Pollination temperature

Technique Flower Initiation
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1

Temperature can influence the success of some crosses. It may also alter the pattern of segregation when some hybrids are used as pollen parents.

Pollen tubes are tiny, multi-cellular plants. As a rule, the optimum temperature for growth of a species’ pollen tubes will correspond to the temperature at which pollination usually occurs in the native habitat of the species. If a species blooms early in the season, when the air is still cool, we may expect that the pollen tubes grow faster and fertilize more successfully at low temperatures. But a tropical species, such as Rosa gigantea growing in Burma, probably favors warmer temperatures for optimum pollen tube growth.

The time of day when pollination occurs also implies differences in optimum temperatures of pollen tube growth. If one species is pollinated by bees or butterflies in the afternoon, while a related species is visited by night-flying moths, hybrids between the two species are likely to be rare if they occur at all.

Takatsu, et al. (2001) discussed the difficulties they encountered in crossing Gladiolus tristis with a garden variety glad. When using G. tristis as the pollen parent, it was necessary to provide the lower temperatures required by the pollen tubes of that species.

I have found little information on pollination of wild roses. Heslop-Harrison (1921) studied pollination in wild roses. “Very early indeed I discovered that, to say the least, pollination in Rosa was conducted under peculiar circumstances. Every morning at 7 a.m. practically every young flower, no matter what its species, provided that its stigmas were mature enough to receive pollen, was already pollinated, and this maturity, since the roses are homogamous, was almost always shown at that hour. Thus it appeared almost certain that, if pollination was effected by insects, it could only be though the action of Noctuidae flying at dusk and dawn, or through Diptera and Hymenoptera busying themselves at daybreak. To determine which was responsible I paid special attention an hour or so after sunset to the blossoms of the day, and to those just ready to burst. At that time, as if by magic, every flower young and old was folded up for the night. Unless then brought about by casual day-fliers like the Noctuids of the genus Miana the agency of moths must be ruled out. There remained then the operations of Diptera and Hymenoptera to be considered. I therefore got up earlier, at 4 a.m. (GMT), before any insects were at work, when I found that even then every newly expanded R. pimpinellifolia had its stigmas powdered with pollen from its own overarching stamens.”

Assuming that the self-pollination of R. pimpinellifolia was successful, the pollen tubes must have been able to grow at the lower temperatures of the early morning.

If a hybrid is produced by crossing a species with cool-growing pollen tubes, and one with pollen tubes that prefer warmth, the temperature at the time of pollination may affect the pattern of segregation.

Pollen tubes are living plants. We may not assume that temperature preference is due to a single gene. Nor may we assume that the gene(s) responsible for pollen tube temperature preference are associated with only one chromosome. Furthermore, gene(s) responsible for pollen tube temperature preference are presumably linked to other genes that affect other characteristics of the species.

Therefore, if the pollen of such a hybrid is used at high temperatures, we should expect the offspring to favor the parent with warm-growing pollen tubes. The same pollen used at low temperatures will tend to favor the characteristics of the species with cool-growing pollen temperatures. Intermediate temperatures may favor a more “Mendelian” segregation of parental traits.

Karl

2

If gigantea pollen tubes favour warmer conditions for pollen tube growth, why is it that gigantea flowers through winter here in Tasmania? The same is true of R. bracteata, and R. clinophylla and of the gigantea hybrids ‘Nancy Hayward’, and ‘Golden Vision’. I have also noted that hip-formation on ‘Mutabilis’ is more successful throughout autumn and winter than it is during spring or summer. One would assume that flowering would be timed to coincide with optimal pollination conditions. Winter here is not cold by North American or European standards with temperatures locally dropping to a minimum of about -7 degrees Celcius at night with light-to-medium frosts (ponds sometimes freeze to a depth of about 1cm here) to about 12 degrees Celius during the day. I have not been able to get R. laevigata to flower down here yet though I am hoping this spring will be different. During winter we have little or no insect activity until about now (to coincide with Echium flowering). I have been wanting to use both bracteata and clinophylla in hybridising; however, they have proven difficult to work with due to their winter-flowering tendencies.

