The genus Streptomyces is the most abundant and essential microbes in the soil microbial community. Streptomyces are familiar and have great potential to produce a large variety of bioactive compounds. This genus considers an efficient biofertilizer based on its plant growth-promoting activities. Based on their ability to produce a wide varieties of bioactive molecules, the present study aimed to explore the potential plant growth promotion of four Streptomyces strains and their role in enhancing cucumber growth and yield under greenhouse conditions. Streptomyces sp. strain HM2, Streptomyces thinghirensis strain HM3, Streptomyces sp. strain HM8, and Streptomyces tricolor strain HM10 were chosen for the current study. Plant growth-promoting (PGP) features, i.e., indole acetic acid (IAA) production, siderophore excretion, and solubilizing phosphate, were evaluated in vitro. All four strains produced IAA, siderophore, and immobilized inorganic phosphate. Following 4 days of incubation at 30 °C, strains HM2, HM3, HM8, and HM10 produced copious amounts of IAA (18, 22, 62, and 146 µg/mL, respectively) and siderophores (42.59, 40.01, 16.84, 64.14% SU, respectively). At the same time, P solubilization efficacy scored 64.3%, 84.4%, 57.2%, and 81.6% with the same frequency. During in planta evaluation, selected Streptomyces strains combined with rock phosphate were assessed as biofertilizers on the growth and yield of cucumber plants. Under all treatments, positive and significant differences in studied traits were manifested except dry stem matter (SDM), net assimilation rate (NAR), relative growth rate (RGR), and fruit firmness (FF). Treatment T4 (rock phosphate + strain HM3) followed by T5 (rock phosphate + strain HM8) revealed the best results for plant height (PH), number of leaves per plant (NLPP), root length (RL), number of fruits per plant (NFPP), fruit length (FL), fruit diameter (FD), fruit fresh weight per plant (FFWPP), soil P (SP) after 21 DAT, and soil P at the end of the experiment. Notably, T6 (rock phosphate + strain HM10) caused a considerable increase in leaf area (LA). Plant growth-promoting bacteria enhance plant growth and yield through phosphorus solubilizing, improve nutrient availability, produce phytohormones, and support plant growth under abiotic stress. These features are important for sustainable agriculture and reducing environmental pollution with chemical fertilizers and pesticides.

The plant-growth-promoting rhizobacteria (PGPR) in the rhizosphere affect plant growth, health, and productivity, as well as soil-nutrient contents. They are considered a green and eco-friendly technology that will reduce chemical-fertilizer usage, thereby reducing production costs and protecting the environment. Out of 58 bacterial strains isolated in Qassim, Saudi Arabia, four strains were identified by the 16S rRNA as the Streptomyces cinereoruber strain P6-4, Priestia megaterium strain P12, Rossellomorea aquimaris strain P22-2, and Pseudomonas plecoglossicida strain P24. The plant-growth-promoting (PGP) features of the identified bacteria involving inorganic phosphate (P) solubilization, the production of indole acetic acid (IAA), and siderophore secretion were assessed in vitro. Regarding the P solubilization, the previous strains’ efficacy reached 37.71%, 52.84%, 94.31%, and 64.20%, respectively. The strains produced considerable amounts of IAA (69.82, 251.70, 236.57, and 101.94 µg/mL) after 4 days of incubation at 30 °C. Furthermore, the rates of siderophore production reached 35.51, 26.37, 26.37, and 23.84 psu, respectively, in the same strains. The application of the selected strains in the presence of rock phosphate (RP) with tomato plants under greenhouse conditions was evaluated. The plant growth and P-uptake traits positively and significantly increased in response to all the bacterial treatments, except for some traits, such as plant height, number of leaves, and leaf DM at 21 DAT, compared to the negative control (rock phosphate, T2). Notably, the P. megaterium strain P12 (T4), followed by R. aquimaris strain P22-2 (T5), revealed the best values related to plant height (at 45 DAT), number of leaves per plant (at 45 DAT), root length, leaf area, leaf-P uptake, stem P uptake, and total plant P uptake compared to the rock phosphate. The first two components of the PCA (principal component analysis) represented 71.99% (PCA1 = 50.81% and PCA2 = 21.18%) of the variation at 45 DAT. Finally, the PGPR improved the vegetative-growth traits of the tomato plants through P solubilization, IAA, and siderophore production, and ameliorated the availability of nutrients. Thus, applying in PGPR in sustainable agriculture will potentially reduce production costs and protect the environment from contamination by chemical fertilizers and pesticides.

