Rice phyllosphere actinomycetes as biocontrol agent of bacterial leaf blight disease on rice

Abstract

Bacterial Leaf Blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is the most destructive and serious disease causing productivity loss, especially in rice, in Asia. The chemical pesticide usage over a long period of time brings about adverse toxic effect on the potential production of the land and the main consumers of the products. Microbes as biocontrol agents have efficiency and safety for humans and other non-target organisms. They leave small amount or no residue in foods. Soil microbes cannot be used directly as biopesticides because common root-colonizers fail to establish on leaves. Actinomycetes are Gram positive bacteria that are known to produce bioactive compound up to 70% of the total compound produced by bacteria, including antimicrobes. Several strains of actinomycetes are known capable of protecting plants against plant disease. The aims of this study were to isolate and screen non-pathogenic phyllosphere actinomycetes of rice which are capable of controlling BLB disease in rice. A total eight isolates are positively capable of controlling Xoo in vitro and four isolates significantly reduce disease severity of BLB. Pellet of STG 15, which is the best, showed 25.87% control efficiency of BLB severity at 14 Days After Inoculation (DAI) using Xoo compared to control. Molecular identification based on 16S rRNA gene performed for six isolates with the highest activity showed that they belongs to genus Streptomyces, Actinomadura, Nonomuraea, Micromonospora. Isolate STG 15 which has the highest capability to control BLB incidenceis identified as Nonomuraeasp.