Induced Systemic Resistance Research Articles

Trichoderma virens and Pseudomonas chlororaphis Differentially Regulate Maize Resistance to Anthracnose Leaf Blight and Insect Herbivores When Grown in Sterile versus Non-Sterile Soils.

Soil-borne Trichoderma spp. have been extensively studied for their biocontrol activities against pathogens and growth promotion ability in plants. However, the beneficial effect of Trichoderma on inducing resistance against insect herbivores has been underexplored. Among diverse Trichoderma species, consistent with previous reports, we showed that root colonization by T. virens triggered induced systemic resistance (ISR) to the leaf-infecting hemibiotrophic fungal pathogens Colletotrichum graminicola. Whether T. virens induces ISR to insect pests has not been tested before. In this study, we investigated whether T. virens affects jasmonic acid (JA) biosynthesis and defense against fall armyworm (FAW) and western corn rootworm (WCR). Unexpectedly, the results showed that T. virens colonization of maize seedlings grown in autoclaved soil suppressed wound-induced production of JA, resulting in reduced resistance to FAW. Similarly, the bacterial endophyte Pseudomonas chlororaphis 30-84 was found to suppress systemic resistance to FAW due to reduced JA. Further comparative analyses of the systemic effects of these endophytes when applied in sterile or non-sterile field soil showed that both T. virens and P. chlororaphis 30-84 triggered ISR against C. graminicola in both soil conditions, but only suppressed JA production and resistance to FAW in sterile soil, while no significant impact was observed when applied in non-sterile soil. In contrast to the effect on FAW defense, T. virens colonization of maize roots suppressed WCR larvae survival and weight gain. This is the first report suggesting the potential role of T. virens as a biocontrol agent against WCR.

Understanding the dynamic interactions of root-knot nematodes and their host: role of plant growth promoting bacteria and abiotic factors

Root-knot nematodes (Meloidogyne spp., RKN) are among the most destructive endoparasitic nematodes worldwide, often leading to a reduction of crop growth and yield. Insights into the dynamics of host-RKN interactions, especially in varied biotic and abiotic environments, could be pivotal in devising novel RKN mitigation measures. Plant growth-promoting bacteria (PGPB) involves different plant growth-enhancing activities such as biofertilization, pathogen suppression, and induction of systemic resistance. We summarized the up-to-date knowledge on the role of PGPB and abiotic factors such as soil pH, texture, structure, moisture, etc. in modulating RKN-host interactions. RKN are directly or indirectly affected by different PGPB, abiotic factors interplay in the interactions, and host responses to RKN infection. We highlighted the tripartite (host-RKN-PGPB) phenomenon with respect to (i) PGPB direct and indirect effect on RKN-host interactions; (ii) host influence in the selection and enrichment of PGPB in the rhizosphere; (iii) how soil microbes enhance RKN parasitism; (iv) influence of host in RKN-PGPB interactions, and (v) the role of abiotic factors in modulating the tripartite interactions. Furthermore, we discussed how different agricultural practices alter the interactions. Finally, we emphasized the importance of incorporating the knowledge of tripartite interactions in the integrated RKN management strategies.

Cadmium toxicity promotes hormonal imbalance and induces the expression of genes involved in systemic resistances in barley.

Cadmium (Cd) is a widely distributed pollutant that adversely affects plants' metabolism and productivity. Phytohormones play a vital role in the acclimation of plants to metal stress. On the other hand, phytohormones trigger systemic resistances, including systemic acquired resistance (SAR) and induced systemic resistance (ISR), in plants in response to biotic interactions. The present study aimed to investigate the possible induction of SAR and ISR pathways in relation to the hormonal alteration of barley seedlings in response to Cd stress. Barley seedlings were exposed to 1.5mgg-1 Cd in the soil for three days. The nutrient content, oxidative status, phytohormones profile, and expression of genes involved in SAR and ISR pathways of barley seedlings were examined. Cd accumulation resulted in a reduction in the nutrient content of barley seedlings. The specific activity of superoxide dismutase and the hydrogen peroxide content significantly increased in response to Cd toxicity. Abscisic acid, jasmonic acid, and ethylene content increased under Cd exposure. Cd treatment resulted in the upregulation of NPR1, PR3, and PR13 genes in SAR pathways. The transcripts of PAL1 and LOX2.2 genes in the ISR pathway were also significantly increased in response to Cd treatment. These findings suggest that hormonal-activated systemic resistances are involved in the response of barley to Cd stress.

