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Improving nitrogen fixation in trees thourgh clonal selection and genetic transformation of the host

Galiana A., Ahée J., Phelep M., Duhoux E.. 1992. In : Ed. Roderic W. Dutton. Prosopis species. Aspects of their value, research and development: Proceedings of the Prosopis Symposium, Durham, 27-31 July, 1992. Durham : Centre for Overseas Research and Development, p. 197-206. Prosopis Symposium, 1992-07-27/1992-07-31, Durham (Royaume-Uni).

To improve N, fixation in trees it is necessary not only to increase the amount of N2-fixed by the host plant in association with its symbiotic micro-organism, but also to improve the tolerance of the whole N2-fixing system to environmental stresses. This goal can be achieved through two main approaches. The first approach (clonal selection) is based on the exploitation of natural genetic variability. The selected phenotypes, vegetatively propagated by in vitro techniques and explants as diverse as young shoots, young roots, and immature female inflorescences, were succcssfull) used for micropropagation. Appropriate nutritional conditions were developed to obtain true-to-type copies of Casuarina equisetifolia, Allocasuasarina verticillata, Acacia mangi m and Acacia albida. With these species it was shown that host plant and microsymbiont strains could be selected separately. The second approach is based on genetic transformation. Transgenic plants of A. verticillata were produced using wild strains (A 4 and 2659) of Agrobacteruim rhi.zogenes. Allocasuarina verticillata is the first N2-fixing tree that has been transformed. Further studies are required to introduce genes of agronomic value into this new system. The preliminary results concerning Casuarinaceae and acacias suggest that in vitro methods are useful tools in improving other N2-fixing trees such as Prosopis spp.
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