| Non-conventional approaches to crop improvement |
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One alternative involves exposing plants to physical or chemical mutagenic agents to induce beneficial mutations—some of which may turn out to be beneficial. The Plant Breeding Unit at the International Atomic Energy Agency assists national programmes to use mutation techniques for developing better varieties of bananas, among other crops. Tissue culture materials are more susceptible to the effects of mutagens than suckers and seeds, but tissue culture alone can also cause mutations and the resulting ‘somaclonal variants’, that occasionally occur when banana plants are multiplied in this way, can also prove useful. In Taiwan, the Taiwan Banana Research Institute has used mass screening of tissue-culture plantlets grown in heavily infested soil to select for variants resistant to fusarium wilt. A number of Giant Cavendish variants (labelled GCTCV for Giant Cavendish tissue culture variant) have been evaluated as part of the International Musa Testing Programme. The appeal of these techniques is that they offer the possibility of preserving the characteristics of the plant to which farmers and consumers are attached, while complementing them with useful traits, such as resistance to biotic and abiotic stresses. Another approach that makes a similar promise is the controlled introduction into a plant of a gene or set of genes. Engineering bananas Responding to a demand from the Ugandan government, Bioversity developed a project with the National Agricultural Research Organization (NARO) to use genetic transformation to improve the disease and pest resistance of East African highland bananas (EAHB), an important staple crop in the region. Started in 2000 with funding from the Government of Uganda and additional financial support from Bioversity, the Rockefeller Foundation, USAID and the Belgian Government, the project is now in its second phase (supported entirely by the Ugandan government). The project has made significant progress in terms of infrastructural developments, technological advances and developing partnerships. A biotechnology centre established at NARO in 2003 enables Ugandan scientists to pursue research on identifying sources of genetic resistance and on refining transformation techniques. The project scientists were the first ones ever to succeed in developing embryogenic cell suspensions for a range of EAHB varieties and the dessert banana Sukali ndizi. They have also identified a number of genes for transfer, including cystatin genes from papaya and various genes from the bacterium Bacillus thuringiensis. The main pests and diseases targeted by this project are black leaf streak disease, nematodes and the banana weevil. Meanwhile, progress in genomics by initiatives such as the Global Musa Genomics Consortium raises the possibility of using genes found in wild and domesticated varieties of bananas instead of ‘borrowing’ genes from other species. For example, wild bananas, especially the ones living at the limits of the species’ range, are very likely to harbour genes that might help the slowly evolving varieties adapt to climate change. These so-called ‘cis-genic’ bananas would be analogous to varieties produced by using conventional breeding methods (or natural evolution) and as such should be more acceptable to consumers concerned about possible consequences, for their health and the environment, of transferring genes across species. The banana genome is also being mined for promoter genes to regulate the expression of the introduced genes. |
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