Growth-Promoting Effects of Ten Soil Bacterial Strains on Maize, Tomato, Cucumber, and Pepper Under Greenhouse Conditions

Abstract

Beneficial interactions between plants and bacteria are crucial in agricultural practices, as bacteria can improve soil fertility, promote plant growth, and protect plants from pathogens. This study aimed to molecularly identify and characterize soil bacterial isolates and evaluate their effect on the growth of maize (Zea mays L.), tomato (Solanum lycopersici L.), cucumber (Cucumis sativus L.), and pepper (Capsicum annuum L.) under greenhouse conditions. Plant growth parameters, including plant height, root length, and fresh (FW) and dry (DW) weights, were measured. Additionally, pigment extraction and element content analysis using leaves were performed. Among the isolates, the most effective strain in the greenhouse experiment was Bacillus safensis SCF6, which significantly enhanced plant height and fresh weight across all tested plants, with the greatest influence observed in maize plant height (439.42 ± 6.42 mm), fresh weight (14.07 ± 0.87 g plant^-1 FW), and dry weight (1.43 ± 0.17 g plant^-1 DW) compared to the control (364.67 ± 10.33 mm, 9.20 ± 1.16 g plant^-1 FW, and 0.92 ± 0.15 g plant^-1 DW, respectively). Other strains also demonstrated notable results, with Microbacterium testaceum SCF4, Bacillus mojavensis SCF8, and Pseudomonas putida SCF9 showing the highest plant growth-promoting effects on pepper, tomato, and cucumber, respectively. Pseudomonas putida SCF9 demonstrated strong antifungal activity against Monilinia laxa, with a percentage of mycelial growth inhibition (PGI) of 72.62 ± 2.06%, while Bacillus subtilis SCF1 exhibited effects against Botrytis cinerea (PGI = 69.57 ± 4.35%) and Cercospora sp. (PGI = 63.11 ± 1.12%). The development and application of beneficial bacterial inoculants or their formulated products can contribute to environmentally friendly farming practices and global food security.

Keywords: characterization; elemental content; identification; pigment content; plant morphological parameters; seed inoculation.

Figure 1

Percentage of mycelial growth inhibition (PGI) in the dual culture method. Results are presented as the means ± standard deviations from three replicates. Isolates that did not inhibit the mycelial growth of phytopathogenic fungi are not included. SCF1—B. subtilis; SCF2—B. subtilis; SCF3—B. paralicheniformis; SCF7—B. pumilus; SCF9—P. putida.

Figure 2

Control plants and plants treated with B. safensis SCF6 (treatment T6) after 35 days of growth: (a) maize, (b) tomato, (c) pepper, and (d) cucumber.

Figure 3

(a) Plant height (mm), (b) root length (mm), (c) fresh weight (FW, in gram per plant), and (d) dry weight (DW, in gram per plant) for the control (C) and treatments (T1–T10). Results are expressed as means ± standard deviations from three replicates. Different letters indicate statistically significant differences among treatments (ANOVA, Tukey’s test, p ˂ 0.05).

Figure 4

Pigment content (mg∙g⁻¹ FW) in fresh leaves of (a) maize, (b) tomato, (c) cucumber, and (d) pepper for the control (C) and treatments (T1–T10). Results are expressed as means ± standard deviations from three replicates. Different letters indicate statistically significant differences among treatments (ANOVA, Tukey’s test, p ˂ 0.05).