading. Besides, the formulation oil dispersion (OD) can significantly reduce the driftable fine fraction and inhibit rebound at dilution ratios of ≤250-fold, thus enhancing dosage delivery. CONCLUSION: SC is prone to rebound on hydrophobic leaf surfaces and shows poor wetting and spreading properties. Appropriate types and concentrations of tank-mix adjuvants and formulation improvement are two effective strategies for improving the dosage delivery of pesticides, whereas the addition of inappropriate adjuvants may cause potential risks instead. These findings provide guidance for the rational selection of tank-mix adjuvants and potential applications of OD for UAV plant protection. © 2023 Society of Chemical Industry.

Multi-omics-driven advances in the understanding of triacylglycerol biosynthesis in oil seeds.

Vegetable oils are rich sources of polyunsaturated fatty acids and energy as well as valuable sources of human food, animal feed, and bioenergy. Triacylglycerols, which are comprised of three fatty acids attached to a glycerol backbone, are the main component of vegetable oils. Here, we review the development and application of multiple-level omics in major oilseeds and emphasize the progress in the analysis of the biological roles of key genes underlying seed oil content and quality in major oilseeds. Finally, we discuss future research directions in functional genomics research based on current omics and oil metabolic engineering strategies that aim to enhance seed oil content and quality, and specific fatty acids components according to either human health needs or industrial requirements.

Multi-Omics Revealed Peanut Root Metabolism Regulated by Exogenous Calcium under Salt Stress.

High salinity severely inhibits plant seedling root development and metabolism. Although plant salt tolerance can be improved by exogenous calcium supplementation, the metabolism molecular mechanisms involved remain unclear. In this study, we integrated three types of omics data (transcriptome, metabolome, and phytohormone absolute quantification) to analyze the metabolic profiles of peanut seedling roots as regulated by exogenous calcium under salt stress. (1) exogenous calcium supplementation enhanced the allocation of carbohydrates to the TCA cycle and plant cell wall biosynthesis rather than the shikimate pathway influenced by up-regulating the gene expression of antioxidant enzymes under salt stress; (2) exogenous calcium induced further ABA accumulation under salt stress by up-regulating the gene expression of ABA biosynthesis key enzymes AAO2 and AAO3 while down-regulating ABA glycosylation enzyme UGT71C5 expression; (3) exogenous calcium supplementation under salt stress restored the trans-zeatin absolute content to unstressed levels while inhibiting the root cis-zeatin biosynthesis.

Global Transcriptome and Co-Expression Network Analyses Revealed Hub Genes Controlling Seed Size/Weight and/or Oil Content in Peanut.

Cultivated peanut (Arachis hypogaea L.) is an important economic and oilseed crop worldwide, providing high-quality edible oil and high protein content. Seed size/weight and oil content are two important determinants of yield and quality in peanut breeding. To identify key regulators controlling these two traits, two peanut cultivars with contrasting phenotypes were compared to each other, one having a larger seed size and higher oil content (Zhonghua16, ZH16 for short), while the second cultivar had smaller-sized seeds and lower oil content (Zhonghua6, ZH6). Whole transcriptome analyses were performed on these two cultivars at four stages of seed development. The results showed that ~40% of the expressed genes were stage-specific in each cultivar during seed development, especially at the early stage of development. In addition, we identified a total of 5356 differentially expressed genes (DEGs) between ZH16 and ZH6 across four development stages. Weighted gene co-expression network analysis (WGCNA) based on DEGs revealed multiple hub genes with potential roles in seed size/weight and/or oil content. These hub genes were mainly involved in transcription factors (TFs), phytohormones, the ubiquitin-proteasome pathway, and fatty acid synthesis. Overall, the candidate genes and co-expression networks detected in this study could be a valuable resource for genetic breeding to improve seed yield and quality traits in peanut.

Identification of QTL for kernel weight and size and analysis of the pentatricopeptide repeat (PPR) gene family in cultivated peanut (Arachis hypogaea L.).

