IN VITRO POLLINATION AND FERTILIZATION IN BROMELIACEAE

In breeding ornamentals hybridization is an important tool to create new cultivars. Bromeliads are known as (sub)tropical ornamentals with a great variety of forms and colors. To overcome fertilization barriers different in vitro pollination techniques are used. Placental pollination results in a low fertilization rate, because pollen tubes are not guided to the ovule micropyle. When a style with active growing pollen tubes is grafted to the ovules (‘placental grafted style pollination’) fertilization rate increases. A possible explanation was found in the absence of spermiogenesis in pollen tubes cultured on in vitro media. When pollen tubes grew through the style, division of the generative nucleus occurred in the first style part. Addition of amino acids to the nutrient medium improved spermiogenesis in Aechmea fasciata pollen tubes in vitro. Especially arginine (1 mM) and methionine (1 mM) had a positive effect, but ornithine (0.2 mM) was negative for the formation of sperm cells. After semi in vivo pollination the sperm cells were situated closer towards the active pollen tube tip than after in vitro pollen germination (201 versus 362 μm). Probably also after other pollen-pistil interactions that are built up during pollen tube growth are important for fertilization.

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