Groundnut Roots Research Articles

Prevalence of groundnut root rot and antifungal potential of wild mushroom extracts against Macrophomina phaseolina

Macrophomina phaseolina is an important pathogen threatening groundnut production, with climate change-induced variations in temperature and precipitation resulting in considerable yield reductions. This research provides a comprehensive evaluation of the root rot prevalence and severity in the primary groundnut-cultivating areas of Tamil Nadu. Findings indicate an incidence range of 32.71% to 85.66%. Pathogenic variability testing identified GMP-3 as the most virulent strain. Morphological differences and sporulation patterns were observed and M. phaseolina isolates were confirmed through ITS 1 and ITS 4-sequencing, yielding Polymerase chain reaction amplicons of approximately 560 bp, which were submitted to Gene Bank. Additionally, a survey was conducted to collect various wild mushroom species from different regions in Tamil Nadu. Phenotypic and morphological characterization and molecular confirmation of the mushroom isolates were performed. The efficacy of these isolates against M. phaseolina was evaluated. The Tricholoma equestre (AWM-4) isolate demonstrated the highest inhibition in dual culture assays at 74.33%. Mushroom extracts prepared using various polar and nonpolar solvents were tested using the poisoned food technique to assess the inhibition percentage of M. phaseolina mycelial growth. Methanol extracts exhibited the greatest reduction in mycelial growth, with an inhibition rate of 75.56%. Gas Chromatography-Mass Spectrometry (GC-MS) analysis was performed to identify the compounds with active antifungal properties.

Assessing the Effects of Integrated Nutrient Management on Groundnut Root Growth and Post-Harvest Soil Properties in Brown Forest Soil of South Odisha

The globe faces food security difficulties because of population increase and resource degradation, both worsened by climate change. Applying chemical fertilizer along with cereal-based cropping systems degrades soil health with respect to physical, chemical, and biological properties, which also results in low crop land productivity. However, adopting legume-based cropping systems with integrated nutrient management provides an appropriate way to reach Sustainable Development Goals (SDGs). Hence, a field trial was conducted on groundnut in 2018 and 2019 at the Post Graduate Research Farm, M.S. Swaminathan School of Agriculture, Paralakhemundi, Odisha, India. The experiment was laid out in a Factorial Randomized Block Design (FRBD) with two factors as seed inoculation (solid carrier-based Rhizobium (SR) and liquid carrier-based Rhizobium (LR)) and nutrient management (N1: 100% N (fertilizer), N2: 75%N (fertilizer) + 25% N (FYM), N3: 50%N (fertilizer) + 50% N (FYM), N4: 25% N (fertilizer) + 75% N (FYM) and N5: 100% N (through farmyard manure, FYM) in ten treatment combinations and replicated thrice. The result revealed that seed inoculation with SR and LR showed an almost similar trend in root length, dry weight and nodule, post-harvest soil pH, organic carbon and Rhizobium population in the soil in both years, which remained statistically at par. However, SR showed the highest value for root growth. Among nutrient management, 100% N (through inorganic fertilizer) recorded the highest root length (11.72, 19.75 and 23.9 cm) and dry weight (0.394, 1.075 and 1.141 cm) at 30, 60 and 90 days after sowing (DAS) respectively. Further, in the pooled data, the interaction effect of seed inoculation and nutrient management significantly impacted both root length and root dry weight. The nutrient management treatment and interaction effect of both factors, seed inoculation and nutrient management, significantly influenced soil organic carbon % and Rhizobium population. The highest and equal value of organic carbon in the soil (0.46%) was recorded from NM3, NM4 and NM5 and the highest Rhizobium population (64.5 x 106 CFU g-1 soil) from 100% N (FYM). The results concluded that integrated nutrient management positively impacted groundnut root growth and post-harvest soil properties. The results concluded that integrated nutrient management positively impacted groundnut root growth and post-harvest soil properties. Integration of Rhizobium as seed inoculation, fertilizer, and organic manure (FYM) influenced soil properties and root growth, enhancing crop productivity.

