IDENTIFICATION OF RAPD MARKERS FOR COMMON ROOT-ROT AND SPOT BLOTCH (COCHLIOBOLUS-SATIVUS) RESISTANCE IN BARLEY

The identification of RAPD markers associated with genes for resistanc e to Cochliobolus sativus in barley would increase the efficiency of g ene manipulation by reducing the number of lines that must be evaluate d from a resistant by susceptible cross and by allowing selection duri ng the off season. Two barley crosses consisting of resistant and susc eptible parent genotypes ('Virden' X 'Ellice' and Fr926-77 X 'Deuce', both 2 row X 6 row 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. Putative RAPD markers were identified using bulked segregant analysis followed by individua l progeny line analyses. Polymorphisms associated with disease reactio n were detected between bulked segregant samples as differences in the band intensity of DNA fragments. The bulked segregant samples were sc reened against 186 RAPD primers (decamers) using the polymerase chain reaction. For the cross Fr926-77 X 'Deuce', one RAPD marker was obtain ed that did not segregate as expected but was associated with both dis eases. For the cross 'Virden' X 'Ellice', a single RAPD marker was obt ained that did not have the expected segregation ratio but was associa ted 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 reactio ns. For the cross 'Virden' X 'Ellice', a linkage group consisting of t hree RAPD markers was associated with common root rot and spot blotch reaction. The genes associated with these markers condition significan t levels of resistance to C. sativus and may be used to increase the s peed and precision of resistance gene manipulation in barley germplasm .