Peanut (Arachis hypogaea L.) is an important oilseed crop worldwide. Improving its yield is crucial for sustainable peanut production to meet increasing food and industrial requirements. Deciphering the genetic control underlying peanut kernel weight and size, which are essential components of peanut yield, would facilitate high-yield breeding. A high-density single nucleotide polymorphism (SNP)-based linkage map was constructed using a recombinant inbred lines (RIL) population derived from a cross between the variety Yuanza9102 and a germplasm accession wt09-0023. Kernel weight and size quantitative trait loci (QTLs) were co-localized to a 0.16 Mb interval on Arahy07 using inclusive composite interval mapping (ICIM). Analysis of SNP, and Insertion or Deletion (INDEL) markers in the QTL interval revealed a gene encoding a pentatricopeptide repeat (PPR) superfamily protein as a candidate closely linked with kernel weight and size in cultivated peanut. Examination of the PPR gene family indicated a high degree of collinearity of PPR genes between A. hypogaea and its diploid progenitors, Arachis duranensis and Arachis ipaensis. The candidate PPR gene, Arahy.JX1V6X, displayed a constitutive expression pattern in developing seeds. These findings lay a foundation for further fine mapping of QTLs related to kernel weight and size, as well as validation of candidate genes in cultivated peanut.

Experimental Comparison between Ethanol and Hexane as Solvents for Oil Extraction from Peanut Press Cake.

Ethanol (Et) has been suggested as a substitute for hexane (Hx) for use in the extraction of oils from different oleaginous matrices. In this study, Et and Hx were used to extract the residual oil present in a peanut press cake (PPC). Certain variables, such as temperature, solid/solvent ratio and the number of contact stages, in the sequential cross-current extraction process were evaluated; additionally, the effects of these variables on oils (POEt and POHx) and defatted solids (DSEt and DSHx) were explored. Hx exhibited an extraction yield of 86 ± 2% in two stages at 55 °C and a solid/solvent mass ratio of 1/4. Compared with Hx extraction, to achieve an Et extraction yield of 87 ± 4%, it was necessary to use a higher temperature (75 °C), a greater amount of solvent (solid/solvent ratio of 1/5) and a greater number of contact stages (3). POEt and POHx presented compositions in terms of fatty acids and triacylglycerols and physical properties similar to that of cold-pressed peanut oil (CPPO). POEt showed a more intense green/yellow hue and higher free acidity (1.47 ± 0.03%) than POHx and CPPO (0.82 ± 0.04 and 0.43 ± 0.02 free acidity mass %, respectively), indicating that the deacidification and bleaching steps in refining should be encumbered. DSEt and DSHx exhibited high protein contents (>45% by mass) and nitrogen solubilities (86 ± 6 and 98 ± 1%, respectively), indicating that they could be used to obtain proteins.

The determination of peanut (Arachis hypogaea L.) pod-sizes during the rapid-growth stage by phytohormones.

BACKGROUND: Pod size is an important yield target trait for peanut breeding. However, the molecular mechanism underlying the determination of peanut pod size still remains unclear. RESULTS: In this study, two peanut varieties with contrasting pod sizes were used for comparison of differences on the transcriptomic and endogenous hormonal levels. Developing peanut pods were sampled at 10, 15, 20, 25 and 30 days after pegging (DAP). Our results showed that the process of peanut pod-expansion could be divided into three stages: the gradual-growth stage, the rapid-growth stage and the slow-growth stage. Cytological analysis confirmed that the faster increase of cell-number during the rapid-growth stage was the main reason for the formation of larger pod size in Lps. Transcriptomic analyses showed that the expression of key genes related to the auxin, the cytokinin (CK) and the gibberellin (GA) were mostly up-regulated during the rapid-growth stage. Meanwhile, the cell division-related differentially expressed genes (DEGs) were mostly up-regulated at 10DAP which was consistent with the cytological-observation. Additionally, the absolute quantification of phytohormones were carried out by liquid-chromatography coupled with the tandem-mass-spectrometry (LC-MS/MS), and results supported the findings from comparative transcriptomic studies. CONCLUSIONS: It was speculated that the differential expression levels of TAA1 and ARF (auxin-related), IPT and B-ARR (CK-related), KAO, GA20ox and GA3ox (GA-related), and certain cell division-related genes (gene-LOC112747313 and gene-LOC112754661) were important participating factors of the determination-mechanism of peanut pod sizes. These results were informative for the elucidation of the underlying regulatory network in peanut pod-growth and would facilitate further identification of valuable target genes.

