Primary Study On Control Of The Corn Southern Leaf Blight

The leaves which appear typical symptoms of corn southern leaf blight from Duo Ying farm in Ya'an were collected and the pathogen was isolated which was identified as Bipolaris maydis.The biological characteristics of Bipolaris maydis was studied.The result showed that corn medium and PDA medium were more suitable for the hyphal growth,the optimum temperature 25℃～35℃,the optimum pH 8,and the optimum C source starch,the optimum N source glycin.And the light had important significance on the sporulation and hyphal growth of the pathogen..Efficiency of the several fungicides was tested in laboratory.The suppression rate of Dimethachlone on the hyphal growth was the best,its EC₅₀ was 4.96μg/ml.The second was Chlorothalonil and Mancozeb,the EC₅₀ was10.3μg/ml and 18.3μg/ml,respectively.The lowest was Sanmate and Mildothane,EC₅₀ was 823μg/ml and 622μg/ml,respectively.Biological control potential of the strains of Gliocladium virens to the pathogen was tested in the following wayes.The different strains of Gliocladium virens had varied inhibiting abilities to the the hyphal growth of Bipolaris maydis when they were cultured in pair.And G..virens could not cover Bipolaris maydis,and there's obvious zone of antagonism.For a long time,the strain of G.virens cannot cross the zone of antagonism continue to grow and cover the colony of pathogen. The inhibition rate of non-volatile products of G27 was the highest,for 64.14%.The inhibition rate of G8 was lowest,16.33%only.On the suppression of volatile metabolites,besides G1 which inhibition rate was 41.47%,those of the rest were less than 40%,which were much lower than volatile metabolites.In the experiment of resistance evaluation,the results turned out that the highest disease index was 35.15%of G1-4,the lowest disease index was 2.13%of G2-8 among 70 materials tested.There's 27 materials were HR,15 materials were MR,23 materials were MS,only 5 materials were HS.The test results of enzymatic activity showed that when the pathogen was not innoculated, POD and SOD of the susceptible and resistant varieties had not obvious change,a slight diference of activity of PAL had hapened between them.But when the pathogen was innoculated,the activity of POD and PAL were positive correlation with variety resistance.And the enzymatic activity of resistant variety rised much faster and higher.SOD of the resistant variety was positive correlation with variety resistance in 0-48hours,as a whole the enzyme activity of resistant variety was more stable.