Common bunt of wheat is a major seed borne disease of wheat worldwide. It is
of particular importance to organic farming, where systemic fungicides cannot be
applied. The knowledge about location and mechanisms of common bunt resistance
in wheat is limited, and only three race specific genes have so far been mapped to
chromosomes, and 9 quantitative trait loci (QTL) have been reported. Infection
with common bunt occurs shortly after wheat sowing, however, symptoms can only
be clearly assessed after the heading stage. Thus a long time for disease assessment
is required. The use of molecular markers for common bunt resistance may potentially
help to speed up resistance breeding by shortening the long time required for
phenotypic disease screening.
Here, we report the results of
1. an association mapping study for common bunt resistance,
2. a QTL mapping study for the localization of common bunt resistance gene Bt 9
and
3. a yield trial assessing yield and yield stability of common bunt resistant wheat
composite cross populations.
Association mapping A collection of 248 wheat accessions was screened for common
bunt resistance during two years under field conditions. Accessions were genotyped
with diversity array technology (DArT) markers. To avoid spurious associations
due to population stratification, DArT markers were used to estimate the
extend of population stratification. Correcting for population stratification by the
inclusion of a kinship matrix, a compressed mixed linear model identified two novel
QTL for common bunt resistance located on wheat chromosomes 2B and 7 A. The
identification of new resistance loci may help to broaden our understanding of common
bunt resistance in wheat, and QTL may potentially be exploited by marker
assisted selection in plant breeding.
QTL mapping The wheat common bunt resistance gene Bt 9 is highly effective
in Denmark, yet its chromosomal location has so far remained unknown. A double
haploid population segregating for Bt 9 was screened phenotypically for common bunt
resistance reactions in three environments, and genotyped with DArTseq markers.
Missing markers between typed markers were imputed on a 1cM grid along the
whole genome, and single marker regression tests located Bt 9 to the dorsal end
of chromosome 6D. The development of molecular markers in tight linkage with
Bt 9 will offer the possibility to apply marker assisted selection for common bunt
resistance in wheat.
Composite cross populations Race specific Bt genes may quickly be overcome by
the development of virulences in the common bunt fungi. By inter-crossing 23 wheat
accessions with common bunt resistances, two wheat composite cross populations
(CCP) were created. Yield of CCP was equal to parental yield, and levels of resistance
to common bunt were high in CCP. It is concluded that CCP can deliver
stable yields, even under common bunt infection.