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Title:   Author  item
                                            GUERRERO-CHAVEZ, ROSA - South Dakota State Universityitem
                                            GLOVER, KARL - South Dakota State Universityitem
                                            Rouse, Matthew

                                                         - *Matt*item
                                            GONZALEZ-HERNANDEZ, JOSE - South Dakota State University
  Submitted to: Molecular Breeding
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 8/13/2014
                                    Publication  Date: 1/15/2015
                                    Citation: Guerrero-Chavez, R., Glover, K.D., Rouse, M.N., Gonzalez-Hernandez, J. 2015. Mapping of two loci conferring resistance to wheat stem rust pathogen races TTKSK (Ug99) and TRTTF in the elite hard red spring wheat line SD4279. Molecular Breeding. 35(8):1-10.Interpretive Summary: Wheat stem rust is a fungal disease of wheat that decreases yield. A strain of this fungus known as Ug99 emerged in Uganda in 1999 and threatens global wheat production for it is able to infect nearly all varieties. Wild relatives of wheat have been used to find new sources of resistance to this and other diseases. Unfortunately, very few modern wheat varieties are resistant to Ug99 or other dangerous stem rust fungus races such as TRTTF. We found that a modern wheat line from South Dakota State University named SD4279 is resistant to both Ug99 and race TRTTF. We determined that a single resistance gene from SD4279 on chromosome arm 2BL confers the resistance. Also, we found that a second resistance gene on chromosome arm 6AS confers resistance to the race TRTTF. We identified molecular markers linked to these resistance genes. These molecular markers could be used in wheat breeding to select for new wheat cultivars with resistance to these races. Data from our study can be used to protect United States wheat production from yield loss from emerging, foreign strains of the dangerous wheat stem rust fungus.
                                Technical Abstract: Since its identification in the late 1990's, the stem rust pathogen (Puccinia graminis. f. sp. tritici (Pgt)) strain Ug99 (race TTKSK) has represented a worldwide wheat production threat due to its ability to overcome most of the resistance genes present in commercial cultivars. In order to address this challenge, progress has been made to identify new resistance genes in wheat cultivars as well as in wild relatives. Because variants of Ug99 have been detected with virulence to additional resistance genes, only few genes are capable of providing resistance to all members of the Ug99 race group. Additionally, stem rust resistance breeding is facing a new challenge with the recent discovery in Ethiopia of a new race of Pgt (TRTTF) capable of defeating Sr13, SrTmp and Sr1RAmigo resistance genes that conferred resistance to the Ug99 race group. As part of an ongoing screening process at USDA-ARS Cereal Disease Laboratory, SD4279, an elite line from the hard red spring wheat breeding program at South Dakota State University, was found to be resistant to both races TTKSK and TRTTF. The objectives posed in this research were 1) to characterize the genetics of resistance to stem rust in SD4279 and 2) identify molecular markers linked to race TTKSK (Ug99) and TRTTF resistance in SD4279. A mapping population composed of 92 F2:3 families was evaluated for resistance to TTKSK and TRTTF and genotyped with a custom 9K iSelect SNP Beadchip Array. A single gene conferring resistance to TTKSK, likely SrWeb, was mapped on chromosome arm 2BL. Also, a single gene was located on chromosome arm 6AS conferring resistance to TRTTF. Based on the type of reaction and map location, we postulate that the 6AS resistance gene is Sr8a which has not been mapped previously using DNA markers. The identified molecular markers linked to race TTKSK and TRTTF resistance could be used in marker-assisted selection to select for resistance to these virulent races of the stem rust pathogen.


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