Recycled Water Acceptable for Some Cut Flowers

Plant physiologist, Catherine Grieve and colleagues at the USDA-ARS George E. Brown, Jr., Salinity Laboratory in Riverside, California, are investigating the use of recycled water for production of various cut flower varieties. The water requirements of urban development and agricultural production strain the already limited water resources of the western United States. Previous research has looked at the use of recycled water for the production of nursery crops and grains, but use on floriculture crops is a new, promising venture.
“Recycled” water presents several concerns when used for plant production. The water is often recycled after use on another crop production area. It can carry with it dissolved salts and ions from previous fertilizer applications which could negatively affect the health of the plant taking up the recycled water. Others along the Pacific coast must deal with intruding seawater in fresh groundwater sources. In either case, the presence of salt is a warranted concern since too much salt may stunt or even kill some plants, and some salt compositions may lead to nutritional deficiencies.
Seedlings were grown with high quality water until they were established. Laboratory-made solutions with increasing concentrations of salts (chlorides and sulfates of calcium, magnesium, sodium and potassium) were applied for the remainder of production. They tested several important cut flower species including statice, stock, celosia and sunflowers.
Statice was the first species tested for its importance to the industry and its supposed salt tolerance. Grieve studied Limonium perezii ‘Blue Seas’ and L. sinuatum ‘American Beauty’. Though statice may perform acceptably in the landscape under high salt conditions, the stem length of plants grown using simulated recycled water was unacceptable for commercial cut flower use.
The other species tested fared better. Matthiola incana ‘Cheerful White’ and M. incana ‘Frolic Carmine’ were found to be salt-tolerant, contrary to previously held believes about stock. Moonbright and Sunbeam sunflowers did exhibit a reduced stem length, but the diameter of the flower head was unaffected. Even at a reduced stem length of 28 to 30 inches the flowers maintain their commercial value for the bouquet market. Celosia argentea var. cristata ‘Chief Gold’ and ‘Chief Rose’ also performed well as a salt tolerant crop.
Further testing at the Salinity Laboratory will focus on how cut flower crops respond to solutions high in nitrogen and other fertilizer effluents found in recycled nursery waters. If recycled water can be used to produce commercially acceptable cut flowers, growers and the public will benefit from lower production costs, conserved resources and reduced discharge of fertilizer, inorganic salts and pesticides into streams, rivers and other environmentally sensitive areas.

Peabody, E. 2004. Salt-Worthy Flowers are Stunning—and Sensible. Agricultural Research Aug. pp 5-7.

Xylem Blockage in Roses, Astilbe and Viburnum

Researchers at Wageningen University and Research Centre in The Netherlands previously found that xylem occlusion in the stems of dry-stored chrysanthemum and Bouvardia was the result of a plant induced wound response. Most cut flowers experience xylem blockage—which inhibits water uptake—due to the presence of bacterial growth. Of further interest was evidence that stem lignification may affect xylem occlusion. This was suggested when mum stems cut closer to the shoot-root junction demonstrated a slower water uptake rate. The current research investigated the causal agent of xylem blockage and resulting decreased vase life of Rosa hybrida ‘Red One’, Astilbe x arendsii ‘Glut’ and ‘Erica’, and Viburnum opulus ‘Roseum’.
The stems were harvested at 60-80 cm long, transported to the research station and recut, removing 20-40 cm. The stems were pulse treated in various solution for 5 hours at 20°C (68°F) and 60% relative humidity. The first dry storage treatment involved placing each flower in a sealed plastic bag and holding for 24 hours at 5°C (41°F). In the bag, relative humidity reached 100% so no detectable water loss occurred. Other flowers were held dry by placing them horizontal on a table at 20°C (68°F). After the storage period, the stems were placed in vases with deionized water and held at 20°C (68°F). Xylem occlusion was measured by the time to severe leaf wilting.
The dry storage treatments had no effect on the rose and Viburnum stems, but resulted in a reduced time to wilting in both Astilbe cultivars. Upon examination however, the Astilbe stems did not have a bacterial presence suggesting an alternative cause for the xylem occlusion.
Peroxidase is an enzyme that may be involved in the wound-induced xylem occlusion. Enzyme inhibitors were used in the vase solution to explore the role of peroxidase. The inhibitor, hydroquinone, considerably delayed the time to wilting in Astilbe, but had no affect on the time to wilting of the rose or Viburnum. Other enzyme inhibitors tested also inhibit bacterial growth. These inhibitors delayed wilting in all flowers tested suggesting bacteria-induced blockage in rose and Viburnum.
The relationship between lignifigation and wound-induced vascular occlusion seems to be species specific considering the woody nature of rose and Viburnum and the lack of wound-induced occlusions in this study.

Loubaud, M. and W.G. van Doorn. 2004. Wound-induced and bacteria-induced xylem blockage in roses, Astilbe, and Viburnum. Postharvest Biology and Technology 32 pp. 281-288.

1-MCP Release Device

Ethylene exposure of some cut flowers results in premature flower abscission and/or senescence. 1-methylcyclopropene (1-MCP) and silver thiosulphate (STS) are two treatment options that inhibit ethylene action in plants. A single application of 1-MCP protects flowering stems for only 48-96 hours. The gas is not still present when new ethylene receptors are formed in the plant. The STS solution has some residual affects since excess silver ions can accumulate in the plant tissue and bind to new receptors as they form. However, environmental concerns over the silver waste solution has resulted in some restrictions on STS use.    
Researchers at The University of Queensland, Australia, have tested four sustained release delivery systems for 1-MCP. Previous research demonstrated  a sustained release of 24 hours for 1-MCP enclosed in a low density polyethylene (LDPE) membrane. The Australian researchers hope to find a delivery method that would release 1-MCP over a period of <100 hours.  
The devices tested were described as follows: 1) Clear glass vial closed by a polypropylene screw-on lid with a rubber septum port, 2) Hollow flexible 14 cm long PVC and natural rubber tubing, sealed at each end with a solid glass stopper, 3) LDPE sachet and 4) Piece of thick natural rubber. Chamelaucium uncinatum ‘CWA Pink’ (Geraldton waxflower) bunches were shipped from Australia to the United Kingdom for evaluation of the affect of sustained 1-MCP release on flowers during intercontinental transport.
Release of 1-MCP from the test devices was consistent with the reported permeability of each membrane. The most desirable delivery system, based on the release kinetics, was the sealed PVC tubes. The tubes release a low level of concentration for the first 12 hours, then increase to a high, constant concentration for 132-156 hours. The initial low release may be due to the time needed for 1-MCP to saturate the PVC tube wall and establish a steady state diffusion gradient. The natural rubber tubing and the LDPE sachets allowed rapid depletion of the 1-MCP source.   
In addition to the sustained release and, therefore, sustained protection from ethylene during transport, the PVC tubes packed in the carton with waxflower bunches provided protection against exogenous ethylene-induced abscission for 3-5 days of post-export vase life. In comparison, flowers treated once with 1-MCP prior to export were protected against exogenous ethylene for 1 day of post-export vase life, and flowers treated with STS were protected for 2 days of post-export vase life.

Macnish, A.J., D.C. Joyce, D.E. Irving, A.H. Wearing. 2004. A simple sustained release device for the ethylene binding inhibitor 1-methylcyclopropene. Postharvest Biology and Technology 32 pp. 321-338.