Exploration of Indigenous Actinomycetes as Biocontrol Agents of Purple Blotch Diseases at Onion

Abstract

Abstract Purple blotch disease caused by Alternaria porri is an essential disease in shallot plants. Actinomycetes microorganisms have potential as A. porri biological control agents because they produce bioactive compounds. The research aimed to select actinomycetes isolates that can suppress the growth of A. porri, stimulate growth, and increase the production of shallots. The study consisted of four stages: isolation, selection, characterization, and identification of potential actinomycetes isolates. The isolation results obtained 35 indigenous isolates, and as many as 16 isolates were successfully selected based on the results of the biosafety test. The antagonism test showed that 12 isolates produced suppression to A. porri by 4.87–63.77%. From 16 selected isolates, 13 isolates could produce chitinase enzymes with a chitinolytic index of 0.61-2.58. Nine selected isolates: AMSN23, AMSN10 AMBP7, AMSP10, AMSR21, AMTE2, AMDK6, AMTD 14, and AMPL24, could dissolve phosphate and produce Indole Acetic Acid (IAA) with a concentration of 34.82–85.98 ppm, but only six isolates were able to fix nitrogen. In the results of the 16S rRNA gene sequence, nine isolates were selected and potentially identified as Streptomyces rameus, S. lydicus, S. panaciradicis, S. seoulensis,S. fuscichromogenes, Streptomyces sp, S. nigrescens, S. viridaris, and S. griseus