Identification Of The Pathogen Causing Corn Anthracnose And Screening Of Effective Fungicides

Corn is one of the three major food crops in China.Corn diseases is one of the important limiting factors affecting the high yield,stable yield and high quality of corn.In this experiment,the identification and biological characteristics of the pathogen of corn anthracnose were studied.On this basis,the inhibitory effects of seven fungicides on mycelial growth and conidial germination of the pathogen were researched.The main research contents are as follows:1.Identification of the pathogen of corn anthracnoseFive strains of corn anthracnose were isolated from the leaves of corn anthracnose collected in Tiantangzhai Town,Jinzhai County,Anhui Province by tissue isolation and single spore isolation method.The strain numbers were TT23,TT37,TT48,TT47 and TT40.According to Koch’s law,the isolated strains were inoculated to healthy corn leaves,and the symptoms of the disease were similar to those of the collected samples.The taxonomic status of corn anthracnose pathogen was analyzed by the colony morphology,sporulation structure and appressorium morphology,and molecular biology methods.The results showed that the colonies were gray white and the aerial hyphae were dense on PDA medium.The average growth rate of hyphae was 7.75 mm/d.The conidia are colorless and transparent,oblong,smooth in surface,blunt at both ends,without septum,length × width=14.5～21 μm × 5.8～8.6 μm.Using the whole genome DNA of the pathogen as template,the target genes of ITS,ACT,CHS-1,β-Tub,and GAPDH were amplified and sequenced by the corresponding primers of the five genes of ITS,ACT,CHS-1,β-Tub,and GAPDH.The sequences of the five genes were compared in genebank.It was found that most of the gene loci of TT23,TT37,TT48,TT47 and TT40 were similar to fruit anthracnose,and the gene sequences of each locus of model strain or authoritative strain was downloaded.The results of phylogenetic analysis showed that all of the five gene loci were classified as C.fructicola by molecular phylogenetic analysis.According to morphology and molecular systematics,the pathogen of corn anthracnose was identified as Colletotrichum fructicola.2.Biological characteristics of corn anthracnose pathogenThe effects of temperature,pH,carbon source,nitrogen source and illumination on the mycelial growth and sporulation of TT37 strain were studied.The results showed that TT37 strain could grow well in the range of 22～31℃.Within the tested temperature ranges,the optimal temperature for mycelial growth and sporulation was 28℃;the mycelium could not grow at 53℃ for 15 min,and conidia could not germinate in 58℃water bath for 15 min The optimal pH for mycelium growth was 7,and the spore yield was the highest when pH was 9.When pH was higher than 9,spore germination was inhibited significantly.According to the results of carbon source and nitrogen sourece,glucose was the best carbon source and peptone was the best nitrogen source.The TT37 strain was sensitive to light.Under dark conditions,the mycelial growth rate was the fast and spore yield was the largest.3.Screening of effective fungicides against corn anthracnoseThe inhibitory effects of carbendazim,pyraclostrobin,fenproconazole,prothioconazole,benzopropiconazole andtebuconazole on the mycelial growth and conidial germination of TT37 strainwere studied by toxicity test in laboratory.The results showed that carbendazim,prothioconazole and tebuconazole had relatively good inhibitory effects on the mycelial growth of TT37 strain,with EC50 values of 0.157 μg/mL,0.244μg/mL and 0.247 μg/mL,respectively.The fungicides with better inhibitory effect on conidia germination were chlorothalonil,fenpropiconazole and tebuconazole,with EC50 values of 0.100 μg/mL,1.001 μg/mL and 1.118 μg/mL,respectively.