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The control of flowering in kangaroo paw (Anigozanthos spp.)
Scientia Horticulturae, 32 (1987) 123-133 Elsevier Science Publishers B.V., AmsterdAm - - Printed in The Netherlands
123
The Control of F l o w e r i n g in Kangaroo P a w (Anigozanthos spp. ) G.J. MOTUM 1 and P.B. GOODWIN
Department of Agronomy and Horticultural Science, University of Sydney, N.S. W. 2006 (Australia) (Accepted for publication 17 November 1986)
ABSTRACT Motum, G.J. and Goodwin, P.B., 1987. The control of flowering in kangaroo paw (Anigozanthos spp.). Scientia Hortic., 31: 123-133. A number of factors affecting flowering in kangaroo paws have been investigated. The most important influences appear to be those listed below. (1) In field grown plants, rhizomes need to be of a certain size before floral initiation is assured, even under conditions favouring initiation. The minimum weights are: A. flavidus, 175 g (fresh weight of rhizome, leaves trimmed to 5 cm above apex); A. manglesii, 75 g; A. viridis, 25 g. Within a plant clump a large proportion of shoots are below this critical size, and they remain vegetative even under conditions favouring initiation. (2) Kangaroo paws are species-specific with respect to daylength response. A. flavidus is a quantitative long-day plant. A. rnanglesii is a quantitative short-day plant. A. rufus, A. pulcherrimus and the Hopper hybrid A. flav/dus X rnanglesii are day-neutral. (3) High temperature (28/13°C) and extended daylength cause more rapid expansion and development of flowers than in plants kept in a shadehouse during the winter. Temperature has a strong influence on the rate of floral development in kangaroo paw. The rate of floral evocation increases as temperature increases to 27 ° C, above which physiological stress results in poor-quality flowers. (4) Colour expression is strongest {most intense) at low temperatures and decreases with increasing temperature. Keywords: Anigozanthos spp.; flowering; photoperiod; rhizome size; temperature.
INTRODUCTION
Once a market has been established for a cut flower, it is advantageous that the demand be met by a continuous year-round supply of a high-quality product. The demand for cut flowers exported from Australia tends to be seasonal. 1Present address: Horticultural Research and Advisory Station, Gosford, N.S.W. 2250, Australia.
0304-4238/87/$03.50
© 1987 Elsevier Science Publishers B.V.
124 During October, November and December, when days are shortening in the northern hemisphere and production of flowers is declining rapidly, there is a strong overseas demand for Australian wildflowers for indoor decoration (Watkins, 1982). In Japan, there is generally an increase in demand for cut flowers for the festive seasons, which include both the summer (June, July, August) and the winter. It is desirable, therefore, to be able to control flowering to coincide with peak periods of demand on the overseas markets. Furthermore, at present flowers cut from the wild and cultivated wildflowers compete with one another on the market. Control of flowering would enable production when there is the least competition with flowers cut from the wild. Early work on the control of flowering in Anigozanthos was carried out by Went at the phytotron in California in 1956 ( Grieve and Marchant, 1963 ). He found that the best growth and colour development ofA. manglesii occurred at 17 ° C ( day ) /11.5 oC ( night ) compared with higher temperatures. Van der Krogt and Vonk Noordegraaf (1976) and Van der Krogt (1977, 1978) carried out a number of experiments at the Aalsmeer Research Station in The Netherlands on the effect of daylength and temperature on A. manglesii. In their first experiment, using seedlings of A. manglesii which had not previously flowered, they found the best flower production at 15-12 °C compared with higher temperatures. These results appear to support Went's findings that mild temperatures are more conducive to flower development. However, in a second experiment on plants which had flowered once, Van der Krogt (1977) found that plants kept at 18-15 °C consistently produced lower numbers of flower stems than plants grown at higher temperatures. In a third trial, dealing with daylength only, he found no response of seedlings to daylength. Hagiladi (1983) obtained essentially similar results. In A. manglesii seedlings, flowering was promoted by chilling or by growth in an unheated glasshouse. Hughes (1983) found that a day/night temperature of 24/19 ° C is optimal for vegetative growth of young A. flavidus and A. manglesii plants, but that plants were stressed at temperatures of 27/22 ° C and above. These experiments suggest that in A. manglesii, young seedlings which have not flowered previously require cool temperatures for good flower production. However, subsequent growth is increased by mild temperatures, in which plants produce more side shoots and hence more potential flowers. In this paper we report the effect of plant size, daylength and temperature on the flowering of a number of species and interspecific hybrids of Anigozanthos. MATERIALSAND METHODS
Field studies. - Mature plants of A. flavidus, A. manglesii and A. viridis were dug from a field-cultivated crop at the University of Sydney's research farm "Lansdowne" from June to August 1983. Floral initiation was known to be occurring during this time. Clumps were divided into individual shoots, leaves