3

Maybe they depend on the calendar, not the daylength. I once read a book about apples which discussed the difficulties of taking the northern hemisphere cultivars to Australia (no joke, from the horticulture section of our university library).

But I think Karl is on to something. For about 35 years I’ve had Frau Karl Druschki in my garden. I never had OP hips formed, nor could I get it to take pollen of other CVs. But this year we had a very early start to the growing season (about a month ahead, after a mild winter) and there were a few hips set. Perhaps it was able to be crossed in northern Europe 100 years ago in a cool climate. Otherwise I don’t know how to explain the HMF pedigrees listing offspring. Of course I will harvest these hips when they’re ready and try to germinate something from them.

Mostly my pollination attempts fail in hot weather but I noticed White Out on campus the other day with apparent successful hip set on recent bloom clusters, despite a month of 100 or so highs. They might be empty of course, I didn’t cut them open to see.

4

[quote=SimonV]

One would assume that flowering would be timed to coincide with optimal pollination conditions. [/quote]

Simon,

Not at all. Many plants can be forced into bloom at times that are far from optimal for pollination.

C. C. Hurst (Mechanism of Creative Evolution, 1932, pp. 112-113) wrote:

“Several external factors may be the cause or occasion of this duplication of chromosomes. A severe frost, for example, will temporarily suspend divisions in the pollen grains and cause some germ-cells to form (provided the frost has not been too severe), bearing twice the normal number. These on fertilising normal egg-cells will produce triploids or, if the egg-cells have been similarly affected, tetraploids. In gardens where many plants are out of their natural environment, having come from countries with more regular climates, such occurrences are not infrequent. In their own country, once the winter is over, they produce their flowers with no set-backs, but in England, where we get a warm spell in the spring long enough to bring out the flowers, often followed by a severe frost for several nights just as the flowers are forming, many aberrations and abnormalities arise. Similarly in a wild state, an unusual season may upset many of the normal mechanisms of the plant. De Mol has discovered that many of the different chromosome types in bulbous plants have been due to the custom of drying off the bulbs after the flowering season and, in the case of bulbs for commerce, the subsequent forcing to produce early-flowering for culture in pots. These bulbs, being subjected to various degrees of temperature at the time of the formation of their germ-cells (these being formed deep down in the bud during the previous summer or autumn before flowering), produce various irregularities of division. Many of these irregularities fail to carry on but the few that struggle through will give rise to new races, sometimes of great beauty, for our gardens.”

[hr]

I do not know that Rosa gigantea is pollinated when the air is warm. Maybe it is native to cooler mountains, or is pollinated at night. My point is that we do not have nearly enough information about the natural history of roses. What are the typical pollinators in their native environments? When (season and time of day) are the flowers pollinated? How are their seeds distributed? What sort of soil do they favor in the wild?

The genus Rosa ranges from the Arctic to the tropics. Species are found high in the mountains and on seashores. Some live in deserts, others in swamps. I doubt that all would be pollinated by the same insects, and under similar conditions (temperature and time of day).

There are many factors that influence flowering time and fertility. Temperature and pollen tube growth is only one aspect of a complex puzzle. I have learned that it is a factor in species isolation in Rhododendrons and Gladioli. It is probably involved in some puzzling hybrid swarms of the Louisiana Irises. It is possibly an overlooked factor among roses.

I have seen bumblebees collecting pollen from my roses. I do not know, however, whether they are successful pollinators – let alone the primary pollinators of any Rosa species. I have read that thrips are common pollinators. Much more information is needed.

[hr]

Temperature may also affect female fertility, though for different reasons. Wulff (1959) discussed one such case:

"The ancestry of Schneeschirm, an ornamental rose, is not quite clear. It blooms twice a year. The first flowering period lasts from June to August. The second begins after a short interval, and ends with the first frosts.

