2012 Fall Research Updates

Short-day Treatments Under Long-day Conditions for ‘Sunrich Orange’ Sunflower

Helianthus annuus ‘Sunrich Orange’ is a quantitative short-day plant, like most ornamental sunflower cultivars. This means that while the sunflowers will flower under any photoperiod, flowering is accelerated under short-day conditions. Demand for sunflowers is highest from May to August, which are long days, resulting in increased production time, and longer and heavier stems than is considered optimal for cut flowers. This study evaluated flower quality after early application of short-day treatments while finishing the plants under long-day conditions.

Three stages of plant development were evaluated: cotyledon, two true leaves and four true leaves. Three durations of short-day treatment were evaluated for each of the plant stages— one, two and three weeks. Short-day conditions (11.5 hour day-length) were created by automatically opening and closing photo-protective plastic film. Following short-day treatment, the plants were returned to long-day conditions until flowering and harvest. Control plants were grown only under long-day conditions.

In this experiment, the sunflowers were responsive to short-day treatments for as little as one week at the cotyledon stage, only 9 days after sowing. The accelerated flower bud initiation was demonstrated by the reduction in the numbers of leaves and nodes. Short-day treated plants for one week at the cotyledon stage flowered 23 days earlier than the control. Short-day treated plants for three weeks at the cotyledon stage flowered 39 days earlier than the control. Accelerated growth (for all short-day treatments) also resulted in reduced stem length, weight, stem diameter and number of ray florets.

This study suggests short-day treatment for 2 weeks beginning at the cotyledon or two true leaves stage can promote earlier flowering of quantitative short-day sunflowers, like ‘Sunrich Orange’, without reducing quality.

Yanez, P., S. Chinone, R. Hirohata, H. Ohno, K. Ohkawa, 2012. Effects of time and duration of short-day treatments under long-day conditions on flowering of a quantitative short-day sunflower (Helianthus annuus L.) ‘Sunrich Orange’ Scientia Horticulturae 140, pp. 8-11.

Longer Vase Life with Lily with Hydrogen Peroxide

Hydrogen peroxide is known to be involved in plant response to various environmental stresses and is known to mediate plant growth and influences various developmental processes; however, there has been no suggestion of positive effects of hydrogen peroxide in cut flower senescence. This study reports the ability of hydrogen peroxide in the vase solution to extend the postharvest life and quality of cut Oriental x Trumpet hybrid lily ‘Manissa’, and looks more broadly at the effects of hydrogen peroxide on flower senescence during the postharvest life of cut flowers.

Vase solution treatments included:
1) Various concentrations of hydrogen   peroxide (0, 200, 400, 600, 800 and   1,200 µM)
2) 6 µM ascorbic acid (ASA)
3) 1 µM diphenylene iodonium (DPI)
4) 600 µM hydrogen peroxide + 6 µM   ASA
5) 600 µM hydrogen peroxide + 1 µM   DPI
6) Contorl (distilled water)

Vase life was terminated when the flowers had no decorative value (color change, wilt, loss of turgidity). Leaf senescence, leaf relative water content, total chlorophyll content, flower opening rate and change in fresh weight were other parameters measured.
In this study, 600 µM hydrogen peroxide vase solution resulted in maximum vase life and the maximum number of days taken for full flower opening (keeping quality). The highest levels of hydrogen peroxide treatments resulted in decreased vase life. Physiologically, hydrogen peroxide treatments retarded the degradation of leaf water and chlorophyll as well as petal carbohydrate. Stems exhibited lower petal electrolyte leakage and fresh weight loss.

Liao, W., M. Zhang, G. Huang, J. Yu, 2012. Hydrogen peroxide in the vase solution increases vase life and keeping quality of cut Oriental x Trumpet hybrid lily ‘Manissa’, Scientia Horticulturae 139:pp. 32-38.

Light Quality and Flowering Gypsophila paniculata

Though incandescent lamps are most commonly used for supplemental lighting in plant growth, LEDs are expected to increase in use given their energy efficiency. LEDs emit a single color of light, such as red (R) or far-red (FR). Most supplemental lighting evaluations have evaluated a R:FR ratio, rather than assessing a single color. In this study, LEDs emitting R, FR and blue (B) were evaluated for their effect on flowering in Gypsophila paniculata.

Plants were grown under natural light from 9:00 a.m. to 5:00 p.m. and under LEDs, incandescent lamps (W), or no light (short-day conditions) with shading from 5:00 p.m. to 9:00 a.m. The number of flowering or budding flower shoots per plant was evaluated, together with the number of nodes to the first flower per shoot. Cut flower quality factors were also assessed.

In this study, flowering and flower budding were promoted under FR light, while no flowering was observed under short-day conditions (no light). However, flower promotion with FR alone was considered insufficient in three independent trials (three separate seasons). Red light is known to inhibit flowering, but flowering and flower budding were promoted under long-day conditions of FR supplemented with R. A R:FR ratio between 0.23 and 0.71 promoted more flowering than FR alone. Gene expression is suspected to play a role in this observation. This study suggests that white LED bulbs and experimental LED modules rich in B and R should be carefully used due to their high R:FR ratios, as this study found a low R:FR ratio was effective in promoting flowering and producing high quality cut flowers of G. paniculata.

Nishidate, K., Y. Kanayama, M. Nishiyama, T. Yamamoto, Y. Hamaguchi, K. Kanahama, 2012. Far-red Light Supplemented with Weak Red Light Promotes Flowering of Gypsophila paniculata, Journal of the Japanese Society of Horticultural Science, 81(2):pp. 198-203.