125 and roots were trimmed to 5 cm and these sections were weighed. Leaves were then removed to reveal the elongating flower stem, or the apex was examined under a binocular microscope to reveal whether it was vegetative or floral. Records were made of the number of vegetative and floral shoots. Growth room studies. - Ten seed-grown, 1-year-old A. flavidus plants, 5 seedgrown A. manglesii, 20 A. pulcherrimus, 5 A. rufus and 10 A. flavidus × manglesii plants grown from tissue culture were potted into 1.25-1 bags of pasteurised potting mix (1 peat:l sand:l loam) containing 2 kg Osmocote 8-9 months (18-2.6-10) 1.5 kg lime, 0.5 kg dolomite, 0.5 kg GU49 and 0.1 kg fritted trace elements m -8, and were placed in each of two growth cabinets on 2 October 1983. One cabinet was set to long days (LD) (16 h light; 8 h dark) and the other was set to short days (SD) (8 h light, 16 h dark). Both cabinets were set at 21 °C day/16 °C night and were provided with 8 h fluorescent lighting. Long days were achieved by incandescent extension at 25 #Moles m-2. Average irradiance was 296 ttMoles m -2 in SD and 342 ttMoles m -2 in LD. Plants were kept moist by hand-watering. None of the plants used in this experiment had flowered previously. The plants were checked regularly for signs of flower initiation. Plants were considered to have initiated when the elongating flower stalk could be felt at the base of the crown. The height of the stem was measured as it expanded to flower. The number of crowns per plant was also recorded at intervals over an 8-month period. Glasshouse studies. - On 8 June 1983, 10 plants each ofA. manglesii, A. viridis, A. pulcherrimus and A. flavidus X onycis, defined as having initiated because a distinct flower stalk was present at the base of the leaf fan, were selected for uniformity. These plants had been growing under shadehouse conditions at the university farm at Camden. Five plants of each species were moved to a nearby controlled-environment glasshouse which was receiving night heating and daylength extension to 16 h at 200 ttMoles m - 2 using high-pressure sodium lamps. The remaining plants were kept in the shadehouse. Temperatures in the glasshouse over the following 6-week period (until 20 July 1983) varied from 28°C day to 13°C night, whilst in the shadehouse under the prevailing winter conditions temperatures were in the range 21-0 oC. In a separate trial commencing on 16 August 1983, three plants each of A. flavidus X onycis, A. flavidus X rufus, A. viridis and A. flavidus were placed at 6 different temperatures (15/10, 18/13, 21/16, 24/19, 27/22 or 30/25°C day/ night, 12 h each) in controlled-environment glasshouses at Darlington (Sydney University). Plants had been growing under glasshouse conditions at 24/19 °C day/night temperatures for 4 months prior to the experiment. The plants chosen had flower stems about 20 cm high. A number of plants of A. flavidus X onycis which had grown at 24/19 °C and had fully elongated flower stems and well-developed buds were transferred to
126 100
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Fig. 1. The effectof rhizome fresh weight on floral initiation either 27/22 or 30/25 ° C to examine the response to temperature changes during flowering. RESULTS
Relationship between weight of rhizome and flower production. - All three species had a substantial number of small rhizomes and fewer large-size rhizomes within a plant clump. The range of sizes varied greatly between species. A. flao/dus rhizomes were in the range 0-650 g, A. manglesii rhizomes were in the range 0-150 g and A. vir/d/s rhizomes were in the range 0-45 g. There is a clear relationship between rhizome size and flowering (Fig. 1). In A. flav/dus, the mean weight of reproductive rhizomes was 218_ 98 g whilst the mean weight of vegetative shoots was 4 7 _ 31 g. All rhizomes above 175 g were reproductive and 69% of the rhizomes sampled were below the size required for initiation and they remained vegetative. In A. manglesii, the mean weight of reproductive rhizomes was 54 _ 32 g. All rhizomes above 75 g were reproductive. The mean weight of vegetative rhizomes was 12 _ 11 g and these represented 45% of the sample. In A. v/r/d/s, all rhizomes above 25 g had initiated flowers. The mean weight of reproductive rhizomes was 18 _ 9 g while vegetative shoots weighed 5.7 ± 2.6 g. Of the rhizomes sampled, 58% had initiated flowers and 42% remained vegetative. :~ : Response of kangar~)o paws: to daylength. - The flowering responses to daylength were species-specific (Table I). In A. flavidus, flowers were produced u p t o 10 weeks earlier under long days. After 6 months, 3 of the 10 plants in SD had flowered whereas al!,plants in LD had flowered (Fig. 2a). Nineteen
127 TABLE I Effect of 8 months of SD or LD on vegetative and reproductive development of 4 Anigozanthos species and 1 hybrid Species
Treatment
Number of plants
Number of plants in flower
A. flavidus
SD LD
10
7
10
10
A. rnanglesii
SD LD
5 5
5 5
A. rufus
SD LD
5 5
A. pulcherrimus
SD LD
A. flavxrnang
SD LD
Total number of flowers
Total length of flower stems (cm)
Total number of crowns
8
196
19
991
70 69
13 6
631 387
26 28
5 5
12 12
523 421
20 28
20 20
7 5
7 5
322 279
38 58
10
4
4
10
2
2
150 99
57 72
flowers were produced within 8 months in LD, while 8 flowers were produced under SD. The same number of crowns (fans) and a similar number of leaves had developed under the two daylength conditions. The average number of crowns per plant was 7.0 + 1.6 in SD and 6.9 _+2.0 in LD. All plants had crowns large enough to flower (i.e. larger than 175 g). In A. manglesii under short days, flowers were produced 6 weeks earlier and the total number of flowers produced was higher (Fig. 2b ). After 6 months the same number of plants were in flower in long and short days, but the total flower number was greater in SD (Fig. 2c). The total number of plant crowns was similar for long and short days, averaging 5.2 + 1.5 in SD and 5.6 _+1.5 in LD per plant. The average number of flowers per plant was 1.2 + 0.4 under LD compared with 2.6 + 0.9 under short days. A. rufus commenced flowering 1-2 weeks earlier in SD than in LD. However, after 8 months the total number of flowers produced (12) was the same under LD and SD. The growth of flowers followed the same pattern under long and short days, with a slightly greater length of stem being produced under SD conditions. Plants appeared to grow best under LD, where 5.6 ___1.1 crowns per plant were produced compared to 4.0 ___1.2 per plant in SD. A. pulcherrimus was the last species to flower in the growth cabinets. It commenced flowering 5 months after the commencement of the experiment and the number of flowers produced and their rate of growth was similar under long and short days. It is likely that more flowers would have been produced by A.
