Viability, storage and ultrastructure analysis of Aechmea bicolor (Bromeliaceae) pollen grains, an endemic species to the Atlantic forest

Bromeliaceae is a large family, and many species are valued ornamentally for their bright colorful flowers. Pollen grain conservation is important for plant breeding and genetic resource conservation increasing the possibilities of crosses between allogamous species, and further hybrid production. The present study aimed to evaluate pollen conservation methodologies for Aechmea bicolor L.B.Sm. using different viability and germination tests and to characterize conservation effects in pollen morphology and ultrastructure. Pollen grains were collected from flowers at anthesis and both (flowers and pollen) were morphologically characterized. Preliminary studies were done to define the best germination medium and dehydration condition. Pollen samples were then subjected to storage under three conditions: freezer (-5 A degrees C), ultra-freezer (-80 A degrees C), or liquid nitrogen (-196 A degrees C), with or without dehydration, at different intervals. In vitro germination and pollen tube length were assessed at 1, 24 h, 8, 30, 180 and 365 days. Pollen grain morphology and ultrastructure were assessed at 24 h, 30 and 365 days. The experimental design was completely randomized in a 2 x 3 + 1 factorial design (2 dehydration conditions, 3 storage conditions, and 1 control). The plot was subdivided by storage time with plots defined by the factorial design, and subplots by storage time and their interaction with plot treatments. The best results were obtained with dehydration and storage in liquid nitrogen (-196 A degrees C) with regard to in vitro germination, pollen tube length, in vivo fertilization and other variables studied, including morphological and ultrastructural integrity. Fruits produced developed normally and produced viable seeds, with germination rates above 92 %.