Effect of Culture Medium Composition and Phenolic Markers on In vitro Conversion of Somatic Embryos into Plantlets in Pineapple (Ananas comosus L. var. Smooth Cayenne) Grown in Côte d’Ivoire

Abstract

Pineapple is a strategic crop in Côte d'Ivoire. However, its declining productivity requires the renewal of orchards using high-performance vitroplants. The aim of this study was to optimize the conversion of mature somatic embryos into plantlets, by evaluating the influence of culture medium composition and phenolic compounds. Six germination media (MIE1 to MIE6) composed of a combination of auxins (picloram or 2,4-D), cytokinins (BAP or kinetin) and amino acids (glycine, glutamine, casein hydrolysate) were tested for their effectiveness in inducing In vitro conversion. In addition, phenolic compounds present in embryos were identified and quantified by spectrophotometry and high-performance liquid chromatography (HPLC). The identified phenolic markers of germination were then added to recalcitrant media to assess their effect on conversion. Results showed that MIE2 (3 mg/L 2,4-D + 1000 mg/L glutamine) and MIE5 (3 mg/L 2,4-D + 2 mg/L glycine + 100 mg/L casein + 0.2 mg/L kinetin) media achieved the best germination rates (75.21% and 79.95%) and the highest mean numbers of germinated embryos (22.7 and 64, respectively). HPLC analysis revealed that resveratrol, trans-methoxycinnamic acid, astragalin, gallic acid, genistein, quercetin and naringenin were associated with In vitro germination. However, exogenous addition of these compounds did not improve germination and caused necrotic browning of the calli, suggesting that only endogenous metabolites promote germination. The MIE5 medium not only promoted the accumulation of these markers, but also stimulated the de novo biosynthesis of gallic acid, genistein, quercetin and naringenin. These results underline that the hormonal and mineral combination of the MIE5 medium is the most efficient for converting pineapple somatic embryos and offers new perspectives for the improvement of vitroplants production.