128 A. f l a v l d u s i
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Ttme
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(weeks)
A. manglesii i
(b) 75 S.D
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~
25
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2'8
A. i
3"2
3'6
Time (weeks)
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12
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/ 16
2.0
2.4
~8
'3.2
3.6
4o
Time (weeks)
Fig. 2. (a) Percentage ofA. flavidus plants in flower over time in long and short daylength. (b) Percentage of A. manglesii plants in flower over time in long and short daylength. (c) Total number of flowers ofA. manglesii produced over time in long and short daylength.
129
(a) A. flavidus X onycis (b) A. viridus Fig. 3. Responseof kangaroopaw to high temperature (28/13°C) and daylengthextensionto 16 h at 200#Moles m- 2after flowerinitiation (left-handgroupin eachphotograph) comparedwith plants kept in a shadehouseduringthe winterwith temperaturesrangingfrom 21°C day to 0°C night (right-handgroup in eachphotograph).
pulcherrimus had the experiment been extended. At the end of the experiment, 7/20 plants had flowered in SD and 5/20 in LD. More shoots were produced under LD. The hybrid A. flavidus X manglesii did not perform better in LD like its parent A. flavidus, nor in SD like its parent A. manglesii. Plants commenced flowering in both LD and SD after 5 months and the quantity and growth of the flowers produced was similar in both cabinets. Response to forcing after flower initiation. - In all cases higher temperatures and extended daylength hastened the expansion of flower heads. In A. flavidus X onycis, flowers at the higher temperature/extended daylength were fully expanded, whilst in those growing under shadehouse conditions the flower stalk had expanded to one third the length of the leaves (Fig. 3a). Similarly in A. viridis, flowers in the glasshouse had reached anthesis after 6 weeks whilst flower stalks on plants growing in the shadehouse had elongated only to the length of the leaves ( Fig. 3b). In A. manglesii, flowers were developed although not yet open in glasshouse-grown plants, whereas those from the shadehouse were still immature (Fig. 3d). In the case of A. pulcherrimus, flower stalks were expanded and clearly visible on glasshouse plants, while shadehouse-grown plants showed no externally visible signs of rachis elongation (Fig. 3c).
130
(c ) A. pulcherrirnus
(d) A. manglesii
Response to temperature during flower bud development. - The effect of temperature was evident within 3 weeks, particularly with A. flavidus X onycis and A. flavidus × rufus. Flowers of A. flavidus X onycis grown at the lowest temperature (15/10 °C) had formed unexpanded buds (Fig. 4) and flower colour was deep red/orange. At 18/13 and 21/16°C, flower buds had elongated but were not open. Flower colour was dark orange/yellow. Flowers at 24/19 ° C were fully developed and at the stage for picking - 2 florets per spike were open. Flower colour was a yellowy orange. At 27/22 ° C flowers were fully expanded and flower
131
Fig. 4. Response of A. flavidus X onycis ('Dwarf Delight') to 6 day:night temperatures (15/10, 18/13, 21/16, 24/19, 27/22 or 30/25°C), each for 12 h, over a 3-week period during flower development.
