Heat, Variation, Flowering and Fertility

Wulff: Triploid Cytology (1959)
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.

Semeniuk: Temperature and Rose fertility (1964)
Thus, temperature causes profound modifications of both the accessory and reproductive parts of the flower. Temperature probably affects the plant mechanisms that control the synthesis and translocation of "hormones," which in turn influence initiation of floral parts, their direction and rate of development. The consequent variations in structure result from a chain of physicochemical reactions initiated by genes but controlled and modified by other genes and the external environment. Temperature effects do not result in any change in or recombination of the genetic factors, and are not transmitted to their descendents. These well-defined morphological characters were affected by the external environment. It is of interest that the lower limit of variability in number of petals imposed by the environment is 5, the basic number in the ancestral species.

Moe & Kristofferson: Temp & Light & Roses (1969)
Smaller flowers were obtained at high than at low temperature due to fewer and smaller petals. This is in agreement with earlier studies with 'Ma Perkins' and 'Crimson Glory' (Semeniuk 1964, Shisa and Takano 1964) In 'Baccara' all the petals were differentiated at stage 5 and 6 (figure 2), 3-4 weeks after cut back. At low temperature (12°C) a great many malformed flowers (bullheads) were present, while bullheads were never observed at high temperature (21°C). The temperature has therefore to be adjusted properly in order to obtain the desired number of petals and normal development of the flower.

de Vries, Dubois: Rose Pollination and Temperature (1987)
The effect of temperature on fruit set, seed set and seed germination was studied in 'Sonia' x 'Hadley' Hybrid Tea-rose crosses. 'Sonia' mother bushes were grown at constant temperatures (10, 14, 18, 22, 26°C) in the greenhouses of the phytotron until fruit ripening. Fruit set, fruit weight and number of seeds increased as temperature was higher. Optimum temperatures were found for days to fruit ripening (18°C), seed germination (22°C) and number of seedlings per pollinated flower (22°C). Fruit weight and number of seeds were positively correlated. For crossing and the subsequent growing of seed-bearing plants 22°C was the most favourable temperature. Effects of temperature on pollen tube growth, fertilization and seed germination are discussed.
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 (VONABRAMS& 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 0C.For the present cross ('Sonia' x 'Hadley'), temperatures between 18 and 26C are suitable for pollination and subsequent growing of seed-bearing plants. Measured by the main criterion PE, 22C 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, 22C may be recommended from pollination to fruit harvest.
[Pollination efficiency (PE) is defined as the number of seedlings obtained per pollinated flower.]

Picone: Rhythmic emission of scent in 'Quatre Saisons' (2004)

Heslop-Harrison (1921) p. 270
I therefore got up earlier, at 4 a.m. (GMT), before any insects were at work, when I found that even then every newly expandedR. pimpinellifoliahad its stigmas powdered with pollen from its own overarching stamens.

W. Paul (1848) pt. 1, p. 84
According to the statements of M. Boitard, there is scarcely any limit to the variation of Roses produced from seed. He affirms that M. Noisette, a French cultivator, has never sown seeds of the Chinese Roses (R.INDICA) without raising some Scotch Roses (R.SPINOSISSIMA) from them. He states, This fact is not supported by a solitary occurrence, but has been frequently observed by that cultivator, and is further attested by the evidence of M. Laffay, who raises seedlings on an extensive scale, and has this year between 200,000 and 300,000. It were easy to conceive a mistake occurring in the gathering, storing, or sowing of the seeds; but when the facts have been noticed repeatedly, and by different individuals of known probity and great horticultural attainments, the evidence, we think, must be deemed conclusive.

Thomas Rivers (1843) pp.102-103
About four years since, in a pan of seedling Moss Roses, was one with a most peculiar habit, even when very young; this has since proved a hybrid rose, partaking much more of the Scotch Rose than of any other, and till the plant arrived at full growth I thought it a Scotch Rose, the seed of which had by accident been mixed with that of the Moss Rose, although I had taken extreme care: to my surprise it has since proved a perfect hybrid, having the sepals and the fruit of the Provence Rose, with the spiny and dwarf habit of the Scotch Rose; it bears abundance of hips, which are all abortive. The difference in the fruit of the Moss and Provence Roses and that of the Scotch is very remarkable, and this it was which drew my particular attention to the plant in question; it was raised from the same seed, and in the same seed-pan, as the Single Crimson Moss Rose: as this strange hybrid came from a Moss Rose accidentally fertilised, we may expect that art will do much more for us.

