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Controlling Soil-borne cereal mosaic virus in the UK by developing resistant wheat cultivars

HGCA PROJECT REPORT 418 

Controlling Soil-borne cereal mosaic virus in the UK by developing resistant wheat cultivars 


by
R. Bayles1, D. O'Sullivan1, V. Lea1, S Freeman1, G. Budge2, K. Walsh2
and C. Henry2


1NIAB, Huntingdon Road, Cambridge, CB3 0LE
2 CSL, Sand Hutton, York, YO41 1LZ.

August 2007

Abstract

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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