Uncovering mechanisms governing stem growth in peanut (Arachis hypogaea L.) with varying plant heights through integrated transcriptome and metabolomics analyses.

The mechanisms responsible for stem growth in peanut (Arachis hypogaea L.) cultivars with varying plant heights remain unclear, despite the significant impact of plant height on peanut yield. Therefore, this study aimed to investigate the underlying mechanisms of peanut stem growth using phenotypic, physiological, transcriptomic, and metabolomic analyses. The findings revealed that the tallest cultivar, HY33, exhibited the highest rate of stem growth and accumulated the most stem dry matter, followed by the intermediate cultivar, SH108, while the dwarf cultivar, Df216, displayed the lowest values. Furthermore, SH108 exhibited a higher harvest index, as well as superior pod and kernel yields compared to both HY33 and Df216. Transcriptome and metabolome analyses identified differentially expressed genes (DEGs) and differentially expressed metabolites (DEMs) associated with phenylpropanoid and flavonoid biosynthesis. Notably, downregulated DEGs in Df216/HY33 and Df216/SH108 included phenylalanine ammonia-lyase (PAL), caffeoyl-CoA O-methyltransferase (COMT), and ferulate-5-hydroxylase (F5H), while downregulated DEMs included p-coumaryl alcohol, chlorogenic acid, and L-epicatechin. Compared to HY33, the reduced activities of PAL, COMT, and F5H resulted in a decreased stem lignin content in Df216. Additionally, downregulated DEGs involved in gibberellin (GA) and brassinosteroid (BR) biosynthesis were identified in Df216/HY33, which contributed to the lowest levels of GA1, GA3, and BR contents in Df216. The results suggest that the dwarf phenotype arises from impaired GA and BR biosynthesis and signaling, resulting in a slower stem growth rate and reduced lignin accumulation.

Transcriptome analysis provides insights into the stress response in cultivated peanut (Arachis hypogaea L.) subjected to drought-stress.

BACKGROUND: Peanut (Arachis hypogaea L.) is one of the valuable oilseed crops grown in drought-prone areas worldwide. Drought severely limits peanut production and productivity significantly. METHOD AND RESULTS: In order to decipher the drought tolerance mechanism in peanut under drought stress, RNA sequencing was performed in TAG - 24 (drought tolerant genotype) and JL-24 (drought susceptible genotype). Approximately 51 million raw reads were generated from four different libraries of two genotypes subjected to drought stress exerted by 20% PEG 6000 stress and control conditions, of which ~ 41 million (80.87%) filtered reads were mapped to the Arachis hypogaea L. reference genome. The transcriptome analysis detected 1,629 differentially expressed genes (DEGs), 186 genes encoding transcription factors (TFs) and 30,199 SSR among the identified DEGs. Among the differentially expressed TF encoding genes, the highest number of genes were WRKY followed by bZIP, C2H2, and MYB during drought stress. The comparative analysis between the two genotypes revealed that TAG-24 exhibits activation of certain key genes and transcriptional factors that are involved in essential biological processes. Specifically, TAG-24 showed activation of genes involved in the plant hormone signaling pathway such as PYL9, Auxin response receptor gene, and ABA. Additionally, genes related to water deprivation such as LEA protein and those involved in combating oxidative damage such as Glutathione reductase were also found to be activated in TAG-24. CONCLUSION: This genome-wide transcription map, therefore, provides a valuable tool for future transcript profiling under drought stress and enriches the genetic resources available for this important oilseed crop.

Genome-wide identification and expression of monoacylglycerol lipase (MAGL) gene family in peanut (Arachis hypogaea L.) and functional analysis of AhMGATs in neutral lipid metabolism.