J. Amer. Soc. Hort. Sci. 131(1): 66-73 (2006)
Characterization and Genetic Relationships of Wild Species and Old Garden Roses Based on Microsatellite Analysis Valentina Scariot, Aziz Akkak, and Roberto Botto
Two cases of uncertain attribution to these sections were examined: 'Andrewsii', considered belonging either to the section Pimpinellifoliae (Beals, 1985) or to the section Rosa, Moss group (Beales et al., 1998), was genetically closer to Pimpinellifoliae; ...

[CybeRose Note: More evience that the pollen remains available after the flowers have self-pollinated.]

Sprenger: Rosa moschata var Korfuana (1923)
They smell particularly fine in the late evening, at night and in the fresh morning. During the day their volatile oil seems to evaporate so rapidly that little or nothing remains perceptible to the human sense of smell. It is a mild, pleasant musky scent. One collects the rosettes for its sake, to put them between the laundry and clothes, but also in winter to stretch the tea with them, which then regulates the digestion better.

Fernald: Rosa nitida (1926)
But we found two other species which we had not previously thought of as peculiarly fragrant. One was the ubiquitous Rosa nitida Willd. This shrub was in such beautiful condition that we yielded to the temptation to put some into our collecting boxes, although herbaria are full of Newfoundland specimens. Opening our boxes in the evening, we were surprised by a delicious and pervading fragrance as of tuberoses (Polianthes tuberosa L.). This came from the flowers of Rosa nitida and our respect for the common rose of southern and central Newfoundland vastly increased.

Allen: Rosa arvensis: A problem wild rose (1987)
After the circulation of my information paper in 1979, John Watts, in North Wales, made some careful observations in the Conwy area, where the species is common locally, and he reported the flowers as scentless by day but sometimes having a faint scent, just discernible, at dusk in warm weather.

HelpMeFind: Rosa clinophylla (5 Mar 2022)
Plazbo (Australia): Not quite night night yet but just past sunset (but can still mostly see without a torch if that makes sense) and it's very mild and inoffensive. The flowers close up at night though so nocturnal pollinators would be "locked out" as it were.

[CybeRose Note: This may explain why it has been so difficult to repeat the cross that produced R. x hardii. The Hulthemia pollen must last long enough to pollinate the R. clinophylla blossoms around dusk.]

Hormaza, Herrero: Pollen Selection (1996)
The first positive results were obtained for tolerance to low temperatures with Lycopersicon esculentum (cold sensitive) and Lycopersicon hirsutum (cold tolerant) by using either a mixture of pollen from the two species (Zamir et al., 1981) or pollen from an F1 generated crossing the two species (Zamir et al., 1982; Zamir and Vallejos, 1983; Zamir and Gadish, 1987). Schön et al. (1991) followed a similar approach with barley (Hordeum vulgare), crossing winter (cold tolerant) and spring (cold sensitive) cultivars. F2 plants generated from self-pollination of F1 plants at low temperatures showed a preferential segregation in favor of a restriction fragment length polymorphism marker from the winter cultivar compared with F2 generated from F1 plants grown under control conditions. In maize, Lyakh and Soroka (1993) reported that the cold tolerance of the F2 generation was higher when pollination of F1 plants was carried out at low temperatures than at normal temperatures. Positive results have also been obtained in alfalfa (Medicago sativa) selecting for high temperature tolerance (Mulinix and Iezzoni, 1988).

Swingle: Hybrids (1897)
Another even more remarkable case is that of certain hybrid foxgloves. Koelreuter, Gaertner, and Focke observed that the hybrids of Digitalis purpurea crossed with D. lutea produced, in addition to a more or less constant intermediate form, a number of forms very different in appearance. Focke observed among the hybrids which grew spontaneously from a cross-fertilized capsule that he had neglected to harvest when ripe, a number of aberrant forms, the most remarkable of them resembling in all particulars a different species (Digitalis tubiflorum). All artificially produced hybrids of these two species have been found to be completely sterile to the pollen of the parent species. The hybrids also occur in nature, in which case they are said to sometimes bear seed.

Hannibal: Crinum moorei pollen (1999)
Crinum moorei pollen: There is nothing wrong with it when you breed Amarcrinum in 70 degree F weather. It's plenty potent. It is the higher temperatures that are a problem.

