CA1137771A

CA1137771A - Treatment of plants of the family compositae

Info

Publication number: CA1137771A
Application number: CA000325274A
Authority: CA
Inventors: Richard P. Pharis
Original assignee: Pharis R P
Current assignee: Pharis R P
Priority date: 1979-04-09
Filing date: 1979-04-10
Publication date: 1982-12-21
Also published as: GB2052466B; GB2052466A; NL7902819A

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a method of inducing flower formation in plants in the family compositae which comprises applying to said plants effective amounts of a cytokinin, a gibberellin and a growth retardant.

Description

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This invention relates to a method of inducing flower formation in plants in the family compositae and par-ticularly, but not exclusively to plants in the genus chrys-anthemum.
It is well known that many plants in the family compositae tend to flower naturally only during so-called "inductive photoperiods", i.e. during periods of relatively short day length, e.g. during later summer, autumn and winter.
In view of the commercial value of such flowers particularly chrysanthemum flowers, it is desirable to induce flower formation during periods when flowering would not normally :
occur naturally, e.g. during the spring and summer.
~litherto, this has been achieved by growing chrys-anthemum plants in green-houses and producing short day length ; conditions artificially by shading the plants during part of : the day over long periods of time, for example several weeks, ` using dark screens. The use of dark screens has certain disadvantages and in particular (1) the use of screens in summer often results in overheating and causes flower defor-mation, (2) screened plants commonly produce inferior blooms ; due to reduced photosynthesis, (3) labour costs for operating manual screens is high, particularly at week-ends and during holidays and ~4) the capital costs of installing automatic screens is high.
Attempts have been made to stimulate flower bud : formation during non-inductive photoperiods by chemical means using e.g. plant hormones. However up till now such attempts have generally resulted in the stimulation only of so-called "crown buds", which do not constitute salable flowers.
A method of treating plants of the family compositae has now been developed which enables the production of flowers - 1 - ~

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during non-inductive photoperiods and which can reduce the extent to which shading is required.
According to one aspect of the present invention there is provided a method of inducing flower formation in plants in the family compositae, which comprises applying to : said plants effective amounts of a cytokinin, a gibberellin and a growth retardant.
Gibberellins are a group of plant growth regulators originally derived commercially from cultures of the fungus Gibberella fujikori. A description oF these substances, which promote cell enlargement and the majority of which contain the gibbane ring is given by J F Grove in "The Gibberellins", Quarterly Reviews, 1961, 15, 56 - 71 published by the Chemical ~ Society (Lond). The gibberellins include, for example, ; gibberellin A3, also known as gibberellic acid, ~hich is dis-closed in United Kingdom Patent Specification No. 783,611 and gibberellin A4. A further example, as disclosed by United Kingdom Patent Specification No. 914,893, is gibberellin A7.
The patent specifications referred to above also disclose the preparation of ammonium, alkali metal and alkaline earth metal salts of gibberellins A3 and A7. Gibberellin A7 is obtained commercially as a mixture with an equal proportion of gibberellin A~, in ~hich form it is used for plant growth regulating purposes.
Although any Cl9 or C20 gibberellin may be employed in carrying out the method of the invention, for example ~.
gibberellins Al to A57, it is preferred to use a gibbèrellin selected from gibberellins Al, A3, A4, A5, A7, A9, A13 and Al41 especially gibberellins A3 and A13.
~ytokinins are a group of substances exhibiting.a stimulatory effect on division of plant cells. Substances :~ 2 .. , ~.1 , ' . :

having cytokinin-like activity frequently influence other aspects of plant growth~ such as, for example retardation of senescence, promotion of cotyledon expansion and inhibition of root development. Examples of cytokinins of biological origin are kinetin and zeatin.
Preferably in view of their more ready availability, synthetic cytokinins are used in carrying out the method of the invention such as9 for example purine derivatives, such as ; 6N-benzyladenine, and phenylurea derivatives. Most prefér-ably, the cytokinin is a substituted urea of the formula RlNHCONHR2 wherein Rl is a hydrogen atom, a substituted or unsubstituted hydrocarbyl group or a substituted or un-substituted heterocyclic group and R2 jS a substituted or un~
substituted phenyl group. The hydrocarbyl groups represented by R may be aliphatic or aromatic, but are preferably aryl groups.
Suitable aliphatic groups include alkyl groups, both straight and branched having 1 to 12 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl; alkenyl and alkaryl groups having 1 to 12 carbon atoms; and cycloalkyl groups such as, for example, cyclohexyl. The preferred aryl group is phenyl, but 1- or 2 naphthyl may also be used. Examples of suitable heterocyclic`
groups include pyridyl, pyrrolyl, quinolyl, indolyl, morpholyl and furyl. The hydrocarbyl and heterocyclic groups repre-sented by Rl and the phenyl groups represented ~y R2 are optionally substituted with one or more of a wide variety of substituents, including in particular alkyl, alkoxy, halo-alkyl, carboxy, carboxyalkyl, cyano, amino and nitro groups,as well as any of the halogens (F, ~1, Br and I). Examples of A - ` :~

