INDIGENOUS PLECTRANTHUS (LAMIACEAE) FROM SOUTH AFRICA AS NEW FLOWERING POT PLANTS

G.J. Brits J. Selchau G. van Deuren (Private Breeder) GPL International as Van Deuren Nursery 28 Flamingo St. P.O. Box 29 Madritten 8 Stellenbosch 7600 Odense V 2370 Arendonk South Africa Denmark-5200 Belgium [email protected]

Keywords: breeding improvement, hybridization, plant breeders’ rights, Plectranthus, seed sterility, spurflower, Trademark

Abstract

Plectranthus L’ Herit (Spurflowers) is a group of soft herbaceous plants, some with unusually beautiful tubular flowers in blue, violet, white and pink. They grow naturally in the subtropical south-eastern parts of South Africa as forest-floor plants and flowering times peak in autumn. Other salient qualities are easy cultivation and propagation, using stem cuttings; semi-drought tolerance and requirement for semi-shade. In South Africa Plectranthus spp. are widely used outdoors as indigenous bedding plants and groundcovers. A few species of this horticulturally neglected genus are used internationally as commercial foliage pot plants, with no or little breeding improvement. However the first distinctive varieties of flowering pot plants have been developed in South Africa over the past ten years. Species were found to hybridize with difficulty and the resulting interspecific hybrids are almost invariably seed sterile. In our breeding programme we focus on developing a wide variety of compact plants with large and floriferous flower types and beautiful foliage. Improved foliage characters include texture (pleasant to touch and sight), shape (attractively rounded leaves), colour (silver-veined, variegated, underside red-tinted) and smell (pleasantly herbal typical of the mint family). A range of natural colours have been selected for and some selections now have the largest flowers in the genus. Product development focuses on flowering pot plants but also include hanging basket plants and floriferous outdoors plants for semi-shaded situations. The new series of hybrid Plectranthus are introduced under the Trademark ‘Blue Angels’. Research and development are done by a group of specialist nurseries in Australia, Europe, Japan, U.S.A. and South Africa. This includes breeding, technical development, propagation / marketing and specialist administration, all by separate companies. Plant Breeders’ Rights have been applied for.

1. Introduction

South African flowering plants have become renowned for their diversity and seemingly endless potential for commercial exploitation. Yet it appears that very few plants of this subcontinent with economic potential have gone unnoticed in floriculture and a large proportion of these have been genetically improved in especially Europe. It could in fact be argued that only relatively few species with exploitable commercial potential remain in the wild. The idea that South Africa could substantially increase its national prosperity through breeding inputs into the indigenous floricultural resource could therefore be little more than a myth. This applies especially to the private breeder who is limited by distance, the absence of a culture of market-oriented breeding improvement, lack of recourse to legal and technical resources in situ and the paucity of necessary market

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experience required to successfully introduce new cultivars to the amenity markets of the nortern hemisphere. This paper reports on a ten-year effort to commercially develop a relatively unknown South African plant from the viewpoint of private breeding, assuming that novelty per se is sought in the pot plant market.

2. Plectranthus breeding

The South African component of the genus Plectranthus has indeed caught the attention of horticulturists for a long time, but has remained a "horticulturally neglected" (van Jaarsveld, 1987) group of plants. These plants are mostly attractive, small-flowered, exceptionally floriferous variants (ecotypes) of species of the subgenus Plectranthus, Section Plectranthus, (Codd, 1985). This closely-knit group is popularly used for outdoors plants, also overseas (Brown, 1997; Hessayon, 1993; Hitchcock, 1990; Hitchcock, 1991). In South Africa the National Botanic Institute at Kirstenbosch has collected and made available a large range of species, ecotypes and cultivars with commercial potential (van Jaarsveld, 1994). Among these is a small group of species with larger flowers and good leaf qualities that could contribute to the concept of Plectranthus as novel flowering and foliage pot plants (Van Jaarsveld, 1987; 1994 - Table 1). Mostly these species have horticultural limitations (Table 1) which can ideally be overcome through conventional breeding methods.

2.1. Materials and methods

Our breeding programme has focussed on the combination of favourable characters of the above species with pot plant potential, since 1991 (Table 1). The objective was to develop a wide variety of compact plants with large and floriferous flower types and attractive foliage. All new cultivars were produced by hybridization and selection, using a wide variety of species combinations (Table 5). In an attempt to overcome sterility in interspecific crosses, some hybrids were polyploidized and the resulting changes in fertility noted. In our breeding programme we tried to incorporate seed sterility into new hybrid cultivars, where possible. Interspecific crossing compatibility, efficiency of hybridization, hybrid seed set and fertility in hybrid progeny was studied.

