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Las associations de chromosomes au cours de Ia mlliose sont aussl diffllrentes chez les clones nlloformlls en fonction du niveau de plo"ldie. L'homologie entre chromosomes est meilleure chez las clones nlloformlls diplo"ldes que chez le tllmoin dihaplo"lde. A !'inverse, chez les clones nlloformlls tlltraplo"ldes lltudills, il y a accentuation de l'asyndllse par rapport au tllmoin 4x. Dans l'llchantillon de clones lltudills, nous n'avons cependant trouvll aucune modification dans Ia structure des chromosomes qui puisse expliquer les variations phllnotypiques lilies fila culture de tissu.Summary.-Phenotype from 9 potato clones [7 regenerated clones and 2 controls of BF15 (2x) and (4x) variety], with different chromosome number and at the flowering state, made the support, in this paper, for analyzing the somaclonal variation. Some morphological characteristics concerning floral bud and stem portion under the inflorescence make the sorting out of dipio"ld or tetraplo"ld clones easy, which permits a preliminary sorting of regenerated plants cultivated in greenhouse. In neofonned clones, chromosome associations during meiosis show a varia· lion depending on the chromosome number of the parents. Homology between chromosomes is better in regenerated diplo"ld clones than in the diha· plo"ld control. On the other hand, asyndesis In regenerated tetraplold clones is accentuated In comparison with the 4x control one. Within the limits of our study, not any chromosome structure modification can be correlated to the observed phenotype variations related to the tissue cui· lure.

Mannopine and cucumopine straios of Agrobacterium rhizogenes were used for genetic transformation in two cultivars of potato (Solanum tuberisum L.). An overnight pretreatment of internodes with c~-naphthaleneacetic acid prior to bacterial infection was found to strongly inhibit shoot formation. On the contrary, infection with bacterial strains enhanced the frequency of shoot formation, compared with the controls, except for the strain 15834 which completely inhibited shoot formation in both potato cultivars. Shoots developed directly from the upper part of both inoculated and control explants, at a frequency ranging from 1 to 5 shoots per fragment. Among 93 shoots regenerated, 9 were found to be opine positive, and exhibited an altered phenotype with shortened internodes. Histological study revealed that the transformed shoots developed directly from cells of the internode sections, and not from induced roots. When grown in an insect-proof tunnel, the transformed plants had both altered and normal phenotypes and were able to produce tubers.