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Resistance to Diseases

Downy mildew

Downy mildew of onion caused by Peronospora destructor is an extrememly damaging foliar disease of both salad and bulb onions with yield losses as high as 70% resulting from defoliation, poor bulb formation and storage. Control relies on regular application of fungicide sprays although there are some more onion varities that are more tolerant to the disease. Current work in VeGIN is developing artificial inoculation systems to allow screening of the onion diversity set.

Fusarium

The soilborne fungus Fusarium oxysporum affects many different crops worldwide and causes some of the most devastating diseases in horticulture. Fusarium oxysporum f.sp. cepae (FOC) which affects onion is a major constraint to production with losses estimated at £11M per annum in the UK. FOC causes a basal rot which is most damaging as bulbs mature in the field or post-harvest in store. FOC produces long-lived spores, and hence control is difficult and relies on soil sterilisation/pasteurisation, fungicide drenches or seed treatments. However, these approaches may not be effective, and can have negative impacts on the environment. Furthermore, legislation surrounding chemical treatment of crops and seeds is changing and some products may not be permitted in future. Plant resistance to basal rot in onion is therefore highly desirable.

Previous work in VeGIN developed both seedling and mature onion plant tests to assess different onion accessions for FOC resistance (Taylor et al., 2012). High levels of resistance were found in certain lines derived from both short day and long day onion plant material. These were taken forward in a BBSRC HAPI project where new onion populations segregating for FOC resistance were developed by Hazera Seeds for genetic analysis and development of a marker assisted breeding program. Further funding is being sought to achieve this and bring a FOC resistant onion cultivar to market.

The FOC screening method has also been used successfully to identify sources of resistance in onion lines generated by other breeding companies.

For further infromation contact John Clarkson