Plant growth-promoting and biocontrol traits of endophytic Bacillus licheniformis against soft rot causing Pythium myriotylum in ginger plant

Abstract

Bacterial endophytes from plants harbor diverse metabolites that play major roles in biocontrol and improve plant growth. In this study, a total of 12 endophytic bacteria were isolated from the ginger rhizome. The strain K3 was highly effective in preventing mycelia growth of Pythium myriotylum (78.5 ± 1.5% inhibition) in dual culture. The cell-free extract (2.5%) of endophyte K3 inhibited 76.3 ± 4.8% mycelia growth, and 92.4 ± 4.2% inhibition was observed at a 5% sample concentration. The secondary metabolites produced by Bacillus licheniformis K3 showed maximum activity against Pseudomonas syringae (24 ± 1 mm zone of inhibition) and Xanthomonas campestris (28 ± 3 mm zone of inhibition). The strain K3 produced 28.3 ± 1.7 IU mL⁻¹ protease, 28.3 ± 1.7 IU mL⁻¹ cellulase, and 2.04 ± 0.13 IU mL⁻¹ chitinase, respectively. The ginger rhizome treated with K3 in the greenhouse registered 53.8 ± 1.4% soft rot incidence, and the streptomycin-treated pot registered 78.3 ± 1.7% disease incidence. The selected endophyte K3 improved ascorbate peroxidase (1.37 ± 0.009 µmole ASC min⁻¹ mg⁻¹ protein), catalase (8.7 ± 0.28 µmole min⁻¹ mg⁻¹ protein), and phenylalanine ammonia-lyase (26.2 ± 0.99 Umg⁻¹) in the greenhouse. In addition, K3 treatment in the field trial improved rhizome yield (730 ± 18.4 g) after 180 days (p < 0.01). The shoot length was 46 ± 8.3 cm in K3-treated plants, and it was about 31% higher than the control treatment (p < 0.01). The lytic enzyme-producing and growth-promoting endophyte is useful in sustainable crop production through the management of biotic stress.