Stem elongation and flowering of the long-day plant Campanula isophylla Moretti in response to day and night temperature alternations and light quality

Abstract

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.