Enhancing Botrytis disease management in tomato plants: insights from a Pseudomonas putida strain with biocontrol activity.

This study explores the biocontrol potential of Pseudomonas putida Z13 against Botrytis cinerea in tomato plants, addressing challenges posed by the pathogen's fungicide resistance. The aims of the study were to investigate the in vitro and in silico biocontrol traits of Z13, identify its plant colonizing efficacy, evaluate the efficacy of different application strategies against B. cinerea in planta, and assess the capacity of Z13 to trigger induced systemic resistance (ISR) in plants. The in vitro experiments revealed that Z13 inhibits the growth of B. cinerea, produces siderophores, and exhibits swimming and swarming activity. Additionally, the Z13 genome harbors genes that encode compounds triggering ISR, such as pyoverdine and pyrroloquinoline quinone. Τhe in planta experiments demonstrated Z13's efficacy in effectively colonizing the rhizosphere and leaves of tomato plants. Therefore, three application strategies of Z13 were evaluated against B. cinerea: root drenching, foliar spray, and the combination of root drenching and foliar spray. It was demonstrated that the most effective treatment of Z13 against B. cinerea was the combination of root drenching and foliar spray. Transcriptomic analysis showed that Z13 upregulates the expression of the plant defense-related genes PR1 and PIN2 upon B. cinerea inoculation. The results of the study demonstrated that Z13 possesses significant biocontrol traits, such as the production of siderophores, resulting in significant plant protection against B. cinerea when applied as a single treatment to the rhizosphere or in combination with leaf spraying. Additionally, it was shown that Z13 root colonization primes plant defenses against the pathogen.

Role of Plant-Growth-Promoting Rhizobacteria in Plant Machinery for Soil Heavy Metal Detoxification.

Heavy metals migrate easily and are difficult to degrade in the soil environment, which causes serious harm to the ecological environment and human health. Thus, soil heavy metal pollution has become one of the main environmental issues of global concern. Plant-growth-promoting rhizobacteria (PGPR) is a kind of microorganism that grows around the rhizosphere and can promote plant growth and increase crop yield. PGPR can change the bioavailability of heavy metals in the rhizosphere microenvironment, increase heavy metal uptake by phytoremediation plants, and enhance the phytoremediation efficiency of heavy-metal-contaminated soils. In recent years, the number of studies on the phytoremediation efficiency of heavy-metal-contaminated soil enhanced by PGPR has increased rapidly. This paper systematically reviews the mechanisms of PGPR that promote plant growth (including nitrogen fixation, phosphorus solubilization, potassium solubilization, iron solubilization, and plant hormone secretion) and the mechanisms of PGPR that enhance plant-heavy metal interactions (including chelation, the induction of systemic resistance, and the improvement of bioavailability). Future research on PGPR should address the challenges in heavy metal removal by PGPR-assisted phytoremediation.

Modern Approaches to Enhancing Rust Resistance in Wheat Leading to Global Food Security

Rust diseases pose significant threats to wheat production. The deployment of wheat cultivars endowed with rust resistance stands as the most potent strategy for effective rust management. This resistance is primarily inherited through Mendelian principles discovered in 1905, but traditional breeding methods are time-consuming. Modern strategies have emerged to develop rust-resistant wheat varieties efficiently. Marker-Assisted Selection (MAS) accelerates the breeding process through precise screening, bringing about a revolution in the creation of rust-resistant wheat varieties. Genetic engineering techniques allow the transfer of resistance genes from other species into susceptible crops, but GMO use remains controversial and regulated. Gene editing, especially with CRISPR-Cas9, is a game-changer, enabling the introduction of natural variations or inactivation of critical genes in rust pathogens, enhancing plant resistance. RNA interference (RNAi) is another promising strategy, using small RNA molecules to inhibit rust pathogen gene expression, reducing disease severity. Induced Systemic Resistance (ISR) primes plant immune systems by treating them with beneficial microorganisms or compounds, fortifying them against subsequent rust infections. Eco-friendly biofungicides with antagonistic microorganisms suppress rust infections as alternatives to chemical fungicides. The development of climate-resilient wheat varieties is essential, as they indirectly enhance rust resistance, ensuring stable production amid changing climate conditions. These efforts to improve wheat productivity and rust resistance are crucial for feeding the growing global population. Integrating modern methods with traditional breeding is key to effectively combatting rust diseases and enhancing food security.

