Effect of Azospirillum lipoferum and Azotobacter chroococcum on germination and early growth of hopbush shrub (Dodonaea viscosa L.) under salinity stress

Abstract

ABSTRACTReduced physiological efficiency as well as low and irregular germination rate under environmental stress conditions (e.g., salinity) are among the major factors affecting the propagation of numerous plants, in particular medicinal ones. A factorial experiment using a completely randomized design was employed to evaluate the effect of plant growth-promoting rhizobacteria (PGPR) on hopbush seed germination and seedling growth under salinity stress. After the seeds were inoculated with the Azospirillum lipoferum, Azotobacter chroococcum, and Azospirillum + Azotobacter and exposed to salinity stress at six levels, they were placed into a germinator at 20°C temperature and 65% relative humidity with a photoperiodic regime of 16 h light/8 h dark at 1,000 lux fluorescent light. The seeds inoculated with the bacterial strains could tolerate salinity levels of up to 50 dS/m and germinate. The combined treatment of Azospirillum + Azotobacter increased germination percentage at 20 and 50 dS/m levels by 21.67 and 10%, respectively. Also, A. chroococcum at 15 and 20 dS/m and Azospirillum + Azotobacter at 50 dS/m stress levels increased germination rate by 88, 316, and 155%, respectively, compared with the control. Furthermore, plant growth parameters—e.g., root and stem length, root and stem dry and fresh weights, as well as the ratios of root length and weight to the stem counterparts—were considerably enhanced by Azotobacter chroococcum treatment under elevated salinity stress (15 and 20 dS/m), relative to the control. Inoculation with A. chroococcum more favorably affected on and was also more compatible with Dodonaea viscosa seedlings leading to considerably improved seedlings growth parameters as well as seed germination under salinity stress.