Monoacylglycerol lipase (MAGL) involved in regulating plant growth and development and stress responses, hydrolyzes monoacylglycerol (MAG) into free fatty acid and glycerol, which is the last step of triacylglycerol (TAG) breakdown. Here, a genome-wide characterization of MAGL gene family from cultivated peanut (Arachis hypogaea L.) was performed. In total, 24 MAGL genes were identified and unevenly distributed on 14 chromosomes, encoding 229-414 amino acids with molecular weights ranging from 25.91 to 47.01 kDa. Spatiotemporal and stress-induced expression was analyzed by qRT-PCR. Multiple sequence alignment revealed that AhMAGL1a/b and AhMAGL3a/b were the only four bifunctional enzymes with conserved regions of hydrolase and acyltransferase, which could also be named as AhMGATs. GUS histochemical assay showed that AhMAGL1a and -1b were strongly expressed in all tissues of the plants; whereas both AhMAGL3a and -3b were weakly expressed in plants. Subcellular localization analysis indicated that AhMGATs were localized in the endoplasmic reticulum and/or Golgi complex. Seed-specific overexpression of AhMGATs in Arabidopsis decreased the oil content of the seeds and altered the fatty acid compositions, indicating that AhMGATs were involved in TAG breakdown but not TAG biosynthesis in plant seeds. This study lays the foundation for better understanding AhMAGL genes biological function in planta.

Multiplexed Host-Induced Gene Silencing of Aspergillus flavus Genes Confers Aflatoxin Resistance in Groundnut.

Aflatoxins are immunosuppressive and carcinogenic secondary metabolites, produced by the filamentous ascomycete Aspergillus flavus, that are hazardous to animal and human health. In this study, we show that multiplexed host-induced gene silencing (HIGS) of Aspergillus flavus genes essential for fungal sporulation and aflatoxin production (nsdC, veA, aflR, and aflM) confers enhanced resistance to Aspergillus infection and aflatoxin contamination in groundnut (<20 ppb). Comparative proteomic analysis of contrasting groundnut genotypes (WT and near-isogenic HIGS lines) supported a better understanding of the molecular processes underlying the induced resistance and identified several groundnut metabolites that might play a significant role in resistance to Aspergillus infection and aflatoxin contamination. Fungal differentiation and pathogenicity proteins, including calmodulin, transcriptional activator-HacA, kynurenine 3-monooxygenase 2, VeA, VelC, and several aflatoxin pathway biosynthetic enzymes, were downregulated in Aspergillus infecting the HIGS lines. Additionally, in the resistant HIGS lines, a number of host resistance proteins associated with fatty acid metabolism were strongly induced, including phosphatidylinositol phosphate kinase, lysophosphatidic acyltransferase-5, palmitoyl-monogalactosyldiacylglycerol Δ-7 desaturase, ceramide kinase-related protein, sphingolipid Δ-8 desaturase, and phospholipase-D. Combined, this knowledge can be used for groundnut pre-breeding and breeding programs to provide a safe and secure food supply.

Gamma irradiation-induced genetic variability and its effects on the phenotypic and agronomic traits of groundnut (Arachis hypogaeaL.).

In order to increase genetic variability for the improvement of groundnut, two varieties, namely Kp29 and Fleur11, were treated with six different gamma irradiation doses. A significant effect of mutagenesis was distinctly observed in the stem lengths, roots, and survival percentage in both varieties. The radio-sensitivity test showed a mean lethal dose of 436.51Gy for Kp29 and 501.18 Gy for Fleur11. Furthermore, this study revealed putative mutants with variable agro-morphological traits. Seven chlorophyll mutants and various seed shape and color mutants were obtained. This study demonstrates the potency of gamma irradiation to induce high genetic variability that led to the emergence of certain mutations of economic importance.

Genetic mapping of AhVt1, a novel genetic locus that confers the variegated testa color in cultivated peanut (Arachis hypogaea L.) and its utilization for marker-assisted selection.

