OrchidSafari Archives

Flower Aging
Moderator: Marilyn Light
Wednesday October 13, 2004

MarilyninOttawa
Anyone who exhibits orchids likely remembers those occasions when a bud opened a bit too soon for a specimen to be at its best for a show or a striking Phragmipedium bloom, apparently still fresh and colorful, dropped just before judging.

Those exhibiting Cymbidiums probably have had the sad experience of dislodged anther caps leading to the discoloration of a delicately patterned lip. Disruption or damage of critical flower parts can lead to the production of ethylene, a natural plant hormone, and a cascade of physiological changes including withering, fading, and color change. One spoiled bloom can ruin the overall effect of an otherwise perfect spray. The presence of even a small amount of anthocyanin pigment as seen here in the underside of the column in Cym. Mini Dream 'Cameo' renders the flower susceptible to premature fading. The discovery and development of Pure Color Cymbidiums has been useful at circumventing the problem. Here we see a pure yellow clone of an unamed hybrid called 'Jenny Wren'. The pristine pure color white blooms of Cym. Sleeping Dream 'King's Ransom' do not discolor.

Those exhibiting Catasetums know that the consequence of dislodged pollinia is no laughing matter. Faded blooms can cost the exhibitor a ribbon or even an award. Unfortunately, there is no way around this challenge other than being very careful during transport and placement in an exhibit.

Commercial pot plant and cut flower producers are concerned about the effects of ethylene-sensitivity during shipping. African violets, begonias, geraniums, Easter lilies, and orchids are some of the plants considered highly sensitive to ethylene which is produced when the plants are stressed. Ethylene production leads to bud and leaf drop. Ethylene-sensitive plants are treated with ethylene blockers before shipment. A weak solution of silver thiosulfate used to be sprayed on a whole plant to reduce flower drop. The silver salt reduces ethylene-induced abscission of buds and flowers by interfering with ethylene oxidation. Silver thiosulphate is no longer used by commercial enterprises because of environmental concerns but an alternative, methyl cyclopropene, can now be used with the same outcome. This gas is sometimes used after the plants are in their shipping container or vehicle. For those interested, there are some scientific papers on the subject such as "Differential Expression of 1-Aminocyclopropane-1-Carboxylate Synthase Genes during Orchid Flower Senescence Induced by the Protein Phosphatase Inhibitor Okadaic Acid", Ning Ning Wang, Shang Fa Yang, and Yee-yung Charng, Plant Physiology 126 (1): 253-260, 2001. button

Flower aging and longevity concern exhibitors and florists but what are the consequences in wild populations? Species have evolved behaviors which have proven to be successful in terms of reproduction and survival. Flowers can remain fresh for only a few hours or they can last for months. Flowers may last longer where pollinators are sporadically available or when there is no pollinator reward; or flowers may be ephemeral when either the cost of maintaining the flowers is high or when an alternate strategy of sequential blooming has evolved.

Flowering costs plants in terms of resources but there is often a trade-off between the need to reproduce and the relative cost of attempting to do so. While many orchids are able to conserve water in their leaves, roots or pseudobulbs, they are generally not able to do so with their flowers. Flowers lose moisture through transpiration. The longer flowers have to remain attractive to pollinators, the more resources are required to support the blooms. If flowers have nectaries then resources are also needed to produce nectar and to maintain that nectar source as a pollinator reward. Two extremes of flower lifespan are seen with insect-pollinated Dendrobium crumenatum, the Pigeon Orchid, which has short-lived flowers. The flowers of hummingbird-pollinated Sophronitis coccinea not only remain fresh but also continue producing nectar weeks after the flowers have been pollinated. In the case of the Pigeon Orchid, all plants bloom synchronously after a sudden drop of about 9C as might occur during a heavy rain shower. Mass flowering can happen often throughout the year although individual flowers last but a day. It is believed that synchronous blooming favors the exchange of pollen between plants similarly affected by a climatic event.

Manuel, Warren, and Miller (1996) observed that the Sophronitis coccinea grows in 'swarms' on tall tree branches. After pollination, flowers do not wither but remain brightly colored and continue to produce nectar for visiting hummingbirds even after fruits begin forming. This strategy could increase hummingbird visit frequency to both pollinated and freshly opened blooms.

Pollination sets off a cascade of events usually beginning with the collapse of the petals and sepals but even pollen removal can lead to fading. Sometimes, flowers do not wither but become green and photosynthetic which could increase the availability of carbohydrate resources needed for fruit production. We see this phenomenon in orchids such as Phalaenopsis and Promenea.

