Inter-species interaction of bradyrhizobia affects their colonization and plant growth promotion in Arachis hypogaea.

Bradyrhizobia are the principal symbiotic partner of the leguminous plant and take active part in biological nitrogen-fixation. The present investigation explores the underlying competition among different strains during colonization in host roots. Six distinct GFP and RFP-tagged Bradyrhizobium strains were engineered to track them inside the peanut roots either independently or in combination. The Bradyrhizobium strains require different time-spans ranging from 4 to 21 days post-infection (dpi) for successful colonization which further varies in presence of another strain. While most of the individual strains enhanced the shoot and root dry weight, number of nodules, and nitrogen fixation capabilities of the host plants, no significant enhancement of plant growth and nodulation efficiency was observed when they were allowed to colonize in combinations. However, if among the combinations one strains is SEMIA 6144, the co-infection results in higher growth and nodulation efficiency of the hosts. From the competition experiments it has been found that Bradyrhizobium japonicum SEMIA 6144 was found to be the most dominant strain for effective nodulation in peanut. The extent of biofilm and exopolysaccharide (EPS) production by these isolates, individually or in combinations, were envisaged to correlate whether these parameters have any impact on the symbiotic association. But the extent of colonization, growth-promotion and nitrogen-fixation ability drastically lowered when a strain present together with other Bradyrhizobium strain. Therefore, it is imperative to understand the interaction between two co-inoculating Bradyrhizobium species for nodulation followed by plant growth promotion to develop suitable consortia for enhancing BNF in peanut and possibly for other legumes.

Validation and identification of promising gene specific markers governing foliar disease resistance in groundnut (Arachis hypogaea L.).

BACKGROUND: Groundnut is vulnerable to the major foliar fungal disease viz., late leaf spot (LLS) and rust in kharif season, which results in severe yield losses. Until now, LLS and rust resistance linked markers were developed based on GPBD 4 as a major donor source and were validated in its derivatives only, which restricted their use in marker assisted selection (MAS) involving other donors. METHODS AND RESULTS: The current study focused to validate LLS and rust resistance linked markers employing advanced breeding lines of F6 generation, derived from nine different crosses involving nine diverse parents, to identify potential markers for marker-assisted breeding of LLS and rust resistance in groundnut. Out of 28-trait linked markers used for validation, 8 were polymorphic (28.57%). Marker-trait association (MTA) and Single Marker Analysis (SMA) revealed that the SSR marker pPGPseq5D05 is significantly associated with both LLS (15.8% PVE) and rust (17.5% PVE) resistance, whereas, the marker IPAHM103 is tightly linked with rust resistance (26.8% PVE) alone. In silico analysis revealed that the marker gene for IPAHM103 is a zinc finger protein and the marker gene for pPGPseq5D05 is an ADP-ribosylation factor GTPase-activating protein. Both these protein products impart resistance or tolerance to biotic stress in crop plants. Two other markers namely, GMLQ975 and pPGPseq13A10 were also found to be associated with LLS resistance explaining MTA up to 60%. CONCLUSION: These gene specific markers will enable us to screen more number of germplasm lines or newly developed lines in MAS schemes for LLS and rust resistance using a wide range of resistant sources.

Metagenomic evaluation of peanut rhizosphere microbiome from the farms of Saurashtra regions of Gujarat, India.

