Variabilidade genética entre e dentro de subpopulações de ipê-roxo Handroanthus heptaphyllus (Vell.) Mattos e seu sistema reprodutivo

Abstract

Handroanthus heptaphyllus (Vell.) Mattos, sinonímia Tabebuia heptaphylla (Velloso) Toledo, known as ipê-roxo, belongs to the Family Bignoniaceae. It is a very important Brazilian forest tree species because of its beautiful flowers, excellent wood quality, and medicinal properties. Its flowers are usually visited by animals, like bees, birds, bats, etc, for feeding and for pollination purposes. The species has also been used in programs of reforestation of degraded areas, landscaping, and restoration. The ipê-roxo is widespread throughout Brazil, from Bahia State to Rio Grande do Sul, Minas Gerais, Mato Grosso do Sul, Santa Catarina, and São Paulo States, from 13oS (BA) to 30oS (RS) latitudes. The research has as objectives to study the genetic diversity within and between subpopulations of H. heptaphyllus by microsatellite molecular markers and to understand its mating system. We collected seeds of 30 trees, through the Botucatu region, Brazil, mostly from the Lageado Experimental Station, São Paulo State University (UNESP) – Botucatu. The seeds were sown in a nursery and the leaves were collected, to extract the DNA, and analyzed through polyacrilamide gels. In a total of eight polymorphic microsatellite loci were analyzed that varied from six alleles (TAU22 locus) to 14 alleles (TAU12, TAU30, and TAU31 loci). The expected heterozygosity ˆ mean ( H e ) for the six subpopulations was 0.7318, the observed heterozygosity mean ˆ ( H o ) was 0.6183, and the average of fixation index (f) between pairs of the six population varied from -0,082 (subpopulation 4) to 0.255 (subpopulation 3), with an average of 0.152. The results of the studied subpopulations have shown acceptable levels of fixation index, presenting an average of 15.2%, therefore, the subpopulation 4 has shown a higher amount of heterozygous than expected. The total genetic diversity ( f IT ) for the six subpopulations was 0.2229 and between subpopulations ( f ST ) was ˆ 0.00538, and the diversity within subpopulations ( f IS ) was 0.1787. The conclusion is that most genetic diversity is within subpopulations and to collect germplasm a bigger sample into the subpopulations, and smaller samples of subpopulations will be interesting. It would be enough to represent the species. The multilocus outcrossing rate ^ ( t m) was of 0.978, meaning that the total of outcrossing, that can be among relative ^ individuals or not. The singlelocus outcrossing rate ( t s) was 0.721, meaning that most ^ ^ outcrossing has occurred among non-relative trees than among relative ones ( t m – t s = ^ ^ 0,257). From inbred crossings 0,022 ( s =1 - t m) was because of selfing. Therefore, we can conclude that H. heptaphyllus is alogamous with low tolerance of selfing. The study of subpopulations has sufficient genetic diversity to support genetic breeding programs and germplasm preservation programs.