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6.4 DISCUSSION
In vitro corm formation and flowering and ex vitro acclimatization
Temperature is the major factor that affects storage organ morphogenesis
(ASCOUGH et al., 2009). Low temperature significantly increased corm formation in
R. minutiflora and R. sabulosa. The highest number of instances of multiple corm
formation for R. sabulosa was also observed at 10 and 15°C.
In a study by ASCOUGH et al. (2008) on Watsonia vanderspuyiae (in the same
subfamily, Ixioideae) the highest percentage corm induction was observed for shoots
placed at low temperatures. This study showed no significant difference between
corm induction percentages of shoots placed on MS media supplemented with
sucrose at 10 and 20 °C. Corm formation at low temperatures has been observed in
vitro for many genera in the Iridaceae (ASCOUGH et al., 2009). An exception to this
is Crinum macowanii, where storage organ formation occurs above 25 °C and is
inhibited at lower temperatures (SLABBERT et al., 1993). The fact that corm
induction was inhibited for R. minutiflora and R. sabulosa at 25 °C in this study
correlates with the results of Gladiolus spp., where corm induction was inhibited at
this temperature (TAN NHUT et al., 2004).
In this study the requirements for corm formation of R. leipoldtii is similar to that
determined in a study involving Crocus sativus corm formation (PLESSNER et al.,
1990). It was however shown by HOMES et al. (1987) that corm formation of Crocus
sativus also occurred at 30°C, a temperature that totally inhibits the corm formation of
R. minutiflora and R. sabulosa and that would probably inhibit the corm formation of
R. leipoldtii as it occurs in the same regions as R. minutiflora (Figure 2.1).
When PP3 and ABA were added to the medium on which R. minutiflora shoots were
placed, these shoots developed corms although they were placed at 25°C, a
temperature that totally inhibits corm formation when these retardants that reduce
leaf elongation and promote storage organ formation are not present. This effect of
PP3 has also been shown for Dierama and Gladiolus species (MADUBANYA, 2004;
STEINITZ & LILIEN-KIPNIS, 1989; ZIV, 1989; ZIV et al., 1998).
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