Enhanced aerobic respiration improves <Emphasis Type="Italic">in vitro</Emphasis> coconut embryo germination and culture

Summary Germination of coconut (Cocos nucifera L.) zygotic embryos was tested in liquid or solid medium. Percent germination was greater when embryos were cultured in solid medium, particularly when embryos were placed with their micropyle end facing upwards in relation to the vial orientation, independently of orientation in relation to gravity. This occurred because solid medium allowed embryos to be positioned with their micropyle end exposed to the ambient atmosphere of the vial. Germination of embryos facing upwards was suppressed when the ambient atmosphere was replaced with N₂ or when aerobic respiration inhibitors were added to the medium, whereas it was not suppressed when the atmosphere was replaced with a N₂/O₂ (50∶50, v/v) mixture, thus indicating that aerobic respiration is required for embryos to germinate. Germination in facing upwards mode also resulted in improved conversion and plantlet development. These improvements in recovery are important since they will help to avoid unintentional selection due to low in vitro germination and corresponding conversion of a population subset. These results set the basis for the improvement of current protocols for in vitro coconut embryo culture, allowing safe movement of germoplasm both in terms of phytosanitation and conservation of genetic diversity in a population of interest.