P. dubium is a tree species native to the Brazilian semideciduous forest. A perennial tree
with an approximate height of 15-25m, it is included among the species considered to be in extinction.
It is often used as an ornamental tree in recomposition programs. Its wood is very durable and has
multiple uses. Due to the importance of studies involving forest species, the aim of this study was to
determine the temperature limits and the impact of thermal stress on the germination process and
dormancy release. Four replicates of 50 seeds were used for each treatment and germination was carried
out in sterilized Petri dishes covered with autoclaved filter paper moistened with Captan solution
(0,2%). The minimal temperature range for germination was 9-12°C, the maximal observed was 36-39°C,
while optimal temperature ranged from 27°C to 30°C. In spite of the addition of GA3 (20 or 40 ppm), the
minimal temperature limit was not extended, but the seed germination rate and percentage increased
significantly at 12°C. In regard to the germination rate, it was verified that it is temperature dependent
and the Arrhenius plot is not linear. The net variation of the activation enthalpy (∆Hn# ) of the germinative
process presented absolute values lower than 12 kcal/mol at optimal range (27-30°C). At temperatures
lower than 18C and higher than 33°C, the absolute values of ∆Hn# were above 30kcal/mol. Analysis
of relative frequency indicated that thermal communication between environment - embryo takes
place through temperature signals superimposed on random molecular collisions. P. dubium seeds may
be considered thermo-resistant, supporting exposures at 45°C or 90°C for 24, 48 and 72 hours, when
intact and not imbibed. The mechanical dormancy was released with application of thermal stress (45°C
- 24 or 48 hours). Thermal stress (90°C - 72 hours) killed intact, not imbibed seeds; while intact and
imbibed seeds died after exposure at 24, 48 and 72 hours at 90°C.