| Clubroot disease is one of the main vegetable diseases, it has restricted the cruciferae vegetables industry development and caused great economic losses. A certain control efficiency can be achieved by using chemical agent, but there are some weaknesses such as high cost and Harm to the ecological security, so it is not suitable for a wide range of promotion. Now, planting resistant varieties is the most economical and efficient control means. However, it brings serious challenges to disease resistance breeding because of the pathogenicity differentiation phenomenon of Plasmodiophora brassicae.so,it makes great sense to undertake the studies of pathogenic races and genetic diversity to breeding and rational distribution of disease-resistant varieties. From these perspectives, this study research the P. brassicae field isolates which collect from regions of Hubei province. Main results are as follows:1.This experiment has observed the Infection and development process of P. brassicae by phase contrast microscope, we find that the infection process of P. brassicae includes the following several aspects:(1) After the cruciferous has been planted, the resting spores germinate under suitable conditions and release primary zoospores.(2) The primary zoospores come into the organization by germ tube when they come into contact with the host plants’ root hair surface, after infection, the zoo-spores develop to primary plasmodium, and then the primary plasmodiums develop to zoosporangium and release secondary zoospores.(3) The secondary zoospores are infection source as cortex infection, they intrude cortical cells and develop to secondary plasmodiums which widely distributed in the root tissue. In late infection, the secondary plasmodium develops to resting sporangium which is full of the whole cell.(4) After the death of the host, resting sporangiums release resting spores,the resting spores will survive in soil for a long time as the primary infection source for next infection.2. The identification of pathogenic races to37field isolates which is collected from Hubei province is performed in this test with the help of Williams systerm. As is demonstrated in the results, the clubroot diseases group in Hubei province include No.1、No.2、No.4、No.7and No.10pathogenic race, the dominant race is No.4, followed by No.7. The pathogen population construction in one region differs from another. The pathogenic races in Changyang is No.1、No.4、No.7, the dominant race is No.4; The pathogenic races in Dangyang、Zhijiang、Hefeng is No.4; The pathogenic races in Xuanen is No.2、No.4, the dominant race is No.4; The pathogenic races in Lichuan is No.4、No.7and No.10, the dominant race is No.4and No.7. In this test, we compare the field isolates from a same field and find that the pathogenicity difference is evident and non-regularity. In addition, we also compared the field isolates from different host plants, the result shows that, there is pathogenicity difference in P. brassicae population which infect the different hosts. The pathogenic type is most abundant in Chinese cabbage, and the population in rape is all of No.4race. 3.On the basis of race identification, we also analysised the genetic diversity of P. brassicae population by RAPD technique.136alleles were detected by13RAPD primers from24samples, with an average of10.46, Including115polymorphic markers. When the genetic similarity coefficient is0.59,24field isolates can be divided into3RAPD groups. When the genetic similarity coefficient is0.70, the third group can be divided into8subgroups A-H, these results show that there is no significant correlation between genetic background and geographical origin of P. brassicae. When the genetic similarity coefficient is0.79, the field isolates which is collected from a same field of Lichuan can be divided into5subgroups, This indicated that there is genetic variation between isolates which from a same field. |
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