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Novel sources of resistance to septoria nodorum blotch in the Vavilov wheat collection identified by GWAS

Huyen Phan: Curtin University

<div>The fungus Parastagonospora nodorum is the causal agent of septoria nodorum blotch of wheat. This disease is the outcome of multiple fungal necrotrophic effector-host sensitivity gene interactions that include SnToxA-Tsn1, SnTox1-Snn1and SnTox3-Snn3. Previous work demonstrated that the triple-knockout strain P. nodorum toxa13 maintained the ability to infect most modern bread wheat cultivars as effectively as the wildtype SN15. This suggests that other effectors and sensitivity genes may be relevant. To search for additional sensitivity/resistance genes, as well as putative genes, a diversity panel of 295 historic wheat accessions from the N. I. Vavilov Institute of Plant Genetic Resources in Russia was acquired. This collection comprises both genetically diverse landraces and historic breeding lines registered from 1920 to 1990. Both P. nodorum SN15 and toxa13 were assayed on the Vavilov panel. SN15 was more virulent than toxa13. The subset of wheat lines insensitive to all three effectors showed significantly lower levels of disease when infected with SN15. However, the subset were no less susceptible to the toxa13 than the rest of the Vavilov collection. GWAS using SN15 assay detected quantitative trait loci (QTL) on chromosomes 1BS (Snn1), 2DS, 5AS, 5BS (Snn3), 3AL, 4AL, 4BS and 7AS. For toxa13 infection, a similar QTL was detected on 5AS, plus two additional QTL on 2DL and 7DL. This study further revealed that plant breeders had inadvertently selected for effector insensitivity from 1940 onwards. This study will help to identify accessions for development of bi-parental mapping populations to characterize resistance-associated alleles for subsequent retrogression into modern bread wheat.</div>