Allelopathic effect of metabolites produced by Streptomyces sp. HU2014 on wheat and green bristlegrass

Abstract

Plant growth-promoting rhizobacteria widely exist in the plant rhizosphere. They provide nutrition and produce some antibiotic substances to suppress the plant diseases and promote the growth of plants. Therefore, the study of allelopathy is a very important part in the interaction between rhizobacteria and plant. Streptomyces, a genus of actinomycetes, is well known for its bioactive metabolites, mainly including antibiotics, hormones, and hydrolase, which can affect plants growth. In the present study, the allelopathic effect of Streptomyces sp. HU2014 metabolites on wheat (Triticum aestivum L.) and green bristlegrass (Setaria viridis (L.) Beauv.) were estimated using the response index (RI). Negative RI values indicated inhibition of plant growth; positive values indicated stimulation of plant growth. Four fractions (F2, F4, F6 and F8) from the cell-free filtrates of HU2014 culture broth had a certain effect on the shoot and root length of above tested plant seedlings. For wheat, the results showed that fraction of F2 at 10 mg/ml had the strongest inhibition on the shoot length (RI = -0.53) and root length (RI = -0.22). However, fraction of F2 at 1 mg/ml promoted the shoot length (RI = 0.01). Fraction of F4 and F6 at 10 mg/ml had strongest inhibition on the shoot and root length. Fraction of F8 had the highest inhibition on the shoot length (RI = -0.66) at 5 mg/ml, and the root length (RI = -0.66) at 10 mg/ml. For green bristlegrass, F2 fraction at 10 mg/ml had the strongest inhibition on the shoot (RI = -0.73) and root length (RI = -1.00). F4 fraction had the highest inhibition on the shoot length (RI = -0.69) at 5mg/ml, and the root length (RI = -0.85) at 10 mg/ml. Fraction of F6 had the highest inhibition on the shoot length (RI = -0.59) at 10 mg/ml, and the root length (RI = -0.80) at 5 mg/ml. Fraction of F8 had the highest inhibition on the shoot length (RI = -0.47) at 5mg/ml, and the root length (RI = -0.93) at 10 mg/ml. From the above results, we can draw a conclusion that four fractions had the allelopathic effects on the shoot and root length of two tested plants except F2 fraction at 1 mg/ml promoting the wheat shoot length. Thus, at an early stage of plant growth, the low concentration of allelopathic substances produced by HU2014 may promote the growth of wheat, while these agents inhibit the growth of green bristlegrass. Therefore, this strain can be promising both as a biofungicide and as a bioherbicide.