The present investigation was conducted at the nursery
of Hort. Res. Inst., ARC, Giza, Egypt during 2013 and 2014 seasons to
study the effect of different pre-sowing seed treatments, viz., untreated
seeds (control), soaking in tap water for 24 h at room temperature,
soaking in previously boiling water for 24 h at room temperature,
boil/cold water dipping (thermal shock treatment), soaking in
concentrated H2SO4 for either 2 or 4 min (chemical scarification) and
abration testa with rough emery paper (mechanical scarification) on
seed germination and seedling growth of Powder Puff (Calliandra
haematocephala Hassk.) shrub.
The obtained results indicated that most of the used treatments
improved germination % and velocity, mean germination rate,
germination rate and vigour indices, seed viability and epicotyl length
of germinated seeds, as well as seedling growth with various
significant differences compared to control in the two seasons, except
for thermal shock treatment which completely failed to induce
germination. It was also noticed that seed viability markedly decreased
as a result of mechanical scarification with emery paper to reach the
least values at all. Content of total indoles and phenols in the untreated
seeds was stable as they were not subjected to any treatment, but in
treated seeds, it was increased where total indoles reached the
maximum by soaking in either concentrated H2SO4 or boiling water,
while these two treatments caused a nil increment in seed content of
total phenols relative to control and other pre-sowing treatments. In
addition, content of chlorophyll a, b, carotenoids and total soluble
sugars in the leaves of seedlings raised from the treated seeds was
greatly increased, especially by chemical and thermal scarification.
Generally, the mastery in all previous measurements was for soaking
in either concentrated H2SO4 for only 2 min or boiling water for 24 h,
as they recorded the utmost high means in the majority of measured
traits in both seasons.
Hence, it is recommended to treat seeds of Calliandra
haematocephala pre-sowing by soaking in either previously boiling
water for 24 h. or in concentrated H2SO4 for only 2 min. to obtain the
best germination and seedling growth.