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In vitro corm formation and flowering and ex vitro acclimatization
During this period new axillary buds are formed. The axillary buds gradually form
their own corm at the base as conditions for growth becomes less suitable at the end
of flowering in September. During September and October the averaged daily
minimum temperatures are 6.3 ± 0.7°C and 8.2 ± 0.3°C and the averaged daily
maximum temperatures are 21.3 ± 0.7°C and 25.6 ± 0.4°C. The maximum
temperature of periods of vegetative growth and corm induction is close to 15°C and
the minimum and maximum temperatures are close to 10 and 20°C during periods of
senescence, when accumulated carbohydrates may be reallocated to the corm in the
natural habitat of R. sabulosa. Although such an explanation is plausible, the
interactions of factors that influences the climate of Namaqualand is very complex
and it is therefore a difficult topic (DESMET, 2007).
The corm production rate of various Gladiolus cultivars was also increased by a two
step bud-culture technique, involving short-term exposure to a medium with plant
growth regulators and subsequent withdrawal from plant growth regulators in a liquid
medium (SEN & SEN, 1995).
The specific temperature needed for carbohydrate accumulation for R. sabulosa,
compared to that of Tritonia gladiolaris may be explained by its very restricted
distribution compared to that of the widespread T. gladiolaris. An adaptation to
accumulate carbohydrates above a certain temperature and to induce corms below
this temperature would allow a species to spread to a variety of habitats where this
temperature is observed, whereas a specific carbohydrate accumulation temperature
range will limit the populations to an area with periods of this temperatures long
enough to accumulate sufficient carbohydrates to be able to survive the dry seasons
underground in a dormant state and to produce enough vegetative growth in the next
season for the accumulation of additional carbohydrates.
The fact that corms did not flower in vitro is probably because these plants need
much colder minimum temperatures (below 5°C) such as in their natural environment
for growth and development. The one corm of R. minutiflora which flowered in vitro at
20°C was perhaps a mutation.
Plantlets of Romulea species develop viable corms after 6 months, which can be
commercialized as propagation units. Corm formation speeds up the
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