Screening Ornamental Sunflowers in the Seedling Stage for Flowering Reaction to Photoperiod

Abstract

<jats:p>Ornamental sunflower (<jats:italic>Helianthus annuus</jats:italic>) cultivars grown as cut flowers range in sensitivity to photoperiod with regard to flowering from facultative short day (SD) to facultative long day (LD), with others insensitive to daylength. SD sensitivity is a problem for production in tropical areas, or in early spring sowings when the daylength triggers early flowering, and leads to small flowers and production of unsightly axillary buds. In the current work, 59 cultivars of sunflower were exposed to either 12- or 16-hour photoperiod in seedling trays in a greenhouse for 3 weeks, and transplanted outside. At flowering, plant height, leaf number, and flower diameter were measured. The studies were conducted in 2006, 2007, 2009, 2011, and 2012 with two cultivars (Procut Lemon and Sunrich Orange) serving as controls in each trial. Of the 59 cultivars screened, 52% were found to be day-neutral, 44% were SD, and two (3%) had a LD reaction. Two standard cultivars grown in each season showed consistent reactions to the photoperiod treatments in each year. The seedling screen is useful to identify cultivars suited for production in early spring in a temperate environment.</jats:p>

Response of Branching and Nonbranching Cut Flower Cultivars of Sunflower to Pinching and Planting Density

“…In 2015, seeds were sown on 20 May and transplanted on 10 June, with pruning treatments on 22 and 27 June. Although two of the cultivars used in this study are hastened to flower by short days in the seedling stage (Wien, 2014), seedlings experienced long days in both studies in spite of the differing sowing times. Statistical analysis was done on each year's data separately, using Statistix software.…”