Exploration on Soil Actinomycetes Against Phytophthora sp. Causing Root Rot of Cassava sad Plant Growth Promoting Activities

摘要

Actinomycetes have been promised as biocontrol and stimulating agents for use in agriculture without detrimental effects to the environmental due to their antifungal with secondary metabolites produced. The aim of this study was to screen soil actinomycetes according to its ability to produce various secondary metabolites against Phytophthora sp. that causing root rot disease of cassava and stimulating agent has also determined. Firstly, soil actinomycetes were isolated and tested for antagonistic activity toward the fungus by the dual culture technique. After that the selected isolate was determined on the stimulating agent as IAA production. Finally, extracellular anti-fungal metabolites produced by selected isolates were evaluated for anti-fungalpotential toward the fungus with agar core technique. The result showed that 98 isolates from soil samples were screened on their anti-fungal activity. Among these, 38 isolates showed the inhibition activities against Phytophthorasp. in which was isolated from infected cassava.The culture supernatants without cell obtained from 16 isolates were affective against the fungus whereas 10 isolates produced affective thermostable compound. In total, the isolate LB35 was most promising on the basis of its interesting antimicrobial activity and could produce IAA with 50 ug mL~(-1). Based on its 16S rDNA sequence and phylogenetic tree analysis, isolate LB35 belong to the Streptomyces malaysiensis. The addition of isolate LB35 as fresh inoculums to the cassavafield, the cassava showed more height comparing to control experiment. Moreover, S. malaysiensis has not to be phytopathogenic microorganism of cassava. This finding has been increased scope of agriculturally important actinomycetes applications.