|Kistler, H - Corby|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2002
Publication Date: N/A
Citation: N/A Interpretive Summary: Fusarium head blight is perhaps the most important disease of wheat and barley in the U.S. This disease also is important in China, where varieties of wheat with resistance to the disease have been identified. To determine whether these resistance varieties in China would also be useful in the U.S., differences in the disease causing pathogen between the two countries also must be considered. However, previous to this work, no effort had been made to examine the diversity of the Fusarium head blight pathogen in China or to compare the pathogen populations from China with those in the United States. The objectives of this project were to determine the levels of genetic diversity in the pathogen responsible for causing Fusarium head blight on wheat and to compare populations in China and the U.S. Our results indicate that the pathogen population in China is genetically distinct and isolated from the pathogen population found in the United States. While the population was genetically diverse in China, there is evidence to suggest that the pathogen does not freely undergo sexual reproduction, limiting its ability to develop new strains. This research will benefit scientists working to develop wheat varieties resistant to the Fusarium head blight pathogen by alerting them to the fact that the pathogen strains in China and in the US are genetically different. Thus special care must be taken to assure that wheat varieties are resistant to both the U.S. and Chinese strains of the pathogen. Ultimately, this research will benefit producers of wheat and barley worldwide by assuring that resistant varieties are resistant to all strains of the pathogen.
Technical Abstract: Wheat heads showing symptoms of Fusarium head blight were collected from four commercial fields in Zhejiang Province, China, an area where epidemics occur regularly. A total of 225 isolates were subjected to population-level analyses using RFLPs as markers. Diagnostic RFLP probes established that all isolates belonged to Fusarium graminearum lineage 6. Nine polymorphic, single-copy probes were hybridized to all isolates, which resulted in 65 multilocus RFLP haplotypes (MRH). Probing with the telomeric clone pNla17, which reveals differences among isolates in the hypervariable subtelomeric region, differentiated the 65 MRH into 144 clonal genotypes. Mean gene diversity for the four field populations was similar, ranging from H = 0.306 - 0.364 over the nine RFLP loci for clone-corrected data. High levels of gene flow were observed among all field populations, indicating that they were part of the same geographic population. Pairwise linkage disequilibrium measures did not unequivocally support a random mating population, as 1/3 of loci pairs were significantly different from the null hypothesis of no-association between alleles. We conclude therefore that sexual recombination may not be frequent and that high levels of genotypic diversity may be maintained by relatively low selection pressure acting on a highly diverse population.