Actinomycetes are considered to be the biggest producer of bioactive compounds which are expected to have antifungal activity for controlling many fungi such as Rhizoctonia solani. The objective of this study was to obtain potential soybean rhizosphere actinomycetes as a biocontrol agent for R. solani which cause damping-off disease both in vitro and in vivo, including their ability to produce siderophore, chitinase, and HCN. Out of 26 isolates, 18 (56%) showed diverse antifungal activities against R. solani with percentages of inhibition radial growth (PIRG) from 18.9 to 64.8%, as evaluated by a dual culture method. Ten isolates with the strongest antifungal activity were numbered for further characterization. All the tested isolates were not antagonistic towards Bradyrhizobium japonicum. These isolates were able to suppress damping-off disease caused by R. solani in the greenhouse experiment. Isolate ASR53 showed the highest disease suppression, 68% and 91% in sterile and non-sterile soil, respectively. Based on 16S rRNA sequence analysis this isolate belonged to Streptomyces violaceorubidus LMG 20319 (similarity 98.8%) according to GenBank data base available at www.ncbi.nlm.gov.nih. Furthermore, isolate ASR53 had significantly longer roots and shoots, as well as greater fresh and dry weights of seedlings than the control. Crude extract derived from ASR53 isolates contained 10 dominant compounds that were biologically active against fungal pathogens. Thus, this study suggests that the application of potential actinomycetes of the soybean rhizosphere can act as a promising biocontrol agent against damping-off disease caused by R. solani.

Rice blast is the main disease of rice plants in Indonesia and several countries worldwide. Controlling this disease using chemical fungicides has harmful effects on the environment. Therefore, we need biocontrol agents which are more environmentally friendly such as rice phyllosphere bacteria. This study aimed to explore bacteria producing bioactive compounds from the rice phyllosphere environment to control blast disease. A total of 88 isolates were successfully isolated from rice leaves in Sukabumi, Situgede, and Jasinga (West Java, Indonesia). From them, we obtained 22 bacteria isolates with antifungal activity against Pyricularia oryzae in vitro assay. In addition, seven non-pathogenic bacteria were obtained from further screening in hypersensitivity, hemolysis and pathogenicity assays, namely STGG 3, STGG 7, STGG 8, STGG 14, SKBV 1, STGV 8, and SKBG 78. To show their antifungal activity, we tested crude extracts of these seven isolates and the results revealed that all the crude extracts can inhibit the growth of P. oryzae. Based on a genetic approach, isolates STGG 3, STGG 7, and STGG 14 were found to have both nonribosomal peptide synthetases (NRPS) and polyketide synthases (PKS) genes, while isolate SKBV 1 only had the NRPS gene. The NRPS and PKS genes from potential isolates were similar to NRPS and PKS genes of Bacillus sp. in different strains. Furthermore, molecular identification based on the 16S rRNA gene revealed that the seven potential isolates belong to three genera, i.e. Bacillus (STGG 3, STGG 7, STGG 8, STGG 14, SKBV 1), Enterobacter (STGV 8) and Brachybacterium (SKBG 78). We suggest that the seven isolates found in this study have potency and could be recommended as biocontrol agents of blast disease caused by P. oryzae.