Effect of Plant Growth Promoting Rhizobacteria and Extracted Humic Substances from Biochar of Platanus orientalis Tree on the Germination and Growth Indices of Sesbania rostrata

Difficulties in seed germination for many medicinal plants have led to significant limitations in cultivating these plants in managed ecosystems, such as agricultural lands, where they are grown in large areas with a uniform green surface. Given the necessity for medicine production, the raw materials used should possess superior quality and minimum pollution. It seems that investigating the effectiveness of Sesbania rostrata seed priming techniques with biological fertilizers, such as plant growth promoting rhizobacteria, and organic fertilizers, such as humic acid and fulvic acid, is essential, because these fertilizers are compatible with natural ecosystems and align with sustainable agricultural policies. Hence, this research was conducted to investigate the effect of Sesbania rostrata seeds priming with plant growth promoting rhizobacteria as well as fulvic and humic acid (extracted from Oriental plane tree biochar) on the indices of seed germination and seedling growth.

In-vitro cultivation was carried out in a factorial and completely randomized design (CRD) with four replications in a total of 36 experimental units. The first factor, which was implemented at three levels, included seed priming with distilled water (control), humic acid, and fulvic acid; and the second factor, which was implemented at three levels, included seed priming with physiological serum (control), as well as Staphylococcus sp. R38N2 and Pseudomonas sp. R27N7 bacteria strains. Ten surface-sterilized seeds were placed on a filter paper inside each petri dish. Then, the treatments were added to the experimental units and placed in the germinator at a temperature of 25±2 degrees Celsius. Germinated seeds were counted daily from 13 to 30 days after the start of the experiment.

Results showed that fulvic acid- physiological serum was the best treatment compared to the control in terms of improvement of all measured traits. This treatment increased the seed germination indices, including seed germination percentage, germination rate, mean daily germination, peak value, germination value and seedling vigor I and II by 2, 4.5, 2, 3.19, 7.13, 5.66, and 18.96 times, respectively. In addition, it reduced mean germination time by 24.46%. Additionally, seedling growth indices including seedling height, shoot height, root length, and seedling dry weight were increased by 7.44, 20.32, 4.74, and 9.5 times, respectively.

Fulvic acid-physiological serum treatment was found to be the most effective in enhancing all indicators of seed germination and seedling growth in Sesbania rostrata, when compared to the control. Furthermore, the following treatments were ranked right after each other for their ability to enhance seed germination and seedling growth in Sesbania rostrata: fulvic acid-Pseudomonas sp. R27N7, distilled water-Staphylococcus sp. R38N2, humic acidStaphylococcus sp. R38N2, and fulvic acid-Staphylococcus sp. R38N2.