"It is a very remarkable fact that the flowers of both periods differ in their meiotic behavior; only those produced during the first period are able to produce hips and viable achenes. Their reduction division is characterized by the occurrence of only 0-3 trivalents, with pairing to 7 bivalents and 7 univalents or 1 trivalent, 6 bivalents and 6 univalents. This reduction division proceeds rather regularly. The univalents, splitting twice, are mostly taken up into the young tetrad nuclei. Chromosome elimination is low, and so viable pollen grains and egg cells will contain 14 chromosomes.

“The offspring of about 60 plants were tetraploid, each seedling having 28 chromosomes in the root tips.”

He concluded,

“What we are learning from the differences in the meiotic behavior of the flowers of both periods is that the reduction division of the triploid Schneeschirm can be rather easily affected by environmental conditions. It seems reasonable to suppose that the warm temperature from June to the end of August causes the formation of no or few trivalents. This prevents chromosome elimination, and favors the production of hips and achenes. On the other hand, the colder temperatures of September and later months seem to be responsible for the high meiotic irregularities and the failure of fruit-setting.”

Karl

5

This thread also reminds me of something David Zlesak said to me back in 2009:

Roses have a self incompatibility mechanism and the form that it has is a gametophytic system rather than a sporophytic system. Diploid roses tend to express SI more than tetraploids, even though if we get down to it our polyploids likely express it in some ways as well. With a gametophytic system the pollen germinates and the tube gets stalled out within the style from pollen grains of self pollination or pollen that has the same particular alleles for the S gene from a different parent. There are proteins in the style that interact with the pollen tubes. Those pollen grains from different parents (with different S alleles) do not get stalled in the style and have the advantage of getting to the ovules at all or faster and participate in fertilization.

Heat can denature proteins and make them less effective at their job and allow pollen tubes from self pollen to grow through and participate in fertilization. I have had this happen in the greenhouse in summer with many diploid normally self incompatible polyanthas. I raised seedlings from those hips and am convinced they are selfs due to particular traits. For instance, thornless stems are recessive in this germplasm and the seedlngs from the one thornless rose I had in the greenhouse were all thornless even though there were thorny roses all around it. Flower color and double versus single blooms were all consistent with self fertilization as well.

The gametopytic SI system is more leaky and easier to work around than the sporophytic system and thankfully roses are have the one we can work around if for our objectives we would want to.

Don answered by asking:

David, is it possible to check for the presence of the S allele?

David’s response was:

I don’t think we have the tools readily handy in roses to do a good job at that. For instance, in cherries I believe and maybe in apples different S alleles have been numbered and cultivars characterized. It is so important for those crops because it influences which cultivars to put together in an orchard for cross pollination and good fruit set. In order to characterize S alleles and begin seeing how many different ones there are there needs to be series of crosses made and understanding of which combinations work and don’t work to build the matrix of data to assign numbered alleles to different clones.

One interesting thing that is in the literature and suggested, is that often at the diploid level we have SI expressed in crops, but at the tetraploid level it breaks down and selfing is more common. This is true with the polyantha roses I doubled as well as common in modern potatoes too. The idea is that the diploid may be S1S2 and then the induced tetraploid S1S1S2S2. SI is still active to some degree. Gametes that are S1S1 or S2S2 supposedly stall out in the style, but only those that are S1S2 get through. Somehow having this heterozygosity in the gamete even if it is the same alleles found in the maternal tissue can allow those gametes to go through. The induced 4x polyanthas set hips routinely in the greenhouse when the temp was moderate and the diploid polyanthas couldn’t it seemed due to SI.

So there is a genetic component to pollen tube growth/fertlisation as it relates to temperature as well, it seems.

6

Simon,

Yes, temperature has a variety of effects on fertility and growth. So does ploidy. Diploid hyacinths express self-incompatibility, but triploids and tetraploids do not – or at least not to the same degree.

