Scientia Horticulturae, 29 (1986) 191--197 191 Elsevier Science Publishers B.V., Amsterdam - -Pr in ted in The Netherlands

FLOWER COLOUR SPORTS IN SAINTPAULIA CULTIVARS

TOSHIO ANDO, YASUO AKIYAMA AND MASATO YOKOI

Laboratory of Floriculture and Ornamental Horticulture, Faculty of Horticulture, Chiba University, Matsudo, Chiba Prefecture 271 (Japan)

(Accepted for publicat ion 20 February 1986)

ABSTRACT

Ando, T., Akiyama, Y. and Yokoi, M., 1986. Flower colour sports in saintpaulia cultivars. Scientia Hortic., 29: 191--197.

Sport emergences during vegetative propagation of edged and Geneva~edged types of saintpaulia cultivars were observed when compared with centred-type cultivars. Ac- cording to the frequency and the definite trend in this sport emergence, they are con- sidered as periclinal chimeras. The mechanism of persisting chimeric structures during vegetative propagation is discussed in relation to the origin of adventitious shoots.

Keywords: African Violet; chimera; leaf cutting, saintpaulia; sport; tissue culture.

INTRODUCTION

Leaf cutting is a routine technique for propagating commercial saintpaulias. Tissue culture of leaves or floral organs is also successfully employed (Vazquez et al., 1977; Vazquez and Short, 1978) and the annual world production of saintpaulia plants through tissue culture is estimated at 2 000 000 (Jones, 1983).

Some cultivars such as 'Valencia', however, cannot be propagated through leaf cutting or tissue culture, because the flower colourations of plants propagated in this way are entirely different from the original. Also they are propagated only ineffectively by crown removal followed by stem cutting of offsets (Eyerdom, 1981; Kawakami, 1981).

The cultivars mentioned above are regarded as periclinal chimeras (Eyerdom, 1981), and are easily recognized by the characteristic appearance of a distinctive two-tone corolla, in which paler or darker zones extend radially from the centre to the apices of the lobes and form star-like blotches. 'Valencia' and similar cultivars will be referred to as centred-type saintpaulias.

Preliminary observation revealed the frequent occurrence of flower colour sports in some commercially propagated salntpaulias which were not typical

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of the centred-type, but exhibited patterns of flower pigmentation like the edged or Geneva-edged type (Hamilton, 1981).

In this report, changes in the phenotypes after leaf cutting or tissue culture in selected saintpaulia cultivars are presented and possible causes are discussed.

MATERIALS AND METHODS

P l a n t m a t e r i a l . - Following the system of Hamilton (1981) for classification of saintpaulia cultivars, 19 edged-type (white corolla with pigmented outer edge) and 9 Geneva-edged-type cultivars (pigmented corolla with white outer edge) were selected as original material (Fig. 1, cultivar names in Table I).

G r e e n h o u s e o b s e r v a t i o n s . - - Frequencies of sport production were recorded in the greenhouses of saintpaulia nurseries where they were propagated by leaf cutting or tissue culture of leaf blades.

M i c r o s c o p i c o b s e r v a t i o n s . - - Sections were made free-hand with a razor blade to observe the distribution of anthocyanin pigment in the tissue of corolla, sepal, pedicel, petiole and leaf blade.

T i s s u e c u l t u r e . - - In order to check reversibility relative to sport production, several organs from 'Ms. Pretty' , an edged-type, and its sport were cultured

Fig. 1. General trends of the emergence of flower colour sports in the edged (above) and Geneva-edged (below) types of saintpaulia cultivars. The direction of sport emergence is always from left to right.

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in vitro following the technique of Vazquez et al. (1977), with minor modifi- cation by adding 10-6 M BA and NAA. Cultures were maintained at about 20 ° C under continuous illumination of about 1000 pW cm -2 (400--700 nm). After about 4 months, plantlets were planted in vermiculite and grown to the flowering stage.

TABLE I

Changes in the phenotypes and the frequency of sport occurrence of 19 edged and 9 Geneva-edged types cultivars of saintpaulia which were propagated by leaf cutting or tissue culture of leaf blade

Cultivar Method Width of of propa- edge 2 gation ~

Pigmentation of corolla and number (No.) of plants % of observed sports

Original form Sport

Edge Inside 3 No. Edge Inside No.

