United Kingdom
August 14, 2007
Source: Home-Grown Cereals
Authority - CropResearchNews - Issue 32 / August 13 2007
Controlling soil-borne cereal
mosaic virus in the UK by developing resistant wheat cultivars
by R. Bayles, D. O'Sullivan, V. Lea and S Freeman of NIAB,
and G. Budge, K. Walsh and C. Henry of CSL.
HGCA Project No: 2616, Price: £5.00
Soil-borne cereal mosaic virus (SBCMV) was detected in the UK
for the first time in 1999. The virus, which is transmitted by
the soil-borne protist Polymyxa graminis can cause serious yield
losses in susceptible wheat cultivars. SBCMV is able to survive
in the soil in the resting spores of P. graminis in the absence
of wheat plants for at least 15 years. The development of
resistant wheat cultivars for use in the UK is therefore
essential if high yielding wheat cultivation is to be maintained
on infested land.
The main objective was to identify genes involved in SBCMV
resistance in wheat and develop molecular marker tags so that
plant breeders can incorporate these genes in their breeding
material. Resistance segregating in three populations derived
from crosses between SBCMV resistant and susceptible parents was
mapped using genome-wide QTL scanning. Two major resistances
were identified, Sbm1, on chromosome 5DL and Sbm2, on chromosome
2BS. Lines carrying both genes showed significantly lower virus
levels than lines carrying either gene alone, implying that the
two resistances act in distinct and complementary ways to limit
viral spread. AFLP markers closely linked to two resistance
genes were identified for use in marker assisted selection.
An accelerated test for screening lines for SBCMV resistance was
developed, using contained automatic immersion systems in
controlled environments. Optimum conditions for virus
multiplication were temperatures of 12-15°C with 2 hours
watering in every 12 hours and material harvesting after 8
weeks. Testing root material for virus gave a better indication
of resistance than testing leaf material. The test produced
results which were very highly correlated with conventional
field tests.
Representational Difference Analysis (RDA) was used to try to
identify biosynthetic pathways activated during the onset of a
resistance reaction. This knowledge could inform about the
mechanism of resistance to SBCMV and contribute to an
understanding of the likely durability of resistance. Results
indicated that resistance mechanisms were activated as early as
12 days after introduction of the inoculum. A difference product
was identified that increased only in resistant lines,
indicating the involvement of the gene in the resistance
mechanism.
Tests of the resistance of UK cultivars to a number of other
closely related soil-borne viruses indicated that cultivars
resistant to SBCMV are likely also to be resistant to soil-borne
wheat mosaic virus (SBWMV) and vice-versa. In contrast,
resistance to SBCMV and wheat spindle streak mosaic virus
(WSSMV) do not appear to be related. |
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