MORPHOLOGICAL VARIATION OF Taxus globosa Schltdl. SEEDS COLLECTED FROM TWO GEOGRAPHICAL REGIONS OF MÉXICO

Abstract

Taxus globosa Schltdl. is the only species of the genus Taxus that grows in Mexico and is protected by the Mexican government. Its bark and leaves contain taxol, a high value compound used as a cancer drug. Natural regeneration of Taxus globosa is by seeds which germinate scarcely and present dormancy. The present study was done in order to determine the morphological variation of Taxus globosa seeds and to learn if seed dormancy is caused by physical factors. Collected seeds from northern (Nuevo León) and central (Hidalgo and Queretaro) México were used to measure seed dimensions (length, width, area, perimeter and embryo/megagametophyte ratio) by image analysis, in addition to volumetric weight, and weight of 1000 seeds. To evaluate the physical characteristics of the seed coat, a scarification test with sulfuric acid for 5, 10, 15, 20, 25 and 30 min was done followed a tetrazolium viability test. Seed coat hardness and imbibition rate were also measured. There were differences in seed size betwee geographical origins(28 % bigger in the northern region). The embryo/megagametophyte ratio of was only 4 % in seeds from the northern region and 3 % in the central region. Seeds of both regions only supported 5 min immersed in H₂SO₄, and seeds from the northern region were harder (1.29 vs. 0.86 kg cm^-2). Seeds from the northern absorbed more water than those from the central region. Taxus globosa seeds do not need scarification to soften the seed coat, and the possible cause of seed dormancy appears to be their undeveloped embryos.