Validation of molecular markers associated with net blotch resistance and their utilization in barley breeding
With the advancement of molecular marker technology and computer software, mapping quantitative trait loci (QTL) for complex traits in agricultural crops is frequent; however, exploitation of these QTL in practical breeding programs is limited. Here we report the validation of molecular markers linked to net blotch resistance QTL and their utilization in a barley (Hordeum vulgare L.) breeding program. Barley net blotch, caused by Pyrenophora teres Drechs. [anamorph: Drechslera teres (Sacc.) Shoemaker], is a serious foliar disease in Canada and other parts of the world. Simple sequence repeat (SSR) markers linked to net-form net blotch (NFNB) resistance QTL (QRpt6) and spot-form net blotch (SFNB) resistance QTL (QRpts4) were validated in two barley populations unrelated to the original mapping population. Marker-assisted selection (MAS) was performed with SSR markers to select resistant and susceptible lines in two other populations. The lines homozygous for the resistant-parent alleles at both marker loci had significantly lower infection than lines homozygous for the susceptible-parent alleles at both markers, indicating that MAS for net blotch resistance is practical. Since the major QTL, QRpt6, may provide adequate NFNB field resistance in western Canada, the plan for the Crop Development Centre (CDC) barley breeding program is to routinely utilize MAS for QRpt6 followed by normal field screening in disease nurseries to select the most resistant lines having additional resistance provided by less critical genes associated with other identified QTL. The CDC program has implemented routine MAS for QRpt6 and recommends this approach to other barley breeding programs.