The narrow zone of soil around the plant roots with maximum microbial activity termed as rhizosphere. Rhizospheric bacteria promote the plant growth directly or indirectly by providing the nutrients and producing antimicrobial compounds. In this study, the rhizospheric microbiota of peanut plants was characterized from different farms using an Illumina-based partial 16S rRNA gene sequencing to evaluate microbial diversity and identify the core microbiome through culture-independent (CI) approach. Further, all rhizospheric bacteria that could grow on various nutrient media were identified, and the diversity of those microbes through culture-dependent method (CD) was then directly compared with their CI counterparts. The microbial population profiles showed a significant correlation with organic carbon and concentration of phosphate, manganese, and potassium in the rhizospheric soil. Genera like Sphingomicrobium, Actinoplanes, Aureimonas _A, Chryseobacterium, members from Sphingomonadaceae, Burkholderiaceae, Pseudomonadaceae, Enterobacteriaceae family, and Bacilli class were found in the core microbiome of peanut plants. As expected, the current study demonstrated more bacterial diversity in the CI method. However, a higher number of sequence variants were exclusively present in the CD approach compared to the number of sequence variants shared between both approaches. These CD-exclusive variants belonged to organisms that are more typically found in soil. Overall, this study portrayed the changes in the rhizospheric microbiota of peanuts in different rhizospheric soil and environmental conditions and gave an idea about core microbiome of peanut plant and comparative bacterial diversity identified through both approaches.

Non-destructive SPE-UPLC-based Quantification of Aflatoxins and Stilbenoid Phytoalexins in Single Peanut (Arachis spp.) Seeds.

Aflatoxins are highly carcinogenic secondary metabolites of some fungal species, particularly Aspergillus flavus. Aflatoxins often contaminate economically important agricultural commodities, including peanuts, posing a high risk to human and animal health. Due to the narrow genetic base, peanut cultivars demonstrate limited resistance to fungal pathogens. Therefore, numerous wild peanut species with tolerance to Aspergillus have received substantial consideration by scientists as sources of disease resistance. Exploring plant germplasm for resistance to aflatoxins is difficult since aflatoxin accumulation does not follow a normal distribution, which dictates the need for the analyses of thousands of single peanut seeds. Sufficiently hydrated peanut (Arachis spp.) seeds, when infected by Aspergillus species, are capable of producing biologically active stilbenes (stilbenoids) that are considered defensive phytoalexins. Peanut stilbenes inhibit fungal development and aflatoxin production. Therefore, it is crucial to analyze the same seeds for peanut stilbenoids to explain the nature of seed resistance/susceptibility to the Aspergillus invasion. None of the published methods offer single-seed analyses for aflatoxins and/or stilbene phytoalexins. We attempted to fulfill the demand for such a method that is environment-friendly, uses inexpensive consumables, and is sensitive and selective. In addition, the method is non-destructive since it uses only half of the seed and leaves the other half containing the embryonic axis intact. Such a technique allows germination and growth of the peanut plant to full maturity from the same seed used for the aflatoxin and stilbenoid analysis. The integrated part of this method, the manual challenging of the seeds with Aspergillus, is a limiting step that requires more time and labor compared to other steps in the method. The method has been used for the exploration of wild Arachis germplasm to identify species resistant to Aspergillus and to determine and characterize novel sources of genetic resistance to this fungal pathogen.

Osmolyte-producing microbial biostimulants regulate the growth of Arachis hypogaea L. under drought stress.

Globally, drought stress poses a significant threat to crop productivity. Improving the drought tolerance of crops with microbial biostimulants is a sustainable strategy to meet a growing population's demands. This research aimed to elucidate microbial biostimulants' (Plant Growth Promoting Rhizobacteria) role in alleviating drought stress in oil-seed crops. In total, 15 bacterial isolates were selected for drought tolerance and screened for plant growth-promoting (PGP) attributes like phosphate solubilization and production of indole-3-acetic acid, siderophore, hydrogen cyanide, ammonia, and exopolysaccharide. This research describes two PGPR strains: Acinetobacter calcoaceticus AC06 and Bacillus amyloliquefaciens BA01. The present study demonstrated that these strains (AC06 and BA01) produced abundant osmolytes under osmotic stress, including proline (2.21 and 1.75 µg ml- 1), salicylic acid (18.59 and 14.21 µg ml- 1), trehalose (28.35 and 22.74 µg mg- 1 FW) and glycine betaine (11.35 and 7.74 mg g- 1) respectively. AC06 and BA01 strains were further evaluated for their multifunctional performance by inoculating in Arachis hypogaea L. (Groundnut) under mild and severe drought regimes (60 and 40% Field Capacity). Inoculation with microbial biostimulants displayed distinct osmotic-adjustment abilities of the groundnut, such as growth parameters, plant biomass, photosynthetic pigments, relative water content, proline, and soluble sugar in respective to control during drought. On the other hand, plant sensitivity indexes such as electrolyte leakage and malondialdehyde (MDA) contents were decreased as well as cooperatively conferred plant drought tolerance by induced alterations in stress indicators such as catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD). Thus, Acinetobacter sp. AC06 and Bacillus sp. BA01 can be considered as osmolyte producing microbial biostimulants to simultaneously induce osmotic tolerance and metabolic changes in groundnuts under drought stress.

