| Rice blast disease,caused by the fungus Magnaporthe oryzae,is a leading constraint to rice production and is a serious threat to food security worldwide.Rice blast disease has been found in more than 85 countries.Rice is vulnerable to M.oryzae wherever it is grown.Between 10%and 30%of the annual rice harvest is lost due to infection by the M.oryzae.But even 10%is significant,being sufficient to feed 60 million people for one year.Chemical control is widely used for its advantages of economy,efficiency and convenience.At present,the fungicides for controlling the disease are limited.So the development of new chemical control techniques for rice blast is particularly important.In response to the development needs of the green control technology of rice blast,this paper developed a synergistic agent for synergistic prevention and control of rice blast by screening the host defense system or the low toxicity bactericide with high activity against rice blast fungus.To provide new technologies for rice blast prevention and control that reduce the amount of pesticides and improve the control effect.The induction effect is affected by many factors.This paper mainly studies the effect of spore concentration on the induction effect,as well as the effect of treatment time and concentration of the six agents of methyl thiamylamine,Jinggangmycin,oligosaccharides,thiamine,thiazole zinc and benzothiadiazole on the induction of rice blast.The results showed that methotrexate,thiamine,thiazole zinc and benzothiadiazole have no induced resistance to rice blast.Oligosaccharides and jinggangmycin have induced resistance to rice blast,but the control effect is poor.When the concentration of Jinggangmycin is 30 μg/mL,the control effect is preferably 30%.When the concentration of the Jinggangmycin reaches 100 μg/mL,the control effect does not increase with the increase of the concentration of the drug.And the control effect is independent of the spore concentration.The induction effect of oligosaccharides and Jinggangmycin is obvious at 12h and 24h of treatment,and the control effect was optimal at 24h of treatment.When treated with oligosaccharides for 6h and 48h,it not only inhibited,but also promoted the growth of pathogenic bacteria.In this paper,tricyclazole and azoxystrobin,which are currently the best in controlling rice blast,are used as reference agents.The inhibitory activities of common fungicides of EBIs,QoIs,SDHIs and MBIs Magnaporthe oryzae were studied.The results showed that benzofenflurazole,pyraclostrobin,coumoxystrobin and isopyrazam have high activity against M.oryzae.And its have both protective and therapeutic effects.In particular,benzotrifenazole and pyraclostrobin have much higher control effects than tricyclazole and azoxystrobin.In the synergistic composition study of different action mode fungicides,it was found that the combination of benzotrifenazole and tricyclazole in 1:3 and 1:1 had synergistic effect and the synergistic coefficient was 1.89 and 2.22.When the syringo ester and the tricyclazole are used in combination at a ratio of 1:10,1:5,1:3,1:1,3:1,5:1,and 10:1,there is also a synergistic effect.Among them,the 1:3 composition had the highest synergistic coefficient,reaching 2.38.In this study,there was no variation to coumoxystrobin sensitivity in the 100 strains of M.oryzea by mycelial growth assay.EC50 values ranged from 0.0089 to 0.029μg/ml with the average value of 0.01632±0.0003610μg/ml for mycelial growth.No resistant population were found.The frequency distribution curves of the EC50 value was unimodal.After treatment with coumoxystrobin,the cell secretion,mycelium electrolyte leakage,hyphae of offshoot increased and hyphae occurred distortion,fungu grew slowly or stop,rate of cellular respiration decreases significantly.In conclusion,coumoxystrobin had strong activity against M.oryzae in vitro and had an excellent protective and curative effect on leaves of rice against M oryzae,which indicated that coumoxystrobin is a potential fungicide for controlling rice blast. |
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