MANAGEMENT OF FUSARIUM BASAL ROT DISEASE OF ONION (ALLIUM CEPA L.) BY USING PLANT GROWTH PROMOTING RHIZOBACTERIA IN SEAWEED FORMULATION

Abstract

Onion (Allium cepa L.) is one of the most important vegetable crops cultivated around the world. The production of onion is negatively affected by fungal and bacterial diseases. Ascophyllum nodosum extract (ANE) could increase plants' resistance to pathogenic fungi and bacteria. Plant growth-promoting rhizobacteria (PGPR) have been widely used as effective biocontrol agents. The present study explored the efficiency of three PGPR strains (Pseudomonas protegens CHA0, Bacillus subtilis, and Enterobacter cloacae CAL2), ANE, and the combination of ANE and each PGPR strain in controlling onion Fusarium basal rot disease caused by Fusarium oxysporum f. sp. cepae (FOC). Under in vitro conditions, all PGPR strains showed antagonist activity against FOC, especially E. cloacae CAL2 displayed the highest antagonistic activity. Under in vivo conditions, E. cloacae CAL2, ANE, and their combined applications had no positive effects on onion biomass in the presence/absence of pathogen challenge, and 0.5% ANE had a negative effect on the biomass parameters (shoot and root fresh weight) of onion plants. All the treatments provided no control of the relative biomass of FOC in onion root tissues, especially ANE application resulted in the highest FOC biomass. Meanwhile, no significant changes in the activity of the defence-related enzymes and total phenolics and hydrogen peroxide contents were found. The results of the present study provide a basis for better exploring the combined application of PGPR and seaweed extract or other biocontrol agents to control plant diseases.