Genome-wide association mapping of tan spot resistance in a worldwide collection of durum wheat

Authors: GALAGEDARA, NELOMIE - North Dakota State University; LIU, YUAN - North Dakota State University; Fiedler, Jason; SHI, GONGJUN - North Dakota State University; Chao, Shiaoman; Xu, Steven; Faris, Justin; LI, XUEHUI - North Dakota State University; LIU, ZHAOHUI - North Dakota State University

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2020
Publication Date: 4/16/2020
Citation: Galagedara, N., Liu, Y., Fiedler, J.D., Shi, G., Chao, S., Xu, S.S., Faris, J.D., Li, X., Liu, Z. 2020. Genome-wide association mapping of tan spot resistance in a worldwide collection of durum wheat. Theoretical and Applied Genetics. 133:2227–2237. https://doi.org/10.1007/s00122-020-03593-1.
DOI: https://doi.org/10.1007/s00122-020-03593-1

Interpretive Summary: Tan spot is a major foliar disease worldwide in both bread and durum wheat. Genes that confer resistance to tan spot are important for the development of new cultivars that are not negatively impacted by this disease. To identify these genes, we evaluated tan spot in a durum population of lines from all over the globe and searched the genomes for resistance or susceptibility gene regions. We identified two previously known gene regions that promote susceptibility to two major tan spot toxins and identified two previously known gene regions that promote susceptibility to the two major races of the tan spot pathogen. We also found new gene regions in the durum genome that conferred resistance to either specific races or all the races tested. Taken together, this work highlights the complexity of the disease mechanism for plant pathologists and assists the durum breeding program to develop lines that are resistant to Tan spot.

Technical Abstract: Tan spot, caused by the necrotrophic fungus Pyrenophora tritici-repentis, is a major foliar disease on all cultivated wheat crops worldwide. Compared to common wheat, much less work has been done to investigate the genetic basis of tan spot resistance in durum. Here, we conducted disease evaluations, necrotrophic effector (NE) sensitivity assays, and a genome wide association study (GWAS) using a collection of durum accessions. The durum accessions segregated for the reaction to disease inoculations and NE infiltrations with eighteen accessions being highly resistant to all races and most of them insensitive to both Ptr ToxA and Ptr ToxB. Over 65,000 SNP markers were developed from genotyping-by-sequencing (GBS) for the association mapping. As expected, sensitivity to Ptr ToxA and Ptr ToxB was mapped to the chromosome arms 5BL and 2BS, respectively. For the fungal inoculations, a QTL on chromosome 3B was associated with resistance to all races and likely corresponds to the race-nonspecific resistance QTL previously identified in common wheat. The Tsn1 locus was not significantly associated with tan spot caused by the Ptr ToxA-producing isolates Pti2 and 86-124, but the Tsc2 locus was significantly associated with tan spot caused by the Ptr ToxB-producing isolate DW5. Another QTL on chromosome arm 1AS was associated with tan spot caused by the Ptr ToxC producing isolate Pti2 and likely corresponds to the Tsc1 locus. Additional QTL for specific races were identified on chromosome 1B and 3B. Our work highlights the complexity of genetic resistance to tan spot and further confirms that the Ptr ToxA-Tsn1 interaction plays no significant role in disease development in tetraploid wheat.