Exploring the biocontrol potential of rocket (Eruca sativa) extracts and associated microorganisms against Verticillium wilt.

This study aimed to assess the impact of rocket (Eruca sativa) extract on Verticillium wilt in eggplants, explore rhizospheric microorganisms for disease biocontrol, and evaluate selected strains' induced systemic resistance (ISR) potential while characterizing their genomic and biosynthetic profiles. Rocket extract application led to a significant reduction in Verticillium wilt symptoms in eggplants compared to controls. Isolated microorganisms from treated soil, including Paraburkholderia oxyphila EP1, Pseudomonas citronellolis EP2, Paraburkholderia eburnea EP3, and P. oxyphila EP4 and EP5, displayed efficacy against Verticillium dahliae, decreasing disease severity and incidence in planta. Notably, strains EP3 and EP4 triggered ISR in eggplants against V. dahliae. Genomic analysis unveiled shared biosynthetic gene clusters, such as ranthipeptide and non-ribosomal peptide synthetase-metallophore types, among the isolated strains. Additionally, metabolomic profiling of EP2 revealed the production of metabolites associated with amino acid metabolism, putative antibiotics, and phytohormones. The application of rocket extract resulted in a significant reduction in Verticillium wilt symptoms in eggplants, while the isolated microorganisms displayed efficacy against V. dahliae, inducing systemic resistance and revealing shared biosynthetic gene clusters, with metabolomic profiling highlighting potential disease-suppressing metabolites.

Induced Resistance Mechanism in Plant and Its Importance in Agriculture

The search for a successful and efficient natural phenomenon of induced resistance in plants was prompted by the harmful effects that chemical pesticides and their degradation products had on the environment and human health. Ray was the first to identify plant resistance to diseases in 1901. When arabidopsis plants were injected with the pathogenic bacteria Pseudomonas fluorescens, which colonises roots, induced resistance was initially observed in these plants. There are two different kinds of induced resistance: induced biochemical defense and induced structural defense. Biochemical defense includes phytoalexins, PR-proteins, and secondary metabolites; structural defense includes cytoplasmic reactions, cell wall defense structure, and histological defense structure (development of cork layers, abscission layer, and tylose). Induced systemic resistance (ISR) and systemic acquired resistance (SAR) are the foundation of the induced resistance process. While the defense mechanism in ISR is mediated by jasmonic acid and ethylene and additionally triggered by non-pathognic rhizobacteria (Pseudomonas fluorescens), the defense mechanism in SAR is salicyclic mediated, namely alterations in gene expression. Plants can develop resistance to specific diseases by applying exogenous doses of 2, 6-dichloroisonicotonic acid and benzo-thiadiazole-7-carbothioic acid S-methyl ester (BTH). Induced resistance in plants, while still poorly understood, offers up new possibilities for plant protection and presents a viable strategy for sustainable agriculture and environmentally friendly disease control. It continues to be a problem for both basic and practical research.

Terpenoids are involved in the expression of systemic-induced resistance in Austrian pine.