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useful compounds include the following:

Compound ~o. Rl R2 C6H5 C6~15

2 C6H5 p-F.C6H4

3 H p-Br.C6H4

4 4-pyridyl C6H5 C6H5 No2-4cH3-c6H3 6 ~l 3'4C12-C6~l3 8 m CH3.C6H4 m-F.C6H4 Further examples of phenylureas having cytokinin-like activity are cited in an article entitled "Retardation of Leaf Senescence by Urea Cytokinins in Raphanus Sativus"
(Kefford et al, Phytochemistry 1973, 12 995).
Preferably, however, diphenylurea itselF is used in the method of the invention in view of its relatively high activity ease of manufacture and apparently favourable toxi-cological and environmental properties.
Any growth retardent capable oF inhibiting stem extension may be used in the method of the invention, but preferably ~-cyclopropyl-~-(4-methoxyphenyl)-5-pyrimidine methanol (also known as ancymidol or EL-531) is used. Other examples~of growth retardants include:
'Phosfo (2,4-dichlorobenzyl-tributyl phosphonium chloride) (Virginia - Carolina Chemical Co) 'Cycocel' (2-chloroethyl ammonium chloride) (Americas Cyanamid Co) 'B-Nine' otherwise 'ALA (daminozide ~ 2,2-dimethylhydrazide) (Uniroyal Ltd) (N-pyrrolidine succinamic acid) - 4 _ 7~L

(Uniroyal Ltd) 'Etheph~n' (2-chloroethane phosphoric acid) and ' 'Alden' (Piproctanylium bromide) (Dr R Maag Ltd Switzerland) Only relatively small quantities of gibberellin, cytokinin and growth retardant need be applied to plants in order to stimulate flower formation in accordance with the invention. For example, expressed in terms of the amounts applied per plant the gibberellin and cytokinin are preferably each applied at a rate of from 10 ~g to 1 mg per plant, preferably 20 to 500 ~g per plant and most preferably 50 to 250 ~g per plant. The amount of growth retardant required will depend on the degree of activity of the particular retardant used. Thus~ the growth retardant EL-531 is prefer-ably applied at a rate of from 50 ~g to 5 mg per plant, and most preferably 100 ~g to 1 mg per plant. Larger quantities of the other growth retardants referred to are likely to be required.
The gibberellin, cytokinin and growth retardant may be applied to the plants in any convenient manner, for example in combination with an inert diluent or carrier in liquid formulations or powders. Most preferably the gibberellin and cytokinin are applied to the foliage in the Form of a spray solution or suspension containing from 1 to 1000 mg/litre preferably 10 to 100 mg/litre of each substance. The liquid carrier for such sprays may comprise an aqueous base contain-ing surfactants, but optimum results have been observed using a spray composition based on an organic solvent, particularly a water-miscible organic solvent such as ethanol.
The growth retardant is preferably applied to the soil or other medium in which the plants are growing in the form of an aqueous solution or suspension which in the ease of

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the growth retardant EL-531 preferably contains up to 1 g/litre of the growth retardant, most preferably 10 to 500 mg/litre.
Although the number of applications of gibberellin, ; cytokinin and growtn retardant which need be applied to the plants in accordance with the invention is not unduly criti-cal, it is preferred to apply at least the gibberellin and cytokinin repeatedly at intervals of from 2 to 10 days. Par-ticularly satisfactory results have been obtained using twice weekly applications of gibberellin and cytokinin. Generally only a single application of growth retardant is needed.
Although treatment with gibberellin, cytokinin and growth retardant in accordance with the invention can result in flower production under lony day conditions without any need to subject the plants to short day conditions arti-ficially, it has been found that by subjecting plants treated in the manner described above to short day length photoperiods , for a relatively short period of time, e.g. for less than three weeks, the degree of flowering and/or the quality of flowers obtained may be enhanced. A particularly effective regime is to subject the plants to alternating periods of short and long day length. Preferably such periods are from 1 to 10 days duration. Most preferably the short day length periods comprise from 3 to 6 successive short days and long day length periods comprise from 1 to 5 successive long days.
Most preferably the plants are subjected to a regime com-prising two periods of short days intercalated with one period of long days.
With the use oF alternating periods of short and long day length as described above in combination with the application of cytokinin and gibberellin as described above,

