The Infection Process Of Puccinia Xanthii Schwein. F. Sp. Ambrosiae-trifidae S. W. T. Batra And Its Molecular Genetic Variation

Ragweeds (Ambrosia L.) are alien invasive species for China. How to control the grasses has been closely noticed by weed scientists and public. It appears that it is an effective way to control the grasses by absolute parasitic pathogens. Puccinia xanthii f. sp. ambrosia-trifidae S. W. T. Batra was a microcyclic rust fungus for biological control of giant ragweed, Ambrosia trifida. Thereafter the paper is made to investigate its infection process and genetic variation in order to provide a theoretical base for biocontrol of the grasses by the fungus. The paper conducted the following research aspects:(1) The study illustrated the infection process of P. xanthii f.sp. ambrosiae-trifidae by means of light microscopy associated with Coomassie Brilliant Blue R-250 staining method. The infecting process was divided into the following phases: teliospore germination, basidiospore formation, prepenetration development, penetration and postpenetration development. The typical infection structures included germ tube, appressorium, penetration peg, intraepidermal vesicle, primary hypha, intracellular hyphae, M-haustorium (Chapter one).(2) The genomic DNA of P. xanthii f. sp. ambrosiae-trifidae was extracted by nine methods from the teliospores of the rust fungus. The results show that the methods of CTAB-steel balls, modified mini-drill and modified EZ-Kit were better than the other six methods due to their higher quality of DNA extraction with less impurity. The template DNA samples generated from these methods were detected by methods of ITS-PCR and ISSR-PCR with the primer UBC#835. They all produced expected band patterns. The research confirms that the DNA samples generated from these three methods could be used for further molecular study of the rust fungus (Chapter two).(3) The genetic diversity within and among 16 populations of P. xanthii f.sp. ambrosiae-trifidae from Liaoning province was investigated using ISSR and SRAP molecular markers. The percentages of polymorphic bands were 72.62% for 11 ISSR primers and 71.05% for 13 SRAP primers. The results showed that, the Nei′s genetic diversity and Shannon′s information indexes were 0. 0028—0. 3933 and 0. 0047—0. 5703 in ISSR assay at the population level, and the Nei′s genetic diversity and Shannon′s information indexes were 0.2991—0.3869 and 0.4445—0.4750 in SRAP assay. Based on Nei′s genetic diversity analysis, the genetic diversity coefficient (Gst) of ISSR and SRAP data was 0.2537 and 0.2330, respectively. Analysis of the molecular variance (AMOVA) showes that the genetic variance accounted for 5.70% with ISSR primers and 4.60% with SRAP primers of the total variation among the populations, while it was 94.30% with ISSR primers and 95.40% with SRAP primers within the populations. By employing both ISSR and SRAP markers, this study suggests that the level of genetic diversity among populations of rust in Liaoning province is lower than that within population. Overall, UPGMA obtained from SRAP analysis was nearly consistent with that obtained from the combination analysis of ISSR and SRAP data. In conclusion, the SRAP Marker system is a simple and efficient marker system that can be adapted for a variety of purposes in rust, including map construction, gene tagging and genomic fingerprinting (Chapter three).