Propagation of IMC67 Plants, Universal Cacao (Theobroma Cacao L.) Rootstock via Somatic Embryogenesis

Abstract

One major problem with cacao crops is the variability of plantings obtained from seeds. This has led to considering somatic embryogenesis (SE), a means of obtaining stable clones with minimal somaclonal variation; however, achieving this has not been possible with many genotypes. In this work, we used IMC67 genotype (rootstock in the traditional grafting process) to evaluated various SE protocols; four culture media for induction and expression primary embryogenesis (PSE): induction medium (INDI), expression medium (INDIEXP), primary callus induction medium (PCG), and secondary callus growth medium (SCG), as well as two explants (petal and staminode). Different culture times for PSE (15, 25, 35, 45, 55, 65 days) and SSE (10, 20, 30, 40, 50, 70, 80 days) were evaluated in terms of callus formation, PSE, and SSE. For acclimation, seven substrates were evaluated for plantlet survival. One hundred percent callogenesis was achieved at 50 days with the staminode in INDI, and the most PSE per explant (8) in INDIexp was achieved at 45 days. Secondary somatic embryogenesis (SSE) obtained the most globular and cotyledonary embryos (30) at 30 days in callus multiplication (CM2). The embryos achieved conversion and development into plantlets in maturation medium (MM6). Embryogenic efficiency from explants was 11.7 for PSE, and 15.2 for SSE. Acclimation obtained a 42.1% survival rate in the 70% sand- 30% soil substrate. This work reports a complete regeneration protocol via somatic embryogenesis up to plantlet development in a nursey for the IMC67 rootstock genotype; contributing to standardizing a high-quality plant production system.

Keywords

• somatic embryo
• cacao
• grafting
• clonal propagation
• in vitro regeneration