Edged-type Alabama LC M Purple White 342 Purple Purple 25 6.8 Betcha LC N Purple White 50 Purple Purple 2 3.8 Beth Ellen LC M Pink White 55 Pink Pink 12 17.9 Candy Dandy LC N Pink White 30 Pink Pink 15 33.3 Denise LC N Reddish White 83 Reddish Reddish 28 25.2

purple purple purple Rhapsodic Gigi LC M Purple White 58 Purple Purple 55 48.7 Julianne LC N Purple White 185 Purple Purple 42 18.5 Laura Ann LC N Pink White 103 Pink Pink 1 1.0 Leila LC N Purple White 114 Purple Purple 13 10.2 May Dance LC N Pink White 33 Pink Pink 39 54.2 Merry May LC N Pink White 161 Pink Pink 119 42.5 Monaco LC N Purple White 133 Purple Purple 34 20.4 Ms. Pretty TC M Pink White 183 Pink Pink 83 31.2

LC 144 Pink Pink 34 19.1 Nevada LC M Red White 130 Red Red 11 7.8 Princess Grace TC M Pink White 5 Pink Pink 11 68.8 Rose Frost LC N Red White 234 Red Red 12 4.9 Serenity LC M Purple White 139 Purple Purple 22 13.7 Snow Orchid TC M Pink White 52 Pink Pink 54 50.9 Verna Lynn LC VN Purple White 126 Purple Purple 7 5.3

Geneva-edged type Blue Yonder LC VN White Purple Cabaret TC N White Red Chipper TC M White Blue Count Down TC N White Purple Firebird LC W White Red

Garnet Elf LC W White Red Like Wow LC N White Purple Regalaire LC VN White Purple Rose Triumph LC N White Pink

101 - 213 White White

29 White White 107 White White 229 White White

White 4 Red 82 White White 37 White White 28 -- 39 White White

0 0.0 213 50.0

1 3.3 1 0+9 5 2.1 5 2.1

27 24.8 5 11.9 0 0.0

15 27~8

LC, leaf cutting; TC, tissue culture. : VN, very narrow; N, narrow; M, medium; W, wide.

"White" does not mean pure white, but an "extremely pale colour". 4 Much narrower edge than original form.

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RESULTS

Frequencies o f sport emergence. -- T h e s e l e c t e d c u l t i v a r s p r o d u c e d s ingle- c o l o u r s p o r t s (F ig . 1) w i t h f r e q u e n c i e s r a n g i n g f r o m 0 .9 t o 6 8 . 8 % a n d a m e a n o f 22%, e x c e p t f o r ' B l u e Y o n d e r ' a n d ' R e g a l a i r e ' ( T a b l e I) . In c o n t r a s t , n o s p o r t s w e r e o b s e r v e d in a n y s i n g l e - c o l o u r c u l t i v a r s o b s e r v e d in t h e s e g r e e n h o u s e s .

Phenotypes o f the sports which emerged. -- All s p o r t s e m e r g e d f r o m e d g e d - t y p e h a d s i n g l e - c o l o u r e d c o r o l l a s , i .e . p i g m e n t e d c o r o l l a s o v e r t h e i r w h o l e a rea . In c o n t r a s t , G e n e v a C d g e d t y p e s p r o d u c e d s p o r t s w i t h w h i t e o r e x t r e m e l y p a l e c o r o l l a s , e x c e p t f o r ' F i r e b i r d ' , w h e r e t w o t y p e s o f s p o r t o c c u r r e d ; w h i t e c o r o l l a a n d G e n e v a - e d g e d c o r o l l a w i t h a n a r r o w e r edge ( T a b l e I) .

