Genetic Diversity Of Fusarium Graminearum In China And Its Comparison With The Isolates From Of Nepal, Europe And USA

Fusarium graminearum isolates collected from China, Nepal, Europe and USA were selected for this study. It was the first time to analysis the isolates at molecular level with AFLP, SCAR, SSCP and species-specific PCR technology to reveal genetic diversity of the isolates and compare the difference of the isolates from several continents.Species-specific PCR revealed that there were six types of PCR fragments based on their size among the isolates analysed (type 1 to 6) from different continent. There were only two types (types 1 and 5) present in the Chinese isolates. The type 5 was a main F. graminearum population in China, about 79% of the isolates were typeS, especially in the warm area. It was divided into 'warm-type' isolates. But the type 1 only was a small F. graminearum population, about 21%, and existed in the cool area in China. It was divided into 'cool-type' isolates. Most isolates from Northwest Europe and North America where it is cool were type 1, whereas a small proportion was type type 6. The results indicate that there were various types of F. graminearum isolates related to geographical environment and ecosystems in F. graminearum.SSCP analyses not only confirm six types identified by species-specific, but also further divided the type 1 into three subtypes (1A, IB and 1C). All the isolates from China and Europe, and most isolates from USA belonged to type 1A, while some American isolates were type IB and Nepalese isolates were type 1C. There were no subtypes within each of other five types detected with SSCP. SCAR analyses of the twenty isolates indicated that the six types contain almost identical sequences of about 380bp and the differences among the six types were mainly due to variation within the regions from nucleotides 79 to 168 and 440 to 526. There were only several single nu-cleotide mutations in the sequences outside of these two regions.AFLP revealed much more molecular diversity among the isolates and there were high polymorphisms even among the isolates from the same geographic locations. The results suggest the presence of a high degree of genetic diversity in the F. graminearum population, implying that sexual recombination ofF. graminearum exist in the fields.AFLP revealed for the first time the correlation between the two F graminearum classes and the geographic origin. Dendrogram analyses of AFLP patterns with UPGMAinprogram showed two main classes in F. gramineantm populations. Class I represented the isolates of Europe, USA and the Chinese type 1, which consisted of types 1 and 6 ; Class II represented the Asian isolates, it was consisted of Chinese type 5, Nepalese types 2 to type 5, and the Japanese (type 5) isolates. Some AFLP markers indicated a clear correlation between the isolates and the origin in the classes, while other AFLP bands suggested possible association to pathogenesis of the isolates.Chinese isolates were also divided into two classes by dendrogram analyses. But there was only typel in Chinese class I, and only type 5 in Chinese class II. Each class further consists of many subclasses.Pathogenicity test was carried out with 76 isolates from different continents by scoring penetration ability and scaling spreading rate based on the necrotic symptoms of the coleoptiles and leaves. The results showed that the isolates varied significantly in their pathogenicity towards wheat. Correlation analysis showed a significantly direct correlation co-efficiency (r = 0.95, R2 = 0.9025), indicating that both penetration ability and spreading rate can be used for evaluation of the pathogenicity of F. graminearum isolates.The high degree of variation of pathogenicity among the isolates is in accordance with the diverse genetic diversity observed in AFLP analysis. Different types or origination of the isolates may be associated with ecological conditions and local climates. The warm-type isolates are the predominant fungal pathogens causing epidemics in Yangtze river valleys where the climates is warm. In cooling regions for wheat growing such as...