Sclerotinia sclerotiorum causes white mold disease, resulting in losses of up to 50% in several host plants worldwide. It is a harmful fungus as it infects plants at any stage of development, in the field, or in storage; this includes young seedlings, mature plants, and fruits. The accessibility of molecular and biological methods has contributed significantly to our understanding of S. sclerotiorum etiology and progression. The present research aimed to characterize S. sclerotiorum causing white mold disease in eggplant (S. melobgena), evaluate the potentiality of some bio-agents for inhibiting the fungus growth and develop a strategy for dealing with the disease challenge. Eggplants grown in open fields and greenhouses showed cottony growth on their stems, followed by the emergence of sclerotia. A fungal growth with fluffy mycelium and considerable sclerotia was isolated from the infected tissues. Polyphasic characterization and phytopathological analysis identified the fungus as S. sclerotiorum. The symptoms previously seen in the field were reproduced by inoculating healthy eggplant roots, stems, and leaves with the fungus. The ITS rDNA sequencing (564 bp) homology and phylogenetic analysis showed 99% sequence similarity of the isolate with multiple S. sclerotiorum. A wide range of strategies are required for disease management. S. sclerotiorum is sensitive to competition from other bacteria. Such a technique might act as an initial basis for effective biological control of white mold. The results demonstrated that eight isolates have very strong antagonistic activity against S. sclerotiorum. Reduced rates ranged from 63.1% (65 D) to 39.0.1% (75 A1). At the same time, the effect of the Trichoderma harzianum fungus against the pathogen S. sclerotium was apparent in restricting mycelium growth and inhibiting the fungus growth. ITS sequencing identified the mycopathogen. The interaction of seven Bacillus spp isolates with S. sclerotiorum on PDA culture media highlighted these isolates' capacity to limit the pathogen's mycelial growth. Furthermore, the antimicrobial agent must remain in the same environment for an extended period while also being active against the pathogen.

Plant growth-promoting bacteria (PGPB) have a wide range of applications in agriculture and environmental management. They act as biostimulants and biofertilizers to enhance crop quality and yields in a more sustainable way. The present research aimed at isolating three active strains from the arid rhizosphere soil to act as biofertilizer. The plant growth-promoting features were evaluated in vitro and their implementation on pepper growth and yield were assessed and measured. Regarding IAA and ammonia production, the three designated isolates (P21, P22-1 and P58) showed patterns of high IAA production, producing 154.47 µg/mL, 155.03 µg/mL, and 188.65 µg/mL, respectively. Furthermore, considerable amounts of ammonia were detected in the supernatant of peptone water medium after 72 h of growth. Isolate P21 produced the maximum amount and generated 17.38 μmol/mL, whereas both P22-1 and P58 displayed lower amounts (15.47 and 15.92, respectively), without significant differences. P-solubilization efficacy calculated 18.7% (isolate P21), 64% (isolate P22-2), and 54% (isolate P58) when compared with un-inoculated medium. The molecular identification by 16S rRNA displayed that the three isolates belonged to Pseudomonas alkylphenolica strain P21 (PX257452), Pantoea agglomerans strain P22-1 (PX257453), and Pantoea brenneri strain P58 (PX257454). Applying the selected strains with sweet pepper in the presence of rock phosphate (RP) was assessed under greenhouse conditions. Three treatments (adding bacterial suspension at 0, 10 and 20 days after transplanting) from P21, P22-1, and P58 strains revealed that P21(3), P21(2), P22-1(3), and P58(3) treatments are considered the most promising treatments related to plant height, root length, leaf area, number of leaves per plant, leaf P-uptake, and stem P-uptake in addition to total plant P-uptake. In addition, the PCA biplot showed that MSP (mono-super phosphate), P22-1(3), and P58(3) are closely associated with high phosphorus uptake, indicating their effectiveness in enhancing phosphorus absorption by solubilizing insoluble forms. Eventually, PGPB will help the environment by improving soil fertility and structure, decreasing the need for toxic chemical fertilizers, and improving ecosystem health overall.

The purpose of this study was to assess the effectiveness of two nanostructures (MgO and Zn/MgO) against Sclerotinia sclerotiorum, which causes white mold disease in peas, as direct antifungal agents or resistance inducers in pea plants. The direct antifungal activity of these nanostructures was evaluated by assessing their ability to inhibit S. sclerotiorum growth in vitro and reduce white mold severity in the greenhouse. The induction of resistance in pea plants was examined by assessing the expression of three defense-related genes using quantitative real-time PCR and measuring the phenolic compounds content in treated pea plants relative to untreated controls. The effect of the tested control agents on the growth and yield of pea plants was investigated. In comparison to the untreated control, S. sclerotiorum growth was markedly suppressed following treatment with the investigated compounds. The complete suppression (100%) of S. sclerotiorum growth was achieved with concentration levels of 100 mg/L for both MgO and Zn/MgO nanostructures. In greenhouse conditions, pea plants treated with the investigated chemicals showed a considerable reduction in the severity of white mold disease when compared to the untreated control plants. The transcript levels of 12-oxophytodienoate reductase 11 (OPR1), antioxidant peroxide (PsOXII), and chlorophyll a-b binding protein genes increased significantly in treated plants with MgO (3.1, 2.7, and 3.5-fold), fungicide (3.2, 2.8, and 2.8-fold), and Zn/MgO (3.5, 3, and 5-fold) compared to control, respectively. Pea plants treated with the tested nanoparticles generated more phenolic content than untreated controls. The application of fungicide and tested nanoparticles to peas greatly enhanced their growth properties. In light of our results, the application of these nanoparticles may represent a novel approach for controlling this pathogen.