Biology Reference
In-Depth Information
inbreeding, and the small chromosome number,
extensive genetic studies have been conducted in
barley starting from morphological and isozyme
markers (e.g., Benito et al. 1988) via restric-
tion fragment length polymorphisms (RFLPs,
Graner et al. 1991), PCR-based marker tech-
niques (e.g., Varshney et al. 2007), and high-
throughput SNP genotyping (Close et al. 2009)
to genome sequencing (Mayer et al. 2011).
Aside from fungal pathogens, barley is a host
to more than 50 different viruses (
http://www
um%20vulgare).
However, on the worldwide
level, only a few viruses cause economically
important diseases. These are the soil-borne
Bar-
ley yellow mosaic virus
(BaYMV) and
Bar-
ley mild mosaic virus
(BaMMV), belonging to
the genus
Bymovirus
within the family
Potyviri-
dae
, as well as the aphid-transmitted
Barley
yellow dwarf virus
(BYDV) and
Cereal yellow
dwarf virus
(CYDV), which are members of the
genera
Luteovirus
and
Polerovirus
, respectively.
Besides this,
Wheat dwarf virus
(WDV) belong-
ing to the genus
Mastrevirus
and being trans-
mitted by the leaf hopper
Psammottetix alienus
causes severe yield losses in barley in restricted
areas of Europe. But, although intensive screen-
ing programs for resistance to WDV have been
conducted (Vacke and Cibulka 2001; Bukvay-
ova et al. 2006), tolerance to WDV has been
only observed in the barley cv. “Post” up to date,
and nothing is known about the genetics of this
tolerance (Habekuss et al. 2008).
First molecular maps for barley have been
developed in the early 1990s (Graner et al. 1991),
and since that time molecular markers have been
developed for many resistance genes and quanti-
tative trait loci (QTL) against the aforementioned
viral pathogens (Ordon et al. 2009). Today, high-
density maps (e.g., Sato et al. 2009; Close et al.
2009), physical maps (Schulte et al. 2011), and
much sequence information (Mayer et al. 2011)
are available, opening the way for genomics-
based breeding for virus resistance in barley.
The present chapter focuses on resistance
viruses, namely BaMMV/BaYMV and BYDV/
CYDV, giving a brief overview on (1) bio-
logical properties and economic importance
of BaMMV/BaYMV and BYDV/CYDV, (2)
sources and genetics of resistance or tolerance,
respectively, (3) molecular markers available,
(4) strategies for molecular breeding, and (5)
genomics-assisted breeding for virus resistance
in barley.
ImportantViralPathogens
of Barley
BarleyYellowMosaicVirus/BarleyMild
MosaicVirus
Barley yellow mosaic virus disease was first
detected in Japan in 1940 (Ikata and Kawai
1940). Today it is known in East Asian countries
and especially in Europe, where the disease is
present in numerous countries (Kuhne 2009). In
Europe, barley yellow mosaic virus has become
one of the most important diseases of winter bar-
ley since its first detection in Germany in 1978
(Huth and Lesemann 1978).
Both BaMMV and BaYMV have filamen-
tous particles with two modal lengths of 500-
600 nm and 250-300 nm, containing two species
of ssRNA (Huth et al. 1984). Sequencing data
revealed that BaMMV and BaYMV share only a
limited sequence homology (e.g., Peerenboom
et al. 1992), meaning that these two viruses
are related but distinct members of the genus
Bymovirus.
In Japan, at least seven strains of
BaYMV and two strains of BaMMV are known
(Kashiwazaki et al. 1989), while in Europe, two
strains of BaYMV and three of BaMMV have
been described (Habekuss et al. 2008). Both
viruses are transmitted by the soil-borne plas-
modiophorid
Polymyxa graminis
(Adams et al.
1988), which is distributed worldwide (Anony-
mous 2011; Thompson et al. 2011). Therefore,
chemical measures are not efficient to prevent
yield losses, which can reach 50%. Therefore,
the only way to ensure winter barley cultivation
to
the
economically
most
important
barley
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