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.

In rice, cytoplasmic male sterility (CMS) represents an irreplaceable strategy for producing high-yielding hybrid rice based on the commercial exploitation of heterosis. Thereupon, enhancing floral traits and outcrossing rates in CMS lines increase hybrid seed production and ensure global food security. The exogenous application of cyanobacteria could enhance outcrossing rates in CMS lines and, accordingly, hybrid rice seed production. In the present study, we aimed at exploring the impact of cyanobacteria implementation such as Anabaena oryzae, Nostoc muscorum, and their mixture to promote the floral traits, outcrossing rates, and seed production in hybrid rice. The impact of cyanobacteria (Anabaena Oryza (T2), Nostoc muscorum (T3), and their combination (T4) versus the untreated control (T1) was investigated for two years on the growth, floral, and yield traits of five diverse CMS lines, namely IR69625A (L1), IR58025A (L2), IR70368A (L3), G46A (L4), and K17A(L5). The evaluated CMS lines exhibited significant differences in all measured floral traits (days to heading (DTH), total stigma length (TSL), stigma width (SW), duration of spikelet opening (DSO), spikelet opening angle (SOA)). Additionally, L4 displayed the uppermost total stigma length and stigma width, whereas L1 and L5 recorded the best duration of spikelet opening and spikelet opening angle. Notably, these mentioned CMS lines exhibited the highest plant growth and yield traits, particularly under T4 treatment. Strong positive relationships were distinguished between the duration of the spikelet opening, panicle exertion, panicle weight, seed set, grain yield, total stigma length, spikelet opening angle, stigma width, and number of fertile panicles per hill. Cyanobacteria is a potential promising tool to increase floral traits and seed production in hybrid rice.

Drought stress, which is the most serious environmental factor reduces crop productions, might be balanced by some free living and symbiotic soil microorganisms. The physiological response of sweet sorghum plants to inoculation with arbuscular mycorrhizal (VAM) fungi and three potassium fertilizer levels (75, 100 and 125% of recommended rate) was evaluated under three different irrigation intervals (8, 12, and 16 days). A factorial experiment was conducted based on a randomized complete block design (RCBD) with three replications in sandy loam calcareous soil at the El-Nubaria region. The results evidenced that water deficit stress inhibited the growth, biomass of vegetative and reproductive parts, and grain and sugar yield. In all inoculated and uninoculated plants, decreased 1000 grains weight, stalk, grain, biomass, dry matter and sugar yields with increasing irrigation intervals. At the same time, inoculation of sweet sorghum with mycorrhiza resulted in a significant increase in the root colonization, number of mycorrhizal spores, alkali phosphatase, the biomass and sugar yield. Also, increase significantly the content of N, P and K nutrients in plant tissue underwater deficit in calcareous soils compared with non-inoculated plants. Potassium fertilizer in combination with mycorrhizal inoculant on all measured traits could make the plants more tolerant to water stress higher than non-mycorrhizal treatments. In general, the results of this study presented that the sweet sorghum plants inoculated with mycorrhiza and 115 kg K2O ha-1 of potassium sulphate fertilizer improved water stress tolerance, increased the sweet sorghum biomass and sugar yield under water deficit stress in comparison to uninoculated plants.

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.

To evaluate the effect of mycorrhiza (Glomus macrocarpium) with two phosphorus and nitrogen levels (50 and 75 % Optimal dose) and two water salinity levels (2800 ppm (S1) and 3800ppm (S2)) on yield, nutrients uptake and growth parameters of tomato plant. A field experiment was conducted at El Sheikh Zowaied Research Station, North Sinai, Egypt during two successive seasons. The obtained results showed that inoculation with mycorrhizal fungi reduces the negative impact of salinity in growth parameters, nutrient contents and yield of tomato by increasing significantly the shoot and root weights by 38.6, 48.65% and 38.7, 47.86%; leaf area and chlorophyll content by 12.36, 29.90% and 12.93, 30.87%; root/shoot ratio by 19.17 and 11.43% and marketable yield by 29.99 and 33.63%. While significantly reduce the loss of unmarketable yield from 11.05 to 8.86% for the two seasons, respectively. Also, mycorrhizal inoculation increases significantly the plant N by 6.34 and 5.31%; P by 23.66 and 22.03% ad K by 3.64 and 3.15% for both seasons respectively. Similarly, mycorrhizal inoculation significantly improved microbial activities in the soil rhizosphere area of tomato plants. The total microbial counts, phosphatase enzyme, root colonization and soil mycorrhizal spores increases by 33.60 and 35.00%; 45.92 and 52.88%; 257.14 and 257.89% and 34.18 and 34.47% for two seasons, respectively. Mineral fertilizers at 75% of optimal dose increase all traits parameters compared with 50%. In general, these results showed that mycorrhizal fungi represent a promising resource for improving both sustainable food production under salt conditions and human nutritional needs.