Floral Form Research Articles

Enantiostyly in angiosperms and its evolutionary significance

Enantiostyly, deflection of style to left or to right side of floral axis, is a kind of style polymorphism. Based on organization of left- and right-styled flowers present on individual plants, enantiostyly can be expressed as two quite distinct forms: monomorphic and dimorphic enantiostyly. In monomorphic enantiostyly, individual plants produce both floral forms, either mixed within an inflorescence or segregated between left- and right-styled inflorescences, and this condition is not a genetic polymorphism. In dimorphic enantiostyly, plants are exclusively left- and right-styled, and this condition is a genetic polymorphism. Based on patterns of arrangement of style and stamens in individual flowers, enantiostyly can be expressed as reciprocal and nonreciprocal enantiostyly. Reciprocal enantiostyly is commonly associated with the reciprocal deflection of a pollinating anther, but in nonreciprocal enantiostyly there are no pollinating anther deflections. Enantiostyly has been reported in 11 families of angiosperm. It is generally considered to play an important role in (1) protecting the functional pistil and stamens, (2) insuring reproduction by selfing, and (3) increasing male fitness and outcrossing rates by reducing sexual interference between female and male function. Enantiostyly has been hotly-debated in plant reproductive biology. The purpose of this paper is to review and analyze recent advances in enantiostyly research, with emphases on 1) types of enantiostyly and morphological differentiation and floral characteristics of mirror-image flowers; 2) taxonomy, genetics and evolution of angiosperms that exhibit enantiostyly; and 3) the evolutionary biology of mating patterns and pollinating characteristics associated with enantiostyly. Finally, prospects for further research in this area are discussed. Our review provides a database for further study of the evolutionary biology of enantiostylous species and points out the significance of enantiostyly in the evolution of breeding systems of plants.

Environment and pollinator‐mediated selection on parapatric floral races of Mimulus aurantiacus

We tested whether selection by pollinators could explain the parapatric distribution of coastal red- and inland yellow-flowered races of Mimulus aurantiacus (Phrymaceae) by examining visitation to natural and experimental populations. As a first step in evaluating whether indirect selection might explain floral divergence, we also tested for local adaptation in early life stages using a reciprocal transplant experiment. Hummingbirds visited flowers of each race at similar rates in natural populations but showed strong (>95%) preference for red flowers in all habitats in experimental arrays. Hawkmoths demonstrated nearly exclusive (>99% of visits) preference for yellow flowers and only visited in inland regions. Strong preferences for alternative floral forms support a direct role for pollinators in floral divergence. Despite these preferences, measures of plant performance across environments showed that red-flowered plants consistently survived better, grew larger and received more overall pollinator visits than yellow-flowered plants. Unmeasured components of fitness may favour the yellow race in inland habitats. Alternatively, we document a marked recent increase in inland hummingbird density that may have caused a change in the selective environment, favouring the eastward advance of red-flowered plants.

Supplementary data: Assessment of genetic diversity ofLycoris longituba (Amaryllidaceae) detected by RAPDs

Lycoris longituba Y. Hsu et Q. J. Fan is a perennial, bulbiferous, herbaceous plant of the family Amaryllidaceae. It is endemic in China, with a very limited distribution, being found only at Langyashan in Anhui province, and Baohuashan and Xuyi city in Jiangsu province, all located about 50 km from one another (see figure 1 and table 1 in electronic supplementary material at http://www.ias.ac.in/jgenet/). A unique biological characteristic of this plant is that its leaves come out in spring and die in early summer, followed by flowering. Thus, its vegetative growth and reproduction are discrete, which is rare in angiosperms. With a vigorous and long scape, its flowers are diverse in both colour and floral form, and fragrant in smell, and have high ornamental value. Also called Chinese tulip, this species is ideal for ikebana, and its bulb has medicinal properties. We have collected more than 70 variants of this species in our laboratory with different floral colours and forms. Population-genetic structure is considered as spatiotemporal distribution of genetic variation (Ge 1997), and reflects evolutionary processes in populations (Hamrick and Loveless 1989). To take right measures to protect wild resources of L. longituba, it is important to study the range of genetic variation, genetic structure, diversification trend and other factors affecting genetic structure of the populations of this important and sparsely distributed species. Presently, many biochemical and DNA-based markers are used in studies of population structure. The random amplified polymorphic DNA (RAPD) method (Williams et al. 1990) is frequently applied to reveal population-genetic variation, divergence and biogeography (Schaal and Leverich 2001). A large number of studies have successfully applied this method to study genetic variation in plants owing to

The sweet stench of decay

The sweet stench of decay

Phylogenetics of the florally diverse Andean clade Iochrominae (Solanaceae)

