Aspectos da germinação e da conservação de sementes de espécies do gênero Tabebuia (Bignoniaceae)
Resumen
The genus Tabebuia in the family Bignoniaceae comprises
about 100 species, several of which have medicinal, ornamental, and timber value, in
addition to their environmental importance. These species produce large amounts of
seeds, with a short viability period under natural conditions. In the present research,
studies were developed on germination and conservation aspects of seeds in
species of the genus Tabebuia. Initially, substrates were evaluated to be used in
seed germination tests for the species T. aurea (Manso) Benth. & Hook., T.
impetiginosa (Mart.) Standl., T. ochracea (Cham.) Standl., T. roseo-alba (Ridl.)
Sand., and T. serratifolia (Vahl.) Nich. The following substrates were tested: on sand,
on vermiculite, on sand+vermiculite, on paper (two sheets of blotting paper) and
between sheets (two sheets of blotting paper under and one sheet over the seeds).
For T. impetiginosa seeds, these substrates are suitable for use in germination tests.
For the other species, the most suitable substrates were: on sand, on paper, and
between sheets for T. aurea; between sheets for T. ochracea and T. roseo-alba; and
on sand and between sheets for T. serratifolia. In another study we attempted to
identify a suitable condition to store T. roseo-alba and T. impetiginosa seeds, as well
as to evaluate methods to estimate alterations in the viability and vigor of those
seeds. Different groups of seeds were placed in clear plastic bags, Kraft paper bags,
and cans. The seeds were then stored for up to 300 days under laboratory,
refrigerator, and refrigerated chamber conditions. Seed water content, germination
percentage and velocity, and electric conductivity were determined at the onset of
storage and thereafter at every 60 days. The best T. roseo-alba and T. impetiginosa
seed conservation condition was obtained with cans maintained in the refrigerator. T.
impetiginosa seeds can also be kept in plastic bags, paper bags, or cans when
stored in refrigerated chamber. Seed vigor alterations in these species are initially
identified based on germination velocity. In the third study, we evaluated accelerated
aging effectiveness in detecting vigor variations in T. roseo-alba and T. impetiginosa
seeds. Seeds of these species were submitted to accelerated aging under
temperatures of 40 or 45ºC, for periods of 24, 48, 72, 96, 120, and 144 hours. After
those periods, germination and plantlet emergence tests were conducted, and field
emergence index values were calculated. We verified that accelerated aging is
effective to detect seed vigor variations in T. roseo-alba and T. impetiginosa. When
aging is conducted at 45°C, differences in viability and vigor occur first. Traits such
as germination percentage and velocity, plantlet emergence, and incorporated
biomass can be recommended as seed vigor indicators, using accelerated aging.
Under more drastic accelerated-aging conditions, no correspondence is observed
between data obtained in the field and in the laboratory.