In comparison with the present study, Bormashenko et al. (2012)
used a RF discharge in air to treat wheat seeds, at a pressure of
6.7 × 10−2
Pa and power of 20W. The exposure time was quite short,
in the range 15 s to 2 min. For the longest treatment time used, the en-
ergy introduced in the plasma is comparable to that in the present ex-
periments (2.4 kJ). A very pronounced change in the wettability was
observed by Bormashenko et al. (2012): the contact angle decreased
from 115 ± 2° to zero. Surprisingly, the effect on water absorption
was less pronounced, with only a slight increase of water imbibition
for the plasma treated wheat seeds. In our experiments the decrease
in contact angle due to plasma treatment (92 ± 0.73° to 53 ± 0.85°)
was accompanied by a 10–15% rise in water absorption. Faster wetting
of the plasma treated wheat seeds as compared with the control ones
was also visually observed by Sera et al. (2010), but water imbibition
was not quantified. The seeds were treated in the afterglow of a micro-
wave discharge,with very high power (500W), at a pressure of 140 Pa.
It was found that the plasma treated seeds germinated faster, but
the germination rate was higher for the treated seeds only during
the first days, while after longer cultivation time no significant dif-
ference was observed. Significantly faster germination was also
reported in Bormashenko et al. (2012) during the first 12 h. In
our experiments the germination rate after four days had similar
values for the untreated and plasma treated seeds (95% and 98%,
respectively).