Distribution o f anthocyanins in the tissue. As s h o w n in T a b l e I I , e d g e d

t y p e s h a d a n t h o c y a n i n p i g m e n t s in t h e e p i d e r m i s ( o n e l a y e r ) o f t h e o u t e r

TABLE II

Distribution of anthocyanin pigment in the tissue of edged and Geneva-edged cultivars and their sports 1

Groups of Corolla Sepal Pedicel Petiole Leaf blade cultivar

Ep P Ep P Ep P* Ep P* Ep P**

Ed In Ad Ab Ad Ab

Edged types Group A

Original ++ -- + + . . . . Sport ++ ++ ++ ++ -- ++ --

Group B Original ++ - - + + - - - - - -

S p o r t ++ ++ ++ ++ -- ++ -- Group C

Original ++ - - + + - - - - - -

S p o r t ++ ++ ++ ++ -- ++ --

Geneva edged types Group D

Original - - ++ ++ ++ -- ++ -- S p o r t -- -- + + -- -- --

m

÷ +

m

+ ÷

E

+ + + +

+ + + +

1Ep, epidermis; P, parenchyma; Ed, edge; In, inside; Ad, adaxial side; Ab, abaxial side. Group A, 'Beth Ellen', 'Leila ' , 'Ms. Pret ty ' ; Group B, 'Serenity ' , 'Laura Ann' , 'Merry May', 'Verna Lynn' ; Group C, 'Denise'; Group D, 'Garnet Elf ' , 'Firebird ' , 'Cabaret ' . ++, deeply pigmented; +, pigmented ;-- , non-pigmented. *Outermost 2 or 3 layers of parenchyma. **Inner parenchyma cells in the vicinity of the mesophyll.

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edge of the corolla, the abaxial epidermis of the sepal and the outermost 2 or 3 layers of the parenchyma of the pedicel. In their single-colour sports, however, pigmented areas were extended to the whole of the epidermis in the corolla and the outermost 2 or 3 layers of parenchyma. The number of pigmented cells and the density of pigment were increased in the epidermis of the sepal and the parenchyma of the pedicel.

In the sports from edged types, the abaxial side of the leaf blade was coloured to a distinct red. This colouration was caused by pigmented cells in the parenchyma vicinity of the mesophylls (Group A), abaxial epidermis (Group B), or both (Group C).

Distribution patterns of anthocyanin pigments in Geneva-edged type were the same as those of sports from Group C of edged-type, except for the corolla, where the abaxial epidermis of sepal and leaf blades, the parenchyma of the pedicel and the leaf blades were deeply pigmented. Their sports lost all pigments from the corolla, petiole and leaf blade, and sepals and pedicels turned almost green.

I r r e v e r s i b i l i t y . - - As shown in Table III, several organs of 'Ms. Pret ty ' (edged form) produced single-colour sports through propagation by tissue culture. In contrast, single~olour sports of 'Ms. Pret ty ' never produced edged form.

TABLE III

Changes in the phenotype and number of sports after propagation by tissue culture of several organs of 'Ms. Pretty' (edged form)

Excised organs Explants were excised from:

Edged form Single-colour sport

Edged form Single-colour Edged form Single-colour

Leaf blade 26 2 0 24 Leaf vine 1 9 0 22 Petiole 6 0 0 15 Corolla (edge) 7 9 0 13 Corolla (inside) 15 3 0 18 Sepal 7 0 0 11 Pedicel 20 3 0 12 Axillary bud on peduncle 19 2

DISCUSSION

In general, it is possible to visually distinguish the sports of edged or Geneva~edged types before blooming, because edged types lack anthocyanin pigments in petioles and leaf blades, but their sports retain pigments in these parts (Table II). In contrast, Geneva-edged types have anthocyanin pigments in petioles and leaf blades, whereas their sports do not.

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Frequencies of sport-emergence from edged or Geneva-edged types were high due to mutation. With a few exceptions, the corolla of the sport was single-coloured and its colour was identical to that of the marginal part of the corolla lobes in the original plant. In addition, single-coloured sports persisted their phenotypes through tissue culture even under the condition leading the edged form to frequent emergence of sports. This tendency towards changes in the phenotypes and its irreversibility excludes the possibility that these phenomena have to be ascribed to mutable genes.

Thus, it is reasonable to say that the frequent appearance of sports was caused by the breaking-down of the structure of a periclinal chimera consti tuted in edged or Geneva-edged types, whilst the sports were their solid forms.