2.2. Results and discussion

Plectranthus species were found to hybridize artificially with difficulty and the resulting interspecific hybrids are almost invariably seed sterile (Table 3). Low fertilization rate and seed set, sterility in flowers and poor seed set in resulting hybrids were the most common incompatibility reactions (Table 4). Polyploidization gave a measure of success in increasing fertility in some sterile interspecific crosses (results not presented). Limited progress has been made in combining the above-mentioned (Table 1) favourable characters over species (Table 5). Improved foliage characters include texture (pleasant to touch and sight), shape (attractively rounded leaves), colour (silver-veined, variegated, underside red-tinted) and smell (pleasantly herbal typical of the mint family). A range of natural colours have been selected for and some selections now have the largest flowers in the genus (Table 5).

3. Production

Research and development (R&D) of production technology and marketing requirements go hand-in-hand with genetic improvement. We based the R&D for

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Plectranthus on growing conditions in the natural environment. In the wild, species of the Section Plectranthus are typically subtropical, perennial, forest-margin and forest-floor inhabitants, shallowly rooted in compost / leaf litter / humus-rich ground, and which require 60 - 80% shade for normal growth (van Jaarsveld, 1987). They are thus "tender" plants (van Jaarsveld, 1987) adapted to protected niches in mild climates and with minimal tolerance to frost and infertile soil, however they are semi-drought tolerant. These natural conditions are the basis of cultivation characters such as ease of cutting propagation, requirement for semi-shade, mild temperature and for protection of soft plant parts during transport. Detailed studies for individual cultivars are however necessary. Tall-growing items require compaction in pots. Plectranthus are short-day (SD) plants and P. oertendahlii ‘November Lights’ flowering period is manipulated commercially using artificial SD, in Denmark. Their growth and nutrient requirements are comparable to that of other Lamiaceae: Salvia, Lamia, Coleus, Plectranthus coleoides (=madagascariensis), etc. Plectranthus R&D are done by a group of specialist nurseries in Australia, Europe, Japan, U.S.A. and South Africa. In South Africa, the horticultural group of Plectranthus species is not aggressively invasive and consequently there appears to be little risk in growing them outdoors.

4. Marketing

Interest in Plectranthus as novel pot plants is developing strongly in Europe and elsewhere and this has been influenced, through association, by the established trade in Plectranthus foliage pot plants (Table 2). Two recent development agreements for Plectranthus pot plants in Europe and another in America (reportedly Ball Co.) has been initiated in recent years. The 'Blue Angel' range of Plectranthus cultivars is promoted as a unique collection of superior hybrids from the Cape. About 20 cultivars have been released over the last five years (Table 5). The plants are suitable for niche marketing, such as novel gift articles. The 'Blue Angel' Plectranthus series has been trademarked. In Europe the 'Blue Angel' Plectranthus is under R&D and control by primarily Van Deuren Nursery Group (Belgium), comprising independent young plant and technical development firms. A separate cooperative pot plant producer (Denmark) is also contracted and production is coordinated. In South Africa Plectranthus has been submitted to a consortium of local R&D nurseries who specialize in introducing new plants to the South African market. Several articles have been published in national garden magazines. Herbal qualities. Belonging to the important herbal family, Lamiaceae, some Plectranthus species have herbal uses and a good smell of leaves.

5. Specialist administration

The new varieties of Plectranthus will be protected through the European Community Plant Variety Rights (Directive No. 2100/94) system. GPL International is responsible for the filing procedure as well as the subsequent monitoring and collection of appropriate royalties in close cooperation with the head licensee (Van Deuren Nursery Group). Plectranthus agreements are also compiled and overseen by GPL International.

6. Conclusions

The ‘Blue Angel’ Plectranthus represent a significant advance in new marketable pot plant types. They clearly excel the natural product in vigour, floriferousness and showiness. The plants were specially selected as compact flowering pot plants but some

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also excel as showy garden-landscape subjects. They cover a wide range of appealing plant, leaf and flower shapes as well as colours. Investigation into improved production and marketing methods will now be conducted.

Acknowledgements

The assistance of Mr E. van Jaarsveld, National Botanic Institute (Kirstenbosch), in initiating the project, is gratefully acknowledged. The constructive comments of Kirin Co., (Japan) on the breeding programme is appreciated.

References

Anonymous, 1996. P ciliatus 'Easy Gold' - an Australian cultivar. Plant Varieties Journal 9: 50-51 Anonymous, 1998. Plectranthus oertendahlii. In: Danish pot plants. Pot Plant Catalogue, Gasa Odense – Blomster A.m.b.a., Lavsenvaenget 1, DK-5200 Odense V, Denmark (p. 132). Anonymous, 2000. Van der Voorts winnen noviteitenshow. Vakblad voor de Bloemisterij 11: 7. Brown L., 1997. Spur of the moment (Plectranthus). House and Leisure, December 1997: 126-129. Codd L.E., 1985. Plectranthus L'Herit. Part 4. Lamiaceae. Flora of Southern Africa 28: 137-172. Hessayon D.G., 1993. The House Plant Expert. Transworld Publishers, London (p.193). Hitchcock A., 1990. A show of Plectranthus. Veld and Flora, March 1990: 24-26. Hitchcock A., 1991. Plectranthus in the landscape. Parks and Grounds 58: 8-13. van Jaarsveld E., 1987. The Plectranthus Handbook. The National Botanic Gardens, Cape Town. CTP Book Printers, Cape Town. van Jaarsveld E., 1994. The genus Plectranthus and the introduction of recent new cultivars. Hortagro 1: 16-18.

