Induction of somatic embryos of recalcitrant genotypes of <i>Theobroma cacao L.</i>

Abstract

Objective: In cocoa tree (Theobroma cacao L.), some elite genotypes have shown, in standard study conditions, an absence or a very weak response to induction of somatic embryos. This is the case of the original C8 genotype Trinidad. This study aims to improve the production of somatic embryos in this genotype Methodology and results: To do this, staminodes and petals excised from immature buds of genotypes C1, C8 and C14 were used. Genotypes C1 and C14 are embryogenic under standard conditions. These floral explants were cultured on induction media differing by the type and concentration of auxins. Callus induction obtained in the three studied genotypes ranged from 80% to 90% with the petal explants and from 70% to 80% with the staminodes regardless of the type and concentration of auxins. Transfer of callogenic explants to DKW (Driver & Kuniyuki, 1984) medium supplemented with sucrose and glucose allowed the induction of somatic embryos at mean rates varying from 5% to 20% after only 84 days with petal explants and media supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) and 2, 4, 5-trichlorophenoxyacetic acid (2,4,5-T). No induction of somatic embryos was observed on the control medium with the C1, C8 and C14 genotypes. The C1 genotype induced somatic embryos in the presence of all concentrations of auxins. The highest rate of embryogenic callus and somatic embryo induction was obtained with 18 μM of 2, 4, 5-T in all C1 genotypes (39.29 ± 0.28; 17.98 ± 0.10), C8 (36.29% ± 0.26 and 15.01 ± 0.07) and C14 (33.92% ± 0.26 and 14.50 ± 0.16). The 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T). at 18 μM is the most appropriate auxin to remove recalcitrance in cocoa genotype C8. The use of higher 18 μM concentrations of 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T). and its application to other recalcitrant genotypes could confirm its beneficial effect on the removal of recalcitrance to somatic embryogenesis in cocoa. Conclusion and application of results: 18 μM concentration of 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T) gave the best percentage of embryogenic explants and the highest average number of embryos in the three genotypes tested. Therefore, this protocol using 18 μM of 2, 4, 5-trichlorophenoxyacetic acid (2, 4, 5-T) could be used to overcome recalcitrance to somatic embryogenesis in cocoa.

Preferential expression of somatic embryogenesis in five elite genotypes of Theobroma cacao (L.) associated with explant type and protocols used

“…According to their reports, T. cacao flower bud explants yield high percentages of callus during cocoa somatic embryogenesis. Our results show a success that could also be explained by the nutrient composition of the culture medium and the effect of the hormonal balance used (Daouda et al, 2019;Osorio Montoya et al, 2022). The hormonal balance (2,4-D / TDZ) used in the culture medium is the best condition to obtain callus (Boutchouang et al, 2016).…”

“…Indeed, there is an early production of embryos by the C1, C9, C14, and C16 genotypes between the 2nd and 4th weeks in the EDM medium, and a late production of embryos by the C8 genotype between the 12 and 16 th weeks in the EDM medium. These results may be linked to the plant gene, which has an immediate impact on the recalcitrance of certain tissues and genotypes concerning their totipotency (Daouda et al, 2019). Prolonged subculture on the EDM medium of T. cacao is, therefore, necessary to overcome recalcitrance or improve the response of certain genotypes.…”

Primary and Secondary Somatic Embryogenesis of Cacao: The Effect of Explant Types and Plant Growth Regulators

“…Some elite genotypes of cacao showed a low or an absence response to somatic embryogenesis induction (Daouda et al 2019). also reported that the frequency of PSE in nine Indonesian cacao genotypes is varied between 0-67%.…”

Response of the transcription factor BABY BOOM of Arabidopsis thaliana L. in the formation of embryogenic calluses of cocoa leaves (Theobroma cacao L.)

“…Recalcitrance of certain important fruit crops such as Theobroma cacao means a barrier in plant regeneration of plants using somatic embryogenesis, where the high composition of phenols inhibits this process. Furthermore, somatic embryogenesis is a genotype-dependent process that requires development and optimisation of new protocols to overcome this limitation (Pancaningtyas, 2015;Henao et al, 2018;Koné et al, 2019;Pérez-Caselles et al, 2021).…”