Plant regeneration through somatic embryogenesis in three ethiopian <em>Coffea arabica</em> Lin. hybrids

Breeders at Jimma Agricultural Research Center (JARC), Ethiopia, developed three arabica coffee hybrids: Aba Buna, Ghawe and MCH2 that exhibited heterosis over their parents. However, their distribution to farmers had been a bottleneck. This work was carried out at the plant biotechnology laboratory of JARC, with the objective of regenerating these hybrids through somatic embryogenesis. Different combinations of NAA, IBA, Kinetin and Gibberelic acid were tested for callus formation and proliferation, somatic embryo induction, as well as embryo development and growth. In vitro rooted plantlets having 2 to 5 leaf pairs were transferred to acclimatization conditions in seedling trays filled with sterile soil and well decomposed coffee pulp (1:1). Best responding leaf explants for callus formation were those collected from the first and second nodes (top to bottom) of coffee seedlings; MS medium supplemented with 2,4-D (3 mg.l-1) and BA (3 mg.l-1) the best, with 95%, of which 45% were embryogenic. The highest callus fresh weight was recorded from Aba Buna (2.80 g/explant), followed by Ghawe (1.22 g/ explant) and MCH2 (0.47 g/explant). The highest number of heart-shaped somatic embryos per explants was obtained with NAA 0.1 mg.l-1 and Kinetin 0.1 mg.l-1. Culture medium containing a combination of NAA (0.1 mg.l-1) and Kinetin (0.5 mg.l-1) favored the highest number of total somatic embryos. The use of liquid media was beneficial for somatic embryo development. It also reduced the cost of plantlet production. Plants under acclimatization retained proper growth and sanitary conditions. Key words: callogenesis, embryo regeneration, plant conversion, plant growth regulators, somatic embryos Abbreviations: BA (6-benzyladenine); 2,4-D (2,4-dichlorophenoxyacetic acid); IBA (indole-3-butyric acid); MS (Murashige and Skoog); NAA (naphthaleneacetic acid), GA3 (Gibberellic acid), CV (Coefficient of variation), S.E (Standard error).