Effects Of Delayed Sowing Date On The Occurrence Of Verticillium Wilt And The Genetic Diversity Of Verticillium Dahliae

Verticillium wilt is a common disease in sunflower,in recent years due to the frequent transportation of sunflower seeds and the difficulty on the rotation for sunflower,Verticillium wilt become a severity problem for sunflower production.In this research,we studied the effects of delayed sowing date on the occurrence of Verticillium dahliae and sunflower yield,the contamination of V.dahliae on sunflower seed coat,the genetic diversity of V.dahliae,including the division of vegetative compatible groups,dendrogram construction based on IGS sequences,PCR detection of races and mating type,and screening of candidate genes related to pathogenicity of V.dahliae by R-PCR.We concluded our results as the followings:1.In the sunflower sowing experiment at different locations in different years,except for the increase firstly,then decline trendency of Verticillium wilt in the Wuyuan in 2010,the occurrence of Verticillium wilt showed the decrease tendency with the sunflower sowing date,which indicated that the delay the sowing date could reduce the occurrence of Verticillium wilt,subsequently it caused the increase of sunflower yield.2.In the study of seed contamination of sunflower yellow wilt,the double-banding resulted by using ITS 1/4 primers indicates that the seed coats can be colonized by different pathogens.A specific band was amplified by nested PCR using the specific primer VD1/2 of V.dahliae,indicating the contamination of seed coats and the specificity of VD1/2 primer of V.dahliae.Combined with fluorescence microscopy,we determined that sunflower seed coat was the main carrier for long-distance transmission of V.dahliae.3.In this study,57 strains of V.dahliae from different sunflower planting areas were divided into three different vegetative compatible groups by using standard international tester strains.Three VCGs were identified among all tested strains,that is VCG4B,VCG4A and VCG2B;VCG4B is the dominant VCG group.There was no correlation between the VCG type of V.dahliae and the geographical distribution of tested strains.4.The races and mating tpye of V.dahliae were identified by using specific primers.Race 2 is the only race type for sunflower V.dahliae.Also,two kind of mating type:MAT1-1 and MAT 1-2 were identified in all tested strains and MAT1-1 is the dominant type.5.Phylogenetic analysis results based on IGS sequence of tested V.dahliae strains showed that tested strains can be divided into three different genetic groups,the biggested group contain almost all the VCG4 type strains whereas,VCG2B strains were distributed in three different genetic groups,indicating that VCG2B strains are genetically heterogeneous.6.In this study,the ESTs sequence related to the pathogenic genesof V.dahliae were screened out by using R-PCR.Several genes encoding a mannitol-1-phosphate 5-dehydrogenase gene,a calmodulin gene,a glycoside hydrolase gene,a peroxidase gene,and a STI35 protein were involved in the pathogenicity of V.dahliae from sunflower.