Isolation, identification, characterization and in vitro assay of saline tolerant endophytes against groundnut root rot caused by Rhizoctonia bataticola (Taub.) Butler

Groundnut, known as Arachis hypogaea L., is India's significant oil seed crop. Dry root rot, caused by Rhizoctonia bataticola, poses a substantial challenge to cultivating groundnuts. During the roving survey, 60.50% dry root rot disease incidence was recorded in Namakkal district, Tamil Nadu. This study aims to acquire salt-tolerant endophytic bacteria residing in groundnuts with significant antagonistic activity against R. bataticola. A total of 27 bacterial strains were isolated from groundnuts. Among these strains, RMV 3 and RMV 2 are the most effective isolates, exhibiting 60.1% and 50% inhibition zones, respectively. The effective isolates were characterized through morphological, biochemical and phytostimulation activities and 16S rDNA sequencing. Among the isolates, RMV 3 and RMV 2 showed positive results for siderophore, indole acetic acid (IAA) and cellulase test. The strain RMV 3 was identified as Bacillus subtilis through 16S rDNA sequencing. GC-MS analysis identified twenty bioactive compounds produced by B. subtilis RMV 3, such as pyrrolo [12-a] pyrazine-14-dione hexahydro-3 (2-methylpropyl) and hexadecanoic acid methyl ester. The crude metabolite assay demonstrated a 96.6% inhibition of R. bataticola by RMV 3. This study demonstrated that Bacillus subtilis RMV 3, which exhibits a robust antagonistic effect on R. bataticola, can potentially be an effective biocontrol agent for groundnut dry root rot.

Purification and partial characterization of a thermostable peroxidase isoenzyme from Bambara groundnut (Vigna subterranea L. Verdc) seedlings

Thermostable isoperoxidases, especially peroxidase A6, have already been found in seedlings of Vigna sp, indicating their potential for biotechnological applications. In this study, peroxidase A6 was purified from the roots of Bambara groundnut (Vigna subterranea L. Verdc) seedlings by a combination of gel filtration on Sephadex G-100, heat treatment, and ion exchange chromatography on CM cellulose and DEAE cellulose. The 41-kDa enzyme shows high catalytic efficiency in the oxidation of O-dianisidine, ABTS, TMB, DAB and OPD at acidic pH optimum and the reduction of H2O2. It has an optimum temperature of activity of 60 °C and a calculated activation energy of 221.5 KJ/mol for its thermal inactivation at pH 8. Mg2+ inhibits the enzyme. Ca2+ strongly increases its thermal stability, while Mn2+ and Zn2+ decrease it. The enzyme is inhibited by sodium azide at concentrations above 1 µM, with an IC50 value of about 10 µM. This inhibition, in addition to the RZ value of 2.4 (A403nm/A280nm), confirms the presence of a haem group in the active site, which is common for class III plant peroxidases. Due to its unique catalytic and thermal properties, peroxidase A6 has the potential to be a valuable tool for various biotechnological applications, especially for enzyme immunoassays and clinical diagnosis.

Bio efficacy of fungicides against Ground nut root rot caused by Macrophomina phaseolina (Tassi.) Goid

Bio efficacy of fungicides against Ground nut root rot caused by Macrophomina phaseolina (Tassi.) Goid

Genetic transformation of Trichoderma with GUS and Hyg Genes to study root colonisation in Groundnut

A stable β-glucoronidase, hygromycin transformed Trichoderma harzianum was obtained by Agrobacterium mediated transformation.The confirmation was made with PCR and gel electrophoresis. This transformed strain was used to study the activity ofTrichoderma in the groundnut root with the aid of βglucoronidase gene expression. Microscopic analysis revealed Trichoderma colonization and the presence of GUSstained mycelium in the root section.

Impact of Paper Mill Effluent on Groundnut Root Nodulation and Soil Microorganisms for Inclusion of Compost

