Screening of N<inf>2</inf>-fixing and IAA producing bacteria and their potential use as biofertilizer for rice

Abstract

© 2018, Khon Kaen University,Research and Technology Transfer Affairs Division. All rights reserved. The rice-based farming system is widespread throughout Thailand. Approximately 98% of the rice is farmed in a paddy field. The long time inefficient use of chemical fertilizers has dramatically degraded the soil quality and polluted the environment. Rhizosphere-associated nitrogen-fixing bacteria are considered one of the possible alternatives to synthetic nitrogen fertilizer for improving rice growth and yield. The objectives of this study were to isolate bacteria from rice rhizosphere and evaluate their potential in N2-fixation and indole 3-acetic acid (IAA) production. A total number of 31 isolates of Azotobacter and 24 isolates of Beijerinckia were obtained from the rice rhizosphere soils. The results showed that Beijerinckia BCk1 performed maximum nitrogenase activity (68.4 nmole 24h−1tube−1) and Azotobacter AtMh6 showed the highest IAA production (28.0 mg IAA L−1). Nitrogen uptake and rice seedlings growth promotion by six selected isolates; AtMh6, AtCk1, AtMh1, BCk1, BSt3 and BSt12 with high potential in N2-fixation (64.6, 60.2, 56.6, 68.4, 57.0 and 50.4 nmole 24hr−1tube−1, respectively), were investigated. IAA production of the six isolates was 28.0, 7.2, 3.3, 17.3, 1.4 and 6.6 mg IAA L−1, respectively. The application of all the selected isolates provides higher nitrogen uptake and seedlings growth than the uninoculated control. Among Azotobacter, isolate AtCk1 gave the best seedling growth and 91.7% increase in N uptake over the control. The Beijerinckia isolate BCk1 exhibited highest nitrogenase activity and also provide the highest nitrogen uptake in rice seedlings (150% over the control). Our results suggested that isolate AtCk1 and BCk1 have a high potential to develop as biofertilizer for rice.