The experiment reported was set up to investigate ways of delaying flower formation in stock plants of the pot plant, Dianthus caryophyllus ‘Lilipot’. However, data relating to the morphogenesis of the plant were also recorded.
Two months old rooted cuttings were cut back and placed in a phytotron where they were given the following treatments in factorial combination: base temperatures of 16°C or 24°C; high temperature pulses of 32°C for zero (control), four or eight hours applied around midnight; photoperiods of eight or 16 hours.
After one month, lateral branches were removed from each plant, leaving just one which was allowed to continue growth.
Short days (SD) delayed flower formation, giving increases in the number of nodes below the flower and in the number of days to the visible bud stage, compared to plants growing in long days (LD). The time from bud visible to anthesis was not affected by photoperiod.
Internode length was also not influenced by photoperiod, and increased shoot length in SD was entirely due to increased numbers of internodes.
SD increased the number of lateral shoots.
Base temperature had no effect on the number of nodes below the flower, but temperature pulses of 32°C increased the number of nodes, i.e. physiologically delayed flower formation.
A high base temperature combined with high temperature pulses at night shortened both internode length and shoot length.
The time to visible bud was shortened at 24°C compared to 16°C, but high temperature pulse treatment had no effect on this character.
The development phase from visible bud to anthesis was shortened by high base temperature and by high temperature pulses at night.
The number of lateral shoots was reduced at the high base temperature.
At 16°C base temperature, high temperature pulses decreased the number of lateral shoots but at 24°C, high temperature pulses had no additional effect.