Determining the order of resistance genes against three fungal pathogens on wheat chromosome 3BS and molecular mapping of two Stagonospora nodorum blotch resistance genes on wheat chromosome 2DL

Rima Thapa, Purdue University


A variety of diseases of wheat (Triticum aestivum L.) occur every year in the United States of America leading to significant grain yield losses. Stagonospora nodorum blotch (SNB), Fusarium head blight (FHB) and stem rust (SR) are caused by the fungi Phaeosphaeria nodorum, Fusarium graminearum and Puccinia graminis, respectively. These leaf and head diseases penalize not only grain yield but also quality. The most effective and economical means of controlling these diseases is the use of resistant cultivars. Three resistance factors,, Fhb1 and Sr2, conferring resistance, respectively, to SNB, FHB and SR, each from a unique donor wheat parent line, have been mapped to chromosome arm 3BS of the wheat genome and are thought to be closely linked. Based on previously published research, Sr2 is on the distal end, Fhb1 is on the proximal end and is in the middle of Sr2 and Fhb1 in the 3BS region of the wheat genome, but the correct order is not known for certain. Thus, the main objective of this project is to test the hypothesis that these three genes are in the order of Sr2, and Fhb1 on chromosome 3BS. To test this hypothesis, 1,600 F2 plants from crosses between parental lines Arina, Alsen and Ocoroni86, conferring resistance genes, Fhb1 and Sr2, respectively, were screened along with the parental lines, using Kompetitive Allele Specific PCR (KASPar) single-nucleotide polymorphism (SNP) genotyping technology. The results confirmed that is located between the other two resistance genes on chromosome arm 3BS, and lines were identified with two of the resistance genes (SNB-SR and SNB-FHB) in coupling. Knowing the positional order of these disease resistance genes will aid in developing a wheat line with all three genes in coupling. A wheat line with all three genes together can potentially provide broad-spectrum resistance to improve wheat quality and minimize grain yield losses due to these fungal diseases. A second goal was to add molecular markers near two QTL for resistance to SNB on wheat chromosome 2DL by analysis of a 254-member recombinant-inbred (RI) population developed by crossing the two Purdue University winter wheat breeding lines P91193D1 and P92201D5, each of which was shown to contain a different QTL in previous work. The two QTL for resistance to SNB in glumes identified previously were QSng.pur-2DL.1 from P91193D1 and QSng-pur-2DL.2 from P92201D5. Their previous map locations on the 2DL chromosome arm of wheat were confirmed and their map positions were refined using KASPar SNP markers. Twenty-one polymorphic KASPar SNPs were identified between parental lines P91192D1 and P92201D5 and were used to genotype the RILs and parental lines. Eleven KASPar SNPs were used to make the genetic linkage map; the other ten markers were not linked to the resistance QTL. Adding these tightly linked molecular markers can reduce linkage drag associated with marker-assisted selection of QSng.pur-2DL.1 and QSng-pur-2DL.2 and will aid in future advanced breeding projects such as fine mapping, genomic selection, and eventually to clone these genes that are effective against SNB.




Wise, Purdue University.

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