Mitigating microplastic stress on peanuts: The role of biochar-based synthetic community in the preservation of soil physicochemical properties and microbial diversity.

Tire-derived rubber crumbs (RC), as a new type of microplastics (MPs), harms both the environment and human health. Excessive use of plastic, the decomposition of which generates microplastic particles, in current agricultural practices poses a significant threat to the sustainability of agricultural ecosystems, worldwide food security and human health. In this study, the application of biochar, a carbon-rich material, to soil was explored, especially in the evaluation of synthetic biochar-based community (SynCom) to alleviate RC-MP-induced stress on plant growth and soil physicochemical properties and soil microbial communities in peanuts. The results revealed that RC-MPs significantly reduced peanut shoot dry weight, root vigor, nodule quantity, plant enzyme activity, soil urease and dehydrogenase activity, as well as soil available potassium, and bacterial abundance. Moreover, the study led to the identification highly effective plant growth-promoting rhizobacteria (PGPR) from the peanut rhizosphere, which were then integrated into a SynCom and immobilized within biochar. Application of biochar-based SynCom in RC-MPs contaminated soil significantly increased peanut biomass, root vigor, nodule number, and antioxidant enzyme activity, alongside enhancing soil enzyme activity and rhizosphere bacterial abundance. Interestingly, under high-dose RC-MPs treatment, the relative abundance of rhizosphere bacteria decreased significantly, but their diversity increased significantly and exhibited distinct clustering phenomenon. In summary, the investigated biochar-based SynCom proved to be a potential soil amendment to mitigate the deleterious effects of RC-MPs on peanuts and preserve soil microbial functionality. This presents a promising solution to the challenges posed by contaminated soil, offering new avenues for remediation.

Depletion of protective microbiota promotes the incidence of fruit disease.

Plant-associated microbiomes play important roles in plant health and productivity. However, despite fruits being directly linked to plant productivity, little is known about the microbiomes of fruits and their potential association with fruit health. Here, by integrating 16S rRNA gene, ITS high-throughput sequencing data, and microbiological culturable approaches, we reported that roots and fruits (pods) of peanut, a typical plant that bears fruits underground, recruit different bacterial and fungal communities independently of cropping conditions and that the incidence of pod disease under monocropping conditions is attributed to the depletion of Bacillus genus and enrichment of Aspergillus genus in geocarposphere. On this basis, we constructed a synthetic community (SynCom) consisting of three Bacillus strains from geocarposphere soil under rotation conditions with high culturable abundance. Comparative transcriptome, microbiome profiling, and plant phytohormone signaling analysis reveal that the SynCom exhibited more effective Aspergillus growth inhibition and pod disease control than individual strain, which was underpinned by a combination of molecular mechanisms related to fungal cell proliferation interference, mycotoxins biosynthesis impairment, and jasmonic acid-mediated plant immunity activation. Overall, our results reveal the filter effect of plant organs on the microbiome and that depletion of key protective microbial community promotes the fruit disease incidence.

Azole resistance mechanisms and population structure of the human pathogen Aspergillus fumigatus on retail plant products.