colour was pale apricot. At 30/25°C flower development was stunted, many buds had aborted and colour was absent. With A. flavidus X rufus the effect of temperature was less distinct, but the rate of floral development increased with increasing temperature. The best quality blooms were produced in the shortest time at a temperature of 24/19 ° C. At higher temperatures flower quality fell off markedly, with flowers becoming faded and bleached and with flower abortions. A similar trend was evident with A. viridis and A. flavidus. Flower colour was less affected by temperature in these species. The effect of a change to higher temperatures (from 24/19 to 27/22 or 30/25 °C) during flower development was also studied. The initial response was abortion of the youngest buds at the changeover time. Subsequent buds developed at the higher temperatures were of a lighter colour. The overall result was a deformed, unmarketable inflorescence. Flowers of A. flavidus X onycis, once harvested, did not change to a deeper colour when placed in the 15-10°C glasshouse. DISCUSSION
A delay in reproductive development (juvenility) has evolved in many plants to enable them to become large in size before flowering. It may be caused by
132 several physiological systems, for example, the inability of the juvenile meristern to respond to floral stimuli, activity of the root system, insufficient photosynthetic capacity and/or metabolic limitations in the leaves (Evans, 1969; Aitken, 1974). It follows, therefore, that in small seedlings conditions favouring vegetative growth will also favour flower production. This is probably the reason for the contradictory results obtained by Van der Krogt and Vonk Noordegraaf (1976), Van der Krogt (1977, 1978) and Hagiladi (1983) with seedlings compared to older plants. In order to avoid this complication in studies on the control of flower initiation, experimental plants must be large enough, relative to the species, to overcome juvenility effects. A guide to this size requirement can now be given for the Anigozanthos species studied. The flowering season of kangaroo paw species is predictable in the wild within broad limits (Hopper, 1978). A. humilis, A. manglesii, A. viridis, A. bicolor, A. onycis, A. gabriellae and A. kalbarriensis have peak flowering in late winter-spring. A. preissii peak in late spring to early summer. Seasonal variation is considerable. Despite this variability, consistent phenological differences between species are observed. A. humilis, A. bicolor, A. gabriellae and A. onycis flower before A. manglesii and A. viridis, which flower before A. rufus, A. flavidus and A. pulcherrimus. This sequence is adhered to when these kangaroo paws are grown under cultivation. These flowering times are in line with experimental results. A. flavidus flowers naturally from late October to February. Flowers develop under lengthening days. Thus it is not surprising that A. flavidus has a LD response. A. manglesii flowers naturally from June to November (under shorter days than A. flavidus and thus flowers would be developing early in the season under SD. A similar response was observed in this experiment. A. rufus flowers from early August to late January, that is to say mid-way between A. manglesii and A. flavidus. It appears not to be greatly influenced by daylength extremes and naturally develops under daylengths mid-way in the cycle. A. pulcherrimus flowers naturally from November to January. It is usually the last of the species to flower in the wild. The delayed production of flowers by A. pulcherrimus may indicate that the temperature regime was too low for a species which naturally produces flowers in the heat of summer, or the plants may have been too small to flower. Under the artificial conditions of the growth rooms, the kangaroo paws flowered from January to May - they were not seasonal and did not follow the natural phenological sequence of flowering that is observed in the wild. Thus without SD conditions A. manglesii does not flower first, but by manipulating daylength both A. manglesii and A. flavidus flowers can be produced in April or at will. The conditions required for floral initiation are not necessarily those most suitable for the development of flowers. Floral evocation was significantly has-
133
tened by providing high temperatures and extended daylengths. The response was greatest early in the season. With knowledge of when to expect floral initiation coupled with judicious use of temperature and daylength, forcing of kangaroo paws is possible to produce "out of season" flowers. Similarly, cool temperatures could be used to delay flower evocation in times of over-supply. The results also indicate that temperature can be used to manipulate flowering time and colour. There is, however, a trade-off between rapid floral evocation and colour quality. The plasticity of colour quality with temperature could be detrimental if lack of uniformity of product results. Under field conditions, those flowers produced early in the season, when temperatures are still cool, will be darker in colour than those produced later in the season when high summer temperatures will cause colour fading. Fluctuations in temperature when flowers are developing may lead to an inferior product. The results suggested that it is necessary to designate temperature when colour descriptions are made of new varieties and hybrids. Judicious manipulation of temperature could extend the flowering season of various species/hybrids to coincide with peak demands, and colour can be changed to suit market requirements. ACKNOWLEDGEMENT
This work was supported by a grant from the New South Wales Horticultural Stock and Nurseries Act. REFERENCES Aitken, Y., 1974. Flowering Time, Climate and Genotype. Melbourne University Press, 193 pp. Evans, L.T., 1969. The Induction of Flowering. Some Case Histories. MacMillan, Melbourne, 488 pp. Grieve, B.J. and Marchant, N., 1963. The kangaroo paws of W.A. Aus. Plants, 2: 107-115. Hagiladi, A., 1983. Influence of temperature and daylength on growth and flower yield of Anigozanthos rnanglesii. D. Don (Haemodoraceae). HortScience, 18: 369-371. Hopper, S.D., 1978. Speciation in the Kangaroo Paws of South-Western Australia (Anigozantho~s and Macropidia: Haemodoraceae). Ph.D. Thesis, University of Western Australia, pp. 8-31. Hughes, S.M., 1983. Aspects of cultivation of Anigozanthos species as ornamental plants. Dipl. Hort. Sci. Thesis, University of Sydney, 125 pp. Van der Krogt, T.M., 1977. Invloed van der temperatuur op de bloemproduktie van Anigozanthos. Bloemisterij onderzoek in Nederland over 1977. Jaarverslag Bloemisterij Onderzoek. Proefstation voor de bloemisterij in Nederland, Aalsmeer, pp. 20-21. Van der Krogt, T.M., 1978. Invloed van de daglengte op de bloemaanleg van Anigozanthos. Bloemisterij onderzoek in Nederland over 1978. Jaarverslag Bloemisterij Onderzoek. Proefstation voor de bloemisterij in Nederland, Aalsmeer, pp. 28-29. Van der Krogt, T.M. and Vonk Noordegraaf, C., 1976. Invloed van de temperatuur op de bloemproduktie. Bloemisterij onderzoek in Nederland over 1976. Jaarverslag Bloemisterij Onderzoek Proefstation voor de bloemisterij in Nederland, Aalsmeer, p. 16. Watkins, P.A., 1982. Overview of the wildflower industry in West Australia. Proc. National Technical Workshop on Production and Marketing of Australian Wildflowers for Export, Western Australian Department of Agriculture, pp. 9-15.
