Stem elongation and plant height at flowering in Campanula isophylla Moretti were greater when plants were exposed to far red (FR) light or light from incandescent lamps which had a low red (R)/FR ratio (0.7). The difference in final stem length between FR- and R-light-treated plants was greatest when the light treatments were given during the entire night or as a 3 h end-of-day (EOD) lighting period. Only minor differences existed between R and FR light treatments when plants were given light in the middle of the night. However, FR light suppressed lateral branching compared with R light. The reduction in plant height as a result of a lower day temperature (DT) than night temperature (NT) was nullified by day-extension lighting with incandescent lamps. With fluorescent lamps (R/FR ratio 4.2), plant heightwas significantly less at 15/21°C (negative DT-NT (DIF)) than at 21/15°C DT/NT (positive DIF). Continuous lighting (CL) during the entire night or with 3 h night interrupttion (NI) treatments with R or FR light immediately after the middle of the night was equally effective at inducing flowering, and much more effective than EOD or end-of-night (EON) lighting. DIF had a slight influence on the rate of flower development, but negative DIF grown plants had 24% more flowers and flower buds, and 26% higher dry weight, than positive DIF plants. Practical applications of light quality and negative DIF treatments for the production of high-quality pot plants of C. isophylla are discussed.
Bibliographical noteFunding Information:
We are grateful to the National Research Council of Norway and Michigan State University for financial support. The authors also thank I. Okland for technical assistance with these experiments.
- Campanula isophylla
- lateral branching
- light quality
- long-day plant
- night interruption
- stem elongation