USING DIF FOR HEIGHT CONTROL OF SNAPDRAGONS
DIF is a non-chemical height control method that may be useful for greenhouse-grown cut snapdragons (Antirrhinum majus L.). Excessive stem elongation resulting from relatively high temperatures and large plant populations may lead to stem breakage, poor quality and ultimately a reduced price. DIF is the difference in day temperature and night temperature, which results in certain morphological effects, such as decreased stem elongation. It is not cost-effective to control the greenhouse temperature during the entire day and night. Studies have shown that the greatest stem elongation rate occurs at the end of the photoperiod or the beginning of the photoperiod. For snapdragons, the effect of DIF had a major influence on the early morning growth peak.
Researchers at the University of Maryland examined the effect of DIF and red/far red (R/FR) interactions at three stages of plant development—vegetative, pre-anthesis and at anthesis. The treatments for the experiment included positive DIF (day temperature higher than night temperature), negative DIF (night temperature higher than day temperature) or a constant temperature, and high or low R/FR ratios. Natural light has a relatively low R/FR ratio. Two experiments were conducted in growth chambers with a 13-hour photoperiod or a 10-hour photoperiod.
A decrease in stem height of 36% from positive to negative DIF treatments was observed. The reduced height was consistent irrespective of the R/FR ratio. Therefore, this study suggests temperature plays a more important role than the light ratio in snapdragon development.
The change in leaf number was consistent with plant height and the stem diameter was unaffected by DIF treatments. Therefore, this study has shown negative DIF produces a more manageable stem with unreduced photosynthetic capacity. Other observations regarding negative DIF included a delayed final harvest time (14 to 20 days), a longer vase life, and a higher percentage of opened florets at the end of vase life.
Shang, H., G.F. Deitzer and J.D. Lea-Cox. 2003. Differential Temperature (DIF) Effects on the Growth, Morphology and Flowering of Antirrhinum majus L. (snapdragon) Cultivars. Acta Hort. 624, pp. 177-183.
SCHEDULING GLADIOLUS, CELOSIA, HELIANTHUS AND ZINNIA
Louisiana State University looked for optimum scheduling of four specialty cut flower species with regard to the U.S. Gulf Coast climate. The mild winter allows an early growing season while the hot, humid summers create later production challenges. Scheduling, as day length and temperature increases, affects time of flowering, flower quality and yield of flowers. This study aimed to determine planting dates to meet market dates.
Various cultivars of Gladiolus were planted at 2-week intervals beginning February 20 and ending April 3 (10 cm/4 in deep, 15 cm/6 in apart). Transplants of Celosia, Helianthus and Zinnia were planted at 3-week intervals beginning April 3 through June 20.
The number of days to harvest decreased for the later plantings of Gladiolus, Celosia and Helianthus. Of the Zinnia plantings, the number of days to harvest was fewer for the second and third plantings. They hypothesized that the first planting took longer to reach harvest due to cool temperatures and the fourth planting took longer due to longer day length.
Gladiolus corms planted earlier resulted in a higher stem yield than those planted later. Zinnia stems were cut at lengths of 31 cm/12 in and 46 cm/18 in. The longer stems averaged a 36% lower yield overall than the shorter stems. Later planting dates produced fewer 31 cm/12 in stems though the yield of 46/18 in cm stems was consistent with earlier planting dates.
Pollen-producing and pollenless cultivars of Helianthus were studied. There was no correlation between days to harvest and pollen status of the cultivars. Postharvest studies indicated pollenless cultivars lasted 1 to 3 days longer than pollen-producing cultivars.
In general, when photoperiod was optimal, high temperatures had a greater effect on flowering than photoperiod. High temperatures resulted in faster flower bud development, less vegetative growth and shorter stems. Cool temperatures (occurring during early planting) delayed flowering, but produced longer stems.
Young, J.B., J.S. Kuehny, and P.C. Branch. 2003. Scheduling of Gladiolus, Celosia, Helianthus and Zinnia. Acta Hort. 624, pp. 373-378.
DRYING ANNUAL CHRYSANTHEMUM
Researchers in India considered two dehydration methods for drying cut chrysanthemums. More than 60% of the floriculture export from India is in the form of dried flowers. Only 20% of the dried flowers “produced” in India are cultivated with the remainder collected from the wild. This research aimed to determine a standardized dehydration method to avoid over dependency on wild flowers. Traditional methods of drying, including sun drying, press drying or hanging flowers, result in poor quality dried flowers. Newer methods such as embedded drying, freeze drying and glycerol microwaving produce a high quality dried flower. This study considered media, temperature and duration of the drying process for annual chrysanthemum (C. coronarium) flowers.
Yellow, fully opened flowers were dried in a hot air oven by embedding them in river sand or silica gel at 30C/86F, 40C/104F, or 50C/122F for 24, 36, or 48 hours.
As temperature and duration of drying increased, percent loss of weight, moisture content and carotenoid content increased. The maximum percent weight loss (fresh weight to dry weight) and maximum percent moisture loss was obtained by using silica gel at 50C/122F for 48 hours. The lowest percent weight loss and moisture loss occurred with river sand at 30C/86F for 24 hours. This may be due to a greater desiccating capacity of silica gel compared to river sand.
The minimum loss of carotenoid content (more color retained) was observed with silica gel at 30C/86F for 24 hours. Maximum loss occurred in river sand at 50C/122F for 48 hours. High temperatures and long durations may contribute to the breakdown of the carotenoid color pigments.
Highest quality dried flowers were obtained by embedding fresh flowers in silica gel and drying at 50C/122F for 48 hours. River sand not only resulted in high loss of carotenoid pigments, the sand particles stuck to the petals after the drying process. Low temperatures and short drying duration led to a poor quality flower with a high moisture content the resulted in twisted petals.
Dahiya, D.S., D. Unnikrishnan, A.K. Gupta, S.K. Sehrawat, and S. Siddiqui. 2003. Dehydration of Annual Chrysanthemum
(C. coronarium). Acta Hort. 624, pp. 385-388.
ASCFG Research Foundation Cemented
Another milestone has been reached by the ASCFG Research Foundation, now that it has officially become a 501(c)(3) tax exempt organization. Vicki Stamback and, especially, the indefatigable Betsy Hitt should be thanked for their heroic endurance in the face of withering bureaucratic tedium.
The purpose of the Foundation is to provide funding for scientific research and educational programs to benefit cut flower growers. The seeds for the ASCFGRF were planted back in 1990. It was during the reign of George I, who, like his son, was both a Christian Crusader and a practitioner of voodoo, or ‘trickle down’, economics. In those days, as it is today, very little in the way of public funding was finding its way to research projects that could not be contrived to be aiding the Crusades. Dr. Allan Armitage made tactful mention of shortfalls in research revenue in the CFQ, and all across the kindler, gentler ASCFG family farmers reviewed their budgets. A half dozen points of light responded with modest donations, and the notion for an Association Research Fund was conceived.
It has always been the family farmers who have given America its heart. The annual Auction, featuring auctioneers extraordinaire, Pamela and Frank Arnosky, was an immediate success. The fund grew and grew and was soon providing small grants to research projects throughout impoverished land grant academia.
You can become a member of the ASCFG Research Fund with an annual contribution of $25 or more. Contact Vicki Stamback or Betsy Hitt today. And look for more information in the spring issue of The Cut Flower Quarterly.
Contributed by Will Fulton
USING DIF FOR HEIGHT CONTROL OF SNAPDRAGONS