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it has been found that flower production can be induced even when no growth retardant is used or when only one growth regu-lator selected from gibberellins and cytokinins is used. Thus according to a further aspect of the invention there is pro-vided a method of inducing flower formation in plants in the family compositae which comprises applying to said plants effective amounts of a gibberellin and a cytokinin and sub-jecting the plants to alternating periods of short and long day length.
By the term "short and long day length" as used herein is meant that during a period of 24 hours, the plants are subjected to light (natural or artificial) For less than 12 hours, preferably less than 10 hours and most preferably less than 8 hours. Conversely, the term "long day length" as used herein indicates that during a period of 24 hours, the plants are subjected to light (natural or artificial) for more than 12 hours, preferably more than 14 hours and most prefer-ably more than 16 hours.
In view of the great commercial values of chrys~
anthemum flowers, it is particularly advantageous to treat plants of the genus chrysanthemum by the method of invention, particularly the so-called florist's chrysanthemum, i.e.
plants which are variants of the species chrysanthemum morifolium.
The method of the invention may, however, be applied to other plants in the family compositae which normally require short days in order to flower for example plants of the genus cosmos.
The treatment chrysanthemum plants of the cultivar Gt. White Indianapolis in accordance with the invention will now be described by way of example.

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EXAMPLES
Plants were grown in greenhouses under natural photoperiod (supplemented with incandescent light - about 30 ft.-c.) or in growth chambers under approx. 2500 ft. c. for 3 months. Day temperature was about 20C, night temperature about 12C. Long day, when given in growth chambers was 16 hrs, when given in greenhouses was 18 hrs.
Plants were decapitated 3X before starting the tr`eatmen't to'`remove any "memory" of a long night from transport (e.g. rooted cuttings were flown to Calgary, Canada where the experiments were carried out, from Ontario).
The following substances were applied s'ingly and in combination to groups of plants:
N-Benzyladenine (BA) estimated dosage 50 ~g/plant/
twice weekly (e.g. 10 mg/l sprayed to drip-off) Gibberellin A (GA3) estimated dosage 400 ~g/plant/
twice weekly (e.g. 80 mg/l sprayed to drip-off) ;~ 20 Diphenyl urea (DPU~ estimated dosage 100 ~g/plant/
twice weekly (e.g. 20 mg/l sprayed to drip-off) Ancymidol (A rest; EL-531) 0.5 mg/plant/total (e.g. 50 ml of a 10 mg/l soil drench solution).
Groups of plants were also subjected to various-lighting regimes. Particularly some plants were subjected to continuous long day conditions (zero short days~, some plants were subjected to varying periods of short days and so~me plants were subjected to alternating periods of'long and short' days.

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The results of these experiments are set forth in the fo110wing Tables in which the abbreviations used have the following significances 1. Growth regulators GA3 Gibberellic acid (gibberellin A3) DPU N,N'-diphenylurea EL-531 Ancymidol BA 6N-Benzyladenine 2. Photoperiods SD Short day LD Long day 3. Bud morphology v Vegetative buds cr Crown buds fl Flowers cl Crown changing into leaves b Unopened flower buds The numerical values against the types represent the numbers of buds of the given type, expressed as percentages.

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It can be seen from the results in the Tables that , in the cultivar Gt. White Indianapolis crown huds occasionally develop under continuous long day length conditions (LD) and on plants which receive a minimum of 12 short days (SD), but no hormonal treatment. Crown buds regularly develop under ; continuous LD when treated with GA3 and BA.
. Treatment with 200 or 400 yg of GA3 ~ 50 ~g of BA
. resulted in production of flowers after 22 SD. In the paral-. lel control only crown buds were formed (see rable 1).
. The results of Table 2 indicate that the growth retardant, Ancymidol speeds up formation of flowers, if applied together with BA + GA3. A better cytokinin than BA is DPU (see Table 3).
A photoperiod regime where long days are interca-. lated between two short day periods was found to be more effective than the corresponding amount of SD (see Table 4).
Also the intercalated treatment with only one cycle of SD/LD/SD (5/2/5) shows better results when the plants are treated with GA3 t BA.
Experiments have shown that a 4/3/4 cycle of short . .
-~ and long days is even better or the same as 18 continuous SD.
:, Table 5 again confirm that intercalation of short and long days in a 4/3/4 is cycle is as good as 11 SD in a separate . ~ .
;;~ experiment.
. It has been found that DPU alone does not promote flowering even when applied together with ll SD. However, when applied together with GA3~ DPU causes flowering ;n plants `~ receiving 4/3/4 or 11 SD. Given that three long days can be programmed into a week-end treatment, 4/3/4 is economically more useful than shading for ll continuous days.

