Diagnostic DNA markers for cereal cyst nematode resistance in bread wheat

The development of cultivars resistant to cereal cyst nematode (CCN) is a p rimary objective in wheat breeding in the southern wheatbelt of Australia. Nine CCN resistance genes have been identified in wheat and its relatives, some of which confer resistance to the Australian pathotype of CCN (Ha13). Cultivars released in Australia with CCN resistance carry either the Cre1 o r CreF gene, with the Cre3 gene present in advanced breeding lines. The bio logical assay for CCN resistance screening in wheat is time-consuming, not reliable on a single-plant basis, and prone to inconsistencies, thus reduci ng the efficiency of selection amongst breeding lines. Using gene sequences initially isolated from the Cre3 locus, a DNA-based marker selection syste m was developed and applied to unambiguously identify wheat lines carrying resistance alleles at the Cre1 and/or Cre3 loci in breeding populations der ived from diverse genetic backgrounds. Homologues of sequences from the Cre 3 locus, located elsewhere in the wheat genome, can also be used to select wheat lines with a newly identified CCN resistance gene (Cre6) introgressed from Aegilops ventricosa. Application of these markers has become an integ ral part of the southern Australian breeding programs.