Daily Light Integral During Vegetative Propagation Effects the Subsequent Growth and Development of Annual Bedding Plant Species

Daily light integral (DLI) is the rate at which photosynthetically active radiation is delivered over a 24 h period.  In commercial greenhouses, DLI is limiting in northern latitudes during the winter and early spring months when the majority of bedding plants are propagated.  We quantified how DLI during vegetative propagation influences subsequent growth and development of annual bedding plant species.  Angelonia angustifolia Benth. ‘AngelMist White Cloud’, Argyranthemum frutescens (L.) Sch. Bip. ‘Madeira Cherry Red’, Diascia barberae Hook. f. ‘Wink Coral’, Nemesia fruticans (Thunb.) Benth. ‘Aromatica Royal’, Osteospermum ecklonis (DC.) Norl. ‘Voltage Yellow’, Scaevola L. hybrid L. ‘Blue Print’, Sutera cordata ‘Abunda Giant White’, and Verbena Ruiz ×hybrida ‘Aztec Violet’ were callused under a 16 h photoperiod and a DLI ≈5 mol∙m^-2∙d^-1 for 7 d.  Cuttings were then placed under 4 DLIs ranging from 1.4 to 12.3 mol∙m^-2∙d^-1 for 14 d and transplanted under a common finishing environment of 21.5 °C and a DLI of 10 to 12 mol∙m^-2∙d^-1.  As propagation DLI increased from 1.4 to 12.3 mol∙m^-2∙d^-1, days from transplant to first open flower decreased by 24 and 15 d in Angelonia and Nemesia, respectively.  In general, shoot dry mass was lower at the time of flower for plants propagated under higher DLI treatments.  For example, shoot dry mass of Angelonia, decreased from 1.2 to 0.38 grams as propagation DLI increased from 1.4 to 12.3 mol∙m^-2∙d^-1.  However, shoot dry mass accumulation per day increased with increasing DLI for Nemesia, Sutera, Diascia, and Osteospermum. Shoot dry mass accumulation per day was variable for Argyranthemum, Scaevola, and Angelonia.  From this study there are clearly differences among species responses during finishing to propagation DLI.