A Field experiment was conducted at Mondippatti village in Tiruchirappalli district of Tamil Nadu to study the effect of paper mill effluent irrigation with or without compost application on root growth, biological properties and soil nutrient status in Alfisol with groundnut as the test crop. The results revealed that the application of paper mill effluent along with compost favourably increased the soil nutrient status during the crop period. The highest concentrations of available nutrients viz., nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, iron and zinc in the surface layer were 309.4 kg/ha, 14.2 kg/ha, 211.9 kg/ha, 64.9 meq/100g, 32.5 meq/100g, 38.8 mg/kg,11.4 mg/kg and 0.8 mg/kg, respectively in 75% paper mill effluent and press mud compost applications. Similarly, the use of paper mill effluent along with compost has a positive impact on soil microbial properties and highest population of bacteria was observed in 50% paper mill effluent and press mud application was 9.79 CFU (x106/g) followed by 100% paper mill effluent and press mud application (7.63 CFU (x106/g). While fungi and actinomycetes populations are higher in 75% paper mill effluent and farm yard manure application which were 5.64 CFU (x104/g) and 5.62 CFU (x104/g) respectively. The highest number of nodules was noticed in 100% paper mill effluent with press mud at 5 t/ha (45 numbers) followed by 75% paper mill effluent with press mud at 5 t/ha (42 numbers). From the study, it was concluded that the application of paper mill effluent with compost was found to be a promising source for soil fertility and root growth in groundnut.

Occurrence, abundance and distribution of soil nematodes associated with groundnut farming in Kenya

Groundnut is a major cash crop grown in tropical and subtropical regions. In Kenya, groundnut is mostly grown in the Western and Nyanza regions and has been ranked the fourth cash crop of the Lake Victoria Basin (LVB). However, groundnut production in Kenya has continued to decline with farmers attaining less than 50 % of the yield potential of 700 to 1400 kg/ha. Yearly statistical reports by Agriculture and Food Authority (AFA), Nuts and Oil Crops Directorate for the last seven years, show the decline has been consistent. In 2019/2020 AFA reported there was a decrease of 216 Mt in Homa Bay and 30 Mt in Kisumu. Yield loss is attributed to lack of quality improved seed and pests’ infestation during growth and storage. Plant parasitic nematodes (PPN) are the major pests of groundnut worldwide. This study sought to investigate the occurrence of nematode communities (PPN and non-parasitic nematodes (NPN) in soils cultivated with groundnuts in the LVB and to determine the effect of farmyard manure application on their presence. Six peanut varieties (4 improved and 2 local) were cultivated in Nyakach and Karachuonyo in March to August in 2021 and 2022. Soil samples, groundnut roots and pods were collected. A modified Baermann’s, maceration methods and filtration technique was used to isolate nematodes from the soil, groundnut pods and roots. Multi-stage Analysis of variance (ANOVA) was used to determine any significant differences in abundance and richness while the Shannon index compared diversity of PPN and NPN among the farms in two seasons and regions. Eleven genera of PPN: Aphelenchoides, Meloidogyne, Pratylenchus, Helicotylenchus, Tylenchus, Scutellonema, Trichodorus, Hemicycliophora, Tylenchorhynchus, Rotylenchulus and Criconema. spp., and three genera of NPN; Rhabdittes, Dorylaimus spp. and Predators were categorized. Aphelenchoides and Meloidogyne were the most abundant PPN and Rhabdites NPN in both regions and seasons. Application of farm yard manure led to decline of abundance of PPN and an increase in NPN. The results confirm the presence of PPN in the LVB groundnut growing regions and the potential use of farm yard manure in their management. This study recommends further investigation on actual damage potential of these PPN and their management strategies. Key words: Arachis hypogaea, Soil nematodes, Meloidogyne, Aphelenchoides, Rhabdites, Pratylenchus, Helicotylenchus

Isolation and Characterization of a Silicate-Solubilizing Bacterial Strain Associated with the Roots of Groundnut (Arachis hypogaea L.)

The aim of this investigation was to isolate groundnut root-associated rhizobacteria and to study their efficiency to solubilize silicate, synthesize indole acetic acid (IAA), encourage plant growth, and promote silicon (Si) uptake and deposit in plants. Based on silica-solubilizing ability and IAA production, a bacterial strain was chosen in the present study for further studies. The bacterial isolate synthesized more quantities of IAA at pH 8. When the soil fertilized with silica was inoculated with this bacterial strain, there was an improvement in overall growth characteristics of groundnut. It was also found that more Si was deposited in plants fertilized with both insoluble silica and bacterial strain. Bacteria isolated in the present study can synthesize more IAA under alkaline conditions, solubilize silicate, and encourage the growth of groundnut.

