Mycorrhizal fungi and Pseudomonas fluorescens application reduces root-knot nematode (Meloidogyne javanica) infestation in eggplant

Root-knot nematode infections and soil characteristics significantly affected microbial community composition and assembly of tobacco soil microbiota: a large-scale comparison in tobacco-growing areas

Introduction

Tobacco root-knot nematode (RKN) is a highly destructive soil-borne disease worldwide. However, there is a lack of research on the relationship between RKN and tobacco root microbial community composition under large-scale geographical conditions in China.

Methods

In this study, we collected 65 samples from 28 main tobacco-growing areas across 10 provinces in China and conducted 16S rDNA sequencing to investigate the dynamic microbial changes in tobacco soil infected by RKN compared to healthy tobacco soil. Based on the analysis of rhizosphere soil bacterial communities, changes after RKN infection, and soil environmental factors.

Results

We found the 28 tobacco-growing areas could be divided into two distinct groups with different microbial compositions and varying responses to RKN infection. In group1 of the provinces of Anhui, Henan, Shanxi, and Heilongjiang, Vicinamibacteria dominated the bacterial community, while Acidobacteriae was present in low abundance. In contrast, group2 of the other six provinces (Yunnan, Guizhou, Chongqing, Guangxi, Hubei, and Shandong) exhibited an opposite pattern. After infected by RKN, the genera Chitinophaga increased significant in group 1, while the genera Rhodococcus in group 2 exhibited a substantial increase. Alpha-diversity analysis revealed that RKN-infected tobacco exhibited a richer and more diverse rhizosphere soil bacterial community compared to healthy tobacco in most growing areas. A total of 12 kinds of soil environmental factors were measured in healthy and RKN-infected tobacco soil, and based on the co-occurrence and correlation analysis between environmental factors and microbial species, the pH level, calcium (Ca), magnesium (Mg), phosphorus (P), iron (Fe), and sodium (Na) were identified as key environmental factors influencing the population composition of rhizosphere microorganisms during RKN infection. We observed that RKN infection further increased the pH in weakly alkaline group 1 soil, while weakly acidic group 2 soil experienced a further decrease in pH. Furthermore, we identified three genera as potential biocontrol or plant growth-promoting bacteria for tobacco.

Discussion

These findings provide valuable reference data for managing RKN disease in different tobacco-growing areas and contribute to the exploration of new and effective biological control methods.

The Application of Arbuscular Mycorrhizal Fungi as Microbial Biostimulant, Sustainable Approaches in Modern Agriculture

Biostimulant application can be considered an effective, practical, and sustainable nutritional crop supplementation and may lessen the environmental problems related to excessive fertilization. Biostimulants provide beneficial properties to plants by increasing plant metabolism, which promotes crop yield and improves the quality of crops; protecting plants against environmental stresses such as water shortage, soil salinization, and exposure to sub-optimal growth temperatures; and promoting plant growth via higher nutrient uptake. Other important benefits include promoting soil enzymatic and microbial activities, changing the architecture of roots, increasing the solubility and mobility of micronutrients, and enhancing the fertility of the soil, predominantly by nurturing the development of complementary soil microbes. Biostimulants are classified as microbial, such as arbuscular mycorrhizae fungi (AMF), plant-growth-promoting rhizobacteria (PGPR), non-pathogenic fungi, protozoa, and nematodes, or non-microbial, such as seaweed extract, phosphite, humic acid, other inorganic salts, chitin and chitosan derivatives, protein hydrolysates and free amino acids, and complex organic materials. Arbuscular mycorrhizal fungi are among the most prominent microbial biostimulants and have an important role in cultivating better, healthier, and more functional foods in sustainable agriculture. AMF assist plant nutrient and water acquisition; enhance plant stress tolerance against salinity, drought, and heavy metals; and reduce soil erosion. AMF are proven to be a sustainable and environmentally friendly source of crop supplements. The current manuscript gives many examples of the potential of biostimulants for the production of different crops. However, further studies are needed to better understand the effectiveness of different biostimulants in sustainable agriculture. The review focuses on how AMF application can overcome nutrient limitations typical of organic systems by improving nutrient availability, uptake, and assimilation, consequently reducing the gap between organic and conventional yields. The aim of this literature review is to survey the impacts of AMF by presenting case studies and successful paradigms in different crops as well as introducing the main mechanisms of action of the different biostimulant products.

A Novel Robust Screening Assay Identifies Pseudomonas Strains as Reliable Antagonists of the Root-Knot Nematode Meloidogyne incognita

Forty-four bacterial strains isolated from greenhouse soil and beetroots were tested for their antagonistic activity against the plant-parasitic root-knot nematode (RKN) Meloidogyne incognita, which causes significant yield losses in a number of important crops worldwide. Through a novel combination of in vitro and on planta screening assays, Pseudomonas spp. 105 and 108 were identified as the most promising bacterial isolates. Both strains were evaluated for their potential to control different RKN population densities and as root protectants against nematode infestation. Regardless of the application method, both strains significantly reduced root galling caused by M. incognita. These two strains were subjected to whole genome sequencing and de novo genome assembly as a basis for phylogenetic and future functional characterization. Phylogenetic analysis revealed that both Pseudomonas strains cluster within the Pseudomonas fluorescens clade among previously characterized RKN antagonists and Pseudomonas-based biocontrol agents of plant diseases.

Arbuscular mycorrhizal fungi-mediated activation of plant defense responses in direct seeded rice (Oryza sativa L.) against root-knot nematode Meloidogyne graminicola

Rhizosphere is the battlefield of beneficial and harmful (so called phytopathogens) microorganisms. Moreover, these microbial communities are struggling for their existence in the soil and playing key roles in plant growth, mineralization, nutrient cycling and ecosystem functioning. In the last few decades, some consistent pattern have been detected so far that link soil community composition and functions with plant growth and development; however, it has not been studied in detail. AM fungi are model organisms, besides potential role in nutrient cycling; they modulate biochemical pathways directly or indirectly which lead to better plant growth under biotic and abiotic stress conditions. In the present investigations, we have elucidated the AM fungi-mediated activation of plant defense responses against Meloidogyne graminicola causing root-knot disease in direct seeded rice (Oryza sativa L.). The study describes the multifarious effects of Funneliformis mosseae, Rhizophagus fasciculatus, and Rhizophagus intraradices inoculated individually or in combination under glasshouse conditions in rice plants. It was found that F. mosseae, R. fasciculatus and R. intraradices when applied individually or in combination modulated the biochemical and molecular mechanisms in the susceptible and resistant inbred lines of rice. AM inoculation significantly increased various plant growth attributes in plants with simultaneous decrease in the root-knot intensity. Among these, the combined application of F. mosseae, R. fasciculatus, and R. intraradices was found to enhance the accumulation and activities of biomolecules and enzymes related to defense priming as well as antioxidation in the susceptible and resistant inbred lines of rice pre-challenged with M. graminicola. The application of F. mosseae, R. fasciculatus and R. intraradices, induced the key genes involved in plant defense and signaling and it has been demonstrated for the first time. Results of the present investigation advocated that the application of F. mosseae, R. fasciculatus and R. intraradices, particularly a combination of all three, not only helped in the control of root-knot nematodes but also increased plant growth as well as enhances the gene expression in rice. Thus, it proved to be an excellent biocontrol as well as plant growth-promoting agent in rice even when the crop is under biotic stress of the root-knot nematode, M. graminicola.

Metagenomic insights into the changes in the rhizosphere microbial community caused by the root-knot nematode Meloidogyne incognita in tobacco

Root-knot nematode (RKN) disease is a destructive soil disease that affects crop health and causes huge losses in crop production. To explore the relationships between soil environments, rhizobacterial communities, and plant health, rhizosphere bacterial communities were analyzed using metagenomic sequencing in tobacco samples with different grades of RKN disease. The results showed that the community structure and function of the plant rhizosphere were significantly correlated to the RKN disease. RKN density and urease content were key factors affecting the rhizosphere bacterial community. Urease accelerated the catabolism of urea and led to the production of high concentrations of ammonia, which directly suppressed the development of RKNs or by improving the nutritional and growth status of microorganisms that were antagonistic to RKNs. Further experiments showed that the suppression role of ammonia should be attributed to the direct inhibition of NH₃. The bacterial members that were positively correlated with RKN density, contained many plant cell wall degrading enzymes, which might destroy plant cell walls and promote the colonization of RKN in tobacco roots. The analysis of metatranscriptome and metabolism demonstrated the role of these cell wall degrading enzymes. This study offers a comprehensive insight into the relationships between RKNs, bacteria, and soil environmental factors and provides new ideas for the biological control of RKNs.

Rhizophagus irregularis and Nitrogen Fixing Azotobacter with a Reduced Rate of Chemical Fertilizer Application Enhances Pepper Growth along with Fruits Biochemical and Mineral Composition

Bell pepper is an important vegetable crop containing lots of bioactive compounds. The present study was designed to improve the productivity and quality of bell pepper with the application of arbuscular mycorrhizal fungi (Rhizophagus irregularis) and plant growth-promoting bacteria (Azotobacter chroococcum) in a combination of chemical fertilizer. Five treatments consisted of 75% chemical fertilizer (T1), 100% chemical fertilizer (T2), 75% chemical fertilizer + R. irregularis (T3), 75% chemical fertilizer + A. chroococcum (T4) and 75% chemical fertilizer + R. irregularis + A. chroococcum (T5). Out of 18 morphological parameters, 11 morphometric fruit parameters were recorded in detail by a tomato analyzer. The morphological and biochemical (TSS, ascorbic acid and capsaicin content) attributes of bell pepper were recorded higher in the case of a mixed consortium of chemical fertilizers having R. irregularis and A. chroococcum. Similarly, the amount of mineral content recorded was highest after 75% chemical fertilizer + R. irregularis + A. chroococcum, followed by the treatment with only 100% chemical fertilizer. The root mycorrhization (%) and the number of spores were observed highest in 75% chemical fertilizer + R. irregularis + A. chroococcum, and there was no mycorrhization and spore formation in 75% CF, 100% CF and 75% CF+AC. The treatment involving 75% chemical fertilizer + R. irregularis + A. chroococcum proved better for pepper’s growth, yield and yield-related traits.