We have investigated flower aging and fruit production in populations of the Large Yellow Lady's-slipper, C. parviflorum v. pubescens. It might be useful for exhibitors to know how to maintain artificially propagated plants having fresh blooms for a show or other indoor exhibit. picture By noting when each flower opened and faded, as well as the daily minimum and maximum temperatures, we were able to track the behaviour. Flower opening was spread over several weeks. Flowers open sooner in the sunniest spots. Flower fading was likewise spread over several weeks. We found that flower fading in this species is correlated with a cumulated minimum temperature of about 150 degrees Celsius. This effect has been consistent over the years we have observed this population, even between the extreme seasons of 1998 and 1999. In 1998, during an early warm spring season, average flower life was 11 days with flowers fading when increments were consistently above 10C. In 1999, an extended cool spring, with increments generally below 10C, flower life was extended to 13 days on average. picture Since the cumulated minimum temperature increases by daily increments of approximately 10C, we can forecast flower longevity only to within one or two days. The extended spring of the year 2000 permitted us to observe the range of population response to the cumulative minimum temperature where individual flower life ranged from 5 to 23 days although the age at fading was tightly clustered around 15 days.

We found that fruiting outcomes were correlated with weather suitable for pollinator activity. Here we can see that bees were active on warmer sunny days early in the blooming cycle. Flower age impacts differentially on male and female function. Annual fruit set and therefore seed production is primarily a function of pollinator synchronization with receptivity. Pollen remains germinable provided anthers do not become infected with fungi, bacteria or yeasts as might happen during extended wet weather. Here we see a pollinated stigma where the right-hand anther (arrow) has become infected with a fungus.

We found that when pollinators were active only before pollen was available or only after the flowers had been open for more than 7 days, fewer capsules were produced. The highest fruit set was observed when pollinators were active four days after the majority of flowers had opened. Pollinating bees remove sticky pollen without disrupting the entire anther (see right-hand anther) which may explain why no pollen removal effect is observed in this species. When flowers were pollinated after their receptivity point was past, pollen germinated but further capsule development was aborted. picture There was no evidence that flowers faded more rapidly after pollination as has been reported for the Pink Lady's-slipper, C. acaule. Here we see a faded, pollinated Yellow Lady's-slipper flower (black arrow points to pollen on stigma). Fading happens within a day of the expected fading whether or not the flower has been pollinated. picture Extended flower longevity clearly did not increase the opportunity to produce seeds of any one flower but it likely served to continually attract pollinators to the large colony where younger receptive flowers could still profit from pollinator visits. Flower aging may have its origins in evolutionary processes but its impact on horticultural uses makes it an interest subject for further study.

Are there any questions?

John in Arcadia
Can interbreeding help get over some of the early flower fading?

MarilyninOttawa
Yes and no. If we breed species with long and shorter lived flowers, we might expect some progeny to have longer lived flowers. We certainly can exploit albino parents to avoid the color-related premature fading events.

N_Calif_Kathy
Color related premature fading events? That's what I get for coming in late! I'll have to go back and read

MarilyninOttawa
What is the shortest lived flower in your collections? The longest lived?

John
Dend crumentum = shortest. Some Dend hybrids seem the longest or possible some Paph hybrids such as Winston Churchill hybrids.

Jade
Those Winston Churchill Paphs last so long they have to be dusted.

MarilyninOttawa
I would not want to dust blooms! Likewise, although beginners are thrilled to have a Phal in bloom forever, long-lived flowers on a poorly rooted plant do not forecast well for the health of the plant.

janetteh
That is the reason I always advise people to cut their phal spikes off at the leaves....don't force a second blooming. On most plants they should be cut off by the first of May to give the plant plenty of time to grow more roots and leaves and get ready for the next bloom season. But blooms are more important to some people than the general health of their plants.

N_Calif_Kathy
Someone once said the acceptance of cutting away a spike had more to do with the grower's assurance of getting it to bloom next year. If they weren't sure of their growing skills, then they let it branch, if they knew it'd flower again they cut the spike off.

MarilyninOttawa
I give the same advice, Janette, and for the same reasons. The most frequently asked question it seems, is where do I cut it to make it bloom again.

Jade in GR
I have a question regarding the use of the gas to keep plants from reacting to the ethylene. Is this practice allowed when bringing plants to a show? If not, how can it be traced? Seems like it would definitely give the perpetrator an unfair advantage.

MarilyninOttawa
I do not know if the gas residue could be detected. Plants and flowers are not supposed to be manipulated before a show but cut flowers likely would be placed in water treated with some sort of 'flower saver' product which is the same thing. Any opinions?

N_Calif_Kathy
I don't think it could be traced. If you didn't mention it to anyone they'd probably never know.

