Studies On Resistance Mechanism And Fitness Cost Of Sagittaria Trifolia L. To Bensulfuron-methyl

Sagittaria trifolia L.is a common broadleaf weed of rice paddies in northeast China.In the late 1980s,acetolactate synthase inhibiting herbicides were widely used,and S.trifolia had been effectively controlled.However,after 2000,the effect of bensulfuron-methyl on S.trifolia was significantly decreased.In recent years,S.trifolia gradually became the dominant population of weed communities in paddy field.In this study,resistance levels of bensulfuron-methyl in 30 S.trifolia populations and their cross-resistance were measured.The resistance levels of bensulfuron-methyl in the S.trifolia second-generation were determined,simultaneously.The resistance molecular mechanism was studied,and three different biotypes were selected to study the changes of biology,morphology and anatomical characteristics,the competition between different biotypes,as well as the competition effect on rice yield.It can evaluate the resistance risk of S.trifolia,which can provide reference for the rapid identification of resistant S.trifolia in the field,and theoretical support for the treatment of resistant S.trifolia.The main results are as follows:1.Determination of resistance levels of bensulfuron-methyl in the first and second generations of S.trifolia and its cross-resistance by whole plant experiments.Results showed that 30 S.trifolia populations had different level of resistance to bensulfuron-methyl,and resistance index between 15.76-155.96.The resistance level of R-21 was the highest,and the resistance index was 155.96.At the same time,there was no significant difference between the second generation and the first generation.The cross-resistance to ALS inhibiting herbicides in 30 S.trifolia populations was determined.All the S.trifolia populations were cross-resistant to ethoxysulfuron and pyrazosulfuron.Removal of R-29 population resistant to pentafluorfenac,R-21 population resistant to pyrimidine-oxime,other populations are sensitive to pentafluorfenac and pyrimidine-oxime.R-1,R-11,R-21,R-22 and R-29populations showed a lower level of resistance to bispyribac-sodium,and the other populations showed no resistance.2.The mechanism of resistance was elucidated from the molecular level by ALS activity assay and ALS gene comparison.Determination of ALS activity in vitro was further confirmed that S.trifolia populations had different level of resistance to bensulfuron-methyl.As the result of sequence comparison,five mutations at position 197 and 376 were found in ALS gene,in which R-16,R-25 and R-26 resulted in substitution of Pro to Thr at 197,R-4,R-8,R-18,R-24,R-28 resulted of Pro to His at 197,and R-22,R-29 resulted of Asp to Glu at376.ALS gene of the resistant R-5,R-9,R-14,R-15 and R-19 populations did not mutate.Pro-197-Thr,His and Asp-376-Glu were first found in S.trifolia populations.3.Under non-competitive conditions,the biological characteristics of S,R-19 and R-22 were compared.The results showed that S exhibited better than R-19 and R-22 in plant height,plant dry weight,leaf number,leaf area,number and size of corm and flowering.However,there was no significant difference in seed biomass and seed size.There was no significant difference between the resistant biotypes R-19 and R-22.At the same time,the chlorophyll content and photosynthesis of different biotypes were studied.It was found that there were significant differences in the chlorophyll content between S and R-22 at the beginning of growth,but there was no difference with R-19.There was no significant difference in chlorophyll content between S,R-19 and R-22 at 60 d and 90 d after sowing.There was no significant difference in transpiration rate,assimilation rate and stomatal conductance among S,R-19 and R-22,indicating that the absorption of light energy and the formation of assimilates were the same for different biotypes.4.The morphological and anatomical structures of leaves and stems of different biotypes were compared.The stomatal densities of R-19 and R-22 were significantly higher than that of S,but there was no difference between R-19 and R-22.There was no difference in stomatal size among different biotypes.On the other hand,there was no significant difference in leaf thickness,upper and lower epidermis thickness of different biotypes.The stem length and epidermis thickness of S were significantly higher than those of R-19 and R-22,while there was no difference between R-19 and R-22.5.The competitive effects between different biotypes and rice were studied.S showed strong competitive effect when compete with resistant biotypes,and there was no difference between the two resistant biotypes.In the presence of rice competition,rice showed stronger inhibitory effects on R-19 and R-22 relative to S.The results showed that S had the ability to allocate more resources in the case of rice competition.On the other hand,the effects of different densities of different biotypes on the rice were determined.The results showed that the plant height,tiller number,ear number and rice yield decreased with the increase of planting densities.There was no significant difference in the plant height and tiller number of rice at the same densities of different biotypes.When the density reached and exceeded 60 plant m^-2,the effects of R-19,R-22 and S on rice yield were significant differences.S on the rice yield inhibition is stronger than R-19 and R-22.