MATURATION AND GERMINATION OF SOMATIC EMBRYOS OF Coffea arabica CV. COLOMBIA

Abstract

The Colombia coffee variety (Coffea arabica L.) has high resistance to rust and good production characteristics and cup quality. Several protocols have been developed for the propagation of coffee by somatic embryogenesis; however, the rate of maturation, germination and conversion is low. The objective of this study was to determine the effect of growth regulators and osmotic agents on the maturation and germination of coffee somatic embryos and to evaluate, under ex vitro conditions, the physiological characteristics of the regenerated plants. For maturation, globular and early torpedo embryos were cultured on a Yasuda et al. (1985) medium with different concentrations of abscisic acid (ABA) (2-4 mg L^-1), salicylic acid (SA) (1.38 g L^-1), gibberellic acid (GA3) (0.7-1.0 mg L^-1), indoleacetic acid (IAA) (0.3-0.5 mg L^-1), polyethylene glycol 8000 (PEG 8000) (50-75 g L^-1) or sucrose (50-80 g L^-1). For germination, the mature embryos were transferred into a medium with 0.25 mg L-1 of IAA and 0.25 mg L^-1 of 6-benzylaminopurine (BAP). The plants were acclimatized and grown on perlite:peat:volcanic rock (1:1:1) or peat:volcanic rock (2:1) under greenhouse conditions. The maximum value of maturation and germination of globular embryos was observed when 50 g L^-1 of sucrose were added to the medium (81.7 and 53.9 %, respectively). For early torpedo embryos, the highest percentage of maturation was recorded with 80 g L^-1 of sucrose (19.2 %) or a combination of 1.0 mg L^-1 GA3 and 0.5 mg L^-1 of IAA (45.0 %); however, the germination percentages were not significantly different from the control. The osmotic potential of the embryos was not directly related to their degree of maturity. All the plants grown on the substrate mixtures survived and were morphologically and physiologically normal under ex vitro conditions.