Phylogeny Of The Genus Exserohilum And Pathogen Diversity Of Sooty Blotch And Flyspeck Of Apple

There are two parts in the thesis: Phylogenetic analysis of Exserohilum species based on Brn1 genes; Pathogen diversity analysis of Sooty blotch and flyspeck (SBFS) by the internal transcriber spacer (ITS) and larger subunit (LSU) sequences. Part one: Exserohilum species are very common plant pathogenic fungi on graminea and other plants. Some species can cause the weed diseases, which are potential microbe of herbicides. So, phytopathologists and microbiologists have already paid attention to these species.Species classification and identification in this genus has been based mostly on conidial morphology. But conidial morphology is not a stable criterion because of inconsistencies within isolates or with circumstantial condition in culture or cultural condition. So species delimitation is sometimes arbitrary. In the study, We examined Brn1 genes and gene products in strains of Exserohilum spp, in order to clear the relation and their limitation among Exserohilum species, and provide the rapid and accurate method for identification. The results shown:1. We examined Brn1 genes and gene products in strains of Exserohilum spp. Amino acid sequences of the Brn1 gene products were consistent within species. Nucleotide sequence lengths were equal within species and base pair substitutions were identified. Variation appeared were caused by insertions or deletions within intron regions. Coding region lengths for Brn1 genes were identical in all strains. Phylogenetic analysis of nucleotide sequences were conducted using maximum parsimony and neighbor-joining methods. Topologies of most parsimonious and neighbor-joining trees were similar and clearly distinguished species within Exserohilum. These results indicated that the Brn1 gene was suitable for species-level molecular systematics for the genus Exserohilum. Thus the Brn1 gene could be treated as a new classification characters for Exserohilum spp. 2. We examined Brn1 gene sequences data in Exserohilum and its morphological related genera, Bipolaris and Curvularia with Exserohilum spp, The result shown: Strains of different genera were clearly distinguished by sequences of the Brn1 gene. And C. heteropogonicola , a unresolved species from morphology, was ascribed to Curvularia. These data indicated that the Brn1 gene sequences was suitable for genus-level systematics within helminthosporioides fungi.Part two: Sooty blotch and flyspeck are the diseases common on pomaceous fruits. Fungi of Sooty blotch and flyspeck complex colonize the cuticle of apple fruit. Although these fungi do not affect the growth or development of the fruit, the appearance of the fruit is cosmetically damaged with dark smudges (sooty blotch) and groups of tiny spot (flyspeck). Apples with Sooty blotch and flyspeck are generally unacceptable to consumers. The fungi are difficult to isolate, grow extremely slowly, and are not easily maintained in culture collections, In cause of culture most strains can not product conidia. So they can not be classified and identified by traditional method. we examined pathogen diversity of sooty blotch and flyspeck from shaanxi by sequences analysis of the internal transcriber spacer (ITS) and larger subunit (LSU) regions. The result shown: All SBFS fungi from shaanxi were ascribed to 16 species, be long to two classes Dothidiomycetes and Chaetothyriomycetes. Among the species, 1 specie were classified as Leptodontium sp in the class Chaetothyriomycetes, 15 species were sorted into 10 genera in Dothideales (Dothidiomycetes): 2 species were classified Pseudocercosporella, 1 specie in Peltaster, 2 species in Zygophiala,2 species in Xenostigmina,2 species in Mycovelosiella,1 specie in Pseudocercospora, 1 specie in Dissoconium, 3 incertitude species. In all species from shaanxi just 2 species were identical to known species. These results indicated that sooty blotch and flyspeck fungi were different in areas.