2,4‐Di‐tert‐butylphenol and 7‐hydroxy‐3‐(2‐methylpropyl)‐2,3,6,7,8,8a‐hexahydropyrrolo[1,2‐a]pyrazine‐1,4‐dione: two natural products from Serratia marcescens Ha1 and their herbicidal activities

BACKGROUND Weeds are one of the critical factors that negatively affect crop yield and quality. Microbial herbicides are a research hotspot for novel herbicides owing to their environmental safety and lack of weed resistance. In the current study, the active ingredients of Serratia marcescens Ha1, a new microbial herbicide, were investigated for their effectiveness against agricultural weeds using bioassay‐guided fractionation. RESULTS The results revealed that petroleum ether and ethyl acetate extracts of S. marcescens Ha1 had high herbicidal activity. Forty‐nine compounds were identified from the petroleum ether extract, including 2,4‐di‐ tert ‐butylphenol (DB; C 14 H 22 O, 38.82%), ethyl 14‐methyl‐hexadecanoate, 1‐nonadecene, and [1,1′‐biphenyl]‐2,3′‐diol, 3,4′,5,6′‐tetrakis. Of these, DB showed significant inhibitory effects on root and shoot growth in Amaranthus retroflexus , with half‐maximal inhibitory concentration (IC 50 ) values of 389.17 and 832.44 mg L −1 , respectively. In addition, 7‐hydroxy‐3‐(2‐methylpropyl)‐2,3,6,7,8,8 a ‐hexahydropyrrolo[1,2‐a]pyrazine‐1,4‐dione (HPD) was identified as the major active ingredient in the ethyl acetate extract of S. marcescens Ha1 using bioassay‐guided fractionation, with IC 50 values of 439.86 and 476.95 mg L −1 against A. retroflexus shoot and root growth, respectively. Scanning electron microscopy indicated that DB and HPD exert destructive effects on A. retroflexus root, and the damage is gradually aggravated with increasing treatment time and concentration. CONCLUSION The S. marcescens Ha1 extract and its active compounds DB and HPD exhibit significant herbicidal activity, which could be utilized further for the development of microbial herbicides. © 2023 Society of Chemical Industry.