Aspergillus fumigatus is a ubiquitous saprotroph and human-pathogenic fungus that is life-threatening to the immunocompromised. Triazole-resistant A. fumigatus was found in patients without prior treatment with azoles, leading researchers to conclude that resistance had developed in agricultural environments where azoles are used against plant pathogens. Previous studies have documented azole-resistant A. fumigatus across agricultural environments, but few have looked at retail plant products. Our objectives were to determine if azole-resistant A. fumigatus is prevalent in retail plant products produced in the United States (U.S.), as well as to identify the resistance mechanism(s) and population genetic structure of these isolates. Five hundred twenty-five isolates were collected from retail plant products and screened for azole resistance. Twenty-four isolates collected from compost, soil, flower bulbs, and raw peanuts were pan-azole resistant. These isolates had the TR34/L98H, TR46/Y121F/T289A, G448S, and H147Y cyp51A alleles, all known to underly pan-azole resistance, as well as WT alleles, suggesting that non-cyp51A mechanisms contribute to pan-azole resistance in these isolates. Minimum spanning networks showed two lineages containing isolates with TR alleles or the F46Y/M172V/E427K allele, and discriminant analysis of principle components identified three primary clusters. This is consistent with previous studies detecting three clades of A. fumigatus and identifying pan-azole-resistant isolates with TR alleles in a single clade. We found pan-azole resistance in U.S. retail plant products, particularly compost and flower bulbs, which indicates a risk of exposure to these products for susceptible populations and that highly resistant isolates are likely distributed worldwide on these products.IMPORTANCEAspergillus fumigatus has recently been designated as a critical fungal pathogen by the World Health Organization. It is most deadly to people with compromised immune systems, and with the emergence of antifungal resistance to multiple azole drugs, this disease carries a nearly 100% fatality rate without treatment or if isolates are resistant to the drugs used to treat the disease. It is important to determine the relatedness and origins of resistant A. fumigatus isolates in the environment, including plant-based retail products, so that factors promoting the development and propagation of resistant isolates can be identified.

Anti-mildew and fresh-keeping effect of Lactiplantibacillus paraplantarum P3 cell-free supernatant on fresh in-shell peanuts during storage process.

Lactiplantibacillus paraplantarum P3 (L. paraplantarum P3) cell-free supernatant (CFS) with good antifungal effect was sprayed on fresh in-shell peanuts stored at 5 °C and 30 °C to explore its effect on the microorganisms and quality of fresh in-shell peanuts during storage process. Results showed that L. paraplantarum P3 CFS effectively maintained good quality of fresh in-shell peanuts by not only reducing fungi amount and the mildew rate, but also improving the morphology, color and flavor. Besides, L. paraplantarum P3 CFS activated plant mitogen-activated protein kinase signaling pathway and plant hormone signaling pathway to produce more ethylene, gibberellin regulatory proteins and other substances to enhance plant resistance to pathogenic microorganisms. L. paraplantarum P3 CFS could also induce the biosynthesis of glycerophospholipid and arginine to increase the stress resistance of fresh peanuts. This study provides research data for the application of L. paraplantarum P3 CFS in the preservation and antimildew of fresh in-shell peanuts.

A facile dual-mode SERS/fluorescence aptasensor for AFB1 detection based on gold nanoparticles and magnetic nanoparticles.

Aflatoxin B1 (AFB1) is a virulent metabolite secreted by Aspergillus fungi, impacting crop quality and posing health risks to human. Herein, a dual-mode Raman/fluorescence aptasensor was constructed to detect AFB1. The aptasensor was assembled by gold nanoparticles (AuNPs) and magnetic nanoparticles (MNPs), while the surface-enhanced Raman scattering (SERS) and fluorescence resonance energy transfer (FRET) effects were both realized. AuNPs were modified with the Raman signal molecule 4-MBA and the complementary chain of AFB1 aptamer (cDNA). MNPs were modified with the fluorescence signal molecule Cy5 and the AFB1 aptamer (AFB1 apt). Through base pairing, AuNPs aggregated on the surface of MNPs, forming a satellite-like nanocomposite, boosting SERS signal via increased "hot spots" but reducing fluorescence signal due to the proximity of AuNPs to Cy5. Upon exposure to AFB1, AFB1 apt specifically bound to AFB1, causing AuNPs detachment from MNPs, weakening the SERS signal while restoring the fluorescence signal. AFB1 concentration displayed a good linear relationship with SERS/fluorescence signal in the range of 0.01 ng/mL-100 ng/mL, with a detection limit as low as 5.81 pg/mL. The use of aptamer assured the high selectivity toward AFB1. Furthermore, the spiked recovery in peanut samples ranged from 91.4 % to 95.6 %, indicating the applicability of real sample detection. Compared to single-signal sensor, this dual-signal sensor exhibited enhanced accuracy, robust anti-interference capability, and increased flexibility, promising for toxin detection in food safety applications.