English

Groundnut root rot is a complex disease affecting the crop production worldwide. The objectives of this study were to: (1) Assess the occurrence and distribution of groundnut root rot complex in four main groundnut-growing areas of eastern Ethiopia; (2) Identify the major pathogens associated with groundnut root rot complex; and (3) Determine the role of pathogens singly and in combination on root rot severity of groundnut under greenhouse conditions. A total of 240 groundnut fields were surveyed over two seasons, and 75% of the fields were infected with root rot complex. Mean percent disease prevalence and incidence were highest in Babile, followed by Gursum, while Darolebu had the lowest. Fusarium oxysporum (Fo) was the most common fungus isolated from infected groundnut roots, followed by Fusarium solani (Fs) and Rhizoctonia bataticola (Rb). Other fungi less frequently isolated included Sclerotium rolfsii (Sr) and Rhizoctonia solani (Rs). The pathogenicity test showed that all isolated fungi were pathogenic to groundnut, with Fs being the most virulent in causing root rot, followed by Rb and Fo, while Sr and Rs were less pathogenic. Disease severity was higher on plants co-inoculated with Fo, Fs and Rb than with either alone. The Fs, Fo and Rb were found to be the major causal fungi associated with groundnut root rot complex in eastern Ethiopia, with Fs being the most important and destructive pathogen in the complex and acted as synergistic pathogen with Fo and Rb; thus, breeding for resistance and management strategies should focus on these pathogens.   Key words: Fusarium oxysporum, Fusarium solani, incidence, pathogenicity, pathogen interaction, prevalence, Rhizoctonia bataticola, severity.&nbsp

Management of root rot (Macrophomina phaseolina) in peanut with biocontrol agents and studying its root physiology

The efficacy of Trichoderma asperellum (TNAU-Tv) and Pseudomonas fluorescens (TNAU-Pf1) as seed treatment and soil application along with Farmyard Manure against groundnut root rot disease was evaluated under rainfed condition during the years 2016, 2017 and 2018. During the study, the results showed that among the various treatments imposed, seed treatment with Pseudomonas fluorescens10g/kg, Trichoderma asperellum 4 g/kg recorded maximum reduction of root rot incidence over control. Further, the soil applications of biocontrol agents Trichoderma asperellum 2.5 kg + FYM @ 200 kg/ha and 2.5 kg Pseudomonas fluorescens + FYM@ 200 kg/decreases the soil-borne diseases of root rot (80.67) and (79.27)% reduction over control and also recorded higher yield of 1176 kg/ha with simultaneous increase in seedling stands, plant height, and fresh weight, compared with untreated and chemical checks. In addition, BioVis PSM Root – Rhizoscanner study results in root length (361 mm), root tips (35Nos), forks (43Nos) segments (46) and estimated volume (452 cm3) in T. asperellum and P. fluorescens seed treatment.

Soil losses due to leek and groundnut root crop harvesting: An unstudied regional problem in Turkey

AbstractSoil loss from root crops is an increasingly significant problem studied for some species, such as potatoes, sugar beets, carrots, celery, and onions. It reduces soil fertility and, subsequently, soil productivity. For leek (Allium porrum) and groundnut (Arachis hypogaea), however, there is little information to date. More research on this topic could help farmers reduce the process of soil degradation. In some countries, such as Turkey, the production of these crops is perennial to supporting rural communities and ensuring food security. Therefore, it is important to quantify soil losses from leek and groundnut crops in Turkey. This study investigated the factors affecting soil losses and the cost of nutrients lost with the transported soil by analyzing randomly selected plants from 45 harvested leek and groundnut plots. Our results showed that soil losses reached 3.99 Mg ha−1 per harvest for leek and 1.04 Mg ha−1 for groundnut. Prevailing soil moisture explained 59% of the variability in the leek harvest and soil texture and bulk density for leek yield at harvest. In the groundnut harvest, 53% of the variability was explained by antecedent soil moisture and clay fraction for the groundnut yield at the time of harvest. The estimated annual cost of nutrients losses was $US 3.75 ha−1 for leek and $US 0.76 ha−1 for groundnut. It can be concluded that leek and groundnut harvesting causes soil and nutrient losses with considerable economic costs. Therefore, awareness should be raised among farmers and users. In addition, policymakers should consider the management of soil loss by crop harvesting (SLCH) processes.