N_Calif_Kathy
The survival tendency would be towards plants that constantly attract their pollinators succeeding, yes? Because no one know when the plant is most receptive, so if the pollinaors visit more consistently then they have a better chance at setting a pod?

MarilyninOttawa
Kathy, I have found plants of the same species with a range of optimum age receptivity. Some orchids can control their fecundity and so we might never know how every plant behaves but will only be able to generalize.

N_Calif_Kathy
I was amazed that flowers count cumulative temperature days. I never would have thought of it that way, or am I being overly simplistic in stating it that way?

MarilyninOttawa
The correlation is with the cumulative minimum temperature. Daily maximums cannot be correlated with the aging. I suspect that there is a threshhold and I know that there is a maximum life of about 30 days. This species likely came in after the glacier retreat and evolved behaviours in tandem with bee availability.

MarilyninOttawa
I have been speculatively breeding sequential bloomers with those that flower all at once. It seems with Oncidium graminifolium that the sequential blooming trait is easily cancelled. The resulting hybrids bloom many flowers all at once.

N_Calif_Kathy
A stupid question, on your graphs you have the letters Q and M, are those some sort of standard deviation?

MarilyninOttawa
M is median and Q refers to Quartiles.

Mauro_Brazil
Marilyn, don't you think the center of the problem is the relationship with the pollinator agent and how effective is the attraction the flower exerts on the pollinator? Then the duration would be relatively tied to this I guess

MarilyninOttawa
Yes Mauro. Of course, flower life has been linked to the availability of pollinators under different climatic and other conditions. With our Yellow Lady's slipper, it is pollinated by several different kinds of bee. It is a long-lived perennial which could survive as long as the habitat, which in Canada, is related to forest fire risk or about every 300 years. The bees fly only when the weather is suitable. If it is cold and windy, the bees do not fly. The flowers remain fresher longer when it is cold and hopefully, one day, the conditions will suit the orchid, the bee and then seeds are produced.

Mauro_Brazil
I think that we could not forget that the duration of the flower is just part of the game. Once pollinated orchids generally produce thousands of viable seeds. Then one fruit is just something, don't you think?

MarilyninOttawa
The seeds may all or mostly all be viable in vitro but in nature, perhaps there are particular parents siring a population. These may be so because of their location, proximity to good nursery habitat or whatever, perhaps even because they produce more or less scent, a different color, or last somewhat longer than their siblings. Flower longevity in nature is something which has evolved to suit a plant and its survival. Flower longevity for cultivated orchids and cut flowers is something which we might wish to manipulate and so it is interesting to understand how and why it works.

Mauro_Brazil
All right, I understand that. But may I help with a comment about the habitat of Sopro coccinea cited by Manuel, Warren and Miller that you reproduced lines before?

MarilyninOttawa
Yes Mauro. We do not know if there are particular important seed or pollen parents within the swarm of plants growing on the branches. In terms of conservation, those particular branches/trees become important to the Sopronitis habita. Is that what you were thinking?

N_Calif_Kathy
Marilyn, you wrote: "There was no evidence that flowers faded more rapidly after pollination as has been reported for the Pink Lady's-slipper, C. acaule. Here we see a faded, pollinated Yellow Lady's-slipper flower (black arrow points to pollen on stigma). Fading happens within a day of the expected fading whether or not the flower has been pollinated. picture"
Can this work on flower fading be applied to Paphs? Or are the genera just *too* different. There's some real interesting co-relations here.

MarilyninOttawa
I think it can Kathy but we would need a population of the same species to do the experiment. Ideally, we would work with something pure white/yellow like emersonii and another species with color like armeniacum or micranthum. I have been doing the experiment with different cyp species and the result do vary. We cannot consider them to all behave exactly the same way but until we do the experiment with Paphs, we will not know about their behaviour.

end

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Flower Aging

Marilyn H. S. Light
Copyright 2004

Anyone who exhibits orchids likely remembers those occasions when a bud opened a bit too soon for a specimen to be at its best for a show or a striking Phragmipedium bloom, apparently still fresh and colorful, dropped just before judging. Those exhibiting Cymbidiums probably have had the sad experience of dislodged anther caps leading to the discoloration of a delicately patterned lip. Disruption or damage of critical flower parts can lead to the production of ethylene and a cascade of physiological changes including withering, fading, and color change. One spoiled bloom can ruin the overall effect of an otherwise perfect spray. The discovery and development of Pure Color Cymbidiums has been useful at circumventing the problem. Those exhibiting Catasetums know that the consequence of dislodged pollinia is no laughing matter. Faded blooms can cost the exhibitor a ribbon or even an award. Unfortunately, there is no way around this challenge other than being very careful during transport and placement in an exhibit. Flower aging and longevity concern exhibitors and florists but what are the consequences in wild populations?