Efficacy of atoxigenic Aspergillus flavus from southern China as biocontrol agents against aflatoxin contamination in corn and peanuts.

Aspergillus flavus is a ubiquitous facultative pathogen that routinely infects important crops leading to formation of aflatoxins during crop development and after harvest. Corn and peanuts in warm and/or drought-prone regions are highly susceptible to aflatoxin contamination. Controlling aflatoxin using atoxigenic A. flavus is a widely adopted strategy. However, no A. flavus genotypes are currently approved for use in China. The current study aimed to select atoxigenic A. flavus endemic to Guangxi Zhuang Autonomous Region with potential as active ingredients of aflatoxin biocontrol products. A total of 204 A. flavus isolates from corn, peanuts, and field soil were evaluated for ability to produce the targeted mycotoxins. Overall, 57.3% could not produce aflatoxins while 17.15% were incapable of producing both aflatoxins and CPA. Atoxigenic germplasm endemic to Guangxi was highly diverse, yielding 8 different gene deletion patterns in the aflatoxin and CPA biosynthesis gene clusters ranging from no deletion to deletion of both clusters. Inoculation of corn and peanuts with both an aflatoxin producer and selected atoxigenic genotypes showed significant reduction (74 to 99%) in aflatoxin B1 (AFB1) formation compared with inoculation with the aflatoxin producer alone. Atoxigenic genotypes also efficiently degraded AFB1 (61%). Furthermore, atoxigenic isolates were also highly efficient at reducing aflatoxin concentrations even when present at lower concentrations than aflatoxin producers. The use of multiple atoxigenics was not always as effective as the use of a single atoxigenic. Effective atoxigenic genotypes of A. flavus with known mechanisms of atoxigenicity are demonstrated to be endemic to Southern China. These A. flavus may be utilized as active ingredients of biocontrol products without concern for detrimental impacts that may result from introduction of exotic fungi. Field efficacy trials in the agroecosystems of Southern China are needed to determine the extent to which such products may allow the production of safer food and feed.

Peanut supplementation affects compositions and functions of gut microbiome in Ugandan children.

Childhood malnutrition remains a serious global health concern, particularly in low-income nations like Uganda. This study investigated the impact of peanut supplementation on the compositions and functions of gut microbiome with nutritional improvement. School children aged 6-9 years from four rural communities were recruited, with half receiving roasted peanut snacks while the other half served as controls. Fecal samples were collected at the baseline (day 0), day 60, and day 90. Microbial DNA was extracted, and 16S rRNA sequencing was performed, followed by the measurement of SCFA concentration in fecal samples using UHPLC. Alpha and beta diversity analyses revealed significant differences between the control and supplemented groups after 90 days of supplementation. Leuconostoc lactis, Lactococcus lactis, Lactococcus garvieae, Eubacterium ventriosum, and Bacteroides thetaiotaomicron, associated with the production of beneficial metabolites, increased significantly in the supplemented group. Acetic acid concentration also increased significantly. Notably, pathogenic bacteria, including Clostridium perfringens and Leuconostoc mesenteroides, were decreased in the supplemented group. The study indicates the potential of peanut supplementation to modulate the gut metabolome, enrich beneficial bacteria, and inhibit pathogens, suggesting a novel approach to mitigating child malnutrition and improving health status.

Functional Characterization of Core and Unique Calcite-Dissolving Bacteria Communities from Peanut Fields.

