Identification of RAPD markers for common root rot and spot blotch (Cochliobolus sativus) resistance in barley.
Two crosses consisting of resistant and susceptible parent genotypes (Virden × Ellice and Fr926-77 × Deuce, both 2-rowed × 6-rowed crosses) and more than 140 homozygous progeny lines were rated for their reactions in field nurseries to common root rot and in a controlled environment for spot blotch, diseases both caused by C. sativus. Putative RAPD makers were identified using bulked segregant analysis followed by individual progeny line analyses. Polymorphisms associated with disease reaction were detected between bulked segregant samples as differences in the band intensity of DNA fragments. The bulked segregant samples were screened against 186 RAPD primers (decamers) using the polymerase chain reaction. For the cross Fr926-77 × Deuce, one RAPD marker was obtained that did not segregate as expected but was associated with both diseases. For the cross Virden × Ellice, a single RAPD marker was obtained that did not have the expected segregation ratio but was associated with spot blotch reaction. One RAPD marker linked to 2-rowed and 6-rowed spike locus was obtained in each cross, and both the marker and row type were associated with common root rot and spot blotch reactions. For the cross Virden × Ellice, a linkage group consisting of three RAPD makers was associated with common root rot and spot blotch reaction. The genes associated with these markers condition significant levels of resistance to C. sativus and may be used to increase the speed and precision of resistance gene manipulation in barley germplasm.