Developing Flowers That Last Longer After They’re Cut
American consumers spent $9 billion on cut flowers in 1998, according to USDA statistics. But they might buy even more if they knew the flowers would last longer once they were cut.
Help is in the works. University of Wisconsin-Madison researchers want to breed cut flowers that hold their beauty longer. The horticulturists have found that several genes determine how long cut flowers remain attractive, and they are focusing on one plant trait linked to longer-lived cut flowers.
“Flower breeders have focused on the shape and color of flowers and on plant shape,” says Dennis Stimart, a physiologist who studies ornamental plants at the College of Agricultural and Life Sciences. “There”s been almost no systematic work on breeding for plants whose flowers last longer after they are cut.”
Stimart became interested in the topic about 10 years ago when regulators in some European countries restricted the use of two chemical preservatives for cut flowers. Both compounds – STS (silver thiosulfate) and 8-HQC (8-hydroquinoline citrate) – are health hazards, although they are still approved for use in the United States.
The two preservatives shouldn”t be confused with the packets of powder often included with cut flowers, Stimart says. Those packets simply contain sugar, an anti-microbial and chemicals that make water more acidic.
All the treatments have the same purpose, according to Stimart. They extend the time that the water-conducting vessels in plants remain open so flowers don”t wilt rapidly. STS and 8-HQC also cause plants to produce less ethylene, a gas that encourages plants to wilt and decay.
Stimart thought there ought to be a better way to extend the life of cut flowers without using hazardous chemicals. To see if plant breeding might lead to longer-lived cut flowers, he began with snapdragons.
“We looked at more than 60 snapdragon lines,” he says. “These aren”t the hybrid snapdragon varieties that people plant in gardens. They are inbred lines developed specifically for marketing as tall, cut flowers.”
Snapdragons typically live for 7 to 9 days as cut flowers, according to Stimart. However, he found that some of the 60 lines lasted only 2 days after cutting while others bloomed on for 18 or 19 days.
Stimart and his former graduate student Kenneth R. Schroeder conducted a series of crosses beginning with long-lived and short-lived snapdragon lines. They showed that there are at least four or five genes that affect how long the flowers lasted after they were cut. Stimart and Schroeder – now a professor at Kansas State University – demonstrated that breeding could extend the life of cut snapdragons from 4 days to 11 days.
The UW-Madison scientists are showing that one trait that affects the life span of cut flowers is the abundance of small openings in snapdragon leaves. The openings, called stomates, allow plants to take up the carbon they need to grow as carbon dioxide from the air. But the leaves also lose water through the stomates.
Now William J. Martin, also a graduate student researcher with Stimart, has demonstrated a relationship between the density of the stomates and how long snapdragons last after cutting. Fewer openings are better.
“Inbred lines that last only a few days as cut flowers have, on average, two and one-half times as many stomates as lines that remain fresh in water for many days after they”re cut,” Stimart says.
However, the abundance of stomates is only part of the story, according to Martin. “It”s clear from our data that the relationship isn”t as clean as we hoped,” he says. He and Stimart are continuing to look for other traits that explain why some flowers last so much longer after they are cut than others.
Martin believes that research will lead to snapdragon varieties that keep longer after cutting. The market for cut snapdragons is about $40 million, according to the researchers.
Stimart believes the results with snapdragons show the potential to improve many flower species. “Flower breeders should go beyond selecting just for flower and plant color and shape. How well flowers keep after they are cut is a genetically determined trait that breeders should be paying more attention to,” he says.
The research was supported by state funding to the College of Agricultural and Life Sciences as well as a Hatch grant from the College and funds from several foundations and organizations that support research on flowers.