Investigation On Occurrence Of Sorghum Anthracnose In Chongqing And Screening Of Its Control Agents

Sorghum anthracnose caused by Colletotrichum sublineola is one of the main disease in sorghum planting area in Chongqing.It can infect plants from seedling stage to adult stage,seriously affecting the yield and quality of sorghum.At present,there are few studies on the chemical control of sorghum anthracnose in China,and systematic screening of fungicides for sorghum anthracnose has not been reported.Therefore,based on the identification of symptom types,pathogenic bacteria types and occurrence regularity of sorghum anthracnose in Chongqing,high-efficiency single and compound agents were screened in this study for the prevention and control of sorghum anthracnose through indoor toxicity test and field efficacy test.It aims to provide the theoretical basis and technical support for the comprehensive prevention and control of sorghum anthracnose.The main research results are as follows.Symptom types,pathogen isolation and identification of sorghum anthracnose in ChongqingTo clarify the main symptom types and pathogen types of sorghum anthracnose in Chongqing,this study collected several disease samples from different plots in Jiangjin district,the main sorghum production area of Chongqing,and classified the symptoms of sorghum anthracnose in Chongqing into five different types by the observation of symptom types.Morphological and molecular biological identification of the pathogenic bacteria of the collected sorghum anthracnose samples was carried out.The morphological characteristics were found to be similar to those of the reported sorghum anthracnose bacteria by observing their colony morphology,conidial disc morphology and morphology of conidia.ITS sequence analysis was also performed,and the comparison results showed 100%homology with the reported ITS sequences of Colletotrichum sublineola,indicating that the causal agent of sorghum anthracnose in Chongqing is Colletotrichum sublineola.Occurrence of sorghum anthracnose in ChongqingIn order to provide the basis for chemical control of sorghum anthracnose,a field survey was conducted on the relationship between the occurrence of sorghum anthracnose and season,host growth period and meteorological factors in Chongqing.The investigation results showed that the incidence and disease index of sorghum anthracnose were positively correlated with the growth period of the host,and the sorghum can be infected at the seedling stage,with an incidence of 6.77%.At the grain filling maturity stage of sorghum,the disease index could be as high as 31.05.The incidence and disease index of sorghum anthracnose in Chongqing in 2020 were significantly correlated with temperature,but not with relative humidity and rainfall.Screening of single agent for controlling sorghum anthracnoseThe fungicides with better control effects were screened by indoor virulence assays and field efficacy tests against sorghum anthracnose.The results showed that the EC₅₀values of imidacloprid,tebuconazole,pyraclostrobin,carbendazim and chlorothalonil were all less than 0.5μg/m L.The EC₅₀value of pyraclostrobin was 0.026μg/m L,which was the best.The relative efficacy was 82.35%,followed by 450 g/L imazam aqueous suspension and 430 g/L tebuconazole aqueous suspension,with the efficacy of76.92%and 75.11%,respectively.Therefore,imazam,tebuconazole and pyraclostrobin are recommended for field control of sorghum anthracnose.Screening of compound agents against sorghum anthracnoseThe binary combination of mimosamine,tebuconazole and chlormequat chloride with pyraclofop-methyl was used to screen for synergistic combinations against sorghum anthracnose.In the indoor test,the following ratios were found to have synergistic effects:imazam and pyraclostrobin at mass ratios of 8:2 and 6:4,with synergistic coefficients of 1.6695 and 1.5371;tebuconazole and pyraclostrobin were not found to have synergistic effects on Sorghum anthracnose in the measured mass ratios of the compounds;leaf azoxystrobin and pyraclostrobin were found to have synergistic effects at mass ratios of 7.3 and 7.5:The synergistic effect was observed at 7:3 with a synergistic factor of 1.600.The results of the field test showed that the best control effect was achieved at 8:2mass ratio of imidacloprid to pyraclofenoxuron,with a relative efficacy of 90.37%,which was significantly higher than that of the single agents and had a good synergistic effect.Synergistic mechanism of prochloraz combined with pyraclostrobin on sorghum anthracnoseThe results showed that the inhibition of mycelium was 59.38%-63.43%,and the inhibition of mycelium growth was better compared with that of single agent.The effect of compounding agent and single agent on ergosterol content,cell membrane permeability and soluble protein was further determined.The synergistic effect of the compound agent on the inhibition of ergosterol and soluble protein synthesis in the pathogen was not obvious;the relative permeability of the compound agent was higher than that of each single agent,and it had a synergistic effect on the permeability of the cell membrane.The above findings suggest that the compounding agents may show synergistic effect by changing the permeability of cell membrane and accelerating the binding of agent targets.