Diversidade genética e estabelecimento de protocolo para micropropagação de Tectona grandis

Abstract

As breeding strategy, "in vitro'' propagation allows obtaining a large number of plantlets in a short period of time, and studies on genetic diversity also should be practiced in the population to be enhanced by the use of molecular markers. The aim of this study was to develop a protocol for the establishment "in vitro'' of teak explants, as well to assess the genetic diversity of accessions by means of ISSR and RAPD molecular markers Apical meristems and lateral buds were collected from teak plant with 1.5, 2.0, 2.5 and 3.0 years old. The explants were subjected to cleaning with sterile water and neutral detergent, followed by cleaning in 2.5% sodium hypochlorite. After the sterilization, the lateral buds and apical meristems were removed with the aid of a scalpel and placed in vials containing MS medium, supplemented and placed in a dark chamber for ten days, later they were transferred to the culture room in the presence of light. After thirty days the explants were evaluated as for percentage of survival. After selecting the type and age of the explants, apical meristems of 2.5 years old were cultivated in MS medium with 6-BAP (1.25, 1,75, 2.25 and 275 ml. L) and Kinetin 1.0, 1.5, 2.0 and 2.5 ml.L.The interval of subculture was every 30 days. The evaluated characteristics were: shoots length, leaf number, size and presence of callus. The experimental design was completely randomized. The data were subjected to analysis of variance. For works analyzing the genetic diversity, genotypes were collected from two commercial plantations of teak in the North of Minas Gerais. For amplification 10 RAPD primers and 11 ISSR primers were used. A total of 71 and 36 polymorphic loci was generated respectively, and average heterozygosity of 0.75 with RAPD and 0.57 with ISSR and genetic distance of 0.27 and 0.15 respectively. Despite the high average heterozygosity expected, it was observed a low genetic distance between individuals evaluated. By analysis of dendrogram obtained with the Jaccard index, it was observed the formation of five groups using the RAPD primer. Two groups with one genotype each one, another group with 4 genotypes, another one with 26 genotypes and the fifth with 32 genotypes). Eight groups were generated using the ISSR primers (Group 1 and II with one genotype each one, Group III with five genotypes; Group IV with four genotypes; Group V with 1 genotype; Group VI with seven genotypes; Group VII with twelve genotypes and group VIII with 20 genotypes). It was noticed that the S-27 accession was further one using the RAPD and the S 44 accession using the ISSR. The co-phonetic value calculated for RAPD was 0.93 and 0.71 for ISSR reflecting a good agreement with the values of genetic similarity. The Most suitable type of explant for micropropagation of teak is the apical one and the age ranging from one and a half to two and a half years. The growth regulators used in this work were not effective for the multiplication of teak. The RAPD and ISSR primers are effective for conducting studies on genetic diversity in teak and the evaluated individuals show low genetic diversity among themselves.