Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2011
Publication Date: 4/13/2011
Citation: Kendrick, M.D., Harris, D.K., Ha, B., Hyten, D.L., Cregan, P.B., Frederick, R.D., Boema, H.R., Pedley, K.F. 2011. Identification of a second Asian soybean rust resistance gene in Hyuuga soybean. Phytopathology. 101:535-543. Interpretive Summary: Asian soybean rust (ASR) is an economically significant disease caused by a fungus that poses a major risk to U.S. soybean production. Only a few genes that confer resistance to ASR are known, and each resistance gene only provides protection against some isolates of the pathogen. We are currently working towards identifying these genes so that new soybean lines that recognize and defend against more isolates of the pathogen can be produced. Two of the known resistance genes, found in the soybean cultivars “Ankur” and “Hyuuga”, are located in the same physical region of the soybean genome. Due to their proximity and since both cultivars have previously been shown to be resistant to the same isolates of ASR, it was unclear whether the resistance genes in Ankur and Hyuuga were the same. Using additional isolates of ASR collected from geographically diverse locations, we were able to demonstrate that the resistance in the Ankur and Hyuuga soybean cultivars is similar, but that the Hyuuga cultivar was resistant to a few other isolates of ASR. Additional experiments using Hyuuga-derived plants demonstrated that Hyuuga and Ankur do contain a similar resistance gene, but that Hyuuga contains another gene for resistance against ASR elsewhere in its genome. These findings provide new data that should facilitate the identification and cloning of the resistance genes in the soybean cultivars Ankur and Hyuuga, providing genes to breeeders developing new soybean lines with broad spectrum resistance to ASR.
Technical Abstract: Asian soybean rust (ASR) is an economically significant disease caused by the fungus Phakopsora pachyrhizi. The soybean genes Rpp3 and Rpp?(Hyuuga) confer resistance to specific isolates of the pathogen. Both genes map to chromosome 6 (Gm06)(linkage group (LG) C2). We recently identified 12 additional soybean accessions that harbor ASR resistance mapping to Gm06, within 5 cM of Rpp3 and Rpp?(Hyuuga). To further characterize genotypes with resistance on Gm06, we used a set of eight P. pachyrhizi isolates collected from geographically diverse areas to inoculate plants and evaluate for differential phenotypic responses. Three of the isolates elicited different responses from soybean accessions PI 462312 (Ankur) (Rpp3) and PI 506764 (Hyuuga) (Rpp?(Hyuuga)). Eleven of the new accessions yielded responses identical to either PI 462312 or Hyuuga, and one of the new accessions, PI 417089B (Kuro daizu), differed from all others. Additional screening of Hyuuga-derived recombinant inbred lines indicated that Hyuuga carries two resistance genes, one at the Rpp3 locus on Gm06 and a second, unlinked ASR resistance gene mapping to Gm03 (LG-N). These findings reveal a natural case of gene pyramiding for ASR resistance in Hyuuga and underscore the importance of utilizing multiple isolates of P. pachyrhizi when screening for ASR resistance.