Studies On Screening Of Pesticide Formulation For Controlling Rice White-tip And Bakanae Disease

Rice is one of the major grain crops in China,and its production security has a bearing on national economy and people’s livelihood.Rice bakanae disease and Aphelenchoides bessey are the main seed-borne disease in rice production.Seed immersion or seed mixing with insecticides is an effective method to prevent and control rice bakanae disease and A.bessey.In order to screen efficient,low toxicity and safe formula of rice seed immersion agents that can also treat rice bakanae disease and A.bessey,this study first identified the main pathogens of rice bakanae disease in Anhui Province.Two seed impregnating agent formulations were obtained which could treat both rice bakanae disease and A.bessey.The main results were as follows:1.Direct contact method was used to test the toxicity of five kinds of nematicide,including fosthiazate,avermectin,fluensulfone,fluopyram and cyclobutrifluram,to A.bessey.The results showed that all the five kinds of nematicide had good contact effects on A.bessey.The LC₅₀ values of the new fungicide and nematicide agent cyclobutrifluram were 5.7795μg/m L,3.3553μg/m L,1.6655μg/m L for 2 h,12 h and 24h,respectively.2.A total of 146 rice bakanae disease samples were collected from different parts of Anhui Province.TEF-αsequence amplification and comparative analysis were performed after isolation by pathogenic fungus.Fifty-four Fusarium strains were isolated,including 51Fusarium fujikuroi and 3 Fusarium proliferatum.Fusarium verticillioides and Fusarium andiyazi were not isolated.The results showed that F.fujikuroi was the main pathogen of rice bakanae disease in Anhui Province.3.The mycelium growth rate method was used to measure the mycelium growth and the inhibition effect of six fungicides,such as ipconazole,prochloraz,thiophanazole,cyclobutrifluram,pydiflumetofen and fluopyram on F.fujikuroi and F.proliferatum.The results showed that the 6 agents had inhibitory effects on F.fujikuroi and F.proliferatum,and their EC₅₀ values were 0.0565μg/m L and 0.0578μg/m L,respectively.0.0263μg/m L and 0.0358μg/m L;1.3651μg/m L and 1.1521μg/m L;0.9673μg/m L and 1.7038μg/m L;3.2723μg/m L and 5.5107μg/m L;13.8932μg/m L and 15.0725μg/m L.4.According to the results of laboratory virulence test,the combination of the best single dose of fungicide and nematicide agent cyclobutrifluram was selected,and the co-toxicity coefficient method was used to evaluate the control effect of the combination against F.fujikuroi and F.proliferatum.The results showed that:At the ratio of 17:500 and 29:500,6:250 and 3:100,the mixture of ipconazole and cyclobutrifluram,prochloraz and cyclobutrifluram showed obvious synergic effects.5.The biological effects of cyclobutrifluram on F.fujikuroi and F.proliferatum were determined.The results showed that the treatment of F.fujikuroi and F.proliferatum with0.97μg/m L,9.7μg/m L,97μg/m L and 1.7μg/m L,17μg/m L,170μg/m L could cause cell membrane damage and electrolyte exosmosis in the cells,and obvious misshapen phenomenon occurred in mycelia.In addition,with the increase of the concentration of the drug,mycelium morphology had different degrees of mycelium expansion,mycelium branching increased,and cell adenosine triphosphate（ATP）production and sporulation decreased significantly.The fresh weight of mycelia decreased gradually after treated with0.24μg/m L,0.49μg/m L,0.97μg/m L,1.94μg/m L,3.88μg/m L of cyclobutrifluram.There was no significant difference in Fresh weight,germination rate,plant height of rice seeds treated with different concentrations of cyclobutrifluram compared with those treated aquae sterilisata,which proved that cyclobutrifluram was safe for rice.6.Pot experiments were conducted to determine the control effect of six fungicides,such as ipconazole,prochloraz,prothioconazole,cyclobutrifluram,pydiflumetofen and fluopyram on F.fujikuroi and F.proliferatum.The results showed that the best control effect of prochloraz was 85.71%and 85%,and the worst control effect was fluopyram,61.90%and 65%,respectively.Pot experiments were conducted to evaluate the control effect of the combination of prochloraz and cyclobutrifluram,as well as the combination of ipconazole and cyclobutrifluram on rice bakanae disease and A.bessey.The results showed that under the mass ratio of 6:250 and 3:100,The control effects of the combination of prochloraz and cyclobutrifluram on the rice bakanae disease caused by F.fujikuroi and F.proliferatum were92.31%and 91.99%,respectively,and the control effects on the A.bessey were 79.99%and80.55%.Under the mass ratio of 17:500 and 29:500,the control effects of the combination of seed ipconazole and cyclobutrifluram against the rice bakanae disease caused by F.fujikuroi and F.proliferatum were 88.46%and 87.99%,respectively,and the control effects against A.bessey were 81.48%and 81.24%.The control effect of the two compound agents on rice bakanae disease was higher than that of the single agent.