Introduction: Peanut (Arachis hypogaea L.) is an important cash crop worldwide. Compared with the ordinary peanut with pure pink testa, peanut with variegated testa color has attractive appearance and a higher market value. In addition, the variegated testa represents a distinct regulation pattern of anthocyanin accumulation in integument cells. Methods: In order to identify the genetic locus underlying variegated testa color in peanut, two populations were constructed from the crosses between Fuhua 8 (pure-pink testa) and Wucai (red on white variegated testa), Quanhonghua 1 (pure-red testa) and Wucai, respectively. Genetic analysis and bulked sergeant analysis sequencing were applied to detect and identify the genetic locus for variegated testa color. Marker-assisted selection was used to develop new variegated testa peanut lines. Results: As a result, all the seeds harvested from the F1 individuals of both populations showed the variegated testa type with white trace. Genetic analysis revealed that the pigmentation of colored region in red on white variegated testa was controlled by a previous reported gene AhRt1, while the formation of white region (un-pigmented region) in variegated testa was controlled by another single genetic locus. This locus, named as AhVt1 (Arachis hypogaea Variegated Testa 1), was preliminary mapped on chromosome 08 through bulked sergeant analysis sequencing. Using a secondary mapping population derived from the cross between Fuhua 8 and Wucai, AhVt1 was further mapped to a 1.89-Mb genomic interval by linkage analysis, and several potential genes associated with the uneven distribution of anthocyanin, such as MADS-box, MYB, and Chalcone synthase-like protein, were harbored in the region. Moreover, the molecular markers closely linked to the AhVt1 were developed, and the new variegated testa peanut lines were obtained with the help of marker-assisted selection. Conclusion: Our findings will accelerate the breeding program for developing new peanut varieties with "colorful" testa colors and laid a foundation for map-based cloning of gene responsible for variegated testa.

Reduction in Nitrogen Rate and Improvement of Nitrogen Use Efficiency without Loss of Peanut Yield by Regional Mean Optimal Rate of Chemical Fertilizer Based on a Multi-Site Field Experiment in the North China Plain.

It is important to quantify nutrient requirements and optimize fertilization to improve peanut yield and fertilizer use efficiency. In this study, a multi-site field trial was conducted from 2020 to 2021 in the North China Plain to estimate nitrogen (N), phosphorus (P), and potassium (K) uptake and requirements of peanuts, and to evaluate the effects of fertilization recommendations from the regional mean optimal rate (RMOR) on dry matter, pod yield, nutrient uptake, and fertilizer use efficiency. Results show that compared with farmer practice fertilization (FP), optimal fertilization (OPT) based on the RMOR increased peanut dry matter by 6.6% and pod yield by 10.9%. The average uptake rates of N, P, and K were 214.3, 23.3, and 78.4 kg/ha, respectively, with 76.0% N harvest index, 59.8% P harvest index, and 41.4% K harvest index. The OPT treatment increased N, P, and K uptake by 19.3%, 7.3%, and 11.0% compared with FP, respectively. However, the average of yield, nutrition uptake, and harvest indexes of N, P, and K were not significantly affected by fertilization. The peanut required 42.0 kg N, 4.6 kg P, and 15.3 kg K to produce 1000 kg of pods. The OPT treatment significantly improved the N partial factor productivity and N uptake efficiency but decreased the K partial factor productivity and K uptake efficiency. The present study demonstrates that fertilizer recommendations from RMOR improve N use efficiency, and reduce N and P fertilizer application without yield loss in regions with smallholder farmers, and the corresponding estimation of nutrient requirements helps to make peanut fertilization recommendations.

Fungal identification in peanuts seeds through multispectral images: Technological advances to enhance sanitary quality.

The sanitary quality of seed is essential in agriculture. This is because pathogenic fungi compromise seed physiological quality and prevent the formation of plants in the field, which causes losses to farmers. Multispectral images technologies coupled with machine learning algorithms can optimize the identification of healthy peanut seeds, greatly improving the sanitary quality. The objective was to verify whether multispectral images technologies and artificial intelligence tools are effective for discriminating pathogenic fungi in tropical peanut seeds. For this purpose, dry peanut seeds infected by fungi (A. flavus, A. niger, Penicillium sp., and Rhizopus sp.) were used to acquire images at different wavelengths (365 to 970 nm). Multispectral markers of peanut seed health quality were found. The incubation period of 216 h was the one that most contributed to discriminating healthy seeds from those containing fungi through multispectral images. Texture (Percent Run), color (CIELab L*) and reflectance (490 nm) were highly effective in discriminating the sanitary quality of peanut seeds. Machine learning algorithms (LDA, MLP, RF, and SVM) demonstrated high accuracy in autonomous detection of seed health status (90 to 100%). Thus, multispectral images coupled with machine learning algorithms are effective for screening peanut seeds with superior sanitary quality.

A MYB-related transcription factor from peanut, AhMYB30, improves freezing and salt stress tolerance in transgenic Arabidopsis through both DREB/CBF and ABA-signaling pathways.

