Effect of day and night temperature on internode and stem length in chrysanthemum: is everything explained by DIF?

Abstract

In many plant species, including chrysanthemum, a strong positive correlation between internode length and DIF [difference between day (DT) and night (NT) temperature] has been observed. However, Langton and Cockshull (1997. Scientia Horticulturae 69: 229-237) reported no such relationship and showed that absolute DT and NT explained internode length rather than DIF. To investigate these conflicting results and to clarify the validity of the DIF concept, cut chrysanthemums (Chrysanthemum 'Reagan Improved') were grown in growth chambers at all 16 combinations of four DT and four NT (16, 20, 24 and 28 degrees C) with a 12 h day length. Length of internode 10, number of internodes and stem length were measured on days 5, 10, 17, 22 and 27 after starting the temperature treatments. Internode length on day 10 showed a positive linear relationship with DIF (R2 = 0.64). However, when internodes had reached their final length in all treatments (day 27), a much stronger positive linear relation was observed (R2 = 0.81). A model to predict final internode length was developed based on the absolute DT and NT responses: both responses were optimum curves and no significant interaction between DT and NT occurred [final internode length (mm) = -32.23 + 3.56DT + 1.08NT - 0.0687DT2 - 0.0371NT2; R2 = 0.91, where TD is day temperature and TN is night temperature]. It is shown that DIF can predict final internode length only within a temperature range where effects of DT and NT are equal in magnitude and opposite in sign (18-24 degrees C). Internode appearance rate, as well as stem length formed during the experiment, showed an optimum response to DT.

Fig. 1. Elongation patterns of internode 10 as a function of day temperature (DT) and night temperature [16 °C (open circles), 20 °C (open squares), 24 °C (closed circles), 28 °C (closed squares) in chrysanthemum ‘Reagan Improved’. Vertical bars indicate s.e.m. (n = 2) when larger than symbols.

Fig. 2. Relationships between the length of internode 10 and DIF (°C) 10 d (A) and 27 d (B) after treatments started in chrysanthemum ‘Reagan Improved’. Symbols represent 16 day and night temperature combinations, with a day temperature of 16 °C (open circles), 20 °C (open squares), 24 °C (closed circles) and 28 °C (closed squares). Regression lines: A, y = 6·40 + 0·202x, R² = 0·64; B, y = 16·57 + 0·547x, R² = 0·81. Vertical bars indicate s.e.m. (n = 2) when larger than symbols.

Fig. 3. Relationship between the length of internode 10 at 10 and 27 d after treatments started in chrysanthemum ‘Reagan Improved’. Symbols represent 16 day and night temperature combinations, with a day temperature of 16 °C (open circles), 20 °C (open squares), 24 °C (closed circles) and 28 °C (closed squares). Regression line: y = 7·89 + 1·36x, R² = 0·51. Vertical bars indicate s.e.m. (n = 2) when larger than symbols.

Fig. 4. Mean final length of internode 10 as a function of day temperature (DT) and night temperature (NT) in chrysanthemum ‘Reagan Improved’. Symbols represent measured values from 16 day and night temperature combinations, with (A) NT of 16 °C (open circles), 20 °C (open squares), 24 °C (closed circles) and 28 °C (closed squares); (B) DT of 16 °C (open circles), 20 °C (open squares), 24 °C (closed circles) and 28 °C (closed squares). Solid lines represent regression model: final internode length (mm) = –32·23 + 3·56 DT + 1·08 NT – 0·0687 DT² – 0·0371 NT²; R² = 0·909. LSD_{15, 0·05} = 1·08 mm.

Fig. 5. Predicted final internode length in chrysanthemum ‘Reagan Improved’, based on eqn (1), as a function of DIF (°C) in four temperature intervals: (A) 18–24 °C; (B) 16–28 °C; (C) 12–22 °C; (D) 22–32 °C. Symbols represent day and night temperature combinations, with a day temperature of 12 °C (open triangle), 14 °C (grey triangle), 16 °C (black triangle), 18 °C (open diamond), 20 °C (grey diamond), 22 °C (black diamond), 24 °C (open circle), 26 °C (grey circle), 28 °C (black circle), 30 °C (open square), 32 °C (grey square). Solid lines represent linear regressions on the data: A, y = 18·07 + 0·578x, R² = 0·95; B, y = 17·00 + 0·546x, R² = 0·89; C, y = 14·88 + 0·704x, R² = 0·62; D, y = 14·74 + 0·388x, R² = 0·32.

Fig. 6. IAR (A) and stem length formed during the experiment (B) as a function of day temperature (DT) in chrysanthemum ‘Reagan Improved’. Symbols represent 16 day and night temperature combinations, with a night temperature of 16 °C (open circles), 20 °C (open squares), 24 °C (closed circles) and 28 °C (closed squares). Regression curves: A, y = – 0·0022x² + 0·113x – 0·75, R² = 0·88; B, y = –0·146x² + 7·82x – 72·9, R² = 0·88. Vertical bars indicate s.e.m. (n = 2) when larger than symbols.