Resistance to common bunt in the USDA Aegilops tauschii collection

James E. Keach

Common bunt or 'stinking smut', caused by Tilletia caries or T. laevis, is re-emerging as a major pathogen to common wheat, Triticum aestivum when grown in low-input or organic systems. In addition to reducing yields by up to 30%, it imparts a smell like 'rotting fish' that makes contaminated grain unsuitable for export or consumption. The objective of this study was to screen Aegilops tauschii for resistance to 10 races of common bunt, representing virulence against the most common resistance genes, for use in future wheat breeding. Aeg. tauschii is the D-genome donor of wheat and a source of resistance to various other pathogens. Seeds of 117 accessions of Aeg. tauschii from the USDA-ARS National Plant Germplasm System National Small Grains Collection and four susceptible T. aestivum cultivars, as well as one putative resistant cultivar, were inoculated with a mixture of spores from the 10 races of common bunt and maintained under appropriate conditions for disease development. When the plants were between Zadoks stages 73-87, developing seeds were removed and examined for the presence of bunt spores. Accessions with any infected plants were marked as susceptible and excluded from future experiments. The putative resistant lines from each experiment, as well as the lines which did not germinate, were re-tested in the subsequent experiments. A cold stratification performed on all of the seeds for the third and fourth experiments improved germination, permitting screening of larger populations and more accessions. Genotyping of all of the accessions using the Target Region Amplified Polymorphism (TRAP) marker technique, as well as with several standard primers, is also being conducted to elucidate relationships among the accessions and identify other traits. Eighteen resistant accessions were identified, with eight having high probability of not being escapes from infection. All resistant accessions were from Turkey or Iran. A discussion of methods to integrate this resistance, as well as what the resistance might mean, and why infection by this pathogen has not been observed in vivo is included. This is the first known screening of multiple accessions of Aeg. tauschii for resistance to known races of common bunt.

Resistance to common bunt in the USDA Aegilops tauschii collection

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