Key message: Oat crown rust is one of the most damaging diseases of oat. We identified a new source of resistance and developed KASP and TaqMan markers for selection in breeding programs. Abstract: A new highly effective resistance to oat crown rust (Puccinia coronata f. sp. avenae) was identified in the diploid oat Avena strigosa PI 258731 and introgressed into hexaploid cultivated oat. Young plants with this resistance show moderate susceptibility, whereas older plant tissues and adult plants are resistant with no virulent isolates encountered in over 8 years of testing. Resistance was incorporated into hexaploid oat by embryo rescue, colchicine chromosome doubling followed by backcrosses with a hexaploid parent, and selection for stable transmission of resistance. To mitigate flag leaf and panicle chlorosis/necrosis associated with the resistance, crosses were made with derived resistant lines to breeding lines of divergent parentage followed by selection. Subsequently, two F2 sister lines, termed MNBT1020-1 and MNBT1021-1, were identified in which the chlorosis/necrosis was reduced. These two lines performed well in replicated multi-location state trials in 2015 and 2016 out-yielding all cultivar entries. Segregating F2:3 plants resulting from crosses of MNBT lines to susceptible parents were genotyped with the oat 6K SNP array, and SNP loci with close linkage to the resistance were identified. KASP assays generated from linked SNPs showed accurate discrimination of the resistance in derivatives of the resistant MNBT lines crossed to susceptible breeding lines. A TaqMan marker was developed and correctly identified homozygous resistance in over 95% of 379 F4 plants when rust was scored in F4:5 plants in the field. Thus, a novel highly effective resistance and associated molecular markers are available for use in breeding, genetic analysis, and functional studies.
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Acknowledgements Funding for the project was provided by the US Department of Agriculture—Agricultural Research Service and the Minnesota State Agricultural Experiment Station. At the USDA-ARS Cereal Disease Laboratory, we thank Roger Caspers and the late Gerald Ochocki for valued technical assistance in conducting greenhouse and field oat crown rust tests. We thank Dr. Farhad Ghavami and Eurofins BioDiagnostics Inc. in River Falls, Wisconsin, for KASP assay design and execution. We also thank Shalane Porter, Dinesha Walek, and staff at UMGC for assistance with TaqMan assay design and execution, as well as Dr. Kevin Smith and Karen Beaubien for assistance and input with TaqMan marker-assisted selection. M.E.M was partially supported by a USDA-NIFA Postdoctoral Fellowship Award (2017-67012-26117). Mention of trade names or commercial products in this publication is solely for purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture. USDA is an equal opportunity provider and employer.