Identification Of Pathogens,physiological Races And Powdery Mildew Resistance Genetic Analysis In Seed-used Pumpkin(Cucurbita Pepo L.)

In this paper,the seed-used pumpkin(Cucurbita pepo L.)germplasm and powdery mildew pathogens in Inner Mongolia are used as materials,the pathogenic species of powdery mildew on seed-used pumpkin(Cucurbita pepo L.)of Inner Mongolia was identified and analyzed using morphological and molecular biology method,the pathogenicity of the powdery mildew to 20 varieties of seed-used pumpkin(Cucurbita pepo L.)from Inner Mongolia area was determined,and differences in disease resistance of 16 multi-generation homozygous inbred lines were identified using the method of natural disease in the field and artificial inoculation at the seedling stage.The identification test for powdery mildew physiological races of four regions of Inner Mongolia strictly applied international standard system.Using field natural incidence and artificial infection at seedling stage method,segregation-ratios between resistance and susceptible to powdery mildew of six generation plantets was counted and analysised by chi-square test.The main research results are as follows:1.The results of morphological identification methods showed conidia of powdery mildew of seed-used pumpkin(Cucurbita pepo L.)of Inner Mongolia were cluster,cylindrical,no obvious fibrosin body,so pathogens was identified as Podosphaera xanthii.The results of molecular systematic identification showed that the rDNA-ITS sequence of powdery mildew was clustered together with the sequence of Podsphaera xanthii published in GenBank.2.The pathogenicity test results showed that there were 7 disease-resistant varieties,4 medium resistance varieties,1 high resistance variety,8 susceptible varieties among the 20 main cultivars of seed-used pumpkin(Cucurbita pepo L.)in Inner Mongolia area,it showed that the pathogen of powdery mildew in Inner Mongolia had strong pathogenicity.3.Resistant to powdery mildew of 16 seed-used pumpkin(Cucurbita pepo L.)germplasm investigated existed difference.Susceptible to disease accounted for 87.5%of all germplasm,disease-resistant accounted for 12.5%of all germplasm.Disease-resistant germplasm showed same trend between natural infection in open and artificial infection.Susceptible to disease germplasm of natural infection in open were more than that artificial infection.The results indicated that the same seed pumpkin germplasm was more susceptible to powdery mildew in field.4.By using the commonly used 13 different identification melon hosts of powdery mildew and identification system in the international and referring to its resistance and susceptible results,the result showed that melon hosts Iran H,Top mark,Nan tais were all susceptible to powdery mildew,PMR-45,Edisto47,PI414723,PI124112,PMR 6 showed disease resistance.The results preliminarly showed that there were four physiological races of seed-used pumpkin(Cucurbita pepo L.)powdery mildew in Inner Mongolia aera,namely race 4 and race 2F,race 1,and an unknown race.5.150 plants of F2 population were selected,36 plants showed disease resistance,114 strains showed susceptible to disease,XC2 is 0.036 after chi-square test,so the segregation-ratios in F2 populationis in accordance with the theoretical ratio of 1:3.100 plants of BC1P1 isolated population were selected,48 plants showed disease resistance,52 plants showed susceptible to disease.XC2 is 0.09 after chi-square test,so segregation-ratios in BC1P1 populationis was in accordance with the theoretical ratio of 1:1,it was preliminary indicated that the resistance to powdery mildew of seed-used pumpkin(Cucurbita pepo L.)was controlled by a pair of major recessive single genes.The number of resistance and susceptible to disease in F2 population showed continuious distribution,so resistance to powdery mildew of seed-used pumpkin(Cucurbita pepo L.)was infered to quantitative genetic trait.