| In this paper, the Japanese Foxtail (Alopecurus japonicus Steud.), a kind of worstgrass weed in oilseed rape fields in the middle and lower reach of Yangtze valley in China,was chosen as a main research object. The methods of breaking dormancy of A.japonicusseeds and the optimal germinating temperature were studied, the resistance level of A.japonicus to haloxyfop-R-methyl, which is an ACCase inhibitor belonging toaryloxyphenoxypropionates (AOPPs), cross-resistance and the resistacne mechanism of A.japonicus was investigated.It was found that the optimal germinating temperature range of A.japonicus was 15—20℃. The dormancy of seeds from Chuzhou and Hefei could be broken by being buriedunderground 7 cm for 10 d, whose germination rates reach to 87.5％and 90％,respectively. While the germinate rate of seeds from Jurong was only 1.67％. Dormancycould also be broken by being soaked in water at 4℃, and Jurong, Chuzhou and Hefeipopulations could germinate at the same time. It was indicated that the short dormancy of A.japonicus seeds could be broken by lower temperature and higer humidity.The resistance level of A. japonicus to haloxyfop-R-methyl were evaluated byseed-bioassay and whole-plant test, which were collected from different oilseed rape fieldswhere haloxyfop-R-methyl had been continuously applied for different years, and similarresults were obtained by both of methods. In these two methods, the resistance index of A.japonicus to haloxyfop-R-methyl, which were collected from Jurong in Jiangsu province,were 61.13 and 1331.68, respectively, which demonstrated the emergence of A. japonicuspopulation resistant to haloxyfop-R-methyl in fields. The results of cross-resistance revealed that this resistant population was also resistant to some other AOPPs, in which theresistance level was: fluazifop-P-butyl>quizalofop-P-ethyl>fenoxaprop-P-ethyl.However, a relative low resistance level of this resistant population to sethoxydim wasobserved, which was a cyclohexanedione (CHD) herbicide sharing the same target site withAOPPs. And the results obtained in laboratory were agreed with the real fact in fields.To characterize the biochemical differences in haloxyfop-R-methyl-resistant and-sensitive populations of A. japonicus collected from Jurong and Chuzhou, the activities ofantioxidant oxygens, content of reduced/oxydized glutathione (GSH/GSSG),malondialdehyde (MDA), proline, chlorophyll and soluable protein in shoots and leaves ofindividuals treated by haloxyfop-R-methyl were studied. The results showed that theactivities of superoxide dismutase (SOD) decreased significantly in sensitive population,but kept stable in resistant population. The activity of peroxidase (POD) in sensitivepopulation rose obviously in 14 days after treatment, while the eatalase (CAT) increased inearlier period and then decreased, the trends of activities of POD and CAT in resistantpopulation were the same as that of CAT in sensitive population. The content of GSH keptincreasing in experiments, which could also be observed in the contents of superoxideanion radical (O2·-), hydrogen peroxide (H2O2), GSSG, MDA and proline, but not changingin the resistant population. The trends of soluable protein in both populations were oppositeto that of Chlorophyll content in sensitive population. In addition, the activities of aeetylcoenzyme A carboxylase (ACCase) in both of the population were determined. The resultdemonstrated that ACCase activity in sensitive population was inhibited obviously byhaloxyfop-R-methyl. It may be concluded that this herbicide greatly affected some of thephysiological and biochemical pathways in sensitive population, except for ACCase.
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