Resistance to Abiotic Stress and Effectiveness of Native Rhizobia on Bambara Groundnut [<i>Vigna subterranea</i> (L.) Verdc.] in Benin

Bambara groundnut [Vigna subterranea (L.) Verdc.], as a legume, can establish relationships with nitrogen-fixing bacteria such as Rhizobium. However, Rhizobium efficacy is not always optimal due to the lack or poor efficient strains in the soil. This study aimed to evaluate symbiotic efficiency of endogenous Rhizobia nodulating Bambara groundnut and their resistance to abiotic conditions. Root nodules were randomly sampled from three agroecological zones across the country, surface sterilized, ground and paste plated on YEMA media. After 24 hours, the bacterial colonies were purified. The pure cultures were further characterized using morphological and biochemical methods and their resistance to antibiotics and heavy metals was evaluated. Lastly, the symbiotic efficiency of the isolates was assessed through a greenhouse experiment. A total of eighty-five presumptive strains were isolated from Bambara groundnut roots nodules obtained from the farms. The physiological characterization of the isolated showed a decrease in isolates growth when NaCl concentration was more than 7%. In addition, 47% of the isolates were tolerant to a temperature of 40°C. Most of the isolates were highly resistant to Erythromycin in all its concentration levels and to Kanamycin, Spectinomycin, Neomycin and Ampicillin at 10 μg⋅mL−1. Most of them showed resistance to Cu and Zn at 10 μg⋅mL−1. Results of the effectiveness test on two Bambara groundnut varieties yielded dry shoot matter varying from 3.33 g⋅plant−1 to 7.21 g⋅plant−1 for variety 1 and from 4.38 g⋅plant−1 to 8.38 g⋅plant−1 on variety 2. N uptake ranged between 0.09 g⋅plant−1 and 0.29 g⋅plant−1 for variety 1 and between 0.12 and 0.29 g⋅plant−1 for variety 2. The isolates yielding higher shoot dry weight and N uptake were LMSEM312, LMSEM338, LMSEM307, LMSEM351 for variety 1 and LMSEM338, LMSEM309, LMSEM307 for variety 2. The isolates showing better performance can be used to develop bio-fertilizer for sustainable Bambara groundnut production in Benin.

Screening for Drought Tolerance through Root Morphology and Yield Characters of Groundnut (Arachis hypogaea L.) Genotypes

Drought affects the rainfed groundnut (Arachis hypogaea L.) at different phases of development and it is the serious threats on groundnut productivity causing losses than any other abiotic factor under rainfed agriculture. In the world's semiarid regions, groundnut accounts for 90% of worldwide production. Drought mainly affects the pace and pattern of nutrient and water intake from the soil, affecting the architecture of the groundnut root system. Plant selections with desirable root trait have been a major focus in developing drought resistant Groundnut cultivars. In 2019, 60 groundnut genotypes were cultivated in root block design with two different soil water treatments, as well as in the field during the year under same circumstances. The purpose of this study was to see how different groundnut cultivars fared in terms of yield, yield contributing features, root characters, and their relationships with drought tolerance. Drought resistant genotypes had thicker roots, larger roots, and a deeper root system than susceptible genotypes. Recent series in groundnut genotypes of 60 numbers were sown during kharif 2019 (july-september) under rainfed condition (It includes life irrigation and rainfall received during cropping season). Groundnut genotypes were semi spreading with the duration of 110-120 days. Observation on root morphological character viz., roots length, root volume after 20 days of stress imposition of the crop and yield parameters were observed at the harvest. Among the 60 genotypes, 20 genotypes (VG 17008, VG 17046, VG 18005, VG 18102, VG 18077, VG 19572, VG 19709, VG 18111, VG19561, VG19576, VG 19620, VG 19681, VG 19688 etc.,) similarly, yield character were observed for 60 genotypes and all the genotypes given above recorded higher value in Total number of pods per plant, Number of double seeded pods per plant, Pod yield per plant, Harvest index and Total dry matter production. The methods used in this study identified correlation between yield character and root characters. Groundnut genotypes by assessing yield metrics and their relationship with root trait. These findings lay the groundwork for future study aimed at deciphering the molecular pathways underpinning Groundnut drought resistance.

