With increasing environmental issues from synthetic chemical herbicides, microbial originated herbicides could be a fascinating alternative in current agriculture. Natural products have served as leads or starting points for the development and commercialization of numerous agricultural chemicals. Bioherbicidal metabolites produced by Streptomyces sp. are being studied as possible herbicides or herbicidal adjuvants to develop biological agents that are easily degradable and environment friendly. In the course of our screening of bioherbicidal agent, about 1300 different soil actinomycete isolates were tested for control of problematic weeds in korea. One of the isolates, KRA14-329, showed strong herbicidal activity against a grass weed Digitaria sanguinalis. According to the result from 16S rRNA sequence comparison with close starains, the isolate KRA14-329 was identified as Streptomyces sp. Foliar application of the culture broth of KRA14-329 showed strong effect against grass species, Digitaria sanguinalis, Sorghum bicolor, Echinochlia crus-galli, Agropyron smithii and broad leaf species such as Solanum nigrum, Aeschynomene indica, Xanthium strumarium, Calystegia japonica. The culture broth of KRA14-329 by foliar application showed phytotoxic symptoms of desication or burn-down of leaves and stunting and finally plant death. But no effect on pre-emergence application. and also strong herbicidal activity against troublesome weed such as Sciyos angulatus. In crops such as rice, wheat, barley, tomato and hot pepper, herbicidal effect was observed.
Two herbicidal compounds, 329-C1 and 329-C3, were purified by column chromatography and high performance liquid choromatography. By NMR and ESI-MS analysis, the two compounds were identified as Cycloheximide derivatives including glutarimide moiety. thease two metabolites showed strong herbicidal activity. The Herbicidal compound 329-C3 was no significant decrease in chlorophyll content compared with Paraquat. also, leaf electrolyte leakage and MDA production slightly increased but not in a concentration dependent manner. Therefore the main mode of action of herbicidal compound 329-C3 is not inhibit of photosynthesis. These results suggest that Streptomyces sp. KRA14-329 producing bioherbicidal metabolites can be developed as a biocontrol agent (BCA) for weed control and/or may provide as a lead molecule for a more efficient herbicide.