Induction of somatic embryogenesis occurred only in
the nodular and compact callus by gradually decreasing
the concentration of 2,4-D and NAA (1 mg/l) in the
medium, with a corresponding increase in BA concentration
(2.5 mg/l). Complete elimination of 2,4-D and NAA
from the medium resulted in 78% somatic embryo induction.
In the control, where only the MS medium without
PGRs was employed, up to 40% callus lumps showed
greening at the apices of the protuberances, but these did
not grow into plantlets despite continuous culturing on
the same medium. Alternatively, an increase in BA concentration
(up to 2.5 mg/l) and incubation of cultures
under diffuse light (5 mmol m
–2
s
–1
) resulted in prominently
visible, ivory-white embryoids which turned
greenish within 21 days, and upon transfer to the maturation
medium (C2), formed plantlets. Incorporation of GA3
(0.5 mg/l) and IAA (1 mg/l) into the medium did not influence
embryoid formation, except that continuous presence
of these PGRs resulted in the ultimate browning of
callus lumps within 41 days after initial greening. Use of
gelrite and activated charcoal did not help in the induction
of embryogenesis. Occasionally, albino plantlets
(Figure 1 e, right) and floral buds with viable pollen
grains were also induced in the culture vessel on the
same medium