Screening of biological control agent fungi against peanut stem rot (Sclerotium rolfsii Sacc.) in the peatlands of Kuala Pesisir Nagan Raya, Aceh, Indonesia

Peanut stem rot disease caused by Sclerotium rolfsii Sacc. is a problem that needs special attention in peatlands. Peatlands that are wet, acidic and contain high organic matter should be able to support and increase the pathogenicity of S. rolfsii. However, this is not the case for the peatlands of Kuala Pesisir Nagan Raya, have been other components cause these pathogens not to develop. Here we try to examine the biological elements, namely the existence of biological control agents from the fungal group, which generally like the same environmental conditions as pathogens. This study aims to obtain peat soil antagonistic fungi that can control S. rolfsii. This research was conducted in Kuala Pesisir, Nagan Raya Regency, Aceh, Indonesia. Research activities include isolation, morphological identification, pathogenicity testing, antagonist testing, and molecular identification. The results obtained 46 fungal colonies from three sources, namely weed rhizosphere around peanut farming, peanut rhizosphere, and groundnut roots. The results showed that there were antagonistic fungi that could suppress S. rolfsii, namely Trichoderma asperellum.

Efficacy of different fungicides and weedicides against Macrophomina phaseolina (Tassi) Goid causing groundnut root rot

In this study, different systemic, non-systemic, combination fungicides and weedicides at four different concentration were evaluated in vitro against groundnut root rot pathogen Macrophomina phaseolina. Among the non-systemic fungicides, Mancozeb 75% WP and Propineb 70% WP were found most effective and showed (99.98 and 99.96 per cent) mycelia growth inhibition at all concentrations. Whereas in systemic fungicides, Carbendazim 50% WP were found most effective with (94.24 per cent) mean mycelial growth inhibition. Among different combination fungicides tested, Carboxin 37.5% + Thiram 37.5% WP were found most effective with mean mycelial growth inhibition of (97.16 per cent).. In case of weedicides tested, Quizalofo-p-pethyle 5% EC found as most effective inhibiting the mycelial growth of M. phaseolina at all concentrations with (90.92 per cent) mean mycelial growth inhibition. Sclerotial formation was also absent in all this treatments.

Isolation and Identification of ACC Deaminase Producing Bacteria from Rhizosfer and Plant Roots of Maize, Cowpea, and Groundnut Growing under Saline Stress

ACC deaminase producing bacteria reduces the excess ethylene produced by stressed plant because ACC deaminase catalyzes the cleavage of ACC into ammonium and α-ketobutyrate. ACC deaminase is produced by several rhizospheric and endophytic bacteria. This study was aimed to obtain ACC deaminase producing bacteria isolated from rhizosfer and plant roots of maize, cowpea, and groundnut growing under saline stress. Isolation was conducted by surface plating on NA medium. Qualitative selection was based on the growth of isolate on DF salts medium supplemented with AIB. Quantitative selection based on ACC deaminase activity assay. Identification of the isolates was carried out by morphologycally and sequencing of 16S rRNA gene. Isolation and selection resulted four bacterial isolates (AJG3, RJG6, ATL5, and RTN10). Those bacterial isolates have the ACC deaminase activity between 184.65 to 692.54 nmol α-ketobutyrate. mg−1. h−1. Isolate of AJG3, RJG6, and ATL5 were gram negative bacteria, only one isolate was gram positive bacteria (RTN10). Based on 16S rRNA gene sequence, AJG3, RJG6, ATL5, and RTN10 isolates have a high similarity with Klebsiella variicola, Rhizobium pusense, Agrobacterium tumefaciens, and Bacillus stratosphericus respectively.

Changes in Root Exudates and Root Proteins in Groundnut–Pseudomonas sp. Interaction Contribute to Root Colonization by Bacteria and Defense Response of the Host