123
The Control of F l o w e r i n g in Kangaroo P a w (Anigozanthos spp. ) G.J. MOTUM 1 and P.B. GOODWIN
Department of Agronomy and Horticultural Science, University of Sydney, N.S. W. 2006 (Australia) (Accepted for publication 17 November 1986)
ABSTRACT Motum, G.J. and Goodwin, P.B., 1987. The control of flowering in kangaroo paw (Anigozanthos spp.). Scientia Hortic., 31: 123-133. A number of factors affecting flowering in kangaroo paws have been investigated. The most important influences appear to be those listed below. (1) In field grown plants, rhizomes need to be of a certain size before floral initiation is assured, even under conditions favouring initiation. The minimum weights are: A. flavidus, 175 g (fresh weight of rhizome, leaves trimmed to 5 cm above apex); A. manglesii, 75 g; A. viridis, 25 g. Within a plant clump a large proportion of shoots are below this critical size, and they remain vegetative even under conditions favouring initiation. (2) Kangaroo paws are species-specific with respect to daylength response. A. flavidus is a quantitative long-day plant. A. rnanglesii is a quantitative short-day plant. A. rufus, A. pulcherrimus and the Hopper hybrid A. flav/dus X rnanglesii are day-neutral. (3) High temperature (28/13°C) and extended daylength cause more rapid expansion and development of flowers than in plants kept in a shadehouse during the winter. Temperature has a strong influence on the rate of floral development in kangaroo paw. The rate of floral evocation increases as temperature increases to 27 ° C, above which physiological stress results in poor-quality flowers. (4) Colour expression is strongest {most intense) at low temperatures and decreases with increasing temperature. Keywords: Anigozanthos spp.; flowering; photoperiod; rhizome size; temperature.
INTRODUCTION
Once a market has been established for a cut flower, it is advantageous that the demand be met by a continuous year-round supply of a high-quality product. The demand for cut flowers exported from Australia tends to be seasonal. 1Present address: Horticultural Research and Advisory Station, Gosford, N.S.W. 2250, Australia.
0304-4238/87/$03.50
© 1987 Elsevier Science Publishers B.V.
124 During October, November and December, when days are shortening in the northern hemisphere and production of flowers is declining rapidly, there is a strong overseas demand for Australian wildflowers for indoor decoration (Watkins, 1982). In Japan, there is generally an increase in demand for cut flowers for the festive seasons, which include both the summer (June, July, August) and the winter. It is desirable, therefore, to be able to control flowering to coincide with peak periods of demand on the overseas markets. Furthermore, at present flowers cut from the wild and cultivated wildflowers compete with one another on the market. Control of flowering would enable production when there is the least competition with flowers cut from the wild. Early work on the control of flowering in Anigozanthos was carried out by Went at the phytotron in California in 1956 ( Grieve and Marchant, 1963 ). He found that the best growth and colour development ofA. manglesii occurred at 17 ° C ( day ) /11.5 oC ( night ) compared with higher temperatures. Van der Krogt and Vonk Noordegraaf (1976) and Van der Krogt (1977, 1978) carried out a number of experiments at the Aalsmeer Research Station in The Netherlands on the effect of daylength and temperature on A. manglesii. In their first experiment, using seedlings of A. manglesii which had not previously flowered, they found the best flower production at 15-12 °C compared with higher temperatures. These results appear to support Went's findings that mild temperatures are more conducive to flower development. However, in a second experiment on plants which had flowered once, Van der Krogt (1977) found that plants kept at 18-15 °C consistently produced lower numbers of flower stems than plants grown at higher temperatures. In a third trial, dealing with daylength only, he found no response of seedlings to daylength. Hagiladi (1983) obtained essentially similar results. In A. manglesii seedlings, flowering was promoted by chilling or by growth in an unheated glasshouse. Hughes (1983) found that a day/night temperature of 24/19 ° C is optimal for vegetative growth of young A. flavidus and A. manglesii plants, but that plants were stressed at temperatures of 27/22 ° C and above. These experiments suggest that in A. manglesii, young seedlings which have not flowered previously require cool temperatures for good flower production. However, subsequent growth is increased by mild temperatures, in which plants produce more side shoots and hence more potential flowers. In this paper we report the effect of plant size, daylength and temperature on the flowering of a number of species and interspecific hybrids of Anigozanthos. MATERIALSAND METHODS
Field studies. - Mature plants of A. flavidus, A. manglesii and A. viridis were dug from a field-cultivated crop at the University of Sydney's research farm "Lansdowne" from June to August 1983. Floral initiation was known to be occurring during this time. Clumps were divided into individual shoots, leaves
