Day and Night Temperatures, Daily Light Integral, and CO2 Enrichment Affect Growth and Flower Development of Pansy (Viola ×wittrockiana)

in Journal of the American Society for Horticultural Science

Pansy [Viola ×wittrockiana Gams. `Delta Yellow Blotch' (Yellow) and `Delta Primrose Blotch' (Primrose)] plants were grown in a greenhouse under two CO2 concentrations [ambient (≈400 μmol·mol-1) and enriched (≈600 μmol·mol-1)], three daily light integrals (DLI; 4.1, 10.6, and 15.6 mol·m-2·d-1), and nine combinations of day and night temperatures created by moving plants every 12 h among three temperatures (15, 20, and 25 °C). Time to flower decreased and rate of flower development increased as plant average daily temperature (ADT) increased at all DLIs for Yellow or at high and medium DLIs for Primrose. Increasing the DLI from 4.1 to 10.6 mol·m-2·d-1 also decreased time to flower by 4 and 12 days for Yellow and Primrose, respectively. Both cultivars' flower size and Yellow's dry weight [(DW); shoot, flower bud, and total] decreased linearly as plant ADT increased at high and medium DLIs, regardless of how temperature was delivered during day and night. DW in Yellow increased 50% to 100% when DLI increased from 4.1 to 10.6 mol·m-2·d-1 under both CO2 concentrations. Flower size in Yellow and Primrose increased 25% under both CO2 conditions as DLI increased from 4.1 to 10.6 mol·m-2·d-1, but there was no increase between 10.6 and 15.6 mol·m-2·d-1, regardless of CO2 concentration. Plant height and flower peduncle length in Yellow increased linearly as the difference between day and night temperatures (DIF) increased; the increase was larger under lower than higher DLIs. The ratio of leaf length to width (LL/LW) and petiole length in Yellow increased as DIF increased at medium and low DLIs. Carbon dioxide enrichment increased flower size by 4% to 10% and DW by 10% to 30% except for that of the shoot at medium DLI, but did not affect flower developmental rate or morphology. DW of vegetative and reproductive parts of the plant was correlated closely with photothermal ratio, a parameter that describes the combined effect of temperature and light.

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