Effects of GA3 and PGPR on germination and seedling development of Echinacea (Echinacea purpurea L.) across different seed ages

This study investigated the effects of gibberellic acid (GA3) and plant growth-promoting rhizobacteria (PGPR) strains (B. megaterium, B. subtilis, and B. amyloliquefaciens), applied alone and in combination, on germination and early seedling development of Echinacea purpurea L. seeds of different ages. Aging seeds often exhibit reduced germination and seedling vigor, limiting uniform plant establishment. The findings demonstrated that GA3 increased germination percentage, plant height, leaf number, and root weight, reducing the detrimental impacts of seed senescence. Additionally, PGPR inoculation enhanced seedling performance in a strain-specific manner: B. megaterium improved germination, leaf number, and root length, whereas plant height and root weight were increased by B. amyloliquefaciens. The greatest gains were obtained from combined treatments, indicating synergistic effects. Despite these positive effects, seed age remained critical, as older seeds, even after treatment, did not fully match fresh seeds. Overall, these findings indicate that GA3 and PGPR inoculation offer a practical and sustainable approach to enhance seedling establishment and early growth, particularly in aged seeds, as such biostimulants can improve nutrient uptake and stimulate root development. Future research should explore long-term field performance, economic feasibility, and physiological and molecular mechanisms underlying seed aging and its mitigation.