125 and roots were trimmed to 5 cm and these sections were weighed. Leaves were then removed to reveal the elongating flower stem, or the apex was examined under a binocular microscope to reveal whether it was vegetative or floral. Records were made of the number of vegetative and floral shoots. Growth room studies. - Ten seed-grown, 1-year-old A. flavidus plants, 5 seedgrown A. manglesii, 20 A. pulcherrimus, 5 A. rufus and 10 A. flavidus × manglesii plants grown from tissue culture were potted into 1.25-1 bags of pasteurised potting mix (1 peat:l sand:l loam) containing 2 kg Osmocote 8-9 months (18-2.6-10) 1.5 kg lime, 0.5 kg dolomite, 0.5 kg GU49 and 0.1 kg fritted trace elements m -8, and were placed in each of two growth cabinets on 2 October 1983. One cabinet was set to long days (LD) (16 h light; 8 h dark) and the other was set to short days (SD) (8 h light, 16 h dark). Both cabinets were set at 21 °C day/16 °C night and were provided with 8 h fluorescent lighting. Long days were achieved by incandescent extension at 25 #Moles m-2. Average irradiance was 296 ttMoles m -2 in SD and 342 ttMoles m -2 in LD. Plants were kept moist by hand-watering. None of the plants used in this experiment had flowered previously. The plants were checked regularly for signs of flower initiation. Plants were considered to have initiated when the elongating flower stalk could be felt at the base of the crown. The height of the stem was measured as it expanded to flower. The number of crowns per plant was also recorded at intervals over an 8-month period. Glasshouse studies. - On 8 June 1983, 10 plants each ofA. manglesii, A. viridis, A. pulcherrimus and A. flavidus X onycis, defined as having initiated because a distinct flower stalk was present at the base of the leaf fan, were selected for uniformity. These plants had been growing under shadehouse conditions at the university farm at Camden. Five plants of each species were moved to a nearby controlled-environment glasshouse which was receiving night heating and daylength extension to 16 h at 200 ttMoles m - 2 using high-pressure sodium lamps. The remaining plants were kept in the shadehouse. Temperatures in the glasshouse over the following 6-week period (until 20 July 1983) varied from 28°C day to 13°C night, whilst in the shadehouse under the prevailing winter conditions temperatures were in the range 21-0 oC. In a separate trial commencing on 16 August 1983, three plants each of A. flavidus X onycis, A. flavidus X rufus, A. viridis and A. flavidus were placed at 6 different temperatures (15/10, 18/13, 21/16, 24/19, 27/22 or 30/25°C day/ night, 12 h each) in controlled-environment glasshouses at Darlington (Sydney University). Plants had been growing under glasshouse conditions at 24/19 °C day/night temperatures for 4 months prior to the experiment. The plants chosen had flower stems about 20 cm high. A number of plants of A. flavidus X onycis which had grown at 24/19 °C and had fully elongated flower stems and well-developed buds were transferred to
126 100
-g
o~ Eo60 N I
-E::
'6 4o.
8 ao n
~I
I
,~/
2_J 10
20
30 4 0
50
100 Fresh
200 w e i g h t of r h t z o m e
300 (9)
Fig. 1. The effectof rhizome fresh weight on floral initiation either 27/22 or 30/25 ° C to examine the response to temperature changes during flowering. RESULTS
Relationship between weight of rhizome and flower production. - All three species had a substantial number of small rhizomes and fewer large-size rhizomes within a plant clump. The range of sizes varied greatly between species. A. flao/dus rhizomes were in the range 0-650 g, A. manglesii rhizomes were in the range 0-150 g and A. vir/d/s rhizomes were in the range 0-45 g. There is a clear relationship between rhizome size and flowering (Fig. 1). In A. flav/dus, the mean weight of reproductive rhizomes was 218_ 98 g whilst the mean weight of vegetative shoots was 4 7 _ 31 g. All rhizomes above 175 g were reproductive and 69% of the rhizomes sampled were below the size required for initiation and they remained vegetative. In A. manglesii, the mean weight of reproductive rhizomes was 54 _ 32 g. All rhizomes above 75 g were reproductive. The mean weight of vegetative rhizomes was 12 _ 11 g and these represented 45% of the sample. In A. v/r/d/s, all rhizomes above 25 g had initiated flowers. The mean weight of reproductive rhizomes was 18 _ 9 g while vegetative shoots weighed 5.7 ± 2.6 g. Of the rhizomes sampled, 58% had initiated flowers and 42% remained vegetative. :~ : Response of kangar~)o paws: to daylength. - The flowering responses to daylength were species-specific (Table I). In A. flavidus, flowers were produced u p t o 10 weeks earlier under long days. After 6 months, 3 of the 10 plants in SD had flowered whereas al!,plants in LD had flowered (Fig. 2a). Nineteen
127 TABLE I Effect of 8 months of SD or LD on vegetative and reproductive development of 4 Anigozanthos species and 1 hybrid Species
Treatment
Number of plants
Number of plants in flower
A. flavidus
SD LD
10
7
10
10
A. rnanglesii
SD LD
5 5
5 5
A. rufus
SD LD
5 5
A. pulcherrimus
SD LD
A. flavxrnang
SD LD
Total number of flowers
Total length of flower stems (cm)
Total number of crowns
8
196
19
991
70 69
13 6
631 387
26 28
5 5
12 12
523 421
20 28
20 20
7 5
7 5
322 279
38 58
10
4
4
10
2
2
150 99
57 72
flowers were produced within 8 months in LD, while 8 flowers were produced under SD. The same number of crowns (fans) and a similar number of leaves had developed under the two daylength conditions. The average number of crowns per plant was 7.0 + 1.6 in SD and 6.9 _+2.0 in LD. All plants had crowns large enough to flower (i.e. larger than 175 g). In A. manglesii under short days, flowers were produced 6 weeks earlier and the total number of flowers produced was higher (Fig. 2b ). After 6 months the same number of plants were in flower in long and short days, but the total flower number was greater in SD (Fig. 2c). The total number of plant crowns was similar for long and short days, averaging 5.2 + 1.5 in SD and 5.6 _+1.5 in LD per plant. The average number of flowers per plant was 1.2 + 0.4 under LD compared with 2.6 + 0.9 under short days. A. rufus commenced flowering 1-2 weeks earlier in SD than in LD. However, after 8 months the total number of flowers produced (12) was the same under LD and SD. The growth of flowers followed the same pattern under long and short days, with a slightly greater length of stem being produced under SD conditions. Plants appeared to grow best under LD, where 5.6 ___1.1 crowns per plant were produced compared to 4.0 ___1.2 per plant in SD. A. pulcherrimus was the last species to flower in the growth cabinets. It commenced flowering 5 months after the commencement of the experiment and the number of flowers produced and their rate of growth was similar under long and short days. It is likely that more flowers would have been produced by A.
