Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Plant Sciences, Horticulture, Agriculture, Bromeliaceae, pollen germination, pollentube growth, prefertilization barrier, post-fertilization barrier, POLLEN, STIGMA, INCONGRUITY, 0607 Plant Biology, 0706 Horticultural Production, Plant Biology & Botany, 3008 Horticultural production, 3108 Plant biology

Abstract:

Bromeliaceae are tropical ornamentals with a variety of colours and inflorescence shapes. To remain the interest of the public, breeders create new cultivars using interspecific and intergeneric hand-pollinations. In our breeding studies, 4 genera were used: Aechmea (2 species), Guzmania (3 species), Tillandsia (1 species) and Vriesea (3 species). In preparation of crossing experiments, two important flower characteristics were studied: pollen quality and stigma receptivity. Pollen germination of different flower stages was determined by an in vitro germination test. All species, except two of the Guzmania species, possessed viable pollen and germination was always highest at anthesis. Stigma receptivity was studied by pollinating flowers before, at and after anthesis. Pollen germination and pollentube growth on stigma were visualised with fluorescence microscopy (aniline blue staining). All species showed optimal stigma receptivity and ovule penetration at anthesis. Interspecific and intergeneric hand-pollinations were performed with pollen and stigma at anthesis stage. Pollen germination on stigma, pollentube growth in style and ovary and fertilization of ovules was evaluated using fluorescence microscopy. Five species were self-compatible, making emasculation necessary. Half of the interspecific and all of the intergeneric crosses were classified as incongruent because no ovules were fertilised (prefertilization barriers) or no seedlings developed (postfertilization barriers). Prefertilization barriers occurred in the style, mostly the lower part of the style. Only in crosses with the self-incompatible Aechmea species as mother or the extremely short-styled Tillandsia species as father, pollentube growth stopped in the upper part of the style. To understand more about these style barriers, the morphology of the pistil was studied. Styles of all species consisted of a hollow channel, covered with protein-rich cells. These 'feeder'-cells also appeared on the placenta and the ovule funiculus. In this way, pollen tubes could be guided towards the micropyles. Further, Ca-oxalate and starch grains were observed in the style.