Species have evolved behaviors which have proven to be successful in terms of reproduction and survival. Flowers can remain fresh for only a few hours or they can last for months. Flowers may last longer where pollinators are sporadically available or when there is no pollinator reward or flowers may be ephemeral when either the cost of maintaining the flowers is high or when an alternate strategy of sequential blooming has evolved.

Flowering costs plants in terms of resources but there is often a trade-off between the need to reproduce and the relative cost of attempting to do so. While many orchids are able to conserve water in their leaves, roots or pseudobulbs, they are generally not able to do so with their flowers. Flowers lose moisture through transpiration. The longer flowers have to remain attractive to pollinators, the more resources are required to support the blooms. If flowers have nectaries then resources are also needed to produce nectar and to maintain that nectar source as a pollinator reward.

Two extremes of flower lifespan are seen with insect-pollinated Dendrobium crumenatum, the Pigeon Orchid, which has short-lived flowers, and with the hummingbird-pollinated Sophronitis coccinea, whose flowers not only remain fresh but also continue producing nectar weeks after the flowers have been pollinated. In the case of the Pigeon Orchid, all plants bloom synchronously after a sudden drop of about 9C as might occur during a heavy rain shower. Mass flowering can happen often throughout the year although individual flowers last but a day. It is believed that synchronous blooming favors the exchange of pollen between plants similarly affected by a climatic event. Manuel, Warren, and Miller, (1996) observed that the Sophronitis coccinea grows in 'swarms' on tall tree branches. After pollination, flowers do not wither but remain brightly colored and continue to produce nectar for visiting hummingbirds even after fruits begin forming, This strategy could increase hummingbird visit frequency to both pollinated and freshly opened blooms.

Pollination sets off a cascade of events usually beginning with the collapse of the petals and sepals but even pollen removal can lead to fading. Sometimes, flowers do not wither but become green and photosynthetic which could increase the availability of carbohydrate resources needed for fruit production. We see this phenomenon in orchids such as Phalaenopsis and Promenea.

We have investigated flower aging and fruit production in populations of the Large Yellow Lady's-slipper, C. parviflorum v. pubescens. We found that flower fading in this species is correlated with a cumulated minimum temperature of about 150 degrees Celsius. This effect has been consistent over the years we have observed this population, even between the extreme seasons of 1998 and 1999. In 1998, during an early warm spring season, average flower life was 11 days with flowers fading when increments were consistently above 10 C. In 1999, an extended cool spring, with increments generally below 10 C, flower life was extended to 13 days on average. Since the cumulated minimum temperature increases by daily increments of approximately 10 C, we can forecast flower longevity only to within one or two days. The extended spring of the year 2000 permitted us to observe the range of population response to the cumulative minimum temperature where individual flower life ranged from 5 to 23 days although the age at fading was tightly clustered around 15 days.

We found that fruiting outcomes were correlated with weather suitable for pollinator activity. Flower age impacts differentially on male and female function. Annual fruit set and therefore seed production is primarily a function of pollinator synchronization with receptivity. Pollen remains germinable provided anthers do not become infected with fungi, bacteria or yeasts as might happen during extended wet weather. We found that when pollinators were active only before pollen was available or only after the flowers had been open for more than 7 days, fewer capsules were produced. The highest fruit set was observed when pollinators were active four days after the majority of flowers had opened. There was no evidence that flowers faded more rapidly after pollination as has been reported for the Pink Lady's-slipper, C. acaule. Extended flower longevity clearly did not increase the opportunity to produce seeds of any one flower but it likely served to continually attract pollinators to the large colony where younger receptive flowers could still profit from pollinator visits.

Flower aging may have its origins in evolutionary processes but its impact on horticultural uses makes it an interest subject for further study.

References:

Light, M. H. S. and M. MacConaill. Climate Influences on Flowering and Fruiting of Cypripedium parviflorum var. pubescens. In Trends and Fluctuations and Underlying Mechanisms in Terrestrial Orchid Populations, pp. 85-97, P. Kindlmann, J. H. Willems and D. F. Whigham, eds., Backhuys Publishers, Leiden, The Netherlands. (2002).

Manuel, R., Warren, R., and D. Miller. Sophronitis coccinea: A Pollination Study. Orchids, The Magazine of the American Orchid Society, 612-616 (1996).

Van Doorn, W. G. Effects of Pollination on Floral Attraction and Longevity. Journal of Experimental Botany 48: 1615-1622 (1997).