Abiotic stresses such as salinity and low temperature have serious impact on peanut growth and yield. The present work investigated the function of a MYB-related transcription factor gene AhMYB30 obtained from peanut under salt and low temperature stresses by transgenic methods. The results indicated that the overexpression of AhMYB30 in Arabidopsis could enhance the resistance of transgenic plants to freezing and salt stresses. The expression of stress-response genes RD29A (Response-to-Dehydration 29A), COR15A (Cold-Regulated 15A), KIN1 (Kinesin 1) and ABI2 (Abscisic acid Insensitive 2) increased in transgenic plants compared with in wild-type. Subcellular localization and transcriptional autoactivation validation demonstrated that AhMYB30 has essential features of transcription factors. Therefore, AhMYB30 may increase salt and freezing stress tolerance as the transcription factor (TF) in Arabidopsis through both DREB/CBF and ABA-signaling pathways. Our results lay the theoretical foundation for exploring stress resistance mechanisms of peanut and offering novel genetic resources for molecular breeding.

Bacillus lipopeptide-mediated biocontrol of peanut stem rot caused by Athelia rolfsii.

Introduction: Peanut (Arachis hypogaea L.) is a widespread oilseed crop of high agricultural importance in tropical and subtropical areas. It plays a major role in the food supply in the Democratic Republic of Congo (DRC). However, one major constraint in the production of this plant is the stem rot (white mold or southern blight) disease caused by Athelia rolfsii which is so far controlled mainly using chemicals. Considering the harmful effect of chemical pesticides, the implementation of eco-friendly alternatives such as biological control is required for disease management in a more sustainable agriculture in the DRC as in the other developing countries concerned. Bacillus velezensis is among the rhizobacteria best described for its plant protective effect notably due to the production of a wide range of bioactive secondary metabolites. In this work, we wanted to evaluate the potential of B. velezensis strain GA1 at reducing A. rolfsii infection and to unravel the molecular basis of the protective effect. Results and discussion: Upon growth under the nutritional conditions dictated by peanut root exudation, the bacterium efficiently produces the three types of lipopeptides surfactin, iturin and fengycin known for their antagonistic activities against a wide range of fungal phytopathogens. By testing a range of GA1 mutants specifically repressed in the production of those metabolites, we point out an important role for iturin and another unidentified compound in the antagonistic activity against the pathogen. Biocontrol experiments performed in greenhouse further revealed the efficacy of B. velezensis to reduce peanut disease caused by A. rolfsii both via direct antagonism against the fungus and by stimulating systemic resistance in the host plant. As treatment with pure surfactin yielded a similar level of protection, we postulate that this lipopeptide acts as main elicitor of peanut resistance against A. rolfsii infection.

Comparative Transcriptomic Analysis Reveals the Negative Response Mechanism of Peanut Root Morphology and Nitrate Assimilation to Nitrogen Deficiency.

Root architecture plays a fundamental role in crop yield, which is sensitive to nitrogen fertilizer. Although it is well studied that nitrogen fertilizer significantly promotes peanut (Arachis hypogaea L.) growth and yield, less information was available on how its root development responds to nitrogen deficiency. In this study, the growth and development of roots were inhibited, as indicated by the significantly decreased root dry weight and length and the lateral root number, especially under 10 days of nitrogen deficiency treatment. The activities and the expression of the genes related to nitrogen assimilation enzymes including nitrate reductase, glutamine synthetase, glutamate dehydrogenase, and glutamine oxoglutarate aminotransferase and the genes encoding the nitrate transporters were significantly decreased under 10 days of nitrogen deficiency treatment, which may lead to a decrease in nitrate content, as indicated by the significantly decreased nitrogen balance index. Transcriptome sequencing revealed a total of 293 (119 up- and 174 downregulated) and 2271 (1165 up- and 1106 downregulated) differentially expressed genes (DEGs) identified after five and ten days of nitrogen deficiency treatments, respectively. Bioinformatic analysis showed that these DEGs were mainly involved in nitrate transportation and assimilation, phytohormone signal transduction, and the lignin biosynthesis pathway. Furthermore, a putative schematic diagram of nitrogen deficiency inhibiting root growth was established, which gives us a better understanding of nitrogen metabolism in peanut roots and a theoretical basis for improving nitrogen use efficiency.