Djibril Sané

Screening cowpea [ Vigna unguiculata (L.) Walp.] varieties by inducing water deficit and RAPD analyses

The effects of water deficit induced by polyethylene glycol-6000 on some cowpea varieties, which belong to the national germplasm in Senegal are reported. Our results showed that, the length of the epicotyl was not affected by water deficit but the length of primary root was influenced only in Mouride variety. Water deficit influenced mostly the number of lateral roots. The 985 variety showed a great increase of its lateral root numbers and could be considered a drought tolerant variety. In contrast, the IT81D-1137 variety is very sensitive to water deficit because its lateral root number were reduced 3.8 fold compared to the control. These physiological studies were complemented by analyzing the genetic diversity of these varieties with random amplified polymorphic DNA (RAPD). The RAPD analysis suggested that the samples were also genetically diverse.

Direct genetic transformation of Hibiscus sabdariffa L.

Transgenic Hibiscus sabdariffa plants have been produced by a tissue culture independent method using Agrobacterium tumefasciens transformation procedure. Embryo axes of mature seeds with one cotyledon excised were infected by immersion in a suspension of Agrobacterium LBA 4404 strain culture that carries pBal plasmid with β-glucuronidase p35SGUSINT and plant selectable marker Neomycin Phospho-Transferase gene ( npt II). Following a 24 h co-cultivation with Agrobacterium strain and decontamination with cefotaxime, embryos were grown on soil rite containing MS medium added with a killer concentration of kanamycin (100 μg/ml) during 4 weeks at room conditions and thereafter transferred to greenhouse. 54.3% of the seedlings grew well on the selective medium; 68% of the explants excised from putative transformed plants were found to be GUS positive. After 60 days evaluation point, the assessment of the transformation by PCR revealed that H. sabdariffa line tested, carried the npt II gene. Key Words: Hibiscus sabdariffa; genetic transformation. African Journal of Biotechnology Vol. 3 (4), 2004: 226-228

Influence of growth regulators on callogenesis and somatic embryo development in date palm (Phoenix dactylifera L.) Sahelian cultivars.

This study provides a physiological analysis of somatic embryogenesis in four elite cultivars of date palms: Ahmar, Amsekhsi, Tijib, and Amaside, from the initial callogenesis to establishment and proliferation of embryogenic suspension cultures. Somatic embryos development and in vitro plants rooting were also studied. For each step, auxins and cytokinins concentrations were optimised. The primary callogenesis from leaf explants of seedlings appeared highly dependent on genotype. Ahmar (80%) and Amsekhsi (76%) appeared highly callogenic, whereas Tijib (10%) and Amaside (2%) produced low amounts of calluses. 2,4-Dichlorophenoxyacetic acid appeared favorable to the induction of primary callogenesis and its effect was enhanced by the addition of benzyl adenine or adenine sulfate. Secondary friable calli obtained from chopped granular calli were used to initiate embryogenic cell suspensions in media supplied with 2,4-dichlorophenoxyacetic acid. Suspension cultures showed a growth rate of fourfold after four subcultures in presence of 2,4-dichlorophenoxyacetic acid 2 mg/L. Our results showed that a seven-day transitory treatment with benzyl adenine 0,5 mg/L was necessary to optimize embryos development. Naphthalene acetic acid induced the development of primary orthogravitropic roots during embryos germination. The comparison with cytofluorometry of nuclear DNA amounts showed no significant difference in ploidy level between regenerated plants and seedlings.

Evidence of genomic exchanges between homeologous chromosomes in a cross of peanut with newly synthetized allotetraploid hybrids

Cultivated peanut and synthetics are allotetraploids (2n = 4x = 40) with two homeologous sets of chromosomes. Meiosis in allotetraploid peanut is generally thought to show diploid-like behavior. However, a recent study pointed out the occurrence of recombination between homeologous chromosomes, especially when synthetic allotetraploids are used, challenging the view of disomic inheritance in peanut. In this study, we investigated the meiotic behavior of allotetraploid peanut using 380 SSR markers and 90 F2 progeny derived from the cross between Arachis hypogaea cv Fleur 11 (AABB) and ISATGR278-18 (AAKK), a synthetic allotetraploid that harbors a K-genome that was reported to pair with the cultivated B-genome during meiosis. Segregation analysis of SSR markers showed 42 codominant SSRs with unexpected null bands among some progeny. Chi-square tests for these loci deviate from the expected 1:2:1 Mendelian ratio under disomic inheritance. A linkage map of 357 codominant loci aligned on 20 linkage groups (LGs) with a total length of 1728 cM, averaging 5.1 cM between markers, was developed. Among the 10 homeologous sets of LGs, one set consisted of markers that all segregated in a polysomic-like pattern, six in a likely disomic pattern and the three remaining in a mixed pattern with disomic and polysomic loci clustered on the same LG. Moreover, we reported a substitution of homeologous chromosomes in some progeny. Our results suggest that the homeologous recombination events occurred between the A and K genomes in the newly synthesized allotetraploid and have been highlighted in the progeny. Homeologous exchanges are rarely observed in tetraploid peanut and have not yet been reported for AAKK and AABB genomes. The implications of these results on peanut breeding are discussed.

Régénération de vitroplants par embryogenèse somatique à partir d'embryons zygotiques immatures chez une espèce adaptée à la sécheresse: Acacia tortilis subsp. raddiana (Savi.) Brenan

Abstract Using calli from immature zygotic embryos of Acacia tortilis subsp. raddiana, globular somatic embryos are obtained after 90 to 100 days culture in darkness on VA media added with 2,4-D (2,4 and 8 mg/l) alone or in combination with BAP (1 and 0,5 mg/l). Light and transfert on MS/2 medium containing BAP (0,5 mg/l)) and AIB (0,05 mg/l) enhance proliferation of somatic embryos. ABA (2,6 and 5,2 mg/l) or high concentration of sucrose (50 g/l) allow development from globular to bipolar embryos. Development of mature somatic embryos into plantlets are obtained on MS/2 medium without hormon, but supplemented with high concentration of sucrose.