The cereal cyst nematode (CCN, Heterodera avenae) is an important disease in many wheat-growing regions of the world. For several decades up to and including the 1990s, it caused severe losses in southeastern Australia, where on average an 8% reduction in grain yield has been reported; although yield losses in individual fields can be more than 50%. In the late eighty’s the wheat industry in Australia initiated a research program aimed at identifying new sources of CCN resistance, understanding the genetic basis of resistance, and developing efficient means of screening for CCN resistance in wheat breeding programs and carry out targeted breeding to incorporate diverse resistance genes into key cultivars and germplasm. Subsequently, we identified new sources of resistance in Aegilops tauschii (genome designation DtDt) designated Cre3, in Ae. ventricosa (DvNv) introgression lines designated Cre6 and potential novel sources of resistance in synthetic hexaploid wheat against the Australian CCN pathotypes (Ha13). Genes encoding nucleotide binding site-leucine rich repeat (NBS-LRR) proteins that cosegregate with the Cre3 locus cross hybridised to homologues whose restriction fragment length polymorphism patterns were able to distinguish near-isogenic Cre1 nematoderesistant wheat lines as well as Cre6 Ae. ventricosa bread wheat introgression lines. The NBS-LRR gene family derived from the Cre3 founder locus were used to develop diagnostic markers for diverse CCN resistance genes - Cre1, Cre3, Cre5 and Cre6 - to facilitate the introgression of CCN resistance from diverse sources into adapted local cultivars. Consequently, marker-assisted selection for CCN resistance is performed routinely in many wheat-breeding programs worldwide notably in Australia, CIMMYT and ICARDA. The successful control of the disease for over the past two decades with genetic resistance has resulted in a sharp decline in the incidence of CCN infection in wheat fields. In other regions of the world where CCN remains a major production constraint, identifying new sources of resistance, pyramiding different genes and developing adapted resistant cultivars and replacing the susceptible cultivars is the most sustainable strategy to mitigate potential losses.

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CIMMYT Staff Publications Collection