Calcium deficiency is a leading cause of reduced peanut (Arachis hypogaea) seed quality and has been linked to increased disease susceptibility, specifically to soilborne fungal pathogens. Sufficient calcium at flowering time is critical to ensure proper pod development. Calcite-dissolving bacteria (CDB) isolated from farming fields can dissolve calcite (CaCO3) on plates and increase soluble calcium levels in soil. However, the phylogenetic diversity and geographic distribution of CDB is unclear. Here, we surveyed soil samples from 15 peanut-producing fields in three regions in southern Georgia, representing distinct soil compositions. We isolated CDB through differentiating media and identified 52 CDB strains. CDB abundance was not associated with any of the soil characteristics we evaluated. Three core genera, represented by 43 strains, were found in all three regions. Paenibacillus was the most common CDB found in all regions, making up 30 of the 52 identified strains. Six genera, represented by eight strains, are unique to one region. Members of the core and unique communities showed comparable solubilization indexes on plates. We conclude that a diversified phylogenetic population of CDB is present in Georgia peanut fields. Despite the phylogenetic diversity, as a population, they exhibit comparable functions in solubilizing calcite on plates.

Transcriptome sequencing and expression analysis in peanut reveal the potential mechanism response to Ralstonia solanacearum infection.

BACKGROUND: Bacterial wilt caused by Ralstonia solanacearum severely affects peanut (Arachis hypogaea L.) yields. The breeding of resistant cultivars is an efficient means of controlling plant diseases. Therefore, identification of resistance genes effective against bacterial wilt is a matter of urgency. The lack of a reference genome for a resistant genotype severely hinders the process of identification of resistance genes in peanut. In addition, limited information is available on disease resistance-related pathways in peanut. RESULTS: Full-length transcriptome data were used to generate wilt-resistant and -susceptible transcript pools. In total, 253,869 transcripts were retained to form a reference transcriptome for RNA-sequencing data analysis. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis of differentially expressed genes revealed the plant-pathogen interaction pathway to be the main resistance-related pathway for peanut to prevent bacterial invasion and calcium plays an important role in this pathway. Glutathione metabolism was enriched in wilt-susceptible genotypes, which would promote glutathione synthesis in the early stages of pathogen invasion. Based on our previous quantitative trait locus (QTL) mapping results, the genes arahy.V6I7WA and arahy.MXY2PU, which encode nucleotide-binding site-leucine-rich repeat receptor proteins, were indicated to be associated with resistance to bacterial wilt. CONCLUSIONS: This study identified several pathways associated with resistance to bacterial wilt and identified candidate genes for bacterial wilt resistance in a major QTL region. These findings lay a foundation for investigation of the mechanism of resistance to bacterial wilt in peanut.

Seed-borne bacterial synthetic community resists seed pathogenic fungi and promotes plant growth.

AIMS: In this study, the control effects of synthetic microbial communities composed of peanut seed bacteria against seed aflatoxin contamination caused by Aspergillus flavus and root rot by Fusarium oxysporum were evaluated. METHODS AND RESULTS: Potentially conserved microbial synthetic communities (C), growth-promoting synthetic communities (S), and combined synthetic communities (CS) of peanut seeds were constructed after 16S rRNA Illumina sequencing, strain isolation, and measurement of plant growth promotion indicators. Three synthetic communities showed resistance to root rot and CS had the best effect after inoculating into peanut seedlings. This was achieved by increased defense enzyme activity and activated salicylic acid (SA)-related, systematically induced resistance in peanuts. In addition, CS also inhibited the reproduction of A. flavus on peanut seeds and the production of aflatoxin. These effects are related to bacterial degradation of toxins and destruction of mycelia. CONCLUSIONS: Inoculation with a synthetic community composed of seed bacteria can help host peanuts resist the invasion of seeds by A. flavus and seedlings by F. oxysporum and promote the growth of peanut seedlings.

Peanut-based intercropping systems altered soil bacterial communities, potential functions, and crop yield.