Takatsu et al. Temperature and gladiolus pollination (2001)
Air temperature had a marked effect on fertility in controlled crosses (Fig. 2). At 20C, the pollen tube elongated very rapidly, fertilization was accomplished 12 h postpollination, and the fertility increased to 89.9% 5 d postpollination. At 15 and 25C, pollen tube elongation slowed, fertilization was first observed 3 and 1 d postpollination, and the final fertility increased to only 76.4% and 73.2%, respectively. At 30C, pollen tube elongation was inhibited more and the final fertility was very low (1.4%). The final rate of fruit set decreased from 73.1% to 0.0% as the temperature increased, but pollen tube growth and fruit set were found even at 30C following self-pollination of 'Traveller' (Fig. 3). Crossing barriers frequently occur in interspecific crosses, but sexual barriers preventing crossing have been separated into pre- and postfertilization barriers (Van Tuyl, 1997). In this study, the results of self-pollination of 'Traveller' indicated that female fertility is good at 30C. Although fertilization was observed in interspecific crossing at 30C, no fruit set was obtained. The best temperature for fertilization was 20C (Fig. 2), but that for fruit set was 15 C (Fig. 3). These results show that postfertilization barriers inhibit interspecific hybridization between 'Traveller' and G. tristis, and may explain the failure to obtain hybrids without embryo rescue (Takatsu et al., 1996). Our results suggest that lower air temperatures (15 to 20C) increase fertility and may be appropriate to help overcome postfertilization barriers when hybridizing G. x grandiflora and G. tristis. Humidity and air temperature is very high (over 30C) in summer in Japan; thus, crossing in autumn is preferred if the flowering time can be controlled.

Delp: Heat in Hybridizing Rhododendrons (1980)
Based on my experience, rhododendron crosses made under controlled conditions of high temperatures and humidity produce larger and more seeds than those made at cooler temperatures. In certain instances the use of high temperatures and humidity produces seed from wide crosses where normal techniques have been unsuccessful. This new technique seems to have potential for combining the drought resistance and brilliant colors of Malaysian rhododendrons with the cold resistance of hardy hybrids and species.

Focke: Digitalis hybrids
Another even more remarkable case is that of certain hybrid foxgloves. Koelreuter, Gaertner, and Focke observed that the hybrids of Digitalis purpurea crossed with D. lutea produced, in addition to a more or less constant intermediate form, a number of forms very different in appearance. Focke observed among the hybrids which grew spontaneously from a cross-fertilized capsule that he had neglected to harvest when ripe, a number of aberrant forms, the most remarkable of them resembling in all particulars a different species (Digitalis tubiflorum). All artificially produced hybrids of these two species have been found to be completely sterile to the pollen of the parent species. The hybrids also occur in nature, in which case they are said to sometimes bear seed.

Kettlewell: Temperature effect on pigment; Heliothis peltigera and Panaxia dominula (1944)
... the reactions of pupae to a constant, uniform, but normal temperature, whilst producing no shock, nevertheless subjects them to a condition of which the organism has no experience so that the genes which normally come into play in rotation in laying down the normal pattern in a normal and variable environment, are disturbed in relation to one another, with the result that areas of wing, which are normally flooded with pigment at a given period under natural varying conditions, find themselves at a different stage of development and unable to receive their normal pigment.

Jones, D.F.: Maize sterility and Heat (1947)
Three different lots of sprouted seedlings were held at 40, 50 and 60 C. for one hour. (104, 122 and 140 F)
... The result that was not anticipated was the pollen sterility in all treated lots. Normal tassels were produced with well-developed florets but the anthers were small and shriveled and for the most part remained enclosed in the glumes. In view of the fact that high temperatures sterilize the male germ cells in animals, from amphibians to mammals, these results are highly significant. This influence on growth is an anti-vernalization effect and may have wide usefulness in the production of hybrid seed especially if shown by other plants as well as maize.

Went: Thermoperiodicity (1948)
Another set of phenomena, which are closely related to vernalization, are the chilling requirements for development of buds of deciduous trees. In most of these plants the buds are dormant for a considerable part of the winter, and can be forced into growth only after having been subjected to freezing temperatures. In some cases the low temperatures may have no other effect than supplying a stimulus, so that a definite time after being subjected to a sudden drop in temperature, irrespective of the duration of this lower temperature, development occurs. The flower buds of the orchid Dendrobium crumenatum offer a clear-cut example (COSTER 1926, KUIJPER 1933). Nine days after a sufficiently rapid drop in temperature (usually associated with a heavy rainfall) the flowers of this orchid open, causing a sudden burst of flowering over a wide area. Some other orchids seem to behave in the same way, and probably other plants as well (gregarious flowering of Coffea liberica). In these cases the flower buds develop gradually up to a certain point, beyond which no growth is possible under the prevailing temperature conditions. The longer the temperature drop is delayed, the more flower buds will have reached the critical size, and the more abundant the flowering is after the temperature drop.

