RFLP MAPPING OF A NEW CEREAL CYST-NEMATODE RESISTANCE LOCUS IN BARLEY

Cereal cyst nematode (CCN) (Heterodera avenae Well.) is an economicall y damaging pest of barley in many of the worlds cereal growing areas. The development of CCN-resistant cultivars may be accelerated with the application of molecular markers. Three resistance genes against the pest have been mapped previously to chromosome 2 (Hal, Ha2 and Ha3). I n this study, a third gene present in the Australian barley variety 'G alleon' derived from the landrace 'CI3576' was located. Segregation an alysis of CCN resistance data derived from doubled haploid populations of the cross 'Haruna Nijo' x 'Galleon' identified a single major locu s controlling CCN resistance in the variety 'Galleon'. This locus mapp ed to the long arm of chromosome 5H estimated to be 6.2cM. from the kn own function restriction fragment length polymorphism marker XYL (xyla nase). While five genes for CCN resistance, including Ha2, have been m apped to group 2 chromosomes in the Triticeae, no gene other than Ha4 has been identified on group 5 chromosomes.