We have studied the effect of various in-vitro conditions on dormancy of bulblets generated on scale explants of Lilium speciosum Thunb. cv. 'Rubrum' nr. 10. The bulblets were harvested after 11 weeks of culture. Dormancy was measured by determining the percent emergence in soil of viable, non-cold-treated bulblets.
Delvallee, I., Paffen, A. andde Klerk, G.-J. 1990. The development of dormancy in bulblets of Lilium speciosum generated in vitro. IL The effect of temperature. Upon harvest, lily {Lilium speciosum Thunb. cv. Rubrum) bulblets generated in vitro under standard conditions (11 weeks at 2O''C) were dormant and needed a cold treatment prior to planting. During culture in vitro at 20°C, the bulblets proceeded through three phases: (1) at first they were non-viable and non-dormant (up to 5 weeks), (2) then viable and non-dormant (5-9 weeks) and (3) finally viable and dormant (from 9 weeks onwards). At I5°C, the bulblets became viable but did not develop dormancy, even after protracted culture. The restilts suggest that the development of dormancy depends upon an accumulation of 'heat units' occurring at temperatures higher than 15°C, At 25°C, the succession of the three phases occurred more rapidly than at 20°C and heat units were acctimulated more rapidly. Dtiring the third period, the chilling requirement increased showing that heat units continued to be accumulated during this period. Dormancy connotes an arrest of growth. In lily bulblets, however, the number of scales continued to increase after the induction of dormancy at 20 or 25°C. Many of the scales initiated before the onset of dormancy were formed by swelling of a petiole, whereas, after the onset of dormancy, all scales were formed directly from a primordium. We conclude that the development of dormancy corresponds to a switch in the development of the primordium. Thus, after the induction of dormancy the primordium lost the ability to become a leaf and always developed into a scale.
Upon harvest, lily (Lilium speciosum Thunb. cv. Rubrum) bulblets generated in vitro under standard conditions (11 weeks at 20°C) were dormant and needed a cold treatment prior to planting. During culture in vitro at 20°C, the bulblets proceeded through three phases: (1) at first they were non–viable and non‐dormant (up to 5 weeks), (2) then viable and non‐dormant (5–9 weeks) and (3) finally viable and dormant (from 9 weeks onwards). At 15°C, the bulblets became viable but did not develop dormancy, even after protracted culture. The results suggest that the development of dormancy depends upon an accumulation of‘heat units’occurring at temperatures higher than 15°0. At 25°C, the succession of the three phases occurred more rapidly than at 20°C and heat units were accumulated more rapidly. During the third period, the chilling requirement increased showing that heat units continued to be accumulated during this period. Dormancy connotes an arrest of growth. In lily bulblets, however, the number of scales continued to increase after the induction of dormancy at 20 or 25°C. Many of the scales initiated before the onset of dormancy were formed by swelling of a petiole, whereas, after the onset of dormancy, all scales were formed directly from a primordium. We conclude that the development of dormancy corresponds to a switch in the development of the primordium. Thus, after the induction of dormancy the primordium lost the ability to become a leaf and always developed into a scale.
SUMMARY We have examined the effects of environmental conditions on the sprouting of micropropagated bulblets of Lilium speciosum with various levels of dormancy. After planting at low temperature (15°C) or in vitro, a higher percentage of bulblets sprouted than after planting at high temperature (20 or 25°C) or in soil. Dormancy was relative, i.e. bulblets with deep dormancy were capable of sprouting at a limited range of conditions and bulblets with low or no dormancy at a wide range. The promotive effect of the in vitro cultivation was, to a large extent, caused by exposure of the bulblets to light which was absent after planting in soil because of coverage by a layer of soil.
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