Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2008
Publication Date: 4/6/2009
Citation: Carson, M.L. 2009. Broad spectrum resistance to crown rust, Puccinia coronata f. sp. avenae, in U.S. accessions of the tetraploid slender oat, Avena barbata. Plant Disease. 93:363-366.
Interpretive Summary: Oat crown rust is the most destructive disease of oat worldwide. Resistant oat varieties typically have an effective lifespan of only five years before new races of the crown rust pathogen render them susceptible. As a result, there is a lack of effective resistance genes in cultivated oats. Wild relatives of oat are a potential source of new effective genes for crown rust resistance. The wild tetraploid species, Avena barbata, has been unexploited as a source of crown rust resistance. The USDA germplasm collection of A. barbata was screened for resistance to a diverse population of the crown rust pathogen. Over 40 accessions from throughout its native range were found to be resistant to all races of crown rust in the population. Avena barbata appears to be a rich source of new effective, broad-spectrum resistance to oat crown rust. Breeders and geneticists can use this information to begin the process of introgressing this resistance into cultivated oat varieties.
Technical Abstract: The use of race-specific seedling genes for resistance has been the primary means of controlling crown rust of oat (Puccinia coronata). As resistance genes from hexaploid cultivated oat, Avena sativa and later, the wild hexaploid animated oat, A. sterilis were deployed in oat cultivars, corresponding virulence in the crown rust population increased rapidly, such that the effective lifespan of a resistant cultivar in the U.S. is now five years or less. Introgression of resistance genes from diploid and tetraploid Avena species into hexaploid oat has been difficult due to differences in ploidy levels and the lack of homology of chromosomes between the two species. The wild tetraploid slender oat, A. barbata, has been a source of powdery mildew and stem rust resistance in cultivated oat, but has largely been unexploited for crown rust resistance. A total of 359 accessions of A. barbata from the National Small Grains Collection were evaluated in seedling greenhouse tests. Thirty-nine percent of accessions were at least moderately resistant when inoculated with a crown rust race with low virulence (DBBC). When tested further with a highly diverse bulk inoculum from the 2006 and 2007 St. Paul buckthorn nursery, 48 accessions (~13%) were resistant. Many of these accessions were heterogeneous in reaction, but several accessions were uniformly highly resistant in all tests. Resistant accessions were found from throughout much of the natural range of A. barbata. Initial crosses of some of the better accessions have been made to cultivated oat.