Potential applicability of a cyanobacterium as a biofertilizer and biopesticide in rice fields

This study aimed to evaluate the potential applicability of Anabaena variabilis SCAU30 as a biofertilizer and biopesticide in rice fields. The effects of A. variabilis SCAU30 inoculation on disease severity, plant growth, rice yield, and soil nutrients were investigated by microchamber, micro-area, and field experiments. The nitrogen fixation ability was estimated by acetylene reduction activity. Hormones were analyzed using liquid chromatography-tandem mass spectrometry. In microchamber experiments, the control efficacies of A. variabilis SCAU30 against rice sheath blight and bacterial blight were 62.3 ± 8.9% and 45.3 ± 5.6%, respectively. The cell extracts of A. variabilis SCAU30 exhibited high antagonistic effects on corresponding pathogens, whereas volatile compounds only showed inhibition on Xanthomonas oryzae. The results of pond experiments showed that inoculation with A. variabilis SCAU30 could promote the growth of rice plants, increase yield, control diseases, and decrease chemical nitrogen fertilizer input. Moreover, in field experiments, the combined treatment of A. variabilis SCAU30 and 50% topdressing fertilizer increased rice yields by 13.9%–22% compared with the conventional fertilizer treatment. This potentially represents economic gains of 26,753 ~ 38,987 Chinese Yuan ha−1 season−1 if sold as a green food. The present study suggests that A. variabilis SCAU30 may act as a fertilizer and pesticide in developing green rice in South China.