Aspectos reprodutivos no complexo poliploide Lippia alba (Mill) N.E. Br

Abstract

Polyploidy is considered one of the main mechanisms related to evolution and speciation in plants and is often related to the evolutionary success of different species. The genome duplication contributes to increase the genomic and phenotypic plasticity, favoring the adaptation and establishment of plants in the most diverse environments. The Lippia alba (Verbenaceae) species is known by several popular names such as "erva cidreira”, “falsa melissa” and “chá de tabuleiro”, having medicinal importance due to the presence of different chemical components in its essential oils. Despite many studies about its properties, very little is known about the biology of the species. Recent studies have revealed five chromosome numbers for L. alba, which are: 2n= 30, 38, 45, 60 and 90, making the species a particular model for studies of tropical origin of poliploidy. In the present work, information was gathered to contribute to the understand of the reproduction and genetic variation of the species. In order to identify the possible presence of unreduced gametes in the species, the pollen morphometry of 29 diploid individuals was analyzed, as well as the amount of DNA from diploid and tetraploid seeds. The germination rate of open and controlled pollination seeds in individuals of different ploidies of the species, as well as the amount of DNA of the germinated progeny from these individuals were studied. In addition, pollen germination of individuals with different chromosome numbers was also evaluated, and the artificial crossing between individuals of different chromosomal numbers was performed. Among the results obtained, it was possible to infer that Lippia alba species presents a preference for allogamy, the individuals tend to cross among themselves, and it was also possible to observe a tendency of diploid individuals to produce diploid progeny, with few exceptions. The pollen measurement provided us with evidence of a large variation within the same cytotype. Pollen measurements above average suggest that gametic non-reduction is the main mechanism of polyploid formation in the species. The differentiated reproductive behavior between diploid and polyploid individuals Lippia alba complex is noteworthy. Seed germination and progeny analysis allow us to infer that the species performs the process of self-fertilization but that some individuals may present some degree of self-incompatibility. The average pollen germination rate among diploid individuals was significantly higher than among polyploids. The emergence of aneuploids highlights the need to investigate in more detail their role in the formation of the complex.