Another note that may be of interest. Erlanson (1963) described a self-pollination mechanism in some roses: “In many wild roses the petals are past their prime by the third day and the flowers no longer close at night. The stamens may then rise up and their delicate filaments curve over to bring the pollen-bearing anthers onto the receptive stigmatic heads of the ovaries.”

In her study, she listed Rosa spinosissima as lacking this mechanism.

However, Heslop-Harrison (1921) wrote, “I therefore got up earlier, at 4 a.m. (GMT), before any insects were at work, when I found that even then every newly expanded R. pimpinellifolia had its stigmas powdered with pollen from its own overarching stamens.”

There have been some debates about the proper distinctions, if any, between spinosissima and pimpinellifolia. What Erlanson observed might be described as a last-ditch attempt to make seeds (though not in spinosissima). But the pimpinellifolia specimens Heslop-Harrison’s observed seemed to prefer selfing over crossing. I don’t know whether climate played a role, of if there were genetic differences in the plants.

Karl

7

Regarding Rosa gigantea:

The Garden p. 86 (Feb 23, 1907)

The flowers of R. gigantea in Lisbon are much larger than those in Oporto, owing, I suppose, to the soil there being a reddish clay over limestone, whereas in my garden it is a sandy loam on granite; very unfavourable for most Roses. I think that if “W. W.” were to bud or graft R. gigantea on to a strong-growing Rambler stock, he would soon get flowers. The plant should, I think, be against a wall, sheltered and with plenty of sun.—Baron de Soutellinho, Entre Quintas, Oporto, Portugal.

Karl

8

I recently found some more old research on the effect of temperature on pollination success, viability of seeds and on the depth of seed dormancy.

Von Abrams & Hand: Seed Dormancy in Rosa (1956)
“Germination studies have been made of ten hybrid rose seed populations over a five-year period, and the results compared to variations in climate occurring during the 30-day and 60-day periods preceding harvest. Controlled hand pollinations and subsequent growth of fruit and seed were carried out in the field. Year-to-year environmental or circumstantial variations amenable to control in the field were reduced to a minimum, leaving climate as the major variable. The dormancy of hybrid rose seeds, and the consequent germination pattern in time, may vary widely between years, and low-temperature treatment is not invariably prerequisite to extensive germination. Good correlation is indicated 'between germination and preharvest climate, particularly with the mean of the average daily temperatures for the 30-day period preceding harvest. Aseptic culture of excised embryonic plants provided high uniform germination for all five years of the study, indicating that the embryo itself is generally complete and that its potential germinability was not influenced by the climatic variation encountered. The validity of the relationship between pre-harvest climate and seed dormancy is further substantiated by the results of experiments in which seed-bearing plants were transferred to a green-house cubicle in which they were provided high temperature and light. The subsequent germination of seeds from these plants indicates a marked reduction in dormancy as compared to field-grown controls.”
http://bulbnrose.x10.mx/Roses/breeding/VonAbramsDormant1956/VonAbramsDormant1956.html

De Vries & Dubois: Rose Pollination and Temperature (1987)
“The germination percentage of seeds of outdoor-grown rose cvs was positively correlated with the temperature prior to fruit harvest, which would indicate greater after-ripening requirements at low than at high growing temperatures (VON ABRAMS & HAND, 1956). It is, however, the experience over the years of the present authors that independent of temperatures during fruit ripening, viable Hybrid Tea-rose seeds are ready for germination after 4 months stratification at 0°C. For the present experiment this may indicate that most seeds at 14 and all at 10°C did not contain a viable embryo, and that fruits were parthenocarpic. Contrary to the small seeds occurring in parthenocarpic fruits after GA treatment (DUBOIS & DE VRIES, 1986), the seeds present were of ‘normal’ size. For the present cross (‘Sonia’ x ‘Hadley’), temperatures between 18 and 26°C are suitable for pollination and subsequent growing of seed-bearing plants. Measured by the main criterion PE, 22°C or slightly higher appeared to be the most favourable temperature for breeding, thus confirming longstanding experience at IVT with numerous Hybrid Tea cultivars. As long as the separate effects of temperature on gamete functioning, fertilization and embryo growth and development have not been investigated, 22°C may be recommended from pollination to fruit harvest.”
http://bulbnrose.x10.mx/Roses/breeding/DevriesPollen1987/DevriesPollen1987.html

