Submitted to: Journal of Crop Improvement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 30, 2011
Publication Date: April 22, 2011
Citation: Ray, J.D., Smith, J.R., Morel, W., Bogado, N., Walker, D.R. 2011. Genetic resistance to soybean rust in PI 567099A is at or near the Rpp3 locus. Journal of Crop Improvement. 25(3):219-231. Interpretive Summary: Soybean rust is a fungal disease that has the potential to cause significant yield loss of soybean grown in the United States. A soybean line (PI 567099A) was previously shown to have resistance to soybean rust. The objective of this research was to determine the genetic nature of the resistance and determine the location of the gene(s) controlling the resistance in the soybean DNA. The resistance in PI 567099A was found to be primarily controlled by a single gene located at or near a previously identified resistance gene. This information will facilitate the incorporation of the resistance found in PI 567099A into soybean lines more suited to production in the midsouthern USA.
Technical Abstract: Previous research identified soybean accession PI 567099A as resistant to soybean rust (SBR). The objective of this research was to map the resistance genes(s) of PI 567099A. A population segregating for SBR resistance was evaluated in the 2008 and 2009 seasons in Paraguay. In both seasons F2:3 families were grown in a field naturally infested with SBR. Each F2:3 family was rated as resistant, segregating, or susceptible on the basis of the lesion types present and this classification was used to infer the F2-phenotype used for mapping. For the 91 F2:3 families rated in 2008, segregation did not fit a 1:2:1 (resistant:segregating:susceptible) ratio expected for a single gene (P<0.05). However, for the 68 families rated in 2009, segregation fit a 1:2:1 ratio very well ('2 =0.7059, P = 0.7026). Molecular markers flanking five major SBR resistance genes were applied to the F2 population and despite the discrepancy in segregation ratio between years, markers flanking Rpp3 where significantly associated with the observed resistance (P<0.0001) in both years. Analysis of allele frequencies in homozygous F2:3 families in 2009 confirmed an association with Rpp3. However, the phenotype of 24-F1 plants evaluated in the 2008 season indicated that the resistance was recessive. This is the first report of recessive resistance at or near the Rpp3 locus. Knowledge of the location and nature of resistance in PI 567099A will allow its more efficient utilization as a SBR resistance source in breeding programs.