Résumé:
The seedling production potato (Solanum tuberosum L.) is a topical issue in Algeria. Salt stress is one of the limiting factors prompting the state to invest in projects varietal improvement. The variants induction may result in expressive enough adaptation to some stress such as salt stress. Micropropagation in MS2 medium and microtuberization in MS4 have led to the permanent availability of plant material.
The induction of in vitro somaclonal variants requires a careful selection of the explant and a definite hormonal interaction. Organogenesis callus depends on the conditions of the culture medium, including the in vitro incubation temperature. We initiated callogenesis varieties Spunta and Kondor from segments of internodes and leaves, on a culture medium containing MS supplemented with BAP (0,5 mg.L-1) and 2.4-D (0,5 mg.L-1). The explant crops have been exposed to varying temperatures of incubation: 22±1°C, 25±1°C and 28±1°C. The calluses obtained were placed in the same culture medium with the change in the concentration of 2.4-D (0,2; 0,5; 1; 1,5 and 2 mg.L-1). Statistical analysis showed that incubation of 25±1°C is the most suitable for organogenic neoformation of the calluses. Somatic embryogenesis was established only on meristem callus. But the induction of somatic buds was favorable in both varieties. However, Kondor variety was more suitable than the Spunta variety. Thus, the stem is most suitable explant to the induction of organogenic callus that the leaf explants. S.tuberosum is a species which has a better regeneration of these variants by budding meristematic.
The induction of somaclonal variants tolerant to in vitro salt stress requires a selection of tolerant cell lines. An application of salt stress was performed on callus induced by adding to the same medium with the various concentrations of NaCl (from 0 to 14 g.L-1). For concentrations from T1 to T7, tolerant callus had a similar texture to the witness: compact, globular and greenish color. From T8 texture was changed to a friable callus, smooth and brownish. Statistical analysis of the results allowed defining the tolerance threshold, between 4 g.L-1and 7 g.L-1. A second selection of these callus subcultured on these concentrations is performed, and favored the delimitation of tolerance threshold between 4 and 5 g.L-1. Thus, induction of meristematic buds has favored until the third generation of tolerant callus, which is not the case unstressed callus inducing
organogenesis in the first generation. Therefore, the stem calluses are more able to adapt to stress and having a more productive than the leaf callus somatic organogenesis.
Varietal improvement by selection of genotypes was also tested and proved to be more interesting. Repeated vitroplants the same concentrations previously described exposure favored the selection of genotypes having tolerated the sub-lethal concentration of 4 g.L-1. This result is very encouraging, led to the induction of tolerant microtubers. The medium MS4 'proved to be the most suitable for the type of stress. However, the Kondor variety occurs more tolerant in vitro salt stress that Spunta variety.
