It was found that peptone, and silver nitrate at concentrations of 3 mg/l
and above affected the formation of multiple shoots on cultured shoot tips from
a rubber tree, reducing the average number of shoots per explant when
compared with the control medium, although the effect was only significant in
respect of the peptone supplemented medium. The formation of multiple shoots
was detected after 3 weeks of being cultured in SIM containing peptone.
Between 93 and 100% of the explants cultured in SIM supplemented with all
concentrations of peptone produced shoots without significant difference
between explants raised in media containing different concentrations of
peptone, in either the percentage in which multiple shoot formation occurred or
the number of shoots produced per explant (Table1) There was however a
significant difference between the number of shoots produced between the
control medium and the peptone-supplemented media. In addition, some shoots
were small and wilted after 4 weeks of being cultured (Fig. 1b).
The explants cultured in SIM supplemented with silver nitrate formed
multiple shoots at all concentrations. The number of shoots was approximately
three per explant and the number was not significantly different among the
different concentrations tested (Table 1), nor was there any significant
difference between the number of shoots produced in the control medium and
the silver nitrate-supplemented media, although in all instances the number was
less than that in the control medium . After being cultured for 4 weeks, the
shoots had dark green leaves and produced roots in a similar manner to shoots
cultured in the control medium consisting of unsupplemented SIM (Fig. 1a, c).
These findings suggest that silver nitrate plays a more significant role in
shoot formation than peptone. However, the optimum concentration noted in
this phase of the study was not actually optimal for producing the maximum
number of shoots, since the unsupplemented control medium resulted in the
production of the largest number of shoots. Therefore, a further experiment
was conducted to test lower concentrations of silver nitrate (0-2 mg/l) to
establish if they would result in an increase in the number of shoots. The results
showed that decreasing the concentration of silver nitrate to 1-2 mg/l produced
an average of 5 shoots per explant. However, there was no significant
difference among the concentrations tested (Table 2). The shoots cultured on
SIM containing silver nitrate were dark green and exhibited vigorous growth
(Fig. 1e, f) while those cultured on the control medium unsupplemneted with
silver nitrate were pale green and exhibited senescence of the leaves after 4