Selection and Bioassay of Halotolerant Nitrogen-Fixing Endophytic Bacteria for Promoting Rice Seedlings (Oryza sativa L.) under Saline Conditions

Abstract

Nitrogen-fixing endophytic bacteria play an important role in improvingnitrogen availability and supplying growth-promoting factors to plants. This study evaluated the potential of endophytic bacterial isolates obtained from various plants growing under saline conditions based on their nitrogenase activity, indole-3-acetic acid (IAA) production, and ability to promote rice seedling growth. A bioassay was conductedusing rice seedlings grown in Fahraeusmedium adjusted to a salinity level of 4 dS m⁻¹. The experiment was arranged in a randomized complete block design with eight treatments consisting of an uninoculated control and seven selected endophytic bacterial isolates, with three replications. The measured responses included shoot length, root length, shoot dry weight, root dry weight, and total seedling biomass. Based on the bioassay results, two superior isolates, A1 and A2, were identified. The isolates exhibited nitrogenase activities of 1.223 and 1.780 µmol mL⁻¹ g⁻¹ h⁻¹, respectively, and produced IAA at concentrations of 7.819 and 7.794 mg L⁻¹, respectively. They increased root length by 13.66% and 15.44%, respectively, and resulted in numerically higher total seedling dry biomass, with values 51.99% and 34.68% higher than the uninoculated control, respectively. These findings indicate that the selected halotolerant nitrogen-fixing endophytic bacterial isolates can promote rice seedling growth under saline conditions and have potentialfor further development as biological fertilizers for rice cultivation on saline soils.