Terpenoids are defense metabolites that are induced upon infection or wounding. However, their role in systemic-induced resistance (SIR) is not known. Here, we explored the role of terpenoids in this phenomenon at a very early stage in the interaction between Austrian pine and the tip blight and canker pathogen Diplodia pinea.We induced Austrian pine saplings by either wounding or inoculating the lower stems with D. pinea. The seedlings were then challenged after 12 h, 72 h, or 10 days with D. pinea on the stem 15 cm above the induction. Lesion lengths and terpenoids were quantified at both induction and challenge locations. Key terpenoids were assayed for antifungal activity in in vitro bioassays.SIR increased with time and was correlated with the inducibility of several compounds. α-Pinene and a cluster of β-pinene, limonene, benzaldehyde, dodecanol, and n-dodecyl acrylate were positively correlated with SIR and were fungistatic in vitro, while other compounds were negatively correlated with SIR and appeared to serve as a carbon source for D. pinea.This study shows that, overall, terpenoids are involved in SIR in this system, but their role is nuanced, depending on the type of induction and time of incubation. We hypothesize that some, such as α-pinene, could serve in SIR signaling.

Disease-suppressive soils induce systemic resistance in Arabidopsis thaliana against Pseudomonas syringae pv. tomato

Arabidopsis thaliana accession Col-0 seedlings were transferred into an autoclaved potting soil/sand mixture amended with either 10 or 20% (weight/weight) soil from fields in Washington State USA that are suppressive to take-all or Rhizoctonia root rot of wheat. Three weeks after transplanting, these plants had population sizes of 2,4-diacetylphloroglucinol (DAPG)- or phenazine-1-carboxylic acid (PCA)-producing pseudomonads of greater than 5 x 105 colony forming units per gram fresh weight of root with rhizosphere soil. When the plants were challenge-inoculated with Pseudomonas syringae pv. tomato, both soils displayed induced systemic resistance in the leaves against bacterial speck to a level similar to that induced by Pseudomonas simiae WCS417r, P. fluorescens Q2-87 (DAPG+), P. brassicacearum Q8r1-96 and L5.1-96 (both DAPG+), and P. synxantha 2-79 (PCA+). Pasteurization of the soils before adding them into the soil/sand mixture eliminated DAPG- and PCA-producing pseudomonads from the A. thaliana rhizosphere and significantly reduced induced systemic resistance activity. However, populations of total culturable heterotrophic aerobic bacteria were similar in the rhizosphere of plants grown in soil/sand mixes amended with untreated or pasteurized suppressive soils. This is the first report of induction of systemic resistance in A. thaliana by take-all and Rhizoctonia suppressive soils and the ability of PCA-producing P. synxantha 2-79 to induce resistance.

Biological control potential of worrisome wheat blast disease by the seed endophytic bacilli.

Crop production often faces challenges from plant diseases, and biological control emerges as an effective, environmentally friendly, cost-effective, and sustainable alternative to chemical control. Wheat blast disease caused by fungal pathogen Magnaporthe oryzae Triticum (MoT), is a potential catastrophic threat to global food security. This study aimed to identify potential bacterial isolates from rice and wheat seeds with inhibitory effects against MoT. In dual culture and seedling assays, three bacterial isolates (BTS-3, BTS-4, and BTLK6A) demonstrated effective suppression of MoT growth and reduced wheat blast severity when artificially inoculated at the seedling stage. Genome phylogeny identified these isolates as Bacillus subtilis (BTS-3) and B. velezensis (BTS-4 and BTLK6A). Whole-genome analysis revealed the presence of genes responsible for controlling MoT through antimicrobial defense, antioxidant defense, cell wall degradation, and induced systemic resistance (ISR). Taken together, our results suggest that the suppression of wheat blast disease by seed endophytic B. subtilis (BTS-3) and B. velezensis (BTS-4 and BTLK6A) is liked with antibiosis and induced systemic resistance to wheat plants. A further field validation is needed before recommending these endophytic bacteria for biological control of wheat blast.

Bacillus Species: Excellent Biocontrol Agents against Tomato Diseases.

