ARS | Publication request: DNA markers linked to the R2 rust resistance gene in sunflower (Helianthus annuus L.) facilitate anticipatory breeding for this disease variant

Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 2010
Publication Date: December 1, 2011
Citation: Lawson, W., Jan, C., Shatte, T., Smith, L., Kong, G., Kochman, J. 2011. DNA markers linked to the R2 rust resistance gene in sunflower (Helianthus annuus L.) facilitate anticipatory breeding for this disease variant. Molecular Breeding. 28:569-576.

Interpretive Summary: The most effective strategy for managing disease outbreaks has been through the utilisation of host resistance. The fungal pathogen, Puccinia helianthi Schwein., is the causal organism of sunflower rust. Before 1983, Aus1 was the only pathotype of P. helianthi identified on wild and cultivated sunflower in Australia. Since then, the rust situation has become more complex with the frequent appearance of new virulent pathotypes. Currently, 77 pathotypes of P. helianthi have been identified. Through the years, MC29 remains resistant to all known Australian pathotypes and therefore, represents an important source of resistance. Because it confers resistance to all known pathotypes, genotypes carrying the MC29 and other resistances cannot be identified using Australian pathotypes. Thus, molecular markers linked to this resistance gene would enable breeders to follow the introgression of this gene in new germplasm, and markers linked to a number of resistance genes can facilitate the simultaneous selection of multiple resistance genes and/or multiple diseases. This study describes the identification and development of closely linked SSR markers to the R2 sunflower rust resistance gene. This gene will likely be a key component in the development of sunflower varieties in Australia with effective resistance to the current pathotypes of sunflower rust, and in delaying the possibility of future pathogen evolution and resistance shifts. Three SSR markers, ORS795, ORS882, and ORS938 were linked in coupling to the gene, while the ORS333 was linked in repulsion. The availability of the SSR markers described in this study represents an important benefit to sunflower breeding programs in Australia, as it now becomes possible to screen for this gene in the absence of the pathogen.

Technical Abstract: Pre-emptive breeding for host disease resistance is an effective strategy for combating and managing devastating incursions of plant pathogens. Comprehensive, long term studies have revealed that virulence to the R2 sunflower (Helianthus annuus L.) rust resistance gene in the line, MC29, does not exist in the Australian rust (Puccinia helianthi) population. We report in this study the identification of molecular markers linked to this gene. The three SSR markers, ORS795, ORS882, and ORS938 were inked in coupling to the gene, while the SSR marker ORS333 was linked in repulsion. Reliable selection for homozygous resistant individuals was efficient when the three markers, ORS795, ORS882, and ORS333, were used in combination. Phenotyping for this resistance gene is not possible in Australia without introducing a quarantinable race of the pathogen. Therefore, the availability of reliable and heritable DNA-based markers will enable the deployment of this gene efficiently, permitting a more effective strategy for generating sustainable commercial cultivars containing this rust resistance gene.