Recent molecular phylogenetic studies of Solanaceae have identified many well-supported clades within the family and have permitted the creation of a phylogenetic system of classification. Here we estimate the phylogeny for Iochrominae, a clade of Physaleae sensu Olmstead et al. (1999), which contains 34 Andean species encompassing an immense diversity of floral forms and colors. Using three nuclear regions, ITS, the second intron of LEAFY, and exons 2 to 9 of the granule-bound starch synthase gene (waxy), we evaluated the monophyly of the traditional genera comprising Iochrominae and assessed the extent of interspecific hybridization within the clade. Only one of the six traditionally recognized genera of Iochrominae was supported as monophyletic. Further, comparison of the individual nuclear data sets revealed two interspecific hybrid taxa and a third possible case. These hybrid taxa occur in the Amotape-Huancabamba zone, a region between the northern and central Andes that has the greatest diversity of Iochroma species and offers frequent opportunities for hybridization in areas of sympatry. We postulate that periodic hybridization events in this area coupled with pollinator-mediated selection and the potential for microallopatry may have acted together to promote diversification in montane Andean taxa, such as Iochrominae.

Mango Malformation Disease and the Associated Fusarium Species

ABSTRACT Mango malformation disease (MMD) occurs in Asia, Africa, and the Americas and was first reported in India in 1891. The vegetative form of MMD was first reproduced in 1966 with Fusarium moniliforme and the floral form with isolates of F. moniliforme var. subglutinans from both vegetative shoots and floral tissue. The fungi were subsequently recognized as F. subglutinans. In 2002, a new species, F. mangiferae, was established based on nuclear and mitochondrial DNA sequences; it included strains of F. subglutinans from Egypt, Florida, Israel, Malaysia, and South Africa, some of which had been shown to cause MMD by artificial inoculation. At least three additional taxa have been associated with MMD: F. sterilihyphosum from Brazil and South Africa, and Fusarium sp. nov. and F. proliferatum (teleomorph: Gibberella intermedia) from Malaysia. To date, Koch's postulates have not been completed with them. In the future, gene sequencing will be essential to identify the Fusarium spp. that are associated with MMD. Work remains to be done on the morphology, sexual compatibility, pathogenicity, and toxigenicity of these taxa.

Bird Pollination in an Angraecoid Orchid on Reunion Island (Mascarene Archipelago, Indian Ocean)

Although numerous angraecoid orchids in Madagascar display typical sphingophilous syndrome (i.e. white, nectariferous, long-spurred flowers, producing a strong scent at the crepuscule that is attractive to moths), three species of Angraecum in Reunion, belonging to the endemic section Hadrangis, have atypical unscented and short-spurred flowers. The aim of the study was to investigate the implication of plant-pollinator interaction on the evolution of floral morphology of these peculiar island floral forms. The flower morphology of A. striatum (one of the three section Hadrangis species) was investigated by performing a set of floral measures, and the reproductive biology was investigated by a set of hand pollination experiments. Natural pollinators were observed by means of a digital video camera. Pollinator efficiency (pollen removal and deposition) and reproductive success (fruit set) were quantified once a week in natural field conditions during the 2005 flowering season (i.e. from January to March). The orchid is self-compatible but requires a pollinator to achieve fruit set. Only one pollinator was observed, the endemic white-eye Zosterops borbonicus (Zosteropidae). These birds perched on inflorescences, and probed most fresh-looking flowers on each plant for nectar. Nectar was both abundant (averaging 7.7 microL) and dilute (averaging 9.7 % sugar in sucrose equivalents). Birds were mostly active between 0830 and 0930 h. Visits to plants were extremely short, lasting from 9 to 27 s. At the study site, 60.9 % of flowers had pollen removed, and 46.4 % had pollinia deposited on stigmas. The proportion of flowers that initiated a fruit averaged 20.6 % in natural conditions. For the first time, a bird-pollinated orchid is described from a sub-tribe that is mainly specialized for moth pollination. This study documents a morphological shift in flowers in response to pollinator adaptations in the insular context of the Mascarene Archipelago.