Tomatoes encounter many pathogens, such as fungi and bacteria, which reduce the yield and quality of plants and lead to large losses in production. The application of plant protection products (PPPs) is still an important and most effective measure to control plant diseases. However, the use of chemicals in agriculture contributes to environmental pollution and biodiversity loss, and it can also threaten non-target living organisms. Biological control is a widely accessible, environmentally safe, and cost-efficient alternative for the prevention and suppression of plant diseases. Bacillus species with antimicrobial and plant growth-promoting effects are most frequently used as biocontrol agents to increase the resilience of agricultural production against biotic stresses. The present review discusses the antagonistic mechanisms and the biocontrol potential of Bacillus spp. against tomato diseases caused by different pathogens. The main mechanisms of Bacillus spp. include the production of antimicrobial compounds (antibiotics, extracellular enzymes, siderophores, and volatile compounds), competition for nutrients and space, and induced systemic resistance (ISR). Although Bacillus-based PPPs have been developed and commercialised worldwide for various crops and pathogens, the efficiency issues are still subject to debate. Additionally, a combined strategy for controlling tomato diseases based on Bacillus spp. and other available methods (conventional or natural-based) is a promising research field.

A comprehensive review on Gossypium hirsutum resistance against cotton leaf curl virus.

Cotton (Gossypium hirsutum L.) is a significant fiber crop. Being a major contributor to the textile industry requires continuous care and attention. Cotton is subjected to various biotic and abiotic constraints. Among these, biotic factors including cotton leaf curl virus (CLCuV) are dominant. CLCuV is a notorious disease of cotton and is acquired, carried, and transmitted by the whitefly (Bemisia tabaci). A cotton plant affected with CLCuV may show a wide range of symptoms such as yellowing of leaves, thickening of veins, upward or downward curling, formation of enations, and stunted growth. Though there are many efforts to protect the crop from CLCuV, long-term results are not yet obtained as CLCuV strains are capable of mutating and overcoming plant resistance. However, systemic-induced resistance using a gene-based approach remained effective until new virulent strains of CLCuV (like Cotton Leaf Curl Burewala Virus and others) came into existence. Disease control by biological means and the development of CLCuV-resistant cotton varieties are in progress. In this review, we first discussed in detail the evolution of cotton and CLCuV strains, the transmission mechanism of CLCuV, the genetic architecture of CLCuV vectors, and the use of pathogen and nonpathogen-based approaches to control CLCuD. Next, we delineate the uses of cutting-edge technologies like genome editing (with a special focus on CRISPR-Cas), next-generation technologies, and their application in cotton genomics and speed breeding to develop CLCuD resistant cotton germplasm in a short time. Finally, we delve into the current obstacles related to cotton genome editing and explore forthcoming pathways for enhancing precision in genome editing through the utilization of advanced genome editing technologies. These endeavors aim to enhance cotton's resilience against CLCuD.

Phylloplane microorganisms and induction of systemic resistance against pathogen Alternaria solani in tomato (Solanum lycopersicum L.)

Phylloplane microorganisms and induction of systemic resistance against pathogen Alternaria solani in tomato (Solanum lycopersicum L.)

Beneficial Microorganisms as Bioprotectants against Foliar Diseases of Cereals: A Review.

Cereal production plays a major role in both animal and human diets throughout the world. However, cereal crops are vulnerable to attacks by fungal pathogens on the foliage, disrupting their biological cycle and photosynthesis, which can reduce yields by 15-20% or even 60%. Consumers are concerned about the excessive use of synthetic pesticides given their harmful effects on human health and the environment. As a result, the search for alternative solutions to protect crops has attracted the interest of scientists around the world. Among these solutions, biological control using beneficial microorganisms has taken on considerable importance, and several biological control agents (BCAs) have been studied, including species belonging to the genera Bacillus, Pseudomonas, Streptomyces, Trichoderma, Cladosporium, and Epicoccum, most of which include plants of growth-promoting rhizobacteria (PGPRs). Bacillus has proved to be a broad-spectrum agent against these leaf cereal diseases. Interaction between plant and beneficial agents occurs as direct mycoparasitism or hyperparasitism by a mixed pathway via the secretion of lytic enzymes, growth enzymes, and antibiotics, or by an indirect interaction involving competition for nutrients or space and the induction of host resistance (systemic acquired resistance (SAR) or induced systemic resistance (ISR) pathway). We mainly demonstrate the role of BCAs in the defense against fungal diseases of cereal leaves. To enhance a solution-based crop protection approach, it is also important to understand the mechanism of action of BCAs/molecules/plants. Research in the field of preventing cereal diseases is still ongoing.

