Exploring the Plant Growth-Promotion of Four Streptomyces Strains from Rhizosphere Soil to Enhance Cucumber Growth and Yield

Abstract

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.

Performance of Plant-Growth-Promoting Rhizobacteria (PGPR) Isolated from Sandy Soil on Growth of Tomato (Solanum lycopersicum L.)

“…Furthermore, enzymes such as phosphatase, phytase, and C-P lyase are involved in organic-phosphate solubilization [31,32]. In our previous publication [14], the S. thinghirensis strain HM3 had a P solubilization efficacy that reached 84.4%, followed by the S. tricolor strain HM10 (81.6%). Yu et al [33] isolated a highly efficient P-solubilizing bacterial strain, Pseudomonas sp.…”

“…Furthermore, it helps to move oxygen throughout plants' parts, producing their green color, and it is a co-factor in many vital enzymes [41]. The Streptomyces tricolor strain HM10 secreted up to 64.14% psu from siderophores after 4 days of incubation [14,15,42]. Cherif-Silin et al [43] isolated thirty-five Bacillus strains from a wheat rhizosphere.…”

“…By producing siderophores (low-molecular-weight molecules, 400-2000 Da), microorganisms chelate iron with high affinity and deposit it within their cells. In this way, siderophores improve plant nutrition (direct effect) and control phytopathogen growth (indirect effect) via the chelation of iron from the surrounding environment [6,8,14,15].…”

Bacillus paralicheniformis RP01 Enhances the Expression of Growth-Related Genes in Cotton and Promotes Plant Growth by Altering Microbiota inside and outside the Root

“…Additionally, they can indirectly promote plant growth by: (a) secreting antibiotics to control pathogens; (b) improving plant resistance to abiotic stresses (drought and salinity); and (c) improving the rhizosphere environment (recruitment of beneficial microorganisms) [ 1 , 2 ]. For example, four Streptomyces strains (HM2, HM3, HM8 and HM10) have been reported to enhance cucumber growth and yield through various mechanisms including indole acetic acid (IAA) production, siderophore excretion and phosphate solubilization [ 3 ]. Sphingomonas sp.…”

Employing a Plant Probiotic Actinomycete for Growth Promotion of Lettuce (Lactuca sativa L. var. longifolia) Cultivated in a Hydroponic System under Nutrient Limitation

“…Currently, there is growing interest among researchers in microorganisms that stimulate plant growth, driven by environmental concerns and the need for sustainable food production [13]. Actinomycetes, a subgroup of plant growthpromoting bacteria (PGPB), have gained popularity as 'plant probiotics' and valuable tools for enhancing crop yields through environmentally friendly agriculture practices [14,15]. Actinomycetes have demonstrated their ability to stimulate the growth of various plants under both normal and stressful conditions [14,16,17].…”