128 A. f l a v l d u s i
i
i
i
i
(a)
L.D 9O o
S.D c "- 6 0
o
/
Q.
3O
/ 2~
16
2'e
32
3's
Ttme
40
(weeks)
A. manglesii i
(b) 75 S.D
o .E 5O
~
25
10
2:4
2'o
2'8
A. i
3"2
3'6
Time (weeks)
40
mang[esii i
i
(c) S.D o
12
~B E L.D -6 4 i---
/ 16
2.0
2.4
~8
'3.2
3.6
4o
Time (weeks)
Fig. 2. (a) Percentage ofA. flavidus plants in flower over time in long and short daylength. (b) Percentage of A. manglesii plants in flower over time in long and short daylength. (c) Total number of flowers ofA. manglesii produced over time in long and short daylength.
129
(a) A. flavidus X onycis (b) A. viridus Fig. 3. Responseof kangaroopaw to high temperature (28/13°C) and daylengthextensionto 16 h at 200#Moles m- 2after flowerinitiation (left-handgroupin eachphotograph) comparedwith plants kept in a shadehouseduringthe winterwith temperaturesrangingfrom 21°C day to 0°C night (right-handgroup in eachphotograph).
pulcherrimus had the experiment been extended. At the end of the experiment, 7/20 plants had flowered in SD and 5/20 in LD. More shoots were produced under LD. The hybrid A. flavidus X manglesii did not perform better in LD like its parent A. flavidus, nor in SD like its parent A. manglesii. Plants commenced flowering in both LD and SD after 5 months and the quantity and growth of the flowers produced was similar in both cabinets. Response to forcing after flower initiation. - In all cases higher temperatures and extended daylength hastened the expansion of flower heads. In A. flavidus X onycis, flowers at the higher temperature/extended daylength were fully expanded, whilst in those growing under shadehouse conditions the flower stalk had expanded to one third the length of the leaves (Fig. 3a). Similarly in A. viridis, flowers in the glasshouse had reached anthesis after 6 weeks whilst flower stalks on plants growing in the shadehouse had elongated only to the length of the leaves ( Fig. 3b). In A. manglesii, flowers were developed although not yet open in glasshouse-grown plants, whereas those from the shadehouse were still immature (Fig. 3d). In the case of A. pulcherrimus, flower stalks were expanded and clearly visible on glasshouse plants, while shadehouse-grown plants showed no externally visible signs of rachis elongation (Fig. 3c).
130
(c ) A. pulcherrirnus
(d) A. manglesii
Response to temperature during flower bud development. - The effect of temperature was evident within 3 weeks, particularly with A. flavidus X onycis and A. flavidus × rufus. Flowers of A. flavidus X onycis grown at the lowest temperature (15/10 °C) had formed unexpanded buds (Fig. 4) and flower colour was deep red/orange. At 18/13 and 21/16°C, flower buds had elongated but were not open. Flower colour was dark orange/yellow. Flowers at 24/19 ° C were fully developed and at the stage for picking - 2 florets per spike were open. Flower colour was a yellowy orange. At 27/22 ° C flowers were fully expanded and flower
131
Fig. 4. Response of A. flavidus X onycis ('Dwarf Delight') to 6 day:night temperatures (15/10, 18/13, 21/16, 24/19, 27/22 or 30/25°C), each for 12 h, over a 3-week period during flower development.