Trichoderma harzianum Cellulase Gene thph2 Affects Trichoderma Root Colonization and Induces Resistance to Southern Leaf Blight in Maize.

Trichoderma, widely distributed all over the world, is commonly found in soil and root ecosystems. It is a group comprising beneficial fungi that improve plant disease resistance and promote plant growth. Studies have shown that Trichoderma cellulases can also improve plant disease resistance. Based on previous studies, we reported that a C6 zinc finger protein (Thc6) regulates two cellulase genes, thph1 and thph2, to induce ISR responses in plants. Therefore, in this study, we focused on the role of thph2 in the colonization of maize roots by T. harzianum and the induction of systemic resistance against southern leaf blight. The results showed that thph2 had a positive regulatory effect on the Trichoderma colonization of maize roots. After the root was treated with Trichoderma, the leaf defense genes AOS, LOX5, HPL, and OPR1 were expressed to resist the attack of Cochliobolus heterostrophus. The pure Thph2 protein also resulted in a similar induction activity of the AOS, LOX5, HPL, and OPR1 expression in maize roots, further demonstrating that thph2 can induce plant defense responses and that signal transduction occurs mainly through the JA signaling pathway.

Systemic resistance induced by plant growth-promoting rhizobacteria in Bhut Jolokia (Capsicum chinense Jacq.) suppressed the collar rot disease

Collar rot disease caused by Rhizoctonia solani is a major constraint to the commercial cultivation of Bhut Jolokia (Capsicum chinense Jacq.) in North-East India. However, the management of the disease is not addressed comprehensively in this plant. Some plant growth-promoting rhizobacteria (PGPR) could control plant diseases by triggering induction of resistance systemically, and emerge as a highly promising approach to reduce the use of chemical fungicides. Therefore, five selected PGPRs were tested for plant growth promotion and induced systemic resistance (ISR) for controlling the disease. Induced systemic resistance was determined in vivo condition. Confocal laser scanning microscopic observation was done to see any harmful effects on cells in the induced plant. The PGPRs could significantly improve plant growth as well as suppress the disease and boost defense-related enzymes activity in the induced plants. Bacillus megaterium JPR68 triggered the maximum ISR in the plant. Expression of the defense-related genes was analyzed which were highly expressed in ISR plants. Microscopic observation revealed that no internal changes occurred in PGPR treated plant cells similar to the untreated plant, and indicated no harmful effect of the bacteria in the host cell. The study demonstrates the possible application of B. megaterium JPR68 as a biocontrol agent for sustainable management of the disease. To our knowledge, this is the first report of ISR against any fungal disease in Bhut Jolokia.

Microbial consortium mediated acceleration of the defense response in potato against Alternaria solani through prodigious inflation in phenylpropanoid derivatives and redox homeostasis

The present study was carried out in a pot experiment to examine the bioefficacy of three biocontrol agents, viz., Trichoderma viride, Bacillus subtilis, and Pseudomonas fluorescens, either alone or in consortium, on plant growth promotion and activation of defense responses in potato against the early blight pathogen Alternaria solani. The results demonstrate significant enhancement in growth parameters in plants bioprimed with the triple-microbe consortium compared to other treatments. In potato, the disease incidence percentage was significantly reduced in plants treated with the triple-microbe consortium compared to untreated control plants challenged with A. solani. Potato tubers treated with the consortium and challenged with pathogen showed significant activation of defense-related enzymes such as peroxidase (PO) at 96 h after pathogen inoculation (hapi) while, both polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) at 72 hapi, compared to the individual and dual microbial consortia-treated plants. The expression of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT) and the accumulation of pathogenesis-related proteins such as chitinase and β-1,3-glucanase were observed to be highest at 72 hapi in the triple microbe consortium as compared to other treatments. HPLC analysis revealed significant induction in polyphenolic compounds in triple-consortium bioprimed plants compared to the control at 72 hapi. Histochemical analysis of hydrogen peroxide (H2O2) clearly showed maximum accumulation of H2O2 in pathogen-inoculated control plants, while the lowest was observed in triple-microbe consortium at 72 hapi. The findings of this study suggest that biopriming with a microbial consortium improved plant growth and triggered defense responses against A. solani through the induction of systemic resistance via modulation of the phenylpropanoid pathway and antioxidative network.

