Light can either stimulate or inhibit seed
germination. As expected, seeds in the
growth chamber that did not need to push
through the growth medium germinated
faster than covered seeds. In the third experiment,
our results showed that seeds flats
placed in the greenhouse were slower to
germinate than seeds that were grown in the
completely dark growth chambers. Evensen
and Loy (1978) had some similar results
working with seeds of a monogenic recessive
dwarf inbred line of watermelon. They foundthat GA3 increased the rate of germination,
but light decreased the rate of seed germination.
The authors suggested that this was the
result of lipid degradation promoted by GA3,
thus providing solutes necessary for seed
germination. Application of GA3 (500
mgL–1) to seeds that were incubated at
alternating temperatures (20/30 C for 16/8
h) in light did not enhance germination of
Echinacea angustifolia (Macchia et al.,
2001). Thus, the consistent warm, not hot,
temperatures in the growth chamber may
have aided germination. For Penstemon digitalis
cv. Husker Red, we hypothesize that the
effect of darkness, consistency of moisture,
and warm temperature together with GA3
soaks helped seeds to overcome endodormancy.
In conclusion, soaking seeds of Penstemon
digitalis cv. Husker Red in 1000 mgL–1
GA3 for 24 h increases the rate and number
of germinating seeds whether seeds are
grown in petri dishes in a dark, warm growth
chamber, or a soilless mix with a clear plastic
dome over the flat in a warm greenhouse.
Soaking seeds in either 500 or 1000 mgL–1
GA3 and then sowing them in a soilless mix
either lightly covered or on the top of the mix
in a flat covered with a plastic dome in the
greenhouse will also increase the number and
rate of germinating seeds.