Variable resistance to spot form net blotch disease at a barley chromosome 7 H locus

Five genetically diverse barley lines were crossed to a modern susceptible cultivar to investigate resistance genes and their allelic variation in response to spot form net blotch. Doubled haploid populations were phenotyped at three growth stages, revealing quantitative trait loci (QTLs) on six of the seven barley chromosomes. A major dominant susceptibility locus on the long arm of chromosome 7 H was present in all populations, with the phenotypic variance explained (PVE) at the heading stage, for example, ranging from 22 to 48%, while being absent in one population except at heading. Genetic mapping separated the locus into three distinct genetic windows, suggesting the presence of different resistance genes, or conversely structural rearrangements or other factors affecting QTL positions. Eleven minor QTLs were evident at different developmental stages, with PVE values ranging from 6 to 14%. Several of these increased in effect size towards heading, coincident with reduced significance of the major 7 H locus, suggestive of epistasis or phased gene expression. The interplay between the minor loci and the 7 H locus further demonstrates the genetic complexity of Pyrenophora teres f. maculata –barley interactions and provides novel genes which may be combined for effective resistance.