The effect of plant growth regulators on callus and somatic embryogenesis induction in four Cocoa (Theobroma cacao) genotypes was studied. Flower explants were harvested early in the morning and cultured on Driver and Kuniyuki Walnut (DKW) medium supplemented with 1 mg·L−1 of five auxins type (2,4 dichlorophenoxyacetic acid (2,4-D), 3,4 dichlorophenoxyacetic acid (3,4-D), 2,4,5 trichlorophenoxyacetic acid (2,4,5-T), 4-amino-3,5,6-trichloropicolinic acid (picloram), and 3,6-dichloro-2-methoxybenzoic acid (dicamba) in combination with 0.25 or 0.5 mg·L−1 of two cytokinins type (benzylaminopurine (BAP) and 6-furfurylaminopurine [kinetin (Kin)] in a factorial experiment. The plant growth regulators 2,4-D and 2,4,5-T proved to have a broad spectrum action on somatic embryogenesis induction compared with 3,4-D or picloram. There were no significant differences between the two concentrations of cytokinins. However, Kin was found to be more effective in promoting somatic embryogenesis than BAP. Combining 1 mg·L−1 2,4,5-T or 2,4-D with 0.25 mg·L−1 Kin had a broad spectrum action on embryogenesis induction. On the other hand, combining mg·L−1 picloram with 0.5 mg·L−1 Kin or 1 mg·L−1 3,4-D with 0.25 mg·L−1 Kin was only able to induce somatic embryogenesis in a few of the genotypes evaluated. The protocol developed during the current study differs from earleir works as the callus (derived from explants cultured on DKW media) was taken directly to embryo development media as opposed to earlier works in which the callus was taken through a secondary media before being transferred to an embryo development media.

For two decades, the combination 2,4-dichlorophenoxyacetic acid (2,4-D)/thidiazuron (TDZ) has been the most used to induce somatic embryogenesis in cocoa. The aim of this study was to compare the effect of combination systems, auxin/TDZ and auxin/kinetin (Kin) systems, as well as the addition of polyvinylpirrolidone (PVP) to these combinations on the induction of embryogenic calli in cocoa (Theobroma cacao L.). To this end, eight induction media combining auxin 2,4-dichlorophenoxyacetic acid (2,4-D) or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 4,5 mM with cytokinin thidiazuron (TDZ) (22.8 nM) or kinetin (Kin) (1.125 mM) supplemented or not with PVP (300 mg / L) were evaluated on induction of embryogenic callus with petals or staminodes in three genotypes of cocoa. The basal salts medium was DKW (Driver and Kuniyuki Walnut medium). This study showed that the effect of 2,4-D combinations with Kinetin or TDZ was statistically identical on the induction of embryogenic callus. On the other hand, with 2,4,5-T, the association with Kin was more embryogenic than with TDZ. Furthermore, addition of PVP improved the induction of embryogenic callus in both combination systems. In the presence of PVP, media containing 2,4,5-T exhibited higher levels of embryogenic callus induction than their counterparts containing 2,4-D. This study allows the expansion of the possibilities of induction of embryogenic callus in cocoa.

The current study aimed at evaluating the effect of gibberellic acid (GA 3 ) and sucrose on in vitro propagation of two elite sweet potato cultivars (Ukerewe and Gihingamukungu). Nodal explants from in vitro growing plantlets were harvested and cultured on Murashige and Skoog media supplemented with 2.5, 5, 10, 20 and 40 μM, GA 3 . In a separate experiment, sucrose was evaluated at 30, 60, 90, 120, 150, 180 and 210 mM. For Ukerewe, the explants cultured on medium supplemented with 10 µM GA 3 recorded the longest (2.78 ± 0.36 cm) microshoots. . On the other hand, cultivar Gihingamukungu explants cultured on media supplemented with 2.5 GA 3 µM produced the longest ((3.23 ± 0.40 cm) microshoots. Nodal explants from the two cultivars cultured on media supplemented with sucrose 150 mM yielded the longest microshoots (2.51 ± 0.26 and 2.34 ± 0.24 cm, respectively). From the results of the current study, it can be concluded that for micropropagation of the cultivar Ukerewe 10 µM GA 3 should be used while 2.5 GA 3 µM should be used for micropropagtion of cultivar Gihingamukungu. The regenerated plantlets were successfully weaned in the greenhouse. The protocol developed in this research will open new prospects for massive propagation of the elite sweet potato cultivars in Rwanda.

No abstract

Accurate identification of varieties is paramount to optimizing efficiencies in the management and conservation of genetic resources. A relatively inexpensive, rapid methodology is required to identify putative duplicates from any collection, when morphological traits give insufficient discrimination. Here we select a panel of 36 SNPs, visualized using the Kompetitive Allele-specific PCR (KASP) system. We used a panel of 95 cassava genotypes from Côte d’Ivoire to identify varieties that are not duplicates and few potential duplicates which could be put forward for further verification. The genetic variability and population structure of the germplasm is also described. 36 SNPs were polymorphic across the panel of 95 varieties with polymorphic information contents ranging from 0.23 to 0.37. Using these SNPs, we were able to identify 66 unique genotypes from the panel of 95 genotypes, discriminate three sets of known duplicates and identify 11 sets of unknown putative duplicates which can be subjected to further verification using higher density genotyping. As expected in an outcrossing species, both expected heterozygosity (0.46) and observed heterozygosity (0.48) were high with an analysis of molecular variance (AMOVA) indicating that the majority of variation was within individuals. Three statistical approaches i.e., hierarchical ascending clustering, Bayesian analysis and discriminant analysis of principal components were used and all revealed low genetic differentiation between sub-populations, a conclusion that was supported by the low value of the fixation index (0.05). This panel of SNPs can be used to enhance cost-effectiveness and efficiency of germplasm conservation and enhance quality control at various stages in the breeding process through varietal tracking.