Bacillus amyloliquefaciens TU ‐Orga12 as a Novel Compost–Microbial Pellet for Plant Growth Promotion and Induced Plant Defence, and Assessment of Its Acute Oral Toxicity
Abstract
This study aimed to identify antagonistic microorganisms for black rot control and plant growth promotion in Chinese kale, and to develop a Bacillus ‐enriched compost‐microbial pellet for sustainable agriculture. Bacterial strains were screened for antagonistic activity, plant growth‐promoting traits, formulation stability, disease suppression efficacy and biosafety. Among the strains, TU‐Orga12 showed the strongest antagonistic activity against a virulent strain of Xanthomonas campestris pv. campestris (Xcc) TU‐D‐LRI001, producing an inhibition zone of 27.0 mm. Morphological, biochemical and 16S rDNA gene sequence analyses identified TU‐Orga12 as Bacillus amyloliquefaciens . TU‐Orga12 exhibited significant plant growth‐promoting properties. It enhanced total chlorophyll content in cucumber cotyledons to 0.52 mg g −1 FW, surpassing the effect of the synthetic cytokinin. High‐performance liquid chromatography confirmed cytokinin production by TU‐Orga12 at 44 mg L −1 , which correlated with improved shoot and root development, biomass accumulation and seed germination rates in Chinese kale. When incorporated into pelleted manure fertilizer, Formula 4, the TU‐Orga12 formulation maintained high microbial viability and significantly reduced black rot disease incidence and severity by up to 89.2% and 89.7%, respectively. This treatment also promoted salicylic acid accumulation, indicating enhanced systemic resistance under both challenged and non‐challenged conditions with Xcc TU‐D‐LRI001. The formulation retained its efficacy after 12 months of storage. Furthermore, a preclinical safety assessment in Wistar Hannover rats, conducted according to OECD 423 guidelines, confirmed the absence of toxicity. These findings support the microbial pellet as having strong potential as a sustainable bioproduct for crop protection and productivity enhancement.