Genetic Characterization and Linkage Mapping of Barley Net Blotch Resistance Genes

Net blotch is one of the most devastating diseases of barley (Hordeum vulgare L.) and occurs in two distinct forms, net-type net blotch (NTNB) and spot-type net blotch (STNB), caused by the fungal pathogens Pyrenophora teres f. sp. teres Smedeg. and P. teres f. sp. maculata Smedeg., respectively. Several sources of resistance have been previously reported, however, few barley cultivars with high levels of resistance have been developed from these sources. Efficient utilization of available resistance sources is dependent upon successful characterization of genes governing resistance in each resistant parent. Five net blotch resistant parents and one susceptible parent were crossed to identify novel resistance genes, postulate gene number and mode of inheritance, and conduct linkage mapping of novel genes for net blotch resistance. Results indicate that the highly resistant spring barley lines CIho 2291 and CIho 5098, and the winter barley cultivar Nomini each have single dominant genes for NTNB resistance. Resistance to NTNB in CIho 5098 is controlled by the same dominant gene conferring resistance in Nomini. Resistance to NTNB in CIho 2291 is controlled by one dominant gene which putatively is the same gene conferring resistance in ND B112, but differs from the resistance genes carried by the other parents in this study. An F2 population of 238 individuals derived from a cross between Nomini and the susceptible parent "Hector", and an F2 population of 193 individuals derived from a cross between CIho 2291 and Hector were used to map the genes governing NTNB resistance in Nomini and CIho 2291. The dominant gene governing resistance in Nomini, temporarily designated Rpt-Nomini, was mapped to a 9.2 cM region near the centromere of barley chromosome 6H between the flanking microsatellite markers Bmag0344a (r2=0.70) and Bmag0103a (r2=0.90), which were 6.8 cM and 2.4 cM away from Rpt-Nomini, respectively. The dominant gene governing resistance in CIho 2291, temporarily designated Rpt-CIho2291, was mapped to the distal region of barley chromosome 6H between the flanking microsatellite markers Bmag0173 (r2=0.65) and Bmag0500 (r2=0.26), which were 9.9 cM and 24.4 cM from Rpt-CIho2291, respectively. Previous studies have reported genes governing net blotch resistance in this region; however, allelism tests have not been conducted to determine the relationship between these genes. Identification of the chromosomal location of Rpt-Nomini and Rpt-CIho2291 will facilitate future efforts in pyramiding multiple independent genes for net blotch resistance.