Intercropping is an efficient land use and sustainable agricultural practice widely adopted worldwide. However, how intercropping influences the structure and function of soil bacterial communities is not fully understood. Here, the effects of five cropping systems (sole sorghum, sole millet, sole peanut, sorghum/peanut intercropping, and millet/peanut intercropping) on soil bacterial community structure and function were investigated using Illumina MiSeq sequencing. The results showed that integrating peanut into intercropping systems increased soil available nitrogen (AN) and total nitrogen (TN) content. The alpha diversity index, including Shannon and Chao1 indices, did not differ between the five cropping systems. Non-metric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM) illustrated a distinct separation in soil microbial communities among five cropping systems. Bacterial phyla, including Actinobacteria, Proteobacteria, Acidobacteria, and Chloroflexi, were dominant across all cropping systems. Sorghum/peanut intercropping enhanced the relative abundance of phyla Actinobacteriota and Chloroflexi compared to the corresponding monocultures. Millet/peanut intercropping increased the relative abundance of Proteobacteria, Acidobacteriota, and Nitrospirota. The redundancy analysis (RDA) indicated that bacterial community structures were primarily shaped by soil organic carbon (SOC). The land equivalent ratio (LER) values for the two intercropping systems were all greater than one. Partial least squares path modeling analysis (PLS-PM) showed that soil bacterial community had a direct effect on yield and indirectly affected yield by altering soil properties. Our findings demonstrated that different intercropping systems formed different bacterial community structures despite sharing the same climate, reflecting changes in soil ecosystems caused by interspecific interactions. These results will provide a theoretical basis for understanding the microbial communities of peanut-based intercropping and guide agricultural practice.

Use of image analysis to assess radial growth of Passalora arachidicola and Nothopassalora personata on solid media.

Despite significant research on early and late leaf spot diseases of peanut, in vitro study of the respective causal agents, Passalora arachidicola and Nothopassalora personata, has been limited due to cultural challenges that make growth of these fungi difficult to quantify with traditional methods. Studies were conducted to evaluate the practicality of image analysis to assess radial growth and tissue volume by correlating these assessments to dry mass. Image analysis was also used to estimate radial growth rates for these fungi over time. Tissue area and volume were significantly correlated to dry mass for P. arachidicola in two separate experiments, and for N. personata when medium had been removed from tissues prior to dry mass assessments. Tissue area densities were the same for P. arachidicola and Pseudocercospora smilacicola, evaluated as a nonstromatal cercosporoid comparison, whereas tissue volume densities were greater for P. archidicola and N. personata than P. smilacicola. A quadratic relationship was observed between radial growth and incubation time for all isolates evaluated. Growth rates of P. arachidicola isolates were 2 to 4 times faster than N. personata during the first week of incubation and slowed over time. Growth rates of NP18R, a phenotype variant of N. personata, increased after neighboring colonies met and was nearly 2.5 times faster than the fastest rates observed for P. arachidicola. These experiments demonstrate that when fungal tissues are observable, image analysis is a useful assessment tool for P. arachidicola and N. personata. Care should be taken to monitor fungal phenotypic changes in these species because phenotype degeneration can affect growth rates.

Measuring the Distance and Effects of Weather Conditions on the Dispersal of Nothopassalora personata.

Nothopassalora personata is one of the most economically severe pathogens of peanut in the United States. The fungus primarily relies on wind and rain for dispersal, which has been documented up to 10 m from an inoculum source. Spore traps have been used in a wide variety of pathosystems to study epidemiology, document detection, develop alert systems, and guide management programs. The objective of this study was to use spore traps and N. personata-specific qPCR primers to quantitatively evaluate dispersal of N. personata conidia at distances up to 70 m from an infected peanut field and to examine relationships between quantities captured and weather variables. Impaction spore samplers were placed at 4, 10, 30, 50, and 70 m from peanut fields at the Edisto Research and Education Center (six fields) and commercial peanut fields in Barnwell and Bamberg counties (one field each) from 2020 to 2022. Following initial detection, samples were collected at a 48-, 48-, 72-h interval until harvest. N. personata conidia were detected at all locations and distances, documenting dispersal up to 70 m from an inoculum source. This result is a reminder that volunteer management is crucial when rotating peanut in nearby fields. A model for predicting log spore quantities was developed using temperature and humidity variables. Temperature variables associated with observed sampling periods had a negative correlation with N. personata quantities, whereas parameters of relative humidity and mean windspeed were positively correlated.

