Pollen and Stigma Morphology, Pollen Viability and Stigma Receptivity of Wittmackia Species (Bromeliaceae) by Light, Fluorescence and Scanning Electron Microscopy.

The genus Wittmackia has 44 species distributed in two centers of diversity: the Brazilian clade and the Caribbean clade. The Brazilian clade includes 29 species, with geographic distribution concentrated in the Northeast of Brazil. This study reports the morphology, ultrastructure, pollen viability and stigma receptivity by different microscopy techniques of 23 species of the genus Wittmackia endemic to Brazil and occurring in Atlantic Forest areas. Pollen morphology was evaluated by scanning electron microscopy and light microscopy by the weak lactic acetolysis method. Histochemical tests were performed with Alexander's solution and fluorescein diacetate. For in vitro germination of pollen grains, two culture media were evaluated. Stigma receptivity was evaluated with hydrogen peroxide and α-naphthyl acetate. The Wittmackia genus presented biporate pollen grains, monads to tetrads, with oblate, suboblate or oblate-spheroidal shape, circular or elliptical scope, and heteropolar or sub-isopolar morphology. The stigmas are of the conduplicate-spiral type, with differences in color and size. In both histochemical tests, high viability was observed, mainly at anthesis, coinciding with in vitro germination. The species presented high enzymatic activity during receptivity, with a very strong positive response, mainly at anthesis. Studies of pollen morphology and viability provide important information for the conservation and genetic improvement of Wittmackia species, also assisting in the taxonomy of the genus and the reproductive success of future controlled crosses.