Abstract
Key messageResistance QTL on chromosomes 1AL and 7AL are effective against common and dwarf bunt, QTL on 1BS affects common bunt and QTL on 7DS affects dwarf bunt in bread wheat.Common bunt, caused by Tilletia caries and T. laevis, and dwarf bunt, caused by T. controversa, negatively affect grain yield and quality of wheat and are particularly destructive in low-input and organic production systems. Two recombinant inbred line (RIL) populations derived by crossing the highly and durably resistant cultivars ‘Blizzard’ and ‘Bonneville’ to the susceptible cultivar ‘Rainer’ were evaluated for their resistance to common and dwarf bunt in artificially inoculated field and greenhouse trials over two growing seasons and genotyped with a 15 K SNP array. Bunt resistance QTL were mapped to chromosomes 1AL, 1BS, 7AL and 7DS. Common bunt resistance was regulated by the major QTL QBt.ifa-1BS and QBt.ifa-1AL together with the moderate effect QTL QBt.ifa-7AL. Dwarf bunt resistance was on the other hand regulated by the QTL QBt.ifa-1AL, QBt.ifa-7AL and QBt.ifa-7DS. Common bunt resistance QTL exhibited pronounced epistatic effects, while epistatic effects were of smaller magnitude for dwarf bunt QTL. Kompetitive Allele-Specific PCR (KASP) markers were developed from SNPs associated with bunt resistance QTL and successfully used for QTL validation in an independent set of RILs. These KASP markers have the potential to support targeted introgression of QTL into elite wheat germplasm and accelerate breeding for enhanced bunt resistance. Durable protection against both common and dwarf bunt can be achieved by combining multiple resistance genes in the same genetic background.
Highlights
The first historical records of bunts in wheat date back to early Greek and Roman times, and bunted heads have likely been observed since the beginning of wheat cultivation (Chen et al 2016; Christensen 1957; Woolman and Humphrey 1924)
Dwarf bunt (DB) infection results from soil-borne T. controversa teliospores that can survive in the soil for over 10 years without losing viability, whereas common bunt (CB) is primarily caused by seed-borne inoculum (Borgen and Davanlou 2000; Goates 1996; Tyler and Jensen 1958)
Quantitative variation was evident for CB and DB incidence in all trials, which generally followed a positively skewed continuous distribution with more than 50% of lines showing low (< 10% bunt incidence) or no infection (Fig. 1)
Summary
The first historical records of bunts in wheat date back to early Greek and Roman times, and bunted heads have likely been observed since the beginning of wheat cultivation (Chen et al 2016; Christensen 1957; Woolman and Humphrey 1924). Given the limited options for organic certified seed treatments and insufficient resistance levels of currently grown wheat cultivars in many areas of the world, breeding for bunt resistance has regained attention and become a high priority for organic wheat breeding (Borgen and Davanlou 2000; Matanguihan et al 2011). Dwarf bunt (DB), caused by Tilletia controversa J.G. Kühn is restricted to regions with extended snow cover, while common bunt (CB), caused by T. caries (DC.) Tul. DB infection results from soil-borne T. controversa teliospores that can survive in the soil for over 10 years without losing viability, whereas CB is primarily caused by seed-borne inoculum (Borgen and Davanlou 2000; Goates 1996; Tyler and Jensen 1958). CB and DB can cause substantial yield losses and reduce grain quality when seed-lots are contaminated with bunt balls at levels as low as 0.05% (Gaudet and Puchalski 1989)
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