Genome-wide association mapping identifies common bunt (Tilletia caries) resistance loci in bread wheat (Triticum aestivum) accessions of the USDA National Small Grains Collection

Abstract

Key message Association mapping and phenotypic analysis of a diversity panel of 238 bread wheat accessions highlights differences in resistance against common vs. dwarf bunt and identifies genotypes valuable for bi-parental crosses. Abstract Common bunt caused by Tilletia caries and T. laevis was successfully controlled by seed dressings with systemic fungicides for decades, but has become a renewed threat to wheat yield and quality in organic agriculture where such treatments are forbidden. As the most efficient way to address this problem is the use of resistant cultivars, this study aims to broaden the spectrum of resistance sources available for breeders by identifying resistance loci against common bunt in bread wheat accessions of the USDA National Small Grains Collection. We conducted three years of artificially inoculated field trials to assess common bunt infection levels in a diversity panel comprising 238 wheat accessions for which data on resistance against the closely related pathogen Tilletia controversa causing dwarf bunt was already available. Resistance levels against common bunt were higher compared to dwarf bunt with 99 accessions showing $$\le$$ ≤ 1% incidence. Genome-wide association mapping identified six markers significantly associated with common bunt incidence in regions already known to confer resistance on chromosomes 1A and 1B and novel loci on 2B and 7A. Our results show that resistance against common and dwarf bunt is not necessarily controlled by the same loci but we identified twenty accessions with high resistance against both diseases. These represent valuable new resources for research and breeding programs since several bunt races have already been reported to overcome known resistance genes.

Identification and characterization of stripe rust, leaf rust, leaf spot, and common bunt resistance in spring wheat

“…Chromosome 2B harbors the Bt1 gene that provides resistance against several T. caries and T. laevis isolates (Goates, 2012; Sears et al., 1960), but we are not sure of the exact physical position of this gene. Minor to moderate effect Cbt resistance QTLs have also been reported in wheat on chromosome 2B by different authors, including at 811 Mb near BS00012463_51 in the Canadian spring wheat diversity panel (Iqbal et al., 2022), 581 Mb near Ku_c71357_859 in a bread wheat accessions of the USDA National Small Grains Collection (Ehn et al., 2022), and 8–9 Mb in a diversity panel of both spring and winter wheat accessions (Steffan et al., 2022), but none of these QTLs are physically close to QCbt.dms‐2B identified in the present study.…”

“…Several studies reported genes ( Bt4 , Bt5 , and Bt6 ) and QTLs associated with Cbt resistance on chromosome 1B (Dumalasová et al., 2012; Ehn et al., 2022; Fofana et al., 2008; Iqbal et al., 2022; Mourad et al., 2018; Muellner et al., 2021; Scmidt et al., 1969; Singh et al., 2016; Wang et al., 2009), 2B (Chen et al., 2016; Ehn et al., 2022; Iqbal et al., 2022; Steffan et al., 2022), and 6D (Gordon et al., 2020; Iqbal et al., 2022; Singh et al., 2016). The positions of the Cbt resistance genes and QTLs on 1B varied across populations and includes 11.2 Mb near BS00032266_51 in a diversity panel of bread wheat accessions from the USDA National Small Grains Collection (Ehn et al., 2022), 4.4–38.9 Mb in two RIL populations derived from Blizzard/Rainer and Bonneville/Rainer (Muellner et al., 2021), and 645.2 Mb in Canadian spring wheat (Iqbal et al., 2022). The physical position of the QCbt.dms‐1B identified in the present study, therefore, overlapped with the QTLs reported in the USDA bread wheat accessions and the two RIL (Blizzard/Rainer and Bonneville/ Rainer) populations.…”

“…We identified three QTLs associated with Cbt resistance in all combined environments at 244.0 Mb on chromosome 2B in Attila/CDC Go ( QCbt.dms‐2B ) and 21.4 Mb on 1B ( QCbt.dms‐1B ) and 7.6 Mb on 6D ( QCbt.dms‐6D ) in Peace/Carberry populations (Table 1). Several studies reported genes ( Bt4 , Bt5 , and Bt6 ) and QTLs associated with Cbt resistance on chromosome 1B (Dumalasová et al., 2012; Ehn et al., 2022; Fofana et al., 2008; Iqbal et al., 2022; Mourad et al., 2018; Muellner et al., 2021; Scmidt et al., 1969; Singh et al., 2016; Wang et al., 2009), 2B (Chen et al., 2016; Ehn et al., 2022; Iqbal et al., 2022; Steffan et al., 2022), and 6D (Gordon et al., 2020; Iqbal et al., 2022; Singh et al., 2016). The positions of the Cbt resistance genes and QTLs on 1B varied across populations and includes 11.2 Mb near BS00032266_51 in a diversity panel of bread wheat accessions from the USDA National Small Grains Collection (Ehn et al., 2022), 4.4–38.9 Mb in two RIL populations derived from Blizzard/Rainer and Bonneville/Rainer (Muellner et al., 2021), and 645.2 Mb in Canadian spring wheat (Iqbal et al., 2022).…”

Genetic Variation in Common Bunt Resistance in Synthetic Hexaploid Wheat

“…These differential lines are available in the Department of Agricultural Research Service, National Small Grains Collection (NSGC) in Aberdeen, ID, and could be easily separated from each other, which makes them globally important [ 40 ]. They are very helpful in identifying the resistant genes as they are isolines carrying only one resistant gene [ 39 , 40 , 42 ]. Based on the results of the differential lines, Bt6 , Bt7 , Bt9 , Bt10 , Bt11 , Bt12 , Bt13 , Bt15 , and Btp are effective resistance genes to the Nebraska common bunt race.…”

Morphological and Molecular Diagnosis the Fungus Species of Tilletia spp That Infect Wheat in Some Provinces of Iraq

“…The results of collection of samples are shown Table 2 spread of covered smut disease in wheat caused by a fungus Tilletia spp. in all areas collection sample and this is compound with what was mentioned [6] from that the disease is widespread in most planted area of wheat in most countries of the world.…”