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Safe genetic transformation for nematode resistant crops

Nematodes cause estimated global losses of 20 percent of banana crops, 12 percent of potatoes and 10 percent of rice. Higher values are probable in subsistence agriculture. Can genetic transformations safely help to reduce these losses?

Parasitic nematodes are worms that obtain their food from animals, humans and plants. Agriculture encourages an increase in parasitic nematodes, which feed on crops. Nematodes can cause crop losses in several ways. Most often, nematode feeding reduces the flow of water and nutrients into the plant, increasing the plant's susceptibility to other stress factors such as heat, water and nutritional deficiencies.

The UK Department for International Development’s Plant Sciences Research Programme and the University of Leeds, UK, are using transgenic approaches (also known as genetic modification) to develop nematode-resistant potatoes, rice and bananas for subsistence growers in developing countries. Transgenic approaches have several advantages:

Traditional breeding for nematode resistance is difficult, because it is a long-term process. Transgenic approaches are much faster.
The three target crops are all damaged by several different nematode species. Genetic modification develops plants resistant to a range of nematodes so growers do not need to know which pests are problems.
The process is highly biosafe. It involves transferring genes from maize or rice that express a protein (cystatin) already found in the grain, so it is already consumed by humans. Cystatin prevents nematodes from digesting proteins so they are malnourished, develop slowly and reproduce less.
To make the process even more biosafe, transgenes have been developed which only express cystatin in plant cells infested by nematodes.

The most advanced research is in potato, with successful field trials in the UK. This showed that using transgenic potato varieties has less impact on soil micro-organisms than differences arising from farmers growing several crop species. For example, there are greater differences in the impact on soil micro-organisms between beans, lupins and potatoes than between transgenic and non-transgenic potato plants. There is even a greater difference in impacts on soil micro-organisms between different potato varieties than between transgenic and non-transgenic potatoes of the same variety.

The research established that transgenic potatoes might cross with wild relatives when they are grown in close proximity in Andean fields. This is unlikely to occur elsewhere. However, it is not yet known if crossing results in the stable transferring of genes from cultivated to wild species. Male sterile potatoes would help prevent this while the risk is evaluated.

The programme is continuing, with further research in several areas:

The findings are already informing the safe uptake of other traits, such as insect resistant potatoes for subsistence growers.
Research to determine the impacts and risks of transferring genes to wild relative species.
To date, nematode resistance in East African Highland bananas is moderate, but additional successes with dessert banana shows that the aim of controlling the five major nematode pests is achievable. Progress will be rapid if funds are available for further banana transformation and evaluation.
Transgenic potatoes from this research have not yet been tested in developing countries. Some transgenic potato cultivars have been prepared for collaborating research institutes in Argentina and China. The researchers are identifying other institutes to test this technology, in developing countries with national biosafety regulations in place.

Source(s):
‘Genetic transformation for nematode resistance in rice, potato and cooking bananas for developing countries’, Department for International Development Plant Sciences Programme, Supplemental Report (2006) Full document.
‘Development of biosafe genetically modified Solanum tuberosum (potato) cultivars for growth within a centre of origin of the crop’ Molecular Breeding, 16, 285-293 by Jayne Green, Mandy T. Fearnehough and Howard J. Atkinson, 2005

Funded by: UK Department for International Development

id21 Research Highlight: 11 May 2006

Further Information:
Clare Stirling
Centre for Arid Zone Studies
University of Wales
Bangor, Gwynedd
LL57 2UW
UK

Tel: +44 (0) 1248 382116
Fax: +44 (0) 1248 371533
Contact the contributor: azsc03@bangor.ac.uk

Centre for Arid Zone Studies, University of Bangor, UK

University of Leeds, UK

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