Selection and application of rhizobacteria, for improved plant health will benefit from a complete understanding of the plant–bacteria interaction. Root exudates (REs) are known to contain signal molecules that facilitate beneficial association of plants with microbes. We have selected a tentatively identified Pseudomonas sp. (RP2), from 126 groundnut (Arachis hypogaea L.)-associated bacterial isolates that significantly promoted growth of groundnut and also induced resistance against the stem rot pathogen Sclerotium rolfsii. REs were collected from 12 to 24 days grown RP2-bacterized and non-bacterized plants and analyzed through gas chromatography coupled with mass spectrometer. Several organic acids, fatty acids, sugars, hydrocarbons, and alcohols were detected. In the untargeted multivariate analysis of the REs, relative content of eight compounds varied significantly on RP2 bacterization. Among these eight compounds, myristic acid, stearic acid, and palmitic acid, positively influenced the root colonization by RP2. Benzoic acid and salicylic acid, increased in RP2-bacterized REs, showed the highest growth inhibition of S. rolfsii. In root proteomics, 11 differentially expressed proteins were identified by 2D-gel electrophoresis followed by matrix-assisted laser desorption ionization-time of flight. Chitinase, thaumatin-like protein, ascorbate peroxidase, and glutathione S-transferase, known to have a role in plant defense against phytopathogens, were upregulated in RP2 interaction. Similarly, upregulation of enolase in roots is likely to improve plant growth in RP2-bacterized groundnut. We conclude that colonization of groundnut roots by RP2 resulted in exudation of metabolites that facilitated root colonization, suppressed fungal growth, promoted plant growth, and also increased the expression of defense-related proteins in the roots.

Partner-triggered proteome changes in the cell wall of Bacillus sonorensis and roots of groundnut benefit each other

Plant growth promoting rhizobacteria (PGPR) promote plant growth and activate defense response against phytopathogens. At the subcellular level plant-PGPR interaction is less understood, which would be essential for future improvement(s) of PGPR formulations. In a rigorous screening process, that also involved efficient PGPR strains, Bacillus sonorensis RS4 was selected to study partner-triggered interactions. The potential of B. sonorensis RS4 to improve growth of groundnut, efficiency to colonize roots, and influence on root topology was assessed. Twenty four cell wall proteins of B. sonorensis RS4 [in presence of groundnut root exudates (REs)], and 22 groundnut root proteins (in RS4-bacterized plants) were differentially expressed. The alterations in cell wall proteins of B. sonorensis RS4 were primarily related to the amino acids synthesis, chemotaxis, antioxidant-metabolism, carbohydrate metabolism, transporters, and antibiosis-related secondary metabolites. Root proteins that were differentially expressed during the interaction may be involved in plant growth, defense responses, and in transportation. The changes in B. sonorensis RS4 cell wall proteome and groundnut root proteome, suggest that at least a part of the proteome changes triggered by each of the partners appear to play a significant role in helping each other akin to symbiosis.

Isolation, characterization and comparative analysis of plant-associated bacteria for suppression of soil-borne diseases of field-grown groundnut in Vietnam

Groundnut (Arachis hypogaea L.) is an important oil seed crop worldwide and used extensively for feed and food. In Vietnam, groundnut cultivation is hampered by several soil-borne fungal pathogens, in particular Sclerotium rolfsii. To develop sustainable measures to control stem rot disease caused by S. rolfsii, plant-associated bacteria were isolated from the stem base and roots of groundnut plants grown in farmer fields in central Vietnam and tested for activity against S. rolfsii. Among a total of 3,360 randomly selected bacterial isolates, only thirteen (0.4%) inhibited hyphal growth of S. rolfsii. BOX-PCR and 16S-rDNA sequence analyses revealed that these bacterial isolates were genetically diverse and belonged to three bacterial Phyla, i.e. the γ-Proteobacteria (Pseudomonas), Firmicutes (Bacillus) and Bacteroidetes (Chryseobacterium). Nethouse and field experiments conducted in central Vietnam showed that treatment of groundnut seeds or field soil with strains of each of these three bacterial genera significantly reduced the incidence of stem rot disease, led to significant yield increases of up to 21% and did not have adverse effects on nodulation. The level of disease protection provided by the bacterial strains was similar to that achieved by the fungicide tebuconazole. Comparative analysis of the biocontrol efficacy of the indigenous Pseudomonas strain R4D2 with that of two exogenous, antagonistic Pseudomonas strains from the Netherlands showed that in field trials the indigenous strain R4D2 better colonized the roots of groundnut, reduced stem rot (S. rolfsii), black collar rot (Aspergillus niger), and bacterial wilt (Ralstonia solanacearum), and more consistently enhanced groundnut yield.