Avaliação da viabilidade das sementes e amplitude térmica de germinação de duas espécies arbóreas amazônicas (Carapa guianensis Aubl. e Carapa surinamensis Miq. – Meliaceae)

Abstract

The species of the Amazon region named andiroba (Carapa guianensis Aubl and Carapa surinamensis Miq) are trees of multiple use, extensively exploited due to their timber and the seed oil, used in phytopharmaceutical products and cosmetics. The seeds are recalcitrant and have slow germination, characteristics which difficult plant propagation and seed trade. The present study aimed to determine the cardinal temperatures of seed germination on several germination criteria observable during initial development, to verify a possible retardation of the germination process by the mechanical resistance of the seed coat and to develop a protocol on tetrazolium staining of the viable seeds, for future physiological studies or seed quality assessment. The dissertation is divided into three chapters: the first and second deal with temperature effects (10 - 40° C) on seed germination and initial plant development of C. surinamensis and C. guianensis, respectively. Here data collected during this master thesis were accomplished with previous results for consolidation. All seeds were collected in forest plantations in the North of Manaus, owned by the Brazilian National Institute for Amazon Research. Seed germination tests of C. surinamensis were done with intact seeds and after removal of the seed coat. Tests of C. guianensis were only done with seeds without seed coat. Germination tests were conducted in chambers with constant temperature (± 1° C) and photoperiod of 12 h. Germination was assessed with three germination criteria (plant development stages): (1) radicle length ≥ 0.5 cm; (2) epicotyl length ≥ 1 cm and (3) epicotyl length ≥ 5 cm. For C. surinamensis all three germination criteria were assessed and for C. guianensis the first and third. The experimental design was completely randomized with four replicates of 20 seeds at each temperature. Data were analyzed for distinct collections by joint variance analysis and simple ANOVA; the comparison of the means at 5% was done by Tukey test. The seeds of C. surinamensis had between 15 and 35° C a high germination percentage. The minimum germination temperature of all three criteria laid between 10 and 15° C. For the radicle the maximum temperature was above 40 ºC, and for both epicotyl lengths between 35 and 40 °C. The germination speed indicated the temperature of 30 ºC as optimum for all criteria. Seed coat removal reduced the time period for radicle protrusion, at the optimum temperature, from 44 to 23 days. The seeds of C. guianensis had a high germination percentage and no significant difference between 15 and 30° C for the radicle protrusion, however the elongation of the epicotyl was restricted to temperatures between 25 and 30° C. Minimum temperatures were similar to those of C. surinamensis and the maximum temperature was between 35 and 40° C for both germination criteria. An optimum temperature of 30 °C was suggested by the germination speed index, for two seed collections from different years. However the results should be confirmed. In the third chapter a protocol for tetrazolium staining was elaborated and validated with germination tests for both species (C.guianensis and C. surinamensis). In a first step the staining intensity was evaluated during a period of up to six hours with different concentrations of tetrazolium (0.05; 0.10; 0.25 and 0.50) at three temperatures (25, 30, 35° C). Comparing good staining results with costs and working time, the concentration of 0.1% at 30° C during three hours was appropriate for both species. Seed preparing was standardized to cut the tiny embryonic axis and expose it to the solution. In a second step the protocol was validated with seeds of different qualities (between 0 – 90% germination capacity), obtained by controlled drying of the recalcitrant seeds over a fan. A germination test was conducted parallel to the viability staining with the same number of seeds. Based on the coloration patterns, the image of the stained seed were classified in four levels of viability. These first classification was compared and validated with the results of two germination criteria (root ≥ 0,5 cm and normal seedling). The proposed protocol of tetrazolium staining was efficient in assessing seed viability of both species. This study determined for the first time the cardinal temperatures for seed germination of andiroba and compared thermal sensitivity of three stages of initial development of C. guianensis and C. surinamensis. The two species had differences in their temperature response. Seed viability of the recalcitrant seeds of andiroba can be assessed in a few hours with the tetrazolium protocol. The method may be usefull in physiological or morphological studies of this or other species of the genus Carapa.