Effects of PGPR inoculation on adventitious rooting and growth attributes in olive microcuttings of 'Mission' and 'Koroneiki' cultivars

Purpose: This study aimed to investigate the synergistic effects of plant growth-promoting rhizobacteria (PGPR) and auxin on olive microcutting rooting, and assess how PGPR and arbuscular mycorrhizal fungi (AMF) inoculation affect the growth of rooted olive plantlets. Research Method: In the first experiment, native PGPR inoculation with indole-3-butyric acid (IBA) and naphthaleneacetic acid (NAA) was tested to enhance rooting in olive microcuttings of 'Mission' cultivar. The second experiment evaluated six inoculation treatments (control, PGPR, Funneliformis mosseae, Claroideoglomus etunicatum, PGPR + F. mosseae, and PGPR + C. etunicatum) for their impact on rooted plantlet growth of 'Mission' and 'Koroneiki' cultivars. Findings: The study showed that PGPR and IBA treatment for 12 weeks resulted in a higher rooting rate (63.33%) and more roots per cutting (4.5) compared to the control. Additionally, PGPR and IBA combination for 16 weeks produced the longest roots (59.03 mm), indicating PGPR's role in enhancing root initiation and growth through auxin modulation. The results also revealed that the 'Mission' cultivar had higher AMF colonization than the 'Koroneiki' cultivar. The inoculation with F. mosseae significantly increased the number of lateral shoots and leaves, stem diameter, and root length in 'Koroneiki', while PGPR + F. mosseae enhanced lateral shoots, leaf number, and stem diameter in 'Mission'. The 'Koroneiki' cultivar also exhibited greater growth responses in stem and root weights, and plant height to AMF and PGPR inoculation. Research limitations: No limitations were identified. Originality/Value: These findings underscore the importance of genetic background in biofertilization strategies for olive cultivation, demonstrating the synergistic potential of PGPR and auxin in rooting and the cultivar-specific benefits of combined PGPR and AMF inoculation.