Growth Inhibition of Fungal Plant Pathogens by Antagonist Bacteria Using Dual Culture Assays

There has been excessive use of chemical-based pesticides globally resulting in significant environmental consequences with adverse effects on human health. Therefore, more sustainable environment friendly alternative solutions are needed to counter such environmental and health challenges. Development of biocontrol method is a sustainable solution to these challenges. The main objective of this research was to investigate the efficacy of potential antagonist bacteria to inhibit important fungal plant pathogens in uitro by applying dual culture assays on potato dextrose agar FDA) or trypticase soya agar (TSA) media, with a view to isolate and screen potential antagonists for development of future biocontrol agents. The target pathogens were Fasariam o y p o r m , Ceratoystis sp., Apergilasj7au.w and Apergillz~s niger, commonly found to infect horticultural plants in Bedugul village in north Bali island. The antagonist bacteria were isolated from various sources such as soil of rhizosphere zone and roots of lettuce plants and mature compost. The potential of antagonist candidates was screened on the basis of inhibitory activity against targeted fungal pathogens. Bacterial antagonists with highest zone of inhibition were identified up to genus level using biochemical tests, and the results were matched with those specified in the Bergey's Manual of determinative bacteriology. Fifteen bacterial isolates were successfully isolated from various sources, and 60% of these isolates showed antagonistic activity in vitm against fungal pathogens with various degree of inhibition. This indicated the initial potential to develop as biocontrol agents. Based on preliminary identification, genera of BaciIIas and Psezldomonas were found to be the predominant isolates and in addition genus Acinetobacter was also identified in this study.