Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2012
Publication Date: 3/15/2012
Citation: Berlin, A., Samils, B., Djurle, A., Wirsen, H., Szabo, L.J., Yuen, J. 2012. Disease development and genotypic diversity of Puccinia graminis f. sp. avenae in Swedish oat fields. Plant Pathology. Available: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-3059. Interpretive Summary: In Sweden, oat is the third most common cereal crop and the number of hectares planted has declined in recent years due to reduced profitability caused by an increase in oat stem rust. The increase in stem rust may be a result of an expanded sexual population of this pathogen due to an increase in the prevalence of the common barberry, the sexual host of this fungal pathogen. I order to access the role of a sexual population of this pathogen, genetic diversity was analyzed in samples collected from oat fields in 2008 and 2009. Using DNA markers, genotypic diversity of the oat stem rust fungus was shown to be high, consistant with a sexual reproduction as the primary source of inoculum. Comparison of genetic diversity between fields indicated that the oat growing region in Sweden consits of a single population and that rust fungal spores are likely wind blown across this region. This study provides the first genetic study of population structure of the oat stem rust pathogen in Sweden and highlights the importance of barberry removal in management of this disease.
Technical Abstract: The disease development and population structure of Puccinia graminis f. sp. avenae, which causes stem rust on oat, were studied to investigate if sexual reproduction plays an important role in the epidemiology of the disease. The genetic population structure of P. graminis f. sp. avenae in Sweden was investigated by sampling 10 oat fields in August 2008 and 7 fields during the same period in 2009. Nine single-pustule isolates were first used to test Simple Sequence Repeat (SSR) markers developed for P. graminis f. sp. tritici. Eleven of the 68 tested SSR markers were useful for genotyping P. graminis f. sp. avenae. For the main study, DNA from single uredinia was extracted and the SSR markers were used to genotype 472 samples. Both allelic and genotypic diversity were high in all fields, indicating that P. graminis f. sp. avenae undergoes regular sexual reproduction in Sweden. No significant relationship between genetic and geographic distances was found. Disease development was studied on two farms during 2008 and 2009. The apparent infection rates ranged between 0.17 and 0.55, which indicates the potential of rapid disease development within fields. The incidence of stem rust in Swedish oat fields has increased recently. One possible explanation is a resurgence of its alternate host, barberry (Berberis spp.), after the repeal of the barberry eradication law in 1994. Barberry is present in several grain producing areas in Sweden, which supports the conclusion that P. graminis f. sp. avenae undergoes regular sexual reproduction there.