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, Although the theoretical basis for the phenomena ~i descrjbed herein is not known for certain, it is possible that the promotive effect of short days is caused by the synthesis of one specific compound capable of promoting development and growth of the initiated flower. However, it is more likely that short days allow an optimal baZan~e of factors promotive to floral development to exist while inhibiting the rapid .., ~"' vegetative growth that would otherwise occur. Such inhibition ~ .
of vegetative growth could take place by reduced photo-.~, synthesis, reduced levels of promotive compounds, and/or increased levels of inhibitory compounds. Changes in levels of promotive and/or inhibitory compounds can be effected by changes in either synthesis or catabolism. Once the balance has swung toward reproductive development the process may be s-elf-catalytic and irreversible. It is also likely that many of the factors promotive of floral growth and development under short day are also used in vegetative development under long day. However, under long day the plant either "does not . .- .
allow them to accumulate to threshold levels sufficient for floral development", or "balances them with substances inhibi-. ,: , .
tory to flora~ development".
It is believed that the process of the invention mimics an endogenous "optimal balance" of growth hormones, the GA and DPU promoting rapid cell division in the apical zone o~
the meristem (e.g. the apex broadens), perhaps mobilizing -~
photosynthate to these zones so that growth is directed toward ~-i~ upper portions of the mer;stem rather than toward the~lower, or sub-apical region (as is the case in continued vegetative growth). The growth retardant (EL-531 ) may reduce sub-apical -`
meristem cell division and elongation so that this region non longer "demancls" photosynthate and other promotive factors to `- -~.` .

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the exclusion of the rest of the apical meristem. The few inductive short days required in order to achieve optimum results in carrying out the process of the present invention ,~ perhaps begin a trend in the production and/or disposition of appropriate endogenous growth hormones or other promotive factors of floral growth and development which normally increase under the inductive short days. When we move the plant, or change the photoperiod back to long days after the m few short days there is no effect on subsequent flower , development as long as the growth regulator comb;nation is administered. It is possible that the exogenous growth regu-. . .
, lators (e.g. GA and DPU) continue to mobilize photosynthate i, toward the upper portion of the meristem, away from the sub-apical meristem. Internal recovery to the "pre-existing"
, ; long-day state after transfer from short day back ;nto day probably takes more than several days. By this time a reversal of floral development and the "auto-catalytic processes" which may accompany it may not be feasible.
'~ Data from my experiments also indicate that 20 treatment with DPU (but without a gibberellin) can increase the percentage of plants producing flower buds or flowers (relative to control plants).
It has also been found that treatment with the growth retardant EL-531 is necessary for DPU to be effective in the absence of a gibberellin. Such a result implies that the growth retardant may be exerting its inhibitory effect on vegetative growth by a mechanism other than that of reducing endogenous gibberellin levels (e.g. endogenous gibberellins available for hastening reproductive development may actually 30 be increased by growth retardant treatment since the block to vegetative growth may occur at another level). Flowers ~11 ~i 1 9 ~;
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obtained using the treatments containing no gibberellin, only DPU and EL-531 are very close to being commercially acceptable.
However, to obtain a consistently high percentage of acceptable flowers the preferred treatment should include a gibberellin in addition to DPU and the growth retardant.
Although either llSD or a sequence of 4SD/3LD/4SD
.:~
, can be used, the latter treatment is economically more useful since three long days can be programmed into a week and f'.: treatment.
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Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A method of inducing flower formation in plants in the family compositae which comprises applying to said plants effective amounts of a cytokinin, a gibberellin and a growth retardant capable of inhibiting stem extension.

2. A method according to Claim 1, wherein the cytokinin and gibberellin are applied to the plant foliage and the growth retardant is applied to the medium in which the plant is growing.

3. A method according to Claim 1, wherein the cytokinin is substituted urea of the formula R'NHCONHR2 wherein R' is a hydrogen atom, a substituted or unsubstituted hydrocarbyl group or a substituted or unsubstituted hetero-cyclic group and R2 represents a substituted or unsubstituted phenyl group, said substituents being selected from alkyl, alkoxy, haloalkyl, carboxy, carboxyalkyl, cyano, amino, nitro and halogen.

