Screening Of Strains With Inhibitory Activity Against Weed And Its Preliminary Inhibitory Mechanisms

In order to develop new strains with biocontrol herbicidal activity,In this study,the inhibitory activity against weed of moderate halophilic bacteria isolated from the Qrhan Salt Lake in Qinghai was screened.The results showed that among 87 moderate halophilic strains,there were 16 strains with inhibitory activities against Avena fatua L.,with active screening rate 18.4%,and 11 strains with inhibitory activities against against Brassica napus L.,with active screening rate 12.6%.There were 3 strains with moderate inhibitory activity,which were D30202,C30101 and D30301,respectively.Using morphological,physiological and biochemical characteristics,and molecular biology methods,active strains D30301,and D30202 were identified as Bacillus altitudinis,and C30101 was identified as Bacillus tequilensis.Strain D30202 with the highest inhibitory activity against weed was fermented.Then,the ethyl acetate and n-butanol extracts of its fermentation broth were obtained by liquid-liquid extraction method.The inhibitory activities of ethyl acetate and n-butanol extracts against germination of A.fatua and B.napus were determined.The results showed that the inhibitory activity against weed of n-butanol extract was higher than that of ethyl acetate extract,with inhibition rate against root length of volunteer oilseed rape 81.64%.The herbicidal spectrum test of n-butanol extract by pot culture experiment showed that the n-butanol extract of strain D30202 at the concentration of 40 mg/m L had inhibitory activity against B.napus and Chenopodium album in grade 1 and grade 5,respectively;inhibitory activity against Elsholtzia densa and A.fatua in grade 8;no inhibitory activity against Galium aparine L.Inactive in grade 9.The crop safety experiments showed that the n-butanol extract of strain D30202 at the concentration of 40 mg/m L had various pesticide damage on the main cropvarieties in Qinghai Province,which were wheat(Triticum aestivum L.)Qingchun 38,quinoa(Chenopodium quinoa)Qingbaili 1,hullessbarley(Hordeum Vulgare L.)Kunlun 14,and maize(Zea mays L.)Jiyuan 8,and had no pesticide damage on broad beans(Vicia faba L.)Qingcan 14 in grade 0.The n-butanol extract of strain D30202 at the concentration of 10 and 20 mg/m L had no pesticide damage on hullessbarley(H.Vulgare)Kunlun 14 and broad beans(V.faba)Qingcan 14 ingrade 0,and had pesticide damage on mazie(Z.mays)Jiyuan 8,wheat(T.aestivum)Qingchun 38 and quinoa(C.quinoa)Qingbaili 1.The preliminary inhibitory mechanism against rape of n-butanol extract at the concentration of 40 mg/m L showed that the content of MDA was significantly higher than that of the blank control,and the activities of CAT,SOD and POD showed a tendency of first upward and then downward.This result indicated that lipid peroxidation damage occurred in the leaves of volunteer oilseed rape,which eventually caused irreversible H2O2 accumulation,peroxidative damage,and death in volunteer oilseed rape.In conclusion,the moderate halophilic bacterium D30202 isolated from the Qrhan Salt Lake on the Qinghai-Tibet Plateau had the biocontrol potential of weed suppression,which provided a theoretical basis for isolating the herbicidal compounds and their leading compounds with higher activity and novel structure in the future.