Role of Different Microbial Biofertilizers in Sustainable Olive Yield Improvement under Salinity Stress

The current study assessed the impact of microbial inoculation on vegetative growth, flowering traits, fruit physical properties, yield, and oil percentage of olive trees grown in saline soil at olive collection farm located in the Al-Moghra area of Matrouh Governorate, Egypt. conditions during two successive years (2024-2025). The treatments were Bacillus velezensis, Bacillus cereus, Trichorums sp, and mycorrhizal fungi, and the control was untreated trees. Microbial inoculation significantly increased vegetative factors such as leaf number, leaf surface area, and chlorophyll content, which cumulatively led to increased photosynthesis. Better vegetative growth led to better reproductive growth, as indicated by longer inflorescences, increased number of flowers, increased percentage of perfect flowers, and flowering density. As a result, fruit growth was positively influenced, as microbial inoculation increased fruit weight, length, and width compared to the control. In addition, microbial inoculation showed a reduction in salinity stress, as indicated by the reduction in proline content and the reduction in markers of oxidative stress, such as total phenols, peroxidase, and polyphenol oxidase activity. These increases cumulatively led to increase per-tree oil yield and oil percentage, with mycorrhizal fungi and Trichorums sp showing the highest values. Microbial inoculation significantly increased soil microbial activity, as indicated by dehydrogenase enzyme activity, and increased indole-3-acetic acid (IAA) concentration in the rhizosphere, as the treated areas had higher values than the control. This increased microbial activity and auxin production led to better nutrient uptake, which in turn positively influenced olive tree growth, fruit development, and oil production. The results of this study emphasize the importance of the integrative function of microbial inoculants in improving growth, reproductive performance, and economic properties of olive trees under stress conditions, as indicated by the effectiveness of mycorrhizal fungi and Trichorums sp.