4. A method according to Claim 3, wherein the cytokinin is N,N'-diphenylurea.

5. A method according to Claim 1, wherein the gibberellin is selected from gibberellins A1, A3, A4, A5, A7, A9, A13 and A14.

6. A method according to Claim 1, wherein the gibberellin is gibberellin A3.

7 . A method according to Claim 1, wherein the gibberellin is gibberellin A13.

8. A method according to Claim 1, wherein the growth retardant is .alpha.-cyclopropyl-.alpha.-(4-methoxyphenyl)-5-pyrimidine methanol.

9. A method according to Claim 5, wherein the gibberellin is applied at a rate of from 10 µg to 1 mg per plant.

10. A method according to Claim 9, wherein the gibberellin is applied at a rate of from 20 to 500 µg per plant.

11. A method according to Claim 10, wherein the gibberellin is applied at a rate of from 50 to 250 µg per plant.

12. A method according to Claim 10, wherein the cytokinin is applied at a rate of from 10 µg to 1 mg per plant.

13. A method according to Claim 12, wherein the cytokinin is applied at a rate of from 20 to 500 µg per plant.

14. A method according to Claim 13, wherein the cytokinin is applied at a rate of from 50 to 250 µg per plant.

15. A method according to Claim 12, wherein the growth retardant is applied at a rate equivalent to from 50 µg to 5 mg of .alpha.-cyclopropyl-.alpha.-(4-methoxyphenyl)-5-pyrimidine methanol per plant.

16. A method according to Claim 12, wherein the growth retardant is applied at a rate equivalent to from 100 µg to 1 mg of .alpha.-cyclopropyl-.alpha.-(4-methoxyphenyl)-5-pyrimidine methanol per plant.

17. A method according to Claim 12 in which the gibberellin and cytokinin are applied in the form of a liquid formulation containing from 1 to 1000 mg/litre of each substance.

18. A method according to Claim 17, wherein the formulation contains from 10 to 100 mg/litre of the gibber-ellin and of the cytokinin.

19. A method according to Claim 18, wherein the gibberellin and cytokinin are applied in the form of a spray composition based on a water-miscible organic solvent.

20. A method according to Claim 19, wherein the solvent is ethanol.

21. A method according to Claim 16 in which the growth retardant is applied to the medium in which the plants are growing in the form of an aqueous solution or suspension.

22. A method according to Claim 21 in which said solution or suspension contains up to 1 g/litre of .alpha.-cyclo-propyl-.alpha.-(4-methoxyphenyl)-5-pyrimidine methanol.

23. A method according to Claim 22 in which said solution or suspension contains from 10 to 500 mg/litre of .alpha.-cyclopropyl-.alpha.-(4 methoxyphenyl)-5-pyrimidine methanol.

24. A method according to Claim 21 in which said plants are subjected to at least one period of short day length.

25. A method according to Claim 24, wherein the plants are subjected to alternating periods of short and long day length.

26. A method according to Claim 25, wherein said periods are from 1 to 10 days duration.

27. A method according to Claim 26, wherein the short day length periods comprise from 3 to 6 successive short days.

28. A method according to Claim 26, wherein the long day length periods comprise from 1 to 5 long days.

29. A method according to Claim 28, wherein the plants are subjected to a regime comprising two periods of short days intercalated with one period of long days.

30. A method according to Claim 29, wherein said plants are of the genus chrysanthemum.

31. A method according to Claim 30, wherein said plants are of the species chrysanthemum marifolium.

32. A method of inducing flower formation in plants in the family compositae which comprises applying to said plants effective amounts of a gibberellin and a cytokinin and subjecting the plants to alternating periods of short and long day length.

33. A method according to Claim 30, wherein the gibberellin and the cytokinin are as defined in Claims 3 and 5.

34. A method according to Claim 30 or Claim 31, wherein the gibberellin and cytokinin are applied in the manner defined in Claims 9 and 17.

35. A method according to Claim 32, wherein said plants are of the genus chrysanthemum.

36. A method of inducing flower formation in plants in the family compositae which comprises applying to said plants an effective amount of at least one growth regulator selected from gibberellins and cytokinins and subjecting the plants to alternating periods of short and long day length.

37. A method of inducing flower formation in plants in the family compositae which comprises applying to said plants an effective amount of a cytokinin and subjecting the plants to alternating periods of short and long day length.

38. A method of inducing flower formation in plants in the family compositae which comprises applying to said plants an effective amount of a gibberellin and subjecting the plants to alternating periods of short and long day length.

39. A method according to any one of Claims 36-38, wherein a growth retardant is additionally applied to said plants.