2.3 Experiment under different light intensities and
wavelengths for germination
In the implementation of the experiment, seeds of M. zehntneriwere immersed in distilled water for 10 minutes, according to results
previously obtained in our laboratory (Magnani and Cardoso, 2022).
Later, using a laminar flow cabinet, seeds were subjected to asepsis,
aiming at the reduction or even elimination of microorganisms. This was
performed in 15 mL Falcon® tubes and seeds were
immersed in 70% alcohol (v/v) for one minute and then in a solution
containing 30% sodium hypochlorite (2.0-2.5% active chlorine) added
with 5 drops of neutral detergent for every 100 mL solution, for 15
minutes under constant stirring, followed by three washes in previously
autoclaved deionized water.
In the last rinse, approximately 2 mL deionized water with pH adjusted
to 5.8 was kept as a vehicle for the inoculation of seeds on the plates.
All seeds, 20 per plate, were sown in clear, smooth, and sterile
polystyrene Petri dishes, previously filled with two layers of filter
paper saturated with 5 mL sterile deionized water at pH 5.8 per dish.
Subsequently, dishes containing the seeds were arranged under different
intensities and wavelengths given by LED lamps and cultivated in a grow
room, as follows: blue LED (Phillips Greenpower LED Research Module
Blue, ⁓440 nm), red LED ( Phillips Greenpower LED module HF deep red,
⁓660 nm), blue(1)/red(1.5) LED (LabPar, with wavelength peaks at 447 nm,
range 420-470 nm - blue and 667 nm, range 625-680 nm – red) and, as a
white LED control (Ourolux®, Brazil), with peaks at
440-450 nm (blue), 540-550 nm (green) and 610-620 nm (red).
The photosynthetically photon flux densities (PPFD) were measured using
a PPFD Quantum meter, Apogee Instruments®, Model
SQ-520 (USA) of each light source and were obtained by placing the
dishes in equidistant proportions from the LEDs (Table 1).
The experiment was a completely randomized design, in a 3 x 4 factorial
(PPFD x wavelength) with four replications composed of individual Petri
dishes containing 20 seeds each.
As a complementary experiment, darkness influence on the germination ofM. zehntneri seeds was tested, with seeds kept protected from
light, in a grow room, for three periods of 10, 20, and 30 days of
darkness. In this case, seeds under germination conditions were only
exposed to a light source after remaining in the respective periods in
the dark. For this, the same procedure of preparation and inoculation of
seeds was carried out and the experimental design was completely
randomized.
Petri dishes from both experiments were sealed with a transparent PVC
film and kept in a grow room at 26 ± 1º C, and a photoperiod of 14
hours. Germination was evaluated twice a week; seeds were considered
germinated when hypocotyl-radicle protrusion was equal to or greater
than 0.1 cm. In the end, the Germination Percentage (G%), Average
Germination Speed (AGS), and Germination Speed Index (GSI) were
calculated.