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  • Author or Editor: David N. Kristie x
  • Journal of the American Society for Horticultural Science x
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Stem elongation rates (SERs) of `Giant Tetra' snapdragon (Antirrhinum majus L.) and `Pompon' zinnia (Zinnia violacea Cav.) were determined in three temperature regimes in which differentials had been established between day and night temperature. The differentials [expressed as day temperature - night temperature (DIF)] were +5 DIF, 21 °C day/16 °C night; 0 DIF, 18.7 °C constant; and -5 DIF, 16.5 °C day/21.5 °C night; daily average 18.7 °C. In each regimes SERs were determined for three developmental stages—vegetative, visible bud, and preanthesis. SER was measured in controlled-environment chambers under 13-hour day/11-hour night photoperiods using linear voltage displacement transducers. Snapdragon and zinnia displayed rhythmic patterns of growth with strikingly different characteristics. SER for snapdragon consisted of a large peak in growth at the day/night (D/N) transition followed by a minimum in SER at the night/day (N/D) transition. The pattern did not change through development. In contrast the SER pattern changed significantly in zinnia. At the vegetative stage, diurnal SER was dominated by a large peak after the N/D transition [an early morning peak (EMP)]. At the later growth stages, the EMP remained visible, but the proportion of growth occurring at night increased. SER was rhythmic in both species for a limited period in continuous light and constant temperature. Zinnia displayed a stronger endogenous rhythm of SER than snapdragon. In both species, only day period growth was affected by DIF. The size of EMPs in both species increased under positive DIF and decreased under negative DIF, resulting in the overall DIF effect on plant height (a progressive increase in total diurnal elongation as DIF increased from -5 to +5). Internode lengths for snapdragon and zinnia were similar for plants grown to full flower at constant 17, 20, or 23 °C (0 DIF), indicating that DIF—not average daily, night, or day temperature—is a major determinant of extension growth.

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Stem elongation rate (SER) in Dendranthema grandiflorum (Ramat.) Kitamura was determined in light and in darkness under various temperature regimes. Stem growth as measured with linear voltage displacement transducers on plants in growth chambers. Under alternating 11-hour days and 13-hour nights, SER was strongly temperature dependent and showed patterns that were characteristic of the particular photoperiod-temperature regime under which the plants were grown. Total daily elongation was similar at constant 18.3C and at 11.5C days and 24C nights, but was much greater at 25.7C days and 12C nights. SER was rhythmic in continuous light with a period of slightly less than 24 hours. In continuous darkness, however, SER declined rapidly and the rhythm disappeared within 11 hours. Low-temperature pulses (a rapid decline from 18.3C to 8.3C) applied for 2, 4, 6, 8, or 11 hours during the day induced an immediate decline in SER followed by a slow recovery and peak shortly after the end of the pulse. Total diurnal stem growth declined with increasing pulse length, although short (2-hour) duration pulses apparently had little effect on growth. The results are discussed in relation to the influence of day and night temperature differentials (DIF) on stem growth in Dendranthema.

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