Caracterização Biométrica das sementes, germinação e desenvolvimento in vitro, e aclimatização de brassavola martiana lindl. (orchidaceae)

Abstract

Brassavola martiana is an epiphytic orchid species appreciated by collectors due to the beauty of its flowers. Because of the decrease of its population in natural habitats caused by several anthropic actions, studies related to the germination and development of this species using in vitro techniques become highly relevant. This investigation aimed to characterize the biometry of seeds, to evaluate the influence of their age on the germination process, to assess the effects of different temperatures on the in vitro development of plants, and to establish an effective protocol for the initial acclimatization of plants originated from in vitro cultures. For the biometric characterization, seeds were photographed with an optical microscope and had their length and width measured by the Anati Quanti program. In order to evaluate the influence of the age of seeds on the germination process, fruits from self-and cross-fertilization were used. Seeds aged 60, 90, 120, 150, 180, 210, 240, 270 and 300 days after pollination were inoculated in half-strength Murashige and Skook (1962) culture medium and kept in a growth room for subsequent evaluation of their germination rates. To verify the influence of temperature on the in vitro development of the species, glass jars containing seedlings of B. martiana were kept in growth chambers adjusted to temperatures of 25, 30 and 35oC. The results were evaluated after 120 days of cultivation based on the variables: number of shoots and roots formed per explant, length of the largest shoot and root. The acclimatization process was divided into two phases. Phase 1 consisted of removing the plants from the culture medium and planting them in plastic containers containing different proportions of two combinations of solid substrates (Bioplant + Sphagnum and Ouro Negro + Bark of Pinus) in two stages. In phase 2, the surviving plants from phase 1 were transferred to the nursery with 75% retention of solar radiation. The evaluation was carried out based on the variables: survival percentage, plant height, number of leaves and roots and length of the largest root. The biometric study revealed that the seeds of B. martiana showed a great variation in their dimensions with averages of 212.67 m in length and 52.33 m in width. The results regarding the effect of seed age on the germination process showed that seeds up to 300 days old, from both self- and cross-fertilization, did not germinate. In terms of temperature, 25 °C was the most suitable for the in vitro development of the species. Concerning the first phase of acclimatization, the best results were obtained with Bioplant + Sphagnum and Ouro Negro + Bark of Pinus both in the proportion of 1:1. For phase 2, the best results were obtained with the substrates Ouro Negro and Bark of Pinus also in the proportion of 1:1. In summary, it was possible to carry out the biometric description of B. martiana seeds, to determine an adequate temperature for plant development in vitro, as well as to develop an initial acclimatization protocol for B. martiana.