The morphological variability within a population of coffee somatic embryos produced in a bioreactor affects the regeneration and the development of plants in the nursery

A 1-liter bioreactor was used to obtain approximately 800 Coffea arabica somatic embryos, 86 percent of which reached the 'germinated' stage but with morphological heterogeneity. The population was subdivided into three categories according to cotyledon area: small, medium and large, that amounted to 32, 36 and 4.5 percent, respectively. The effect of embryo morphology on plantlet conversion after direct sowing in soil and on plant development in the nursery was investigated. Somatic embryos with large cotyledonshad only a 25 percent plantlet conversion rate, whereas somatic embryos with small to medium-sized cotyledons had conversion rates of 47 and 63 percent, respectively. The vigour of the aerial and root systems of regenerated plantlets at the end of the plant conversionstage was also affected as the embryos with small, medium and large cotyledon mostly regenerated small plantlets (0.5-1.5 cm), medium plantlets (1.5-2.5 cm) and large plantlets (2.5-5 cm), respectively. When transplanted in plastic bags, these 3 populations of plantlets exhibited distinct development rates. They had an initial slow growth phase, which was much longer for the small plantlets, followed by a rapid growth phase. After 40 weeks in the nursery, an analysis of the growth parameters of aerial and radical systems showed that the vigour of the plants was strongly related to the vigour of the plantlets transplanted. The heterogeneity of somatic embryos in the bioreactor affected both the plant conversion efficiency in soil and the plant growth in nursery, where it mainly resulted in retarded growth, primarily in plantlets derived from the somatic embryos with small cotyledons.