Systematics and Evolution of the Tropical Monocot Family Costaceae (Zingiberales): A Multiple Dataset Approach

A phylogenetic analysis of molecular (ITS, trnL-F, trnK including the matK coding region) and morphological data is presented for the pantropical monocot family Costaceae (Zingiberales), including 65 Costaceae taxa and two species of the outgroup genus Siphonochilus (Zingiberaceae). Taxon sampling included all four currently described genera in order to test the monophyly of previously proposed taxonomic groups. Sampling was further designed to encompass geographical and morphological diversity of the family to identify trends in biogeographic patterns and morphological character evolution. Phylogenetic analysis of the combined data reveals three major clades with discrete biogeographic distribution: (1) South American, (2) Asian, and (3) African-neotropical. The nominal genus Costus is not monophyletic and its species are found in all three major clades. The Melanesian genus Tapeinochilos is monophyletic and included within the Asian clade. Monocostus and Dimerocostus are sister taxa and form part of the South American clade. The African-neotropical clade is composed entirely of the genus Costus; moreover, there is support for previously recognized subgeneric groupings within the Costus clade. Evolutionary trends in floral morphology show that close associations with pollinators have evolved several times from an ancestral generalist pollinator floral form. Bee pollination has evolved once in the family, arising in Africa from an open-flowered (generalist) ancestor. Bird pollination has evolved multiple times: once from an open-flowered ancestor in Southeast Asia and multiple times from a bee-pollinated ancestor in the neotropics. Additional morphological characters not traditionally used to define taxonomic groups, but having high consistency in the current phylogenetic analysis, are discussed.

Gondwanan Vicariance or Dispersal in the Tropics? The Biogeographic History of the Tropical Monocot Family Costaceae (Zingiberales)

Costaceae are a pantropical family, distinguished from other families within the order Zingiberales by their spiral phyllotaxy and showy labellum comprised of five fused staminodes. While the majority of Costaceae species are found in the neotropics, the pantropical distribution of the family as a whole could be due to a number of historical biogeographic scenarios, including continental-drift mediated vicariance and long-distance dispersal events. Here, the hypothesis of an ancient Gondwanan distribution followed by vicariance via continental drift as the leading cause of the current pantropical distribution of Costaceae is tested, using molecular dating of cladogenic events combined with phylogeny-based biogeographic analyses. Dispersal-Vicariance Analysis (DIVA) is used to determine ancestral distributions based upon the modem distribution of extant taxa in a phylogenetic context. Diversification ages within Costaceae are estimated using chloroplast DNA data (trnL-F and trnK) analyzed with a local clock procedure. In the absence of fossil evidence, the divergence time between Costaceae and Zingiberaceae, as estimated in an ordinal analysis of Zingiberales, is used as the calibration point for converting relative to absolute ages. The results of the temporal analysis based on extant taxa indicate that the initial diversification within Costaceae occurred approximately 65 million years ago, long after the final break up of the Gondwanan supercontinent. Considering this minimum age of diversification, potential scenarios for the current biogeographic patterns found in Costaceae are presented in a temporal and spatial context. The evolution of specialized floral forms associated with specific pollinators is also discussed within the biogeographic framework.

Phylogeny and the Evolution of Floral Diversity in Pedicularis (Orobanchaceae)

Pedicularis has a conflicted infrageneric taxonomic history in which floral and vegetative characters have alternately been interpreted as primary indicators of common ancestry. Recent classifications favor subgenera delimited by similarity in leaf arrangement, on the basis of the premise that corolla morphology has been subject to pollinator‐mediated selection, resulting in the convergent evolution of specialized floral forms from generalized ancestors. In this study, molecular phylogenetic analysis of Pedicularis reveals a low concordance of robust clade support and taxonomic groups. Nevertheless, the basic premise of higher homoplasy in floral characters relative to leaf arrangement is confirmed, although the hypothesized direction of change (from short‐tubed, beakless, toothed corollas to long‐tubed, beaked, toothless forms) is not uniformly upheld. In spite of the high evolutionary lability of floral form in Pedicularis, some character state combinations are rarely or never observed, suggesting functional constraints. Correlation analysis shows a significant association between curved‐rostrate corollas (a marker for nectar production) and long corolla tubes, indicating that access to nectar by pollinators has acted as a constraint on the evolution of corolla tube length.

Variation in daily floral display and the potential for geitonogamous pollination in two monomorphic enantiostylous Monochoria species

Mirror-image flowers (enantiostyly) have long been considered a mechanism to promote cross-pollination between flowers of alternate stylar orientation. However, in monomorphic enantiostyly, the occurrence of both left- and right-styled flowers on the same individual plant might appear to promote geitonogamy rather than outcrossing relative to the condition of dimorphic enantiostyly. We investigated daily floral display during the flowering season in two experimental populations of monomorphic enantiostylous species, Monochoria korsakowii and Monochoria vaginalis (Pontederiaceae) to assess the potential effects of floral display on geitonogamous pollination. The left- and right-styled flowers exhibited a 1:1 ratio both within individuals and populations. In M. korsakowii and M. vaginalis, 86.0% and 71.3% daily floral displays involved fewer than three flowers thus reducing the likelihood of geