The impact of stress on crop productivity and the ecosystem have been magnified by climate changes and mispractices in the agriculture field. Soil microbiome is a diverse system consisting of various microorganisms. Environmental control techniques like the use of arbuscular mycorrhizal fungi (AMF) are necessary to enhance crop productivity. AMF is known as stress regulating organisms that help plants within the nutrient uptake, biotic and abiotic stress management, plant protection, and consequently enhancement on crop yields. Also, host plants can tolerate many difficult situations such as water problems, salt stress, heavy metals, and temperature changes through AMF inoculation. Arbuscular mycorrhizae (AM) enhance plant growth under stress by mediating a series of complex contact events between the two symbiotic partners resulting in a good photosynthetic and gas exchange amelioration. Plants have several tolerance mechanisms to deal with the constraints of environmental changes. The antioxidant ability is the principal tolerance mechanism; it is assisted by osmolytes accumulation and exacting absorption of ions. In this review, we will discuss the effect of AMF colonization on the host plants at different stages of growth, with comprehensively updated knowledge, their roles, and applications for plant growth enhancement and mycorrhizae role on plant resistance induction and stress management.

Excessive use of chemical products in agriculture is causing significant environmental pollution and the loss of lands and fertility of agricultural soils. Plant-growth-promoting bacteria are a valid alternative strategy for sustainable agriculture. The aim of this study was to select actinomycete strains based on their plant-growth-promoting traits and to investigate their root association abilities and biostimulant effects on Solanum lycopersicum. The strains were investigated for their phosphate solubilization ability, production of indole-3-acetic acid, hydrocyanic acid, and ammonia, and several enzymatic activities. Bacteria–plant-root associations were studied by scanning electron microscopy. A greenhouse experiment was carried out to assess inoculation effects. Of sixty isolates, fourteen strains showed significant plant-growth-promoting traits. All fourteen strains solubilized phosphate, produced ammonia, and showed several enzymatic activities at different rates. The production of indole-3-acetic acid was shown by nine strains, while hydrocyanic acid production was observed in eleven of them. Scanning electron microscopy revealed that strains have good in vitro plant root association and colonization abilities. In planta inoculation by actinomycete strains positively influenced plant growth parameters. The best results were shown by seven actinomycete strains, suggesting their possible utilization as biofertilizer agents for sustainable agriculture.

Biotic stress caused by pathogenic microorganisms leads to damage in crops. Tomato and carrot are among the most important vegetables cultivated worldwide. These plants are attacked by several pathogens, affecting their growth and productivity. Fourteen plant growth-promoting actinomycetes (PGPA) were screened for their in vitro biocontrol activity against Solanum lycopersicum and Daucus carota microbial phytopathogens. Their antifungal activity was evaluated against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and Rhizoctonia solani (RHS). Antibacterial activity was evaluated against Pseudomonas syringae, Pseudomonas corrugata, Pseudomonas syringae pv. actinidiae, and Pectobacterium carotovorum subsp. carotovorum. Strains that showed good in vitro results were further investigated in vitro (cell-free supernatants activity, scanning electron microscope observations of fungal inhibition). The consortium of the most active PGPA was then utilized as biocontrol agents in planta experiments on S. lycopersicum and D. carota. The Streptomyces albidoflavus H12 and Nocardiopsis aegyptica H14 strains showed the best in vitro biocontrol activities. The diffusible and volatile compounds and cell-free supernatants of these strains showed both antifungal (in vitro inhibition up to 85%, hyphal desegregation and fungicidal properties) and antibacterial activity (in vitro inhibition >25 mm and bactericidal properties). Their consortium was also able to counteract the infection symptoms of microbial phytopathogens during in planta experiments, improving plant status. The results obtained highlight the efficacy of the selected actinomycetes strains as biocontrol agents of S. lycopersicum and D. carota.

This study aimed to characterize the halotolerant capability, in vitro, of selected actinomycetes strains and to evaluate their competence in promoting halo stress tolerance in durum wheat in a greenhouse experiment. Fourteen isolates were tested for phosphate solubilization, indole acetic acid, hydrocyanic acid, and ammonia production under different salt concentrations (i.e., 0, 0.25, 0.5, 0.75, 1, 1.25, and 1.5 M NaCl). The presence of 1-aminocyclopropane-1-carboxylate deaminase activity was also investigated. Salinity tolerance was evaluated in durum wheat through plant growth and development parameters: shoot and root length, dry and ash-free dry weight, and the total chlorophyll content, as well as proline accumulation. In vitro assays have shown that the strains can solubilize inorganic phosphate and produce indole acetic acid, hydrocyanic acid, and ammonia under different salt concentrations. Most of the strains (86%) had 1-aminocyclopropane-1-carboxylate deaminase activity, with significant amounts of α-ketobutyric acid. In the greenhouse experiment, inoculation with actinomycetes strains improved the morpho-biochemical parameters of durum wheat plants, which also recorded significantly higher content of chlorophylls and proline than those uninoculated, both under normal and stressed conditions. Our results suggest that inoculation of halotolerant actinomycetes can mitigate the negative effects of salt stress and allow normal growth and development of durum wheat plants.

Plants are affected by various biotic and abiotic stresses due to climate change. Tomato and carrots are important crops that are attacked by various pathogens. Fourteen plant-growth-promoting bacteria (PGPB) belonging to the genera Streptomyces sp. and Nocardiopsis sp. were selected for the biocontrol of several common fungal and bacterial pathogens. Antifungal activity was assessed against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) and Rhizoctonia solani (RHS). Antibacterial activity was evaluated against Pseudomonas syringae (PS), Pseudomonas corrugata (PC), Pseudomonas syringae pv. actinidiae (PSA), and Pectobacterium carotovorum subsp. Carotovorum (PCC). In vitro antifungal and antibacterial antagonistic activities were evaluated by the dual culture method. Fungal–bacterial interaction areas were analyzed by scanning electron microscopy (SEM). Cell-free culture filtrates (CFs) from strains showing good biocontrol potential were produced and investigated for their in vitro antifungal and antibacterial activity. The two most effective strains were also combined in consortium and utilized for In Planta pre-emergence biocontrol assays on both S. lycopersicum and D. carota. For each pathogenic strain, four experimental conditions were compared: CNT (no PGPB/no infection), PGPB (with PGPB/no infection), PGPB+INF (with PGPB/with infection), and INF (no PGPB/with infection). Streptomyces albidoflavus strain H12 and Nocardiopsis aegyptica strain H14 showed good in vitro antifungal (inhibition of >50%) and antibacterial (inhibition halo of >10 mm) activity. The SEM micrographs showed deterioration of fungal filaments and modification of hyphal structures. The CFs of both strains were also able to inhibit FORL and RHS in in vitro growth (minimum inhibitory concentration of 0.2–0.8%). In planta biocontrol assessments showed that the consortium was effective in reducing the infection effects of both fungal and bacterial pathogens. Dual consortium allowed regular plant development compared to the control. These results confirm the usefulness of actinomycetes strains as a biocontrol agent and can therefore be an alternative to chemicals used in agriculture.