AUTHOR=Spall Caleb E. , Lopez Roberto G. 

TITLE=Daily light integral and/or photoperiod during the young plant and finishing stages influence floral initiation and quality of witchgrass and marigold cut flowers

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.956157

DOI=10.3389/fpls.2022.956157

ISSN=1664-462X

ABSTRACT=To produce consistent and high-quality specialty cut flowers throughout the year, growers must utilize greenhouses. Therefore, our objectives were 1) to determine the effect of photoperiod during the young-plant and finishing stages on floral initiation and morphology of witchgrass ‘Frosted Explosion’ and marigold ‘Xochi’ and 2) to quantify the effect of daily light integral (DLI) on floral initiation and morphology during the finishing stage. Seeds were sown and placed under 9-, 11- (marigold only), 12-, 13-, 14-, 15-, 16-, 18-, or 24-h photoperiods or a 9-h short day with a 4-h night interruption (NI) from 2200 to 0200 HR. Plugs were distributed among 10-, 11-, 12-, 13-, 14-, 15-, or 16-h photoperiods, or a 4-h NI, for finishing. Marigold and witchgrass were finished under a moderate DLI of 10 mol∙m–2∙d–1 and witchgrass was also finished under a very low ≈3 mol∙m–2∙d–1. Marigold grown under a photoperiod ≥11 h or a 4-h NI as a young-plant and finished under 11- or 12-hrs  had thick stems and consistently met the marketable stem length of ≥65 cm. Up to 29 and 107% more stems were harvestable under 11- and 12-h finishing photoperiods, respectively, compared to a 10-h finishing photoperiod. Marigold visible buds were delayed, and stems were not harvestable under photoperiods ≥13 h, or a 4-h NI. Young witchgrass plants grown under a photoperiod between 14- and 24-h or a 4-h NI and finished under photoperiods ≥14 h or a 4-h NI, and at least a moderate DLI, produced stem ≥50 cm long. All witchgrass stems grown under a very low DLI were shorter and thinner than those grown under a moderate DLI, and none were harvestable. Therefore, we recommend growing marigold ‘Xochi’ young plants under a photoperiod ≥11h or a 4-h NI and finishing under a 12-h photoperiod. Additionally, witchgrass ‘Frosted Explosion’ young plants should be grown under a photoperiod ≥14 h or a 4-h NI, and finished under photoperiods ≥14 h, or a 4-h NI to prevent premature flowering. Cut flowers should be finished under a DLI of >10 mol·m–2·d–1 for consistent production of high-quality stems.