Analysis of appearance features and genetic diversity of Cytospora chrysosperma causing poplar canker

In order to investigate the appearance features and genetic diversity of Cytospora chrysosperma, as well as their relationships with different factions of the host poplar and their geographic origin, in this paper, 106 samples of C. chrysosperma from 14 provinces of China were collected and observed. And the growth of strains was recorded when being cultivated to analyze the cultivated morphological diversity of strains. Then, 34 samples with obviously different background information were selected and genetic diversity was analyzed using two signing methods of SRAP and ISSR. The results showed that C. chrysosperma presented stable cultivated traits in the same strain under different conditions. While different strains had obvious morphological differences, but there were no obvious correlations between their cultivated traits and their host plants or geographic origins. 12 SRAP primers and 20 ISSR primers with decent polymorphism were obtained in total, which were used to analyze and calculate Nei's index of the population diversity. The results were 0.31 (SRAP) and 0.28 (ISSR), indicating that large genetic differences existed among varied strains. On the other hand, population genetic structure was analyzed from the perspective of the host. The results showed that the total population genetic diversity was 0.27 and the genetic diversity within population was 0.23, which can explain 87% of the overall diversity and the genetic separation coefficient (G_ST) was 0.13. All of above showed that the genetic variation mainly existed within the group. From the view of geographical position, the total genetic diversity was 0.28, genetic diversity within population was 0.13, which can explain 48% of overall diversity and the coefficient of genetic separation (G_ST) was 0.52. That means the diversity within population is equivalent to that among populations. The geographic migrations among populations have great impacts on the overall genetic separation. The genetic diversity levels of the populations show a decreasing trend from west to east.