INFLUENCE OF DURATION OF DIFFERENT DAY- AND NIGHT TEMPERATURES ON GROWTH AND FLOWER BUD FORMATION IN EUPHORBIA PULCHERRIMA WILLD.

In order to see whether the plant height of Euphorbia pulcherrima Willd. ‘Lilo’ may be retarded by means of a high temperature pulse before sunrise, rooted cuttings were subjected to pulse DIFs of +4, 0, -4 or -8°C for 2, 6 or 10 hours before sunrise and the growth habit followed through flowering.
DTs and NTs were mutually levelled to give the same diurnal average temperature of 20°C for all treatments.

The typical growth curve over time was sigmoidal.
During the first 43 days, no differences between treatments were observed, however, between day 43 to 71 the plants with negative pulse DIF grew taller than those with zero or positive pulse DIF, irrespective of the duration of the temperature pulse before sunrise.

The explanation of this unexpected result was delayed time to visible bud and the formation of more leaves at negative pulse DIF compared to zero or positive pulse DIF. The best plants were produced at a constant temperature of 20°C, and the plant height could not be reduced by a high temperature pulse before sunrise.
Fresh weight and dry weight were greater at negative pulse DIF before sunrise compared to positive pulse DIF before sunrise.

Workshop on Environmental Regulation of Plant Morphogenesis

H.E. Kresten Jensen

DIF, temperature, plant height, internodes, flower bud, dry weight, fresh weight

https://doi.org/10.17660/ActaHortic.1995.378.4