Vol. 8, Issue 2 (2020)
In the cocoa tree (Theobroma cacao L.), certain elite genotypes have shown in standard study conditions an absence or a very low response to the induction of somatic embryos. This is the case of the recalcitrant genotypes C8 and C15, partially recalcitrant genotypes C14 and C16. This study aims to improve the production of somatic embryos of recalcitrant genotypes. Staminodes and petals excised from the immature buds of the five genotypes C1, C8, C14, C15 and C16 were used as plant material. The C1 genotype is embryogenic under standard conditions. These floral explants were cultured on different media containing different type and concentration of mineral salts such as potassium sulphate (K2SO4) at concentrations 18, 27, 36 and 45 mM and magnesium sulphate (MgSO4) whose concentrations used are 5, 10, 15 and 20 mM. Callus induction was obtained in the five (05) genotypes at percentages ranging from 50 to 100% with staminodes and from 61 to 100% with petals on all media. The transfer of the callogenic explants on the developmental medium allowed the induction of embryogenic callus and somatic embryos after 84 days only with petal explants. The percentage of embryogenic callus (PEC) and the number of somatic embryo (NSE) obtained with different concentrations of mineral salts ranged from 0 to 42.63% and from 0 to 23.53 respectively. The non-recalcitrant genotype C1 performed well on all media. The most important PEC and NSE were obtained with two mineral salts concentrations, 27 mM K2SO4 and 15 mM MgSO4 for all genotypes. The use of 27 mM K2SO4 give for C1: 41.53% and 21.76%, for C8:35.50% and 19.10, for C14: 39.03% and 19.53, for C15: 40.50% and 20.70 and for C16; 39.50% and 19.96 of PEC and NSE respectively. The use of 15 mM MgSO4 give for genotype C1: 42.63% and 23.53), for C8: 36.63% and 19.15, for C14: 40.68% and 20.08, for C15; 40, 81% and 20.10 and for C16: 40.01% and 20.98. Potassium sulphate (K2SO4) at 27 and magnesium sulphate (MgSO4) at 15 mM are the concentrations of the most suitable mineral salts to overcome recalcitrance of cocoa genotypes.
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