Sensor-Based Quantification of Peanut Disease Defoliation Using an Unmanned Aircraft System and Multispectral Imagery.

Early leaf spot (Passalora arachidicola) and late leaf spot (Nothopassalora personata) are two of the most economically important foliar fungal diseases of peanut, often requiring seven to eight fungicide applications to protect against defoliation and yield loss. Rust (Puccinia arachidis) may also cause significant defoliation depending on season and location. Sensor technologies are increasingly being utilized to objectively monitor plant disease epidemics for research and supporting integrated management decisions. This study aimed to develop an algorithm to quantify peanut disease defoliation using multispectral imagery captured by an unmanned aircraft system. The algorithm combined the Green Normalized Difference Vegetation Index and the Modified Soil-Adjusted Vegetation Index and included calibration to site-specific peak canopy growth. Beta regression was used to train a model for percent net defoliation with observed visual estimations of the variety 'GA-06G' (0 to 95%) as the target and imagery as the predictor (train: pseudo-R2 = 0.71, test k-fold cross-validation: R2 = 0.84 and RMSE = 4.0%). The model performed well on new data from two field trials not included in model training that compared 25 (R2 = 0.79, RMSE = 3.7%) and seven (R2 = 0.87, RMSE = 9.4%) fungicide programs. This objective method of assessing mid-to-late season disease severity can be used to assist growers with harvest decisions and researchers with reproducible assessment of field experiments. This model will be integrated into future work with proximal ground sensors for pathogen identification and early season disease detection.[Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Short-term continuous monocropping reduces peanut yield mainly via altering soil enzyme activity and fungal community.

Continuous monocropping can lead to soil sickness and increase of soil-borne disease, which finally reduces crop yield. Microorganisms benefit plants by increasing nutrient availability, participating in auxin synthesis, and defending against pathogens. However, little is known about the influence of short-term successive peanuts cropping on soil properties, enzyme activities, its yield, plant-associated microbes, and their potential correlations in peanut production. Here, we examined the community structure, composition, network structure and function of microbes in the rhizosphere and bulk soils under different monocropping years. Moreover, we assessed the impact of changes in the soil micro-environment and associated soil microbes on peanut yield. Our results showed that increase of monocropping year significantly decreased most soil properties, enzyme activities and peanut yield (p < 0.05). Principal co-ordinates analysis (PCoA) and analysis of similarities (ANOSIM) indicated that monocropping year significantly influenced the fungal community structure in the rhizosphere and bulk soils (p < 0.01), while had no effect on the bacterial community. With the increase of continuous monocropping year, peanut selectively decreased (e.g., Candidatus_Entotheonella, Bacillus and Bryobacter) or increased (e.g., Nitrospira, Nocardioides, Ensifer, Gaiella, and Novosphingobium) the abundance of some beneficial bacterial genera in the rhizosphere. Continuous monocropping significantly increased the abundance of plant pathogens (e.g., Plectosphaerella, Colletotrichum, Lectera, Gibberella, Metarhizium, and Microdochium) in the rhizosphere and negatively affected the balance of fungal community. Besides, these species were correlated negatively with L-leucine aminopeptidase (LAP) activity. Network co-occurrence analysis showed that continuous monocropping simplified the interaction network of bacteria and fungi. Random forest and partial least squares path modeling (PLS-PM) analysis further showed that fungal community, pathogen abundance, soil pH, and LAP activity negatively affected peanut yield. In conclusion, short-term continuous monocropping decreased LAP activity and increased potential fungal pathogens abundance, leading to reduction of peanut yield.