colour was pale apricot. At 30/25°C flower development was stunted, many buds had aborted and colour was absent. With A. flavidus X rufus the effect of temperature was less distinct, but the rate of floral development increased with increasing temperature. The best quality blooms were produced in the shortest time at a temperature of 24/19 ° C. At higher temperatures flower quality fell off markedly, with flowers becoming faded and bleached and with flower abortions. A similar trend was evident with A. viridis and A. flavidus. Flower colour was less affected by temperature in these species. The effect of a change to higher temperatures (from 24/19 to 27/22 or 30/25 °C) during flower development was also studied. The initial response was abortion of the youngest buds at the changeover time. Subsequent buds developed at the higher temperatures were of a lighter colour. The overall result was a deformed, unmarketable inflorescence. Flowers of A. flavidus X onycis, once harvested, did not change to a deeper colour when placed in the 15-10°C glasshouse. DISCUSSION
A delay in reproductive development (juvenility) has evolved in many plants to enable them to become large in size before flowering. It may be caused by
132 several physiological systems, for example, the inability of the juvenile meristern to respond to floral stimuli, activity of the root system, insufficient photosynthetic capacity and/or metabolic limitations in the leaves (Evans, 1969; Aitken, 1974). It follows, therefore, that in small seedlings conditions favouring vegetative growth will also favour flower production. This is probably the reason for the contradictory results obtained by Van der Krogt and Vonk Noordegraaf (1976), Van der Krogt (1977, 1978) and Hagiladi (1983) with seedlings compared to older plants. In order to avoid this complication in studies on the control of flower initiation, experimental plants must be large enough, relative to the species, to overcome juvenility effects. A guide to this size requirement can now be given for the Anigozanthos species studied. The flowering season of kangaroo paw species is predictable in the wild within broad limits (Hopper, 1978). A. humilis, A. manglesii, A. viridis, A. bicolor, A. onycis, A. gabriellae and A. kalbarriensis have peak flowering in late winter-spring. A. preissii peak in late spring to early summer. Seasonal variation is considerable. Despite this variability, consistent phenological differences between species are observed. A. humilis, A. bicolor, A. gabriellae and A. onycis flower before A. manglesii and A. viridis, which flower before A. rufus, A. flavidus and A. pulcherrimus. This sequence is adhered to when these kangaroo paws are grown under cultivation. These flowering times are in line with experimental results. A. flavidus flowers naturally from late October to February. Flowers develop under lengthening days. Thus it is not surprising that A. flavidus has a LD response. A. manglesii flowers naturally from June to November (under shorter days than A. flavidus and thus flowers would be developing early in the season under SD. A similar response was observed in this experiment. A. rufus flowers from early August to late January, that is to say mid-way between A. manglesii and A. flavidus. It appears not to be greatly influenced by daylength extremes and naturally develops under daylengths mid-way in the cycle. A. pulcherrimus flowers naturally from November to January. It is usually the last of the species to flower in the wild. The delayed production of flowers by A. pulcherrimus may indicate that the temperature regime was too low for a species which naturally produces flowers in the heat of summer, or the plants may have been too small to flower. Under the artificial conditions of the growth rooms, the kangaroo paws flowered from January to May - they were not seasonal and did not follow the natural phenological sequence of flowering that is observed in the wild. Thus without SD conditions A. manglesii does not flower first, but by manipulating daylength both A. manglesii and A. flavidus flowers can be produced in April or at will. The conditions required for floral initiation are not necessarily those most suitable for the development of flowers. Floral evocation was significantly has-
133
tened by providing high temperatures and extended daylengths. The response was greatest early in the season. With knowledge of when to expect floral initiation coupled with judicious use of temperature and daylength, forcing of kangaroo paws is possible to produce "out of season" flowers. Similarly, cool temperatures could be used to delay flower evocation in times of over-supply. The results also indicate that temperature can be used to manipulate flowering time and colour. There is, however, a trade-off between rapid floral evocation and colour quality. The plasticity of colour quality with temperature could be detrimental if lack of uniformity of product results. Under field conditions, those flowers produced early in the season, when temperatures are still cool, will be darker in colour than those produced later in the season when high summer temperatures will cause colour fading. Fluctuations in temperature when flowers are developing may lead to an inferior product. The results suggested that it is necessary to designate temperature when colour descriptions are made of new varieties and hybrids. Judicious manipulation of temperature could extend the flowering season of various species/hybrids to coincide with peak demands, and colour can be changed to suit market requirements. ACKNOWLEDGEMENT
This work was supported by a grant from the New South Wales Horticultural Stock and Nurseries Act. REFERENCES Aitken, Y., 1974. Flowering Time, Climate and Genotype. Melbourne University Press, 193 pp. Evans, L.T., 1969. The Induction of Flowering. Some Case Histories. MacMillan, Melbourne, 488 pp. Grieve, B.J. and Marchant, N., 1963. The kangaroo paws of W.A. Aus. Plants, 2: 107-115. Hagiladi, A., 1983. Influence of temperature and daylength on growth and flower yield of Anigozanthos rnanglesii. D. Don (Haemodoraceae). HortScience, 18: 369-371. Hopper, S.D., 1978. Speciation in the Kangaroo Paws of South-Western Australia (Anigozantho~s and Macropidia: Haemodoraceae). Ph.D. Thesis, University of Western Australia, pp. 8-31. Hughes, S.M., 1983. Aspects of cultivation of Anigozanthos species as ornamental plants. Dipl. Hort. Sci. Thesis, University of Sydney, 125 pp. Van der Krogt, T.M., 1977. Invloed van der temperatuur op de bloemproduktie van Anigozanthos. Bloemisterij onderzoek in Nederland over 1977. Jaarverslag Bloemisterij Onderzoek. Proefstation voor de bloemisterij in Nederland, Aalsmeer, pp. 20-21. Van der Krogt, T.M., 1978. Invloed van de daglengte op de bloemaanleg van Anigozanthos. Bloemisterij onderzoek in Nederland over 1978. Jaarverslag Bloemisterij Onderzoek. Proefstation voor de bloemisterij in Nederland, Aalsmeer, pp. 28-29. Van der Krogt, T.M. and Vonk Noordegraaf, C., 1976. Invloed van de temperatuur op de bloemproduktie. Bloemisterij onderzoek in Nederland over 1976. Jaarverslag Bloemisterij Onderzoek Proefstation voor de bloemisterij in Nederland, Aalsmeer, p. 16. Watkins, P.A., 1982. Overview of the wildflower industry in West Australia. Proc. National Technical Workshop on Production and Marketing of Australian Wildflowers for Export, Western Australian Department of Agriculture, pp. 9-15.