Herbicidal Activity of Secondary Metabolites Isolated from Streptomyces sp. NEAU-HV44 on Selected Weeds and Crops.

Streptomyces is an effective source of new natural bioherbicides. In this study, a novel isolated strain NEAU-HV44 showed strong inhibitory activity against Amaranthus retroflexus L. and was concluded to the genus Streptomyces . Strain NEAU-HV44 fermentation conditions were optimized to maximize the herbicidal activity. The supernatant of strain NEAU-HV44 could significantly control the growth of weeds ( A. retroflexus L., Setaria viridis , Portulaca oleracea L., and Chenopodium album ) and crops (maize, soybean, wheat, Chinese cabbage, cucumber, tomato, and romaine lettuce) with dose-dependent in preemergence. Notably, weeds were more sensitive to a low-concentration supernatant extract than crops in preemergence. In postemergence, the 2 mg mL -1 supernatant extract could significantly reduce the height and >50% biomass (fresh weight) of tested weeds. The supernatant extract could cause cell membrane destabilization and the cell death of weeds. In addition, the growth of tomato was also inhibited at a high concentration, but no obvious symptoms were observed on soybean and romaine lettuce after spraying the supernatant extract. Then two novel julichrome monomers, julichromes Q 12 ( 1 ) and Q 13 ( 2 ), and two known julichromes, julichrome Q 3.3 ( 3 ) and julichrome Q 3.5 ( 4 ), were isolated from the supernatant extract of strain NEAU-HV44 by bioactivity-guided approach. This is the first report of the herbicidal activity of julichromes. These four herbicidal compounds could inhibit the shoot and root growth of weeds at 0.2 mg mL -1 , and compound 4 could completely inhibit the growth of P. oleracea L. Thus, julichromes (Q 12 , Q 13 , Q 3.3 , Q 3.5 1 - 4 ) may be new bioherbicidal candidates.