Molecular-genetic characterisation of a new nematode resistance gene in wheat

Bread wheat lines introgressed with Aegilops ventricosa chromosomes were ev aluated for their resistance to the Australian cereal cyst nematode (CCN, H eterodera avenae) pathotype Ha13. Higher levels of resistance relative to t he phenotype of the Cre1 CCN resistance gene in wheat were found in the don or Ae. ventricosa parental lines and chromosome-5N(v) substitution or addit ion lines. The newly identified resistance to pathotype Ha13 on chromosome 5N(v), designated, Cre6, was shown to be independent of the Ae. ventricosa- derived Cre2 gene, effective against several European pathotypes. Another A e. ventricosa derived gene, Cre5, showed partial resistance to pathotype Ha 13. Inhibition of Ha13 female nematode reproduction was ranked in the order Cre6 > Cre1 > CreF greater than or equal to Cre5. Cre6 was inherited as a single dominant locus. Gene sequences encoding nucleotide-binding sites and leucine-rich repeats (NBS-LRR) from the Cre3 CCN-pathotype Ha13 resistance locus were used as probes to isolate related sequences from one of the don or Ae. ventricosa parents. Related sequences from Ae, ventricosa (71-73% si milarity at the amino-acid level to the Cre3-derived sequences) of chromoso me 5N(v) origin were identified and served as diagnostic molecular markers for the presence of 5N(v). CCN-susceptible plants, found as Variants in som e of the purported chromosome 5N(v) lines, were also found to be missing th e diagnostic 5N(v) RFLP markers assayed by the NBS-LRR probe. An alloplasmi c chromosome-5N(v) addition line with Ae. ventricosa cytoplasm in the wheat cultivar, Moisson, background was particularly variable, with 43% CCN-susc eptible plants and a corresponding loss of the diagnostic chromosome-5 mole cular markers.