Rhizophagus irregularis and Nitrogen Fixing Azotobacter Enhances Greater Yam (Dioscorea alata) Biochemical Profile and Upholds Yield under Reduced Fertilization

Greater yam (Dioscorea alata L.) is a tropical plant with a large food reserve in its underground tubers. Cultivating the greater yam is considered an essential food security crop. Yam tuber yield and quality is decreased by poor soil fertility, heavy use of fertilizers and attack of insect pest. The heavy use of fertilizers impaired the soil structure polluted the environment, and adversely impacted human beings. We employed Rhizophagus irregularis (Arbuscular Mycorrhiza Fungus) and nitrogen fixing Azotobacter to help reduce the adverse effects of fertilisers on the plants. In this study, we applied five treatments such as (1) CF: normal with conventional package and practices, (2) 70%CF: 70% chemical fertilizer, (3) 70 %CF + RI: 70% CF + AMF (R. irregularis), (4) 70%CF + AC: 70% CF + PGPB (Azotobacter chroococum), and (5) 70%CF + RI + AC: 70% CF + R. irregularis + Azotobacter chroococum, as donated as T1, T2, T3, T4 and T5, obtained that 70%CF + RI + AC was found to be the most efficient treatment under reduce chemical fertilization for improving morphological traits and biochemical content of greater yam. Although some other treatments such as 70%CF + AC, 70%CF + RI, 70% CF and CF demonstrated considerable effects in yam compared with 70%CF: 70% chemical fertilizer.

Biological control: An effective approach against nematodes using black pepper plants (Piper nigrum L.)

Black pepper (Piper nigrum L.) is one of the oldest spices in the world, additionally, it is highly demanded. Several biotic and abiotic variables pose black pepper production worldwide. Plant-parasitic nematodes play a key role among biotic factors, causing considerable economic losses and affecting the production. Different synthetic nematicides were used for controlling plant nematodes, however the majority of pesticides have been pulled from the market due to substantial non-target effects and environmental risks. As a result, the search for alternative eco-friendly agents for controlling plant-parasitic nematodes populations. Microbial agents are a precious option. In this review the bacterial and fungal agents used as an alternative nematicides, they were studied and confirmed as essential anti-microbial agents against plant nematodes which infected Piper nigrum L. This work examines the most common plant nematodes infected Piper nigrum L., with a focus on root knot and burrowing nematodes, in addition, how to control plant parasitic nematodes using microorganisms.

Natural Plant Extracts and Microbial Antagonists to Control Fungal Pathogens and Improve the Productivity of Zucchini (Cucurbita pepo L.) In Vitro and in Greenhouse

Background: Natural plant extracts and microbial antagonists have the potential for use in increasing the fungal resistance and productivity of horticulture plants. Methods: The purpose of this study was to evaluate the ability of both natural plant extracts and microbial antagonists as a biotical control of some fungal pathogens, i.e., Fusarium ssp., Exserohilum ssp. and Nigrospora ssp., along with improving the growth and productivity performance of zucchini under greenhouse conditions. Eucalyptus camaldulensis leaf extract (LE), Citrus sinensis LE, Ficus benghalensis fruit extract (FE), and two microbial antagonists Pseudomonas fluorescens (accession no. MW647093) and Trichoderma viride (accession no. MW647090) were tested under in vitro and in vivo conditions. Through morphological characteristics and the internal transcribed spacer (ITS) region, Fusarium solani (accession no. MW947256), F. oxysporum (accession no. MW947254), Exserohilum rostratum (accession no. MW947255), and Nigrospora lacticolonia (accession no. MW947253) were identified. HPLC analysis was used for the identification of phenolic compounds (PCs) and flavonoid compounds (FCs) in the extracts. Results: The highest inhibition percentage of fungal growth (IPFG) against F. oxysporum was obtained with P. fluorescens, T. viride, and E. camaldulensis LE (4000 mg/L); F. solani with P. fluorescens, T. viride, and C. sinensis LE (4000 mg/L); Exserohilum rostratum with P. fluorescens, Ficus benghalensis FE (4000 mg/L) and E. camaldulensis LE (4000 mg/L), and N. lacticolonia with P. fluorescens. Using HPLC analysis, the abundant PCs in E. camaldulensis LE were pyrogallol, and caffeic acid, those in C. sinensis LE were syringic acid and ferulic acid, and those in F. benghalensis FE were gallic acid and syringic acid. In addition, the abundant FCs in E. camaldulensis LE were kaempferol, and naringin, those in C. sinensis LE were hesperidin and quercetin, and those in F. benghalensis FE were kaempferol and quercetin. Under greenhouse experiments, T. viride and E. camaldulensis LE (4000 mg/L) followed by P. fluorescens + T. viride treatments gave the best results of zucchini plants in terms of leaf area, fruits number per plant, yield per plant, and total yield (marketable and non-marketable). Conclusions: Plant extracts and bioagents can be used to control some zucchini fungal pathogens and increase the productivity performance of zucchini plants.