Waddington: Crossveinless (1953)

Knight: Effects of high temperature on plants (1819)

Roberts & Struckmeyer: Vernalization (1948)
When plants which come to flower early under relatively warm night temperatures as, Cannabis sativa (hemp), Datura stramonium (Jimpson weed), Euphorbia pulcherrima (poinsettia), Glycine max (soybean, var. Biloxi), Nicotiana tabacum (tobacco var. Maryland Mammoth), Panicum milaceum (millet), Phaseolus vulgaris (kidney bean), Solanum capicastri (ornamental pepper), Xanthium echinatum (cocklebur) and Zea mays (corn) are transferred to an environment with a warm (75°F) dark period of 13 hours and cool light period (55°F) of 11 hours, they soon become nearly etiolated or at least produce new growths with very little green color (23). Such plants are of particular interest from the standpoint of the physiology of sexual reproduction. They differentiate and develop blossoms and may even set fruits at almost the same rates as normally green plants in cool nights and warm days. Long continued development is not usual with such pale plants but the initiation of sexual reproduction is not inhibited and only slightly delayed by a lack of green color.

Highkin: Temperature-Induced Variability in Peas (1958)
Pea (Pisum sativum) plants were grown under conditions of constant temperature and artificial light or in controlled-temperature greenhouses in which there was a diurnally fluctuating temperature. It was found that: (1) A constant temperature is inhibitory for growth despite the fact that it may be the most nearly optimal constant temperature; (2) the inhibitory effect of a continuous exposure to constant temperature is cumulative from generation to generation reaching saturation with approximately the fifth generation; (3) differences in the temperature conditions of growth, whether constant or diurnally fluctuating, result in differences in the growth characteristics of the offspring of plants grown in these controlled conditions. The results of these experiments show that the phenotype of the plant is the summation of its genetic heritage together with the summation of the parent and present environment. Any environmental effect is inversely proportional to the number of generations by which that environment is removed from the generations under consideration.

Highkin: Vernalization & Heat Resistance in Peas (1959)
The effect of a cold treatment on the response of pea plants to high temperature has been studied. It was found that there is a marked increase in heat resistance as a result of a cold treatment. The induction of heat resistance as a result of vernalization appears to be independent of the induction of the floral stimulus resulting from such a treatment. This is indicated by two observations: 1) Vernalization does have an effect in decreasing heat damage as well as effecting seed viability in a strain of peas which is non-vernalizable so far as flowering is concerned. 2) In a strain which is vernalizable, high temperature devernalizes with respect to flowering. However, vernalization markedly increases the heat resistance of this strain.

Clausen: Wimmera Rye grass (1959)
J. P. Cooper (1954) found that when Wimmera ryegrass is sown outdoors in spring it will initiate flowering at the seventh to eighth node (mean 7.2). When it is sown in a heated greenhouse and given continuous light, considerable previously hidden variability is disclosed, and the seedlings initiate flowering at various nodes, ranging from the fourth to the twenty-first, as shown in Table V (mean node, 12.5). The variability will again be hidden if, before the continuous light treatment, the seeds are vernalized for six weeks at 3C. When the cold treatment is followed by continuous light, the plants will initiate flowering at the fourth to the sixth node (mean 5.1).
    The cold treatment apparently starts and equalizes certain gene-controlled processes related to development. No previous selection has taken place for the combination of heated greenhouse and continuous light, and the plants accordingly reveal a considerable degree of residual variability under this artificial condition.


MacDougal: Cypripedium montanum trichomes in darkness (1903)
... the growth of Cypripedium in darkness is characterized by a non-development of the pointed hairs on the leaves, and the excessive development of the glandular trichomes.


Some plants will survive, even thrive, in high humidity all year long, yet will fail to yield fruit unless they experience a period of dry air.

Collins: Mangos (1903)

Collins: Avocados (1905)

Heat and Growth Biblio