Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2003
Publication Date: 1/2/2004
Citation: Castro, A.J., Chen, X., Corey, A., Filichkina, T., Hayes, P.M., Mundt, C., Richardson, K., Sandoval-Islas, S., Vivar, H. 2004. Pyramiding and validation of quantitative trait locus (qtl) alleles determining resistance to barley stripe rust: effects on adult plant resistance. Crop Science. 43:2234-2239. Interpretive Summary: Stripe rust is an important disease on barley. The best control approach of the disease is the use of genetic resistance. In the previous studies, we determined that quantitative resistance is controlled by a few genes, also called quantitative trait loci (QTL) and mapped the genes on barley chromosomes using molecular techniques. The objectives of this study was to combine three genes from two different barley varieties, validate the effect of genes, and determine influence of genetic background on the resistance gene effect. Through marker assisted selection and stripe rust testing, the effect of the three genes were validated in a new background different from their original barley varieties and further demonstrated that relatively few genes confer the most of the total effect of the quantitative resistance. The results show that molecular markers for resistance genes are reliable in marker-assisted selection for developing disease resistant varieties. The barley lines with combined resistance genes will be valuable for developing commercial barley varieties with superior stripe rust resistance.
Technical Abstract: The use of molecular and quantitative trait locus (ATL) analysis tools initially lent support to the idea that relatively few genetic factors were the principal determinants of complex traits, including quantitative resistance (QR) to plant diseases. However, there are concerns regarding bias in QTL estimation and reproducibility of QTL effects in different genetic backgrounds. We are interested in mapping determinants of QR, and pyramiding resistance alleles at QTL loci may lead to durable resistance as well as provide independent validation of QTL effects and estimation of QTL interactions. We used molecular marker information to validate effects resistance alleles at three QTL conferring QR to barley stripe rust (caused by Puccinia striiformis West. f. sp. hordei). Two of the QTL [one on chromosome 4(4H) and one on chromosome 7(5H) trace to one parent, whole another QTL on chromosome 5(1H) trace to a different parent. The pyramide s of these QR alleles provide independent estimates of QTL effects, influence of genetic background on QTL effects, QTL X QTL interaction, and QTL X environment interaction. Our results validate QTL effect estimates, showing that a small number of QTL explained 94% of the genetic variation in trait expression in a new genetic background. Original QTL estimates were quantitatively biased, but that did not preclude the achievement of selection responses. We also confirmed the additive effects of the QTL alleles, as well as the consistent effects of QTL alleles across environments.