| Chestnut blight epidemic is associated with devastation of Castanea,Chestnut blight also one of an important disease in the forests.The population diversity of Cryphonectria parasitica was studied in this thesis.Molecular detection of mating type and crossing were tested in Cryphonectria parasitica.The results show that eight strains were MAT-1 in tested sixteen strains and others were MAT-2. Six kinds of isolates of new genotype were obtained through one or two sexsual crossing group between isolates which have known genotypes.The former crossing results had the same genetic background and the latter crossing results had different genetic background. Obtained new genotype isolates was important to study horizontal virus transmission.Effect of heteroallelism at each vic locus on transmission of hypovirus in Cryphonectria parasitica was characterized.The 16 isolates of different genotype at 4 vegetative incompatibility(vic) loci were obtained through sexsual crossing between isolates which have known genotypes.Virus transmission was assayed by growing donor and recipient isolates together.Virus transmission occured with 100%frequency when donor and recipient isolates had the same vic genotypes but heteroallelism at one of these loci generally reduced virus transmission.Transmission occurred in 87.00%of pairings that were heteroallelic at vic-C while only in 8.79%of pairings that were heteroallelic at vic-D. The average vires transmission rates were 44.12%and 48.93%respectively when vic-A and vic-B were heteroallelic.Virus transmission was asymmetric,at the extremes,pairs that were heteroallelic at vic-B showed strong asymmetry:transmission rate was 83.13%when virus transfer from vic-b isolate to vic-B but occurred only 23.15%when virus transfer from vic-B isolate to vic-b,and in other vic loci this asymmetry were also observed though not significantly.Effect of different vic genes on transmission of hypovirus in Cryphonectria parasitica was characterized in this report.After ten days,virus transmission was assayed by growing donor and recipient isolates together.The results showed that vegetative incompatibility in Cryphonectria parasitica has reduced the transmission of viruses between individuals,but the barrier to transmission is incomplete.Virus transmission occured with 100%frequency when donor and recipient isolates had the same vic genotype.Frequencies of transmission were 44.31%,26.92%,6.85%and 0.59%with different genes from one to four,and were decreased from 88.46 to 9.01%at one difference of four loci.Virus transmission had directed in the pairing of isolates which had difference of the same vic genes and the same transmission direction.Through logistic regression model,four groups of isolates of heteroallelism at two vic loci had statistically significant interactions(epistasis),but effects of heteroallelism at three vic loci were not epistasis.This test showed that Heteroallelism at vic loci,asymmetry,and epistasis were the dominant factors controlling transmission,but host genetic background and genotype of donor and recipient isolates also were statistically signiticant effects,indicating that vic genes alone cannot explain all the variations in virus transmission.This report gives a survey on biological control of chestnut blight with hypovirulence. Hypovirulent isolates were inoculated with different methods,and the investigations were done in every autumn for the virus transmission rate,virus dynamic detection in the field and the control effect.The results show that experimental field of 36 strains were divided into 33 VCGs in Hushan town,every VCG only had 1.09 strain and strains of the same VCG were from the same district.In the experimental field of Dazhe town,VCGs were more complex and every VCG had no more than 1.25 strains on average.Heteroallelism at four vic loci between the pairings in the fields six months after the inoculation,did not happen hypovirus transmission.Half a year after dealing with canks,only two districts had virus transmission and occurred as 280,the rate was 15%and 10%respectively.It means that the strains containing virus 280 were more easily spread in the fields.One and a half years after the inoculation,the virus did not transmit in the fields. |
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