Effect of plant growth regulators on in vitro germination of coffee zygotic embryos
Coffee propagation is performed by seeding. However, germination in coffee seed is slow and uneven. Indeed, the production of plants in field is affected by environmental factors, which retards the germination rates and, in consequence, the number of plants obtained. Plant tissue culture provides the possibility of applying different growing conditions, such as different types of media and using phytoregulators, to induce a response in order to shorten zygotic embryo germination times. Therefore, due to limited understanding of growing zygotic embryos of coffee, we evaluated the effect of certain plant growth regulators on zygotic embryo germination of Coffea arabica. To study germination times, we evaluated the effects of culture media with incubation either at photoperiod or darkness and with certain plant growth regulators [gibberellic acid (GA), abscisic acid (ABA), indole-3-butyric acid (IBA), naphthalene acetic acid (NAA), kinetin (KIN) and salicylic acid (SA), at concentrations of 0.1, 1, and 10 mg l-1 each]. Zygotic embryos were cultured on Murashige and Skoog (MS), and Gamborg media at different concentrations (1/1, ½, and ¼ of its ionic strength) under conditions of darkness and photoperiod. Germination times of zygotic embryos cultured in MS medium had a mean of 5.1 days, whereas zygotic embryos cultured in B5 medium germinated with a mean of 7.5 days. Among the plant growth regulators used, gibberellic acid at 0.1 mg l-1 proved to be the most efficient in germinating zygotic embryos, with 100% germination reached by the 5th day. Germination time of zygotic embryos was 12 days when ABA at 0.1 mg l-1 was used; however, ABA inhibited germination of embryos when it was used at concentrations of 1.0 and 10 mg l-1 since only 10% germination occurred. Regarding the germination times of zygotic embryos of coffee, the priority order of efficiency was GA > KIN > SA > IBA > NAA > ABA. Also, with the exception of SA, concentrations higher than 0.1 mg l-1 increased the zygotic embryo germination rates.
Key words: Zygotic embryos, coffee, germination, phytohormones.