article · Plants
Four Streptomyces strains, namely HM2, HM3, HM8, and HM10, were evaluated for their plant growth-promoting properties and their capacity to enhance cucumber cultivation under greenhouse conditions. Laboratory tests confirmed that all four strains produce indole acetic acid and siderophores while effectively solubilising inorganic phosphate. Strain HM10 produced the highest concentrations of indole acetic acid and siderophores, whereas strains HM3 and HM10 exhibited the highest phosphate solubilisation efficiencies. In planta evaluations combining these bacterial strains with rock phosphate demonstrated significant improvements across multiple agronomic traits. Specifically, rock phosphate paired with strain HM3, followed by strain HM8, produced the most substantial increases in cucumber plant height, leaf count, root length, fruit dimensions, overall fruit fresh weight, and soil phosphorus retention.
Overreliance on synthetic agrochemicals creates substantial environmental pollution and degrades soil health. Utilising beneficial soil microbes capable of releasing bound nutrients and generating natural growth hormones offers a sustainable path forward. Identifying specific bacterial strains that enhance vegetable productivity alongside raw mineral inputs supports the transition towards eco-friendly biofertilisers without sacrificing crop yields.
This research could enable the formulation of microbial biofertilisers tailored for horticulture and greenhouse vegetable producers. The strains offer a natural method to enhance rock phosphate efficiency and crop productivity. Currently at the applied and tested greenhouse stage, the technology requires field-scale trials, shelf-life formulation development, and standard regulatory compliance testing before it can reach commercial deployment.
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The genus <i>Streptomyces</i> is the most abundant and essential microbes in the soil microbial community. <i>Streptomyces</i> 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 <i>Streptomyces</i> strains and their role in enhancing cucumber growth and yield under greenhouse conditions. <i>Streptomyces</i> sp. strain HM2, <i>Streptomyces thinghirensis</i> strain HM3, <i>Streptomyces</i> sp. strain HM8, and <i>Streptomyces tricolor</i> 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 <i>Streptomyces</i> 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.
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DOI: 10.3390/plants11233316
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