Reproductive systems and hybridization of Lymania species (Bromeliaceae) endemic to Northeast Brazil threatened with extinction

Abstract

Reproductive systems among the Bromeliaceae family are very diverse at the species level, including allogamous, autogamous, cleistogamous, agamospermic or mixed plants. Hybridization allows the creation of new genotypes with different combinations of shapes and colors to meet the ornamental plant market's demand for novelty. Knowing the reproductive strategies of the species makes it possible to obtain these new materials with ornamental potential, in addition to being essential to define better conservation strategies. Little is known about the reproductive biology of Lymania species. In addition, at least 60% of these species are on the Brazilian National List of Species Threatened with Extinction. The purpose of this study was to identify the reproductive systems, the possible interspecific hybridizations, and the possible reproductive barriers of nine Lymania species based on the germination of pollen grains and the corresponding growth of the pollen tube in the pistil by using fluorescence microscopy with ultraviolet filtering. Natural and controlled pollinations of the nine species were carried out. The reproductive strategy was defined according to the autogamy index (AI), self-incompatibility index (SII), and reproductive efficiency index (REI). All species were self-incompatible except for L. smithii, which was autogamous. Agamospermy was not observed in any of the studied species. Forty-one hybridization combinations between species were performed, resulting in a 54% success rate, with incongruity in only 12 combinations. The main incongruence phenomena identified after interspecific crosses were: poor germination of pollen grains on the stigma surface; inhibition of pollen tube growth along the style; coiling of pollen tubes along the style; pollen tubes inside the ovary but without penetration into the micropyle; and reticulate deposition of callose in the pollen tube, among others. We suggest that self-incompatibility of the species is gametophytic, preventing self-fertilization. Results showed that it is possible to perform hybridization with some species. However, morphological, genetic, and molecular studies are needed to confirm the potential of these species. Seeds generated in the different reproductive systems, as well as in the hybridizations, had germination rates above 94%. The results presented here make important contributions to the conservation of species, seed generation, and hybridization of Bromeliaceae.