Sustainable zinnia cultivation: influence of rhizobacteria inoculation on emergence and biometric traits

Plant growth-promoting rhizobacteria establish beneficial symbiotic interactions with plants, exerting a positive and sustainable impact on the growth and development of various plant species. The adoption of new sustainable technologies in ornamental plant cultivation can enhance competitive market advantages. This study investigated the effects of rhizobacteria on seedling emergence and growth in Zinnia peruviana L., chosen due to its commercial importance in the ornamental plant industry. The aim was also to evaluate whether reapplications of rhizobacteria are necessary throughout the plant cycle. The experiment had two phases. In phase 1, six treatments were used, corresponding to five rhizobacteria (Azospirillum brasilense, Bacillus amyloliquefaciens, B. megaterium, B. pumilus, B. subtilis) and the absence of rhizobacteria - control; assessing seedling emergence percentage and Speed Index. In phase 2, a 6 x 2 factorial design was used with the same treatments from phase 1, combined with either 1 or 2 applications, to evaluate plant growth and development. Results showed that rhizobacteria did not affect the emergence rate, but B. amyloliquefaciens and B. subtilis accelerated seedling emergence. Additionally, B. subtilis promoted superior growth, development, and flowering. Importantly, there was no need for reapplications during the plant cycle, highlighting the practical benefit of reducing the frequency of treatments, which can lower costs and minimize environmental impact in ornamental plant production.