Bacterial biocontrol potential against Rigidoporus microporus: Hydrolytic enzyme activity and antibiotic inhibition

Rigidoporus microporus is a soil-borne pathogen that causes significant losses in rubber plantations worldwide. As an alternative technique, the development of bacteria as biological control agents capable of producing hydrolytic enzymes and antibiotics has emerged. The in vitro activity of bacterial isolates against R. microporus was assessed using hydrolytic enzyme production and antibiotic inhibition. The research included enzyme activity analyses and antagonism assays against R. microporus, followed by selection of the top ten isolates using the Analytical Hierarchy Process. The 16S rRNA gene sequencing was used to determine compatibility and identification. Twenty-two bacterial isolates produced one or more enzymes, including chitinase, glucanase, and cellulase. These isolates inhibited the growth of R. microporus through diffusible, volatile, and colonized soil, resulting to abnormal mycelial formation. Hierarchical analysis has selected 10 isolates with the highest potency and compatibility. Four isolates (S085, S108, SK909, and SK018) belonged to Serratia surfactantfaciens, while others were identified as Brucella intermedia (basonym: Ochrobactrum intermedium) (S018, T2, and BE60), Bacillus albus (NJ57), Bacillus amyloliquefaciens (P7), and Burkholderia cepacia (SS19.7). The present study demonstrated the ability of bacterial isolates to secrete hydrolytic enzymes and antibiotic metabolites causing permanent abnormalities in R. microporus mycelia, representing the first report of such metabolite activity of rhizosphere and endophytic bacteria as biological control agents against R. microporus. However, further study is needed to assess their performance under field conditions.