Developmental Responses of Zinnia to Photoperiod

Abstract

Abstract Zinnia elegans Jacq. ‘Carved Ivory’, ‘Cherry Ruffles’, and ‘Rosy Future’ were grown under short days (SD) or long days (LD) to determine the effect of photoperiod on flower initiation and morphological development. Plants grown under LD (14, 16, 18, or 24 hours) were greater in height, leaf size, flower diameter, and node number and flowered later compared to plants grown under SD (8, 10, or 12 hours). The greatest increases in plant responses occurred between 12- and 14-hour treatments. Supplemental irradiation (day continuation, night break, and predawn lighting) resulted in LD responses but did not equally affect days to flowering, stem diameter, or node number. Height and ray petal number were greatest for all cultivars under day continuation and flower diameter was largest under day continuation and predawn lighting. More LD before SD resulted in increases in height, stem and flower diameter, node number, ray petal number, and days to flowering, indicating a cumulative effect of LD on morphological development. Results demonstrate that Z. elegans is a facultative SD plant for floral initiation and development and that photoperiodic responses vary between genotypes.