Identification and plant growth promotion of endophyte bacterium T2-29 in lavender seeds

Objective This study aims to isolate endophytic bacteria from lavender seeds cultivated in Yili, Xinjiang province, with a focus on screening for strains exhibiting both antagonistic properties against plant pathogens and plant growth-promoting properties.

Methods Employing tissue homogenization method, we isolated endophytic bacteria from lavender seeds. We then identified strains that displayed antagonism towards plant pathogenic fungi and growth-promoting effects on maize using plate standoff and selective medium methods. The strains were identified through morphological, physiological, and biochemical characteristics, complemented by the phylogeny of 16S rRNA gene sequences. The impact of these bacteria on maize seed germination and seedling growth was evaluated.

Results A total of 85 endophytic bacterial strains were isolated from lavender seeds. Strain T2-29, identified as Paenibacillus polymyxa, demonstrated strong inhibitory effects against six plant pathogenic fungi, including Fusarium oxysporum, the causal agent of melon wilt. This strain also showed capabilities in solubilizing phytate phosphorus and potassium, as well as producing protease, cellulase, siderophore and indole-3-acetic acid (IAA). Strain T2-29 solubilized 3.19 mg/L of organic phosphorus and produced 5.42 mg/L of IAA, with siderophore UP values of 3.63, protease UP values of 8.04, and cellulase UP values of 8.30. Inoculation with strain T2-29 led to a 3.7% increase in maize seed germination rate and significantly enhanced the growth of maize seedlings. The length of maize stems, above-ground fresh weight, underground fresh weight, above-ground dry weight, and underground dry weight increased by 30.3%, 32.5%, 37.4%, 21.1%, and 9.9%, respectively. Moreover, the root length, root surface area, root system volume, and average root diameter of maize plants inoculated with T2-29 increased by 11.0%, 11.7%, 11.6%, and 1.6%, respectively.

Conclusion The endophytic bacterium T2-29, isolated from lavender seeds, is an exceptional strain with both antagonistic and plant growth-promoting functions. It not only stimulates the germination and growth of maize but also serves as a high-quality microbial resource and provides a theoretical foundation for the development and application of microbial fertilizers.