New endophytic strains of Trichoderma promote growth and reduce clubroot severity of rapeseed (Brassica napus).

Rapeseed (Brassica napus L.) is the world's third most important edible oilseed crop after soybean and palm. The clubroot disease caused by Plasmodiophora brassicae poses a significant risk and causes substantial yield losses in rapeseed. In this study, 13 endophytic fungal strains were isolated from the healthy roots of rapeseed (B. napus) grown in a clubroot-infested field and molecularly identified. Based on germination inhibition of resting spores of P. brassicae, two endophytic fungal antagonists, Trichoderma spp. ReTk1 and ReTv2 were selected to evaluate their potential for plant growth promotion and biocontrol of P. brassicae. The Trichoderma isolates were applied as a soil drench (1×107 spore/g soil) to a planting mix and field soil, in which plants were grown under non-infested and P. brassicae-infested (2×106 spore/g soil) conditions. The endophytic fungi were able to promote plant growth, significantly increasing shoot and root length, leaf diameter, and biomass production (shoots and root weight) both in the absence or presence of P. brassicae. The single and dual treatments with the endophytes were equally effective in significantly decreasing the root-hair infection, root index, and clubroot severity index. Both ReTk1 and ReTv2 inhibited the germination of resting spores of P. brassicae in root exudates. Moreover, the endophytic fungi colonized the roots of rapeseed extensively and possibly induced host resistance by up-regulated expression of defense-related genes involved in jasmonate (BnOPR2), ethylene (BnACO and BnSAM3), phenylpropanoid (BnOPCL and BnCCR), auxin (BnAAO1) and salicylic acid (BnPR2) pathways. Based on these findings, it is evident that the rapeseed root endophytes Trichoderma spp. ReTk1 and ReTv2 could suppress the gall formation on rapeseed roots via antibiosis, induced systemic resistance (ISR), and/or systemic acquired resistance (SAR). According to our knowledge, this is the first report of the endophytic Trichoderma spp. isolated from root tissues of healthy rapeseed plants (B. napus.), promoting plant growth and reducing clubroot severity.

Expression of defense responsive genes in tripartite interaction of cucumber mosaic virus and plant growth promoting rhizobacteria in ridge gourd (Luffa acutangula (L.) Roxb)

The mosaic caused by cucumber mosaic virus (CMV) on ridge gourd (Luffa acutangula (L.) Roxb) is an important disease. An attempt was made to use a consortium of plant growth promoting rhizobacteria to manage the disease with an aim to reduce the usage of pesticide to control its vector. Eleven isolates of Bacillus spp. were selected based on their plant gowth promotion ability on ridge gourd cv. COH1. Among these, Bacillus pumilus (BSC 4), B. subtilis (Bbv 57) and B. subtilis (BST 8) had shown their potentiality in reducing the severity of CMV disease under artificial conditions. The compatibility test showed that these isolates were compatible to each other. A Bacillus consortium was prepared and evaluated for its efficacy against CMV on ridge gourd and the results showed a reduction of 49.98 % in disease severity over control. The quantitative gene expression analysis revealed that the defense genes viz., peroxidase, polyphenol oxidase, catalase and super oxide dismutase were upregulated in consortium treated ridge gourd plants. The upregulation of these genes indicated the activation of defense pathways which witnessed the induction of systemic resistance in Bacillus consortium treated plants. All gene expressions were reached its peak nearly two to three fold in the consortium treated plants except catalase, its peak expression was found in salicylic acid treated plants which served as a positive control. Correspondingly, the quantitative enzymatic analysis of these defense enzymes at different time intervals was also reflected in similar manner. The elevated level of defense enzymes in plant growth promoting rhizobacteria consortium treated plants was the evident for the onset of systemic resistance.