Karl

9

Karl, a few years ago I wrote an article in the newsletter on von Abrams and Hand’s work. They were both cutting edge plant physiologists of their time. Very few people have followed up on their observations except perhaps DeVries and Dubois. It was my impression that rose breeding turned out a lot easier further south than up by the Columbia river, so the big breeding operations of the major hybridizers moved to California. Market forces at work.

10

Larry,
The lack of follow-up is frustrating.

The two papers deal only with HTs.
De Vries & Dubois dealt with a single cross. They did not determine whether 22°C is optimum for growth of of ‘Hadley’ pollen tubes, or ‘Sonia’ receptivity. This distinction was beyond the scope of their research.

But the distinction may be relevant in crosses with species, which may differ in their optimum temperatures for both pollen tube growth and receptivity. For example, R. x hardii is thought to be derived from and R. persica. It appeared as a chance. Attempts to duplicate the cross have failed (so far as I have read). Could temperature be the barrier? Pollinating insects may have different schedules than human breeders; some are active in the wee hours when most folks are in bed.

Differences in optimum pollinating temperatures are certainly involved in isolating species on other families, along with differences in pollinators. E.g., the brick-red I. fusca is pollinated during the days by butterflies; I. hexagona var. giganti-caerulea is visited by night-flying moths. The two species can be crossed, artificially and rarely in the wild.
http://bulbnrose.x10.mx/Heredity/Anderson/Anderson_Introgressive/anderson01.htm

Karl

11

Actually von Abrams and Hand dealt with a number of specie introgressions in their set of crosses. It is true that the female in each case was the HT or floribunda if I recall correctly. Also note that these crosses were done around 1950 with CV introduced earlier. My impression is that all of von Abrams breeding was done in a very few years, though the products were not introduced until up to a decade later. The efficiency of crossing was not discussed directly. It was all about germination-dormancy and hormones.

Thrips as pollinators is a very interesting idea. I have lots of problems with finding them in roses when I open them. Of course they are carried along with the collected pollen. I assumed they were pollen eaters, but they might possibly be able to drag a pollen grain in the right general direction. I wonder though what kind of pollen load a single thrips insect can carry.

12

I’ve wondered why many crosses that fail early in the season succeed later in the season. In some cases, the failures are due to botrytis, which is more common in cool damp weather, but in most cases, there is no sign of botrytis. Perhaps the early crosses fail because the temperature is too cool for pollen tube growth.

13

Larry,
Three of the parents used were hybrids of species: “Numbers 39, 24, and 21 are, respectively, hybrids of R. eglanteria, R. wichuraiana and R. rugosa with hybrid Teas.”

What I had in mind (but failed to mention) is the range of temperatures under which species are pollinated in their native seasons and habitats. I should also mention altitude, since this is another factor that influences fertility.

If a particular species is normally pollinated in late Winter, while the snow is still melting, we should expect that the pollen tubes would grow better and fertilize ova most effectively at lower temperatures. On the other hand, a species that blooms during the heat of late Spring would probably have pollen tubes that grow better in heat.
Karl

14

Temperature (and photoperiod) can affect fertility in various ways. In some cases, pollen tube growth may contribute to failure of pollination.

But in other cases, temperature affects the pairing of chromosomes, which can alter the proportion of viable pollen. For example, Wulff (1959) discussed a triploid rose that was fully fertile during its Summer bloom, but became sterile in Autumn. In heat, the unpaired chromosomes became duplicated, leaving the cell with 14 pairs. But at lower temps the 21 chromosomes jumbled together as infertile combinations of uni-, bi- and trivalents.
http://bulbnrose.x10.mx/Roses/breeding/Wulff/Wulff_triploid.html

Karl