As stated earlier, it is well known that centred-type cultivars such as 'Daredevil', 'Desert Dawn', 'Petunia', 'Circus Boy' , 'Valencia' are almost impossible to propagate true to type through leaf cutting (Kawakami, 1981), and that they are recognized as periclinal chimeras (Eyerdom, 1981). Even though the edged or Geneva-edged type produced sports, as revealed in this study, their frequencies were much lower than those of the centred-type. Hence, it is possible that there are at least two kinds of periclinal chimera in saintpaulias relative to the frequency of sport production.

Broertjes and Keen (1980) have reviewed the literature covering the origin of adventitious shoots on leaf blades or petioles in saintpaulias. Some authors stated that the adventitious shoot originated from a single epidermal cell of the leaf blade or petiole, because either completely normal plants or almost exclusively solid, non-chimeric mutations were obtained by irradiation (Sparrow et al., 1960) and colchicine treatment (Arisumi and Frazier, 1968} of saintpaulia leaves. Some histological observations have also shown that adventitious shoots originated from a single cell (Kukulczanka and Suszynska, 1972) or from only the epidermis (Vazquez and Short, 1978). In addition, Broertjes and Keen (1980) postulated that the apex of the adventitious shoot was formed from only one epidermal cell, according to the analysis of a stochastic model describing the pattern of shoot-apex formation.

If adventitious shoots originated either from a single cell or from only epidermis cells, periclinal chimeras could not be maintained through the vegetative propagation by leaf cutting or tissue-culture of leaves. Actually, centred-types of saintpaulia cannot be propagated by leaf cuttings without any changes in corolla colour, as stated above, but edged or Geneva-edged types could be propagated true to type, even though many sports were also produced, as observed in this study.

I f edged and Geneva-edged types are actually periclinal chimeras, adven- titious shoots do not originate from a single cell, or only from epidermal cells, but from a considerable number of epidermal cells and inner parenchyma cells. There should be other cases, of course, where adventitious shoots originate only from the epidermal cells of leaves, leading to the

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p r o d u c t i o n o f solid f o r m s whose g e n o t y p e s are ident ical to those of the e p i d e r m a l cells o f the m o t h e r plants .

Nay lo r and J o h n s o n (1937) , in an extens ive r e p o r t on adven t i t ious shoo t s and roo t s f r o m sa in tpaul ia leaves, s t a ted t ha t " A l t h o u g h the s h o o t has its origin in a single ep ide rma l cell, ad jacen t ep ide rma l cells and p a r e n c h y m a cells wi th in the pe t io le c o n t r i b u t e d to its f inal f o r m a t i o n " . Our resul ts agree wi th this conc lus ion .

ACKNOWLEDGEMENTS

The au tho r s are gra tefu l to Ak iyosh i F u k a y a , T a k a y o s h i Shiraishi, Shuichi Obayash i , T a i y o Kak i Co. Ltd . , Hi tachi Kaki Co. Ltd . , Ozak i Engei and T o k u r a Engei, fo r d o n a t i o n of p l an t mater ia ls .

REFERENCES

Arisumi, T. and Frazier, L.C., 1968. Cytological and morphological evidence for the single-cell origin of vegetatively propagated shoots in 13 species of saintpaulia treated with colchicine. Proc. Am. Soc. Hortic. Sci., 93: 679--685.

Broertjes, C. and Keen, A., 1980. Adventitious shoots: Do they develop from one cell? Euphytica, 29 : 73--87.

Eyerdom, H., 1981. Flower color sports and variations in saintpaulia hybrids. African Violet Mag., 34 (4): 32--37.

Hamilton, R., 1981. African violet flower and leaf types. African Violet Mag., 34 (3): II-14.

Jones, J.B., 1983. Tissue culture takes off. Florists' Rev., 24 March 1983: 28--34. Kawakami, T., 1981. Saintpaulia Colour Meikan. Shufunotomo, Tokyo, p. 104 (in

Japanese). Kukulczanka, K. and Suszynska, G., 1972. Regenerative properties of Saintpaulia

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somatic mutations in saintpaulia. African Violet Mag., 13 (4) : 32- 37. Vazquez, A.M. and Short, K.C., 1978. Morphogenesis in cultured floral parts of African

violet. J. Exp. Bot., 29: 1265-1271. Vazquez, A.M., Davey, M.R. and Short, K.C., 1977. Organogenesis in cultures of Saint-

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