Plant Growth Promoting Bacteria from Uzungöl Forest Stimulate Rice Growth via Seed Biopriming and Root Inoculation: Isolation and Functional Characterization of Potent PGPR Strains from rhizosphere soils of different trees

Saad IshaqAli Osman Belduz^*Esma CeylanAleyna Nalcaoglu SenocakWajeeha MunawarAmir Towfiq Hasan AlkowlaniRabiye TerziKadriye Inan BektasSabriye Canakci

• Faculty of Science, Karadeniz Technical University, Trabzon, Türkiye

Introduction: Rhizobacteria naturally promote plant growth and offer a sustainable alternative to agrochemicals. In contrast to agroecosystems, forest host a diverse community of beneficial rhizobacteria that remains uncharacterized. Moreover, despite extensive research on rhizobacteria associated with cereal crops like rice, their efficacy in hydroponic rice cultivation yet needs to be established. Methods: This study was aimed to isolate, characterize and identify the potential plant growth promoting rhizobacteria (PGPR) of different rhizospheres from Uzungöl forest situated in Trabzon, Turkey and to evaluate their effects on growth of rice through two distinct approaches: (1) seed biopriming to assess germination and (2) root inoculation to analyze seedling growth in hydroponic system. Results: In total, 129 bacteria were isolated from eight different rhizospheres, 109 exhibited Indole-acetic acid (IAA) production. A strain of Bacillus altitudinis from Acer pseudoplatanus rhizosphere produced highest (739.9±251.5 µg/ml) IAA. Siderophore formation was exhibited by 16 isolates including the strains of Lysinibacillus fusiformis, Microbacterium phyllosphaerae and Lelliottia sp. Phosphate solubilisation was observed only in 9 isolates including the strains of Acinetobacter calcoaceticus, and Lelliottia sp. Further, 65 isolates including the strains of Herbaspirillum huttiense, Lelliottia amnigena, Bacillus altitudinis and Acinetobacter calcoaceticus were identified as potential endogenous nitrogen-fixing diazotrophs for rice. Various isolates exhibited salt tolerance, HCN, ammonia and hydrolytic enzymes production. Several of these PGPR strains as well as the strains of Viridibacillus arenosi, Psychrobacillus faecigallinarum, Bacillus siamensis, Micrococcus luteus, Staphylococcus succinus demonstrated positive effects on rice germination or seedlings growth. Herbaspirillum huttiense strain S1(E) from Abies nordmanniana rhizosphere and Pseudomonas mohnii strain SS7(5) from Malus domestica rhizosphere exhibited outstanding response as seed biopriming agents and root inoculants for rice. Discussion: These findings concluded that inoculation with forest-derived rhizobacteria is an effective strategy to enhance early growth of rice in soil-less systems. Understanding the genetic basis of their growth promotion, coupled with large-scale field validation, could advance low-cost, sustainable rice cultivation with minimal reliance on agrochemicals.