The Genetic Diversity Of Cytospora Chrysosperma And The Defense Mechanisms Of Poplar

Poplar is an important ecological and commercial forest tree species. Poplar canker is a major stem disease, which is caused by Cytospora chrysosperma. Forty-six Cytospora chrysosperma strains isolated form31cities or counties of11provinces in China were analyzed for morphological characteristics, pathogenicity and molecular genetic diversity.Research of domestic and foreign experts showed that the application of disease resistant species could be used to control the poplar canker. The interaction between poplar and Cytospora chrysosperma was studied in this paper. The relationship in this interaction between dynamic changes of related enzyme activity, the content of H2O2and MDA in poplar tissues and the host disease resistance was studied. The zinc finger gene expression of P. alba x P. berolinensis was studied after inculation with Cytospora chrysosperma Then resistance mechanisms of the host after inoculated with Cytospora chrysosperma was discussed to provide scientific basis for the molecular mechanism of poplar canker and poplar disease resistance varities screening.The conclusions showed that:1. The46strains of Cytospora chrysosperma causing poplar canker from11provinces in China were classified into two clusters based on the cluster analysis of morphological characteristics. The first cluster was separated into two groups, the first group included4strains of Beijing,4strains of Heilongjian,3strains of Liaoning,3strains of Shandong,1strains of Jilin,1strains of Inner Mongolia. The second group included4strains of Shaanxi,3strains of Xinjiang,3strains of Qinghai. The second cluster included7strains of Inner Mongolia,6strains of Sichuan,6strains of Gansu,1strains of Heilongjiang. The result indicated that there was a certain relationship between the genetic diversity of morphological characteristics and geographical origin.2. There was no significant relationship between the geographical origin and the pathogenicity, but there was a certain relationship between the pathogenicity and the species of host. The strains isolated form poplar showed stronger pathogenicity than non-poplar host.3. There was a relationship between the geographical origin and the molecular genetic diversity. The46strains of Cytospora chrysosperma were divided into two groups with RAPD and SRAP methods. The44strains were separated into the same cluster by RAPD and SRAP methods. The first cluster included all strains of Beijing, Xinjiang, Liaoning, Shaanxi, Jilin, Qinghai, Gansu, Heilongjiang and2strains of Shandong. The second cluster included all strains of Sichuan and7strains of Inner Mongolia. The strains of C18(ManGui Inner Mongolia) and C28(ZhuCheng ShanDong) were not separated into the same cluster.4. In this research, after inculated Cytospora chrysosperma to poplar, the activity of enzyme changed a lot, and the trend of the activities rised first and then decresed. From the results, we found that defense reaction of poplar was activated when the callus tissue was invaded by Cytospora chrysosperma, including the rapid increase of the activities of PAL, SOD, POD and PPO. The H2O2increase rate contrast CK1and CK2of P. alba×P. berolinensis are higher than P. simonii×P. nigra after inoculation C14. The time of reached peak of P. alba x P berolinensis is earlier than P. simonii x P nigra after inoculation C14. The invasion and expansion of pathogen was controlled. The MDA increase rate contrast CK1and CK2of P. alba×P. berolinensis are significantly lower than P. simonii×P nigra after inoculation C14. The MDA content in P. simonii×P nigra increased and did not change evidently in P. alba x P. berolinensis, the results show that an evident membrane lipid peroxidation occurred in the cells of P. simonii×P. nigra.5. Real time RT-PCR was used to study the expression of resistance genes of Populus alba×P. berolinensis in this study. The results showed that the expressions of ZFP1and69-Ⅳ-2-4increased continuously after inoculation. The expressions of ZFP1were4.21times and3.11times of the scalded control and blank control respectively48hours after inoculated. The expressions of69-IV-2-4were9.56times and7.06times of the scalded control and blank control respectively48hours after inoculated. The expression of ZFP1and69-Ⅳ-2-4were higher in early inoculation, it is showed that the zinc finger protein gene may be participated in the processes of plant-pathogen recognition and defense.