Table 1. Plectranthus species with characters useful or limiting for pot plant development

Species Useful characters Limiting characters P. ciliatus Compact, vigorous Small white flowers Leaf underside purple P. ecklonii ‘Erma’ Pink flower (rare) Tall growth habit P. hilliardiae Attractive leaves Poor vigour Leaf underside purple Susceptible to leaf lesions Compact habit Long blue flowers P. oertendahlii ‘Uvongo’ Silver leaf venation Poor vigour Compact habit Small flowers P. praetermissus Mass of violet flowers Flowers small Leaves rounded, furrowed Susceptible to stem-rot P. saccatus var. longitubus Large blue & white flowers Stragly, tall habit 'Umtamvuna’ P. verticillatus ‘Barberton’ Semi-succulent leaves Small white flowers Leaf underside purple P. verticillatus ‘Geelhout- Pink flower (rare) Flowers small boskloof’ Shiny, yellow-green leaf Not floriferous P. zuluensis Partly day-neutral flowering Tall; habit straggly Leaf texture velvety Offensive leaf odour

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Table 2. Examples of established cultivars of Plectranthus (used mostly as foliage pot plants) and new flowering pot plant types, marketed predominantly in Europe

Species Cultivar Product Reference

Established cultivars P. madagascariensis Candle Plant / ‘P. coleoides Foliage Hessayon, 1993 marginatus’ P. verticillatus Moneyplant / ‘P. australis’ Foliage Hessayon, 1993 P. oertendahlii November lights / Flower Anonymous, 1998 Swedish Ivy Hessayon, 1993 New flowering pot plants P. ciliatus Easy Gold Foliage/Fl Anonymous, 1996 P. ambiguus Nico Flower - P. oertendahlii Silver Star Flower Anonymous, 2000 X P. hilliardiae Edelblau Flower - X P. fruticosus Frills Flower Brown, 1997

Table 3. Efficiency of artificial hybridization in Plectranthus, subgenus Plectranthus, Section Plectranthus (haploid n = 14): number of flowers pollinated per cross, total number of ovules involved (flowers x 4), percentage F1-hybrid progeny found and approximate percentage fertility of hybrids

Species Flowers Ovules % Progeny %Fertile Races/ecotypes of P. verticillatus: 52 208 9,6 2 'Barberton' x 'Geelhoutboskloof' P. oertendahlii x P. praetermissus 80 320 1,6 0 P. oertendahlii x P. strigosus 10 40 5 40 P. oertendahlii x P. saccatus 50 200 0 - P. oertendahlii x P. hilliardiae 55 220 0 - P. saccatus x P. hilliardiae 62 248 2,4 0 P. fruticosus x P. ciliatus 32 128 0,8 0 TOTAL 331 1324 2,3 -

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Table 4. Incompatibility reactions in artificial interspecific crosses of Plectranthus (Lamiaceae) and degree of reaction

Reaction Degree Prevention of fertilization Non-germination of pollen on stigma ? Low presence of pollen tubes in style ? Low fertilization rate Often Low seed set Often Poor seed germination Occasionally

Hybrid inviability (F1) Low hybrid growth vigour Occasionally Abnormal / no flowers produced Occasionally Flowers female sterile Often Flowers male sterile Often Low seed set in hybrids Often

Table 5. Examples of ‘Blue Angel’ Plectranthus cultivars, their parentage, product type and salient features

Cultivar Parentage Product Main features Amanda X P. purpuratus Outdoors Strong creeper, sun tolerant Edelblau X P. hilliardiae Fl. potplant Bright blue fl., early, compact Egoli P. verticillatus Hanging b. Golden, shiny leaves, white fl. Frills P. fruticosus x P. Fl. potplant/ Textured, velvety, aromatic ernstii? outdoors leaves; light pink fl., sterile Gurus Choice X P. saccatus: white Fl. potplant/ Large white fl., floriferous, outdoors shiny leaves Lilac Spur X P. oertendahlii Fl. potplant Medium-lilac fl., floriferous Verandah Jacarandah X P. saccatus: blue Fl. potplant/ Large blue fl., floriferous outdoors shiny leaves New: P98 05 02 P. praetermissus x Hanging b./ Bright blue fl.; shiny, semi- P. verticillatus outdoors succulent leaves

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