Vernalization and devernalization of Campanula 'birch hybrid' and Leucanthemum xsuperbum 'Snow Cap'

Abstract

The influence of vernalization temperature and duration and devernalization treatments on subsequent growth and flower development of Campanula 'Birch Hybrid' and Leucanthemum x superbum Bergman ex J. Ingram 'Snow Cap' was determined. In the vernalization experiment, plants of 'Birch Hybrid' were vernalized at 0, 2.5, 5, 7.5, or 10 °C for 2, 4, 6, or 8 weeks. 'Snow Cap' was vernalized at 0, 2.5, 5, or 10°C for 2, 4, 6, or 8 weeks. In another devernalization experiment, plants of both species were moved to a high temperature (30/10°C, day/night) growth chamber for 2 or 4 days at various times during or after the 6-week vernalization period. A 6-week vernalization was necessary to obtain 100% flowering in 'Birch Hybrid', and 8 weeks of vernalization decreased time to flower by 7 to 10 days compared with 6-week vernalization. Exposure to high temperature for 2 days during or immediately after vernalization did not devernalize 'Birch Hybrid' plants, while a 4-day exposure decreased flowering percentage in some treatments and delayed flowering by 7 to 10 days. There were no significant differences in flowering characteristics of 'Snow Cap' plants vernalized at 0 to 5°C for 4 to 8 weeks. A 2-week vernalization at 0, 2.5, 5, or 10°C or 4 to 8 week vernalization at 10°C delayed flowering by 5 to 10 days compared with those vernalized at 0 to 5°C for 4 to 8 weeks. Exposure to high temperature for 2 d did not devernalize 'Snow Cap' plants regardless of exposure times, but a 4-day exposure delayed flowering by 4 to 5 days in some treatments. Combined, the data indicate that 'Birch Hybrid' has an obligate 6-week vernalization requirement and 'Snow Cap' has a facultative 4-week vernalization requirement that can be fulfilled in the 0 to 10°C range. Exposure to temperatures of 30°C (9 h·d-1) for 12 out of 42 days did not devernalize either species but in some cases caused a small delay in time to flower.