Isolation And Identification And Biological Characteristics Of Pathogen Of Corn Stalk Rot And Primary Study On Diseases Biological Control

Three kinds of Pythium spp. and four kinds of Fusarium spp. were isolated and identificated from the infected stem of corn. P. graminicola, F. moniliforme, F. graminearum, and P. inflation had the higher separate frequency, the proportion of which were 37.45%,20.08%,18.53% and 13.13%,respectively.The seedling stage pathogenicity of the 7 strains pathogens of Pythium spp. and Fusarium spp. and Koch rule validation were made. The results showed that both of these two kinds of pathogens had the pathogenicity to corn, although the pathogenicity of the strains were different. The pathogen pathogenicity of P. graminicola, P. inflatum, F. graminearum and P. aphanidermatum were stronger. The experiment showed that the disease index of corn reached 60% or more after inoculated these four pathogens.The disease index was 8.32% after being inoculated F.fusarioidis. The pathogens could re-separatied from the roots of the infected corn.Two kinds of pathogens(strains of F. graminearum F82 and P. graminicola P16) which had high frequency of separation and strong virulence were selected to study their biological characteristics.The results showed that the best medium for the hyphal growth of F. graminearum was PDA; the temperature range was 10℃～35℃, the optimum temperature was 25℃; the optimum pH value was 7;glucose was the best carbon source; peptone was the best nitrogen source; the hyphal growth was best in all dark conditions; the best solid culture for this pathogen grew fastest in the 5th experimental group(25℃,pH 6, dark), and the growth state was significantly better than other experimental groups.In experiments the best medium for P. graminicola was Czapek; the mycelium growth temperature range was 10℃～40℃,the optimum temperature was 28℃;the growth optimum pH value was 8;glucose was the best carbon source; peptone was the best nitrogen source;the mycelial grew best in the half-light conditions; the best solid culture for this pathogen grew fastest in the 9th experimental group(30℃, pH 8, half-light), and the growth state was significantly better than other experimental groups.In the experiments 29 strains of Trichoderma spp. were isolated from the rhizosphere soil of the field crops, four strains of Trichoderma spp. were screened by measuring the growth rate, paired culture with the pathogen and antibiotic effect of volatile metabolites and screened by observing the hyperparasitism of these Trichoderma spp.,It was identified from experiments that T12 was T. longi-brachiatum, T26 was T. aureovirid and T19and T20 were T. viride.The biocontrol effect of pot and field experiments using cultures of 4 strains of Trichoderma spp. against two maize varieties were obtained. The results of the pot experiments showed that four kinds of culture of the strains of Trichoderma spp. had better control effect on the disease.The disease index of cultures of T20 and T12 against F. graminearum of corn stalk rot were highest and the control efficiency were significantly higher than the other two cultures of Trichoderma spp. and triadimefon, the control efficiency of T20 against the variety of maize called Zhenghong 311 achieved 68.06%.The disease index of culture of T12 against Pythium spp. of corn stalk rot was the best,the control efficiency of T12 against Zhenghong 311 and Chuandan 418 were respectively achieved 70.30% and 65.69%.The results of the field experiments under natural conditions showed that the control efficiency of T20 against Zhenghong 311 was the highest of all which achieved 79.14% and the control efficiency against Chuandan 418 was higher than 60%, the control efficiency of T20 was higher than triadimefon. The results under pathogen inoculation showed that the control efficiency of T12 against Zhenghong 311 was 70.22% and the control efficiency of T20 against Chuandan 418 was 69.29%. The control efficiency T12 and T20 were higher than others with potential market value.