| Beckmannia syzigachne is one of the most troublesome weeds in wheat fields taking rice-wheat rotations.Fenoxaprop-P-ethyl is an ACCase-inhibiting herbicide.It has been used to control grass weeds in China since 1990s.With the long-term use of this herbicide,B.syzigachne has evolved serious resistance to fenoxaprop-P-ethyl.Hormesis refers to the phenomenon that the dose of a chemical substance shows an inhibitory effect on the organism at high concentrations and a stimulating effect at low concentrations.A B.syzigachne population R holding putative resistance to different ACCase-inhibitors such as fenoxaprop-P-ethyl,clodinafop-propargyl,and pinoxaden was collected from a wheat field in Jiangdu District,Yangzhou City,Jiangsu Province.A sensitive population S was collected from Liuhe District,Nanjing City,Jiangsu Province.The two populations(R and S)were used to explore the hormesis of fenoxaprop-P-ethyl on B.syzigachne,and chemical control methods for B.syzigachne in wheat lands.The main results are as follows:1.Fenoxaprop-P-ethyl showed a hormesis effect on population R.Whole-plant bioassays showed that low concentration of fenoxaprop-P-ethyl significantly(P<0.05)stimulated the growth of B.syzigachne R seedlings.Thirty-day after treated with 62.10g/hm2(active ingredients,the same below)of fenoxaprop-P-ethyl at the three-to five-leaf stage,the fresh weight of aboveground parts of seedlings was increased by 17%compared with the control.However,a higher dose(248.4g/hm2)inhibited the growth of B.syzigachne,and over 2000g/hm2 fenoxaprop-P-ethyl killed all R seedlings.Pinoxaden,another ACCase inhibitor,also showed a hormesis effect on the R population.Thirty-day after treatment with pinoxaden at 7.5g/hm2,the fresh weight of aboveground parts of R seedlings increased by 23%compared to control.Cultivating experiments conducted in 2020 showed that compared to control,dry weights of aboveground parts of R seedlings surviving 15.52 g/hm2 fenoxaprop-P-ethyl treatment increased by 55%after seeds getting mature.Cultivating experiments conducted in 2021 showed that compared to control,dry weights of aboveground parts of R seedlings surviving 31.05 g/hm2 fenoxaprop-P-ethyl treatment increased by 25.7%after seeds getting mature.2.A target-site mutation of Ile-1781-Leu was found in the ACCase CT gene sequence of B.beckmannia R seedlings,but not in S seedlings.dCAPS molecular detection suggested that overall plant individuals tested of R population holding ACCase Ile-1781-Leu Heterozygous mutations.Many studies has testified that ACCase Ile-1781-Leu mutation conducing resistance to ACCase-inhibiting herbicides.3.Thirty-day after pre-emergence(PRE)applying of proachlamine at recommended dosage(750 g/hm2),the inhibition rates in fresh weight of aboveground parts of R and S seedlings are 67.5%and 80%,respectively.Recommended dose of 553.5 g/hm2 flufenacet totally killed R and S seedlings,30 d after PRE applying,while showed lower control efficacy 30 d after post-emergence(POST)applying at the stage of two-to three-leaf stage.The recommended dose of isoproturon 1125 g/hm2 showed good control efficacies(>95%)both applied at the two-to three-leaf stage or the three-to five-leaf stage.Acetochlor showed inhibiting rates in fresh weight of R and S seedlings of 85%and 88%,respectively,30 d after PRE applying with the recommended dose of 750g/hm2.The recommended dose of mesosulfuron-methyl 15.80g/hm2 showed inhibiting rates in fresh weight of R and S seedlings of 80%and 83%,respectively,30 d after POST apply at the three-to five-leaf stage.The recommended dose of pinoxaden 62.10 g/hm2 showed inhibiting rates in fresh weight of R and S seedlings of 63%and 100%,respectively,30 d after POST apply at the three-to five-leaf stage.4.To study the efficacies of prometryn against 10 serious wheat weed species,Efficacies of prometryn against 10 serious wheat weed species were tested by whole-plant bioassays,including Beckmannia syzigachne,Alopecurus aequalis,Alopecurus japonicas,Alopecurus myosuroides,Lolium multiflorum,Pseudosclerochloa kengiana,Poa annua,Descurainia sophia,Galium spurium and Capsella bursa-pastoris.Each weed species were applied with a serial of prometryn doses as pre-emergence and early post-emergence(2-3-leaf for grasses and 2-whorl-leaf or 2-pair-leaf for broadleaf weed species).Thirty days after early post-emergence treatments with label dose of prometryn(750 g/hm2,active ingredient),inhibition rates in fresh weights of aboveground parts of D.Sophia,G.spurium and C.bursa-pastoris were 89.75%,94.04%and 75.00%,respectively.As well,the early post-emergence treatment with 1/2 × label dose of prometryn inhibited 89.64%aboveground growth of D.Sophia.Thirty days after early post-emergence treatments with label dose of prometryn totally killed seedlings of A.aequalis,A.Japonicas and P.kengiana;and showed inhibition rates of 95.80%,83.58%,82.77%and 60.11%against A.myosuroides,P.annua,B.syzigachne and L.multiflorum,respectively.Moreover,30 days after pre-emergence treatments with label dose of prometryn showed>85%inhibition rates of A.aequalis,P.kengiana,P.annua and B.syzigachne.Early post-emergence applying of prometryn could be used to manage A.aequalis,A.japonicas,A.myosuroides,P.kengiana,P.annua,D.Sophia and G.spurium;and could constrain B.syzigachne and C.bursa-pastoris seedling growths;while holds low efficacy against L.multiflorum.5.Beckmannia syzigachne and Alopecurus spp.seedlings at leaf stage 2-5 can be effectively distinguished by the percentage of flattening in the middle of the leaves and the degree of leaf crimping.Beckmannia syzigachne leaves outside the central leaf slice of flattening percentage is 95%-100%with leaf curl degrees of 178°to 180°;while those for Alopecurus spp.seedlings were 20%-90%in flattening percentage,with the curl degrees of 5°-150°.Central B.syzigachne leaves outside the second blade flattened percentage was 100%,with leaf curl degrees of 180°;while those of Alopecurus spp.seedlings were 20%-90%,with the curl degrees 10°-150°。... |
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