Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2006
Publication Date: 10/11/2006
Citation: Rossi, C., Cuesta-Marcos, A., Vales, I., Gomez-Pando, L., Orjeda, G., Wise, R.P., Sato, K., Hori, K., Capettini, F., Vivar, H., Chen, X., Hayes, P. 2006. Mapping multiple disease resistance genes using a barley mapping population evaluated in Peru, Mexico, and the USA. Molecular Breeding. 18(4):355-366. Interpretive Summary: One of the principal challenges faced by plant breeders is achieving durable disease resistance. We have mapped genes conferring quantitative and qualitative resistance to barley stripe rust (BSR) in multiple germplasm combinations. These genes were introgressed singly, and in combination, into susceptible backgrounds and confirmed that they confer acceptable levels of resistance. In this study, a well-characterized mapping population was used to test the effectiveness of BSR resistance quantitative trait locus (QTL) alleles at Huancayo, Peru. These QTL were then mapped based on disease severity data from Toluca Valley of Mexico and Washington State, USA. We hypothesized that if we detected the same QTL in Peru that we had mapped using Toluca Valley and Washington State, this would mean that (1) there was no new race, or (2) there is a new race but the same QTL resistance alleles are effective. This research was useful in confirming the value of quantitative stripe rust resistance genes, via marker assisted selection MAS, into North American germplasm. These resistance genes were discovered through collaborative efforts with the ICARDA/CIMMYT program and National Program scientists in the Andean region. It is thus fitting that these genes are returned to the Andean National Programs, with value added via marker information that will allow for their efficient introgression. The results of this research will lead to high levels of durable disease resistance, which will benefit growers and producers.
Technical Abstract: We used a well-characterized barley mapping population (BCD 47 × Baronesse) to determine if barley stripe rust (BSR) resistance quantitative trait loci (QTL) mapped in Mexico and the USA were effective against a reported new race in Peru. Essentially the same resistance QTL were detected using data from each of the three environments, indicating that these resistance alleles are effective against the spectrum of naturally occurring races at these sites. In addition to the mapping population, we evaluated a germplasm array consisting of lines with different numbers of mapped BSR resistance alleles. A higher BSR disease severity on CI10587, which has a single qualitative resistance gene, in Peru versus Mexico suggests there are differences in pathogen virulence between the two locations. Confirmation of a new race in Peru will require characterization using a standard set of differentials, an experiment that is underway. The highest levels of resistance in Peru were observed when the qualitative resistance gene was pyramided with quantitative resistance alleles. We also used the mapping population to locate QTL conferring resistance to barley leaf rust and barley powdery mildew. For mildew, we identified resistance QTL under field conditions in Peru that are distinct from the Mla (powdery mildew) resistance that we mapped using specific isolates under controlled conditions. These results demonstrate the long-term utility of a reference mapping population and a well-characterized germplasm array for locating and validating genes conferring quantitative and qualitative resistance to multiple pathogens.