ARS | Publication request: Characterization of novel blast resistant genes for US rice breeding

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 5, 2010
Publication Date: August 12, 2010
Citation: Yan, W., Scheffler, B.E., Correll, J.C., Fjellstrom, R.G., Feng, C.D., Jackson, A.K., McClung, A.M. 2010. Characterization of novel blast resistant genes for US rice breeding [abstract]. Proceedings of 5th International Rice Blast Conference, August 11-14, 2010, Little Rock, Arkansas. p. 36.

Technical Abstract: Blast resistance genes, such as Pi-ta, conveying resistance up to 8 common US races of the blast pathogen (Magnaporthe oryzae), have been used for 20 years in the US rice (Oryza sativa) industry. However, Pi-ta is susceptible to two known US races of blast. Race IE-1K has caused blast outbreaks in Arkansas in the past and IB33 which was identified under greenhouse conditions and found to overcome all known resistance genes in the US. Thus, novel resistant genes are needed for rice production security. Screening the USDA rice world collection has identified resistant germplasm including lines 4484 (PI 615022) and Shufeng (Shu) 121 (PI 615015) introduced from China. Rondo and Shu 121-1655 are selections that were derived using mutation breeding from 4484 and Shufeng, respectively, that have improved agronomic traits, and were found to be resistant to all 10 races of blast commonly found in the US, including IE-1K and IB33. Preliminary analysis with molecular markers linked to Pi-ta, Pi-d, Pi-i, Pi-k, and Pi-z, indicated that none of these resistant genes were present in these two cultivars. Further testing using the Pibdom marker demonstrated that both Rondo and Shu 121-1655 possess Pi-b, which does not convey resistance to races IB33 and IB54. We developed a mapping population derived from Francis (female) and Shu 121-1655 (male) and evaluated 300 F2:3 families for resistance to IB33 and IB54 by scoring homozygous resistance, heterozygous resistance or homozygous susceptibility for each family. Disease segregation data fit a 1:2:1 pattern for both races, indicating a single dominant gene responsible for resistance to both IB33 and IB54. Meanwhile, we identified 108 genome-wide polymorphic SSR markers between Francis and Shu 121-1655. Analysis of the F2 population with these polymorphic markers and with response to IB33 indicated that resistance to this race is not linked to any of the previously mapped US blast resistance genes. Resistance to IB54 mapped between the markers RM7364 at 9.56 Mb and RM3912 at 10.83 Mb on rice chromosome 9. This region has been shown to harbor three resistance genes Pi 5-1, Pi 5-2 and Pi 5-3. Further effort is being applied to fine-map the resistance gene for IB54 and to map the resistance gene for IB-33. While the blast resistant germplasm, Rondo and Shu 121-1655, have been used in several US breeding programs, the development of markers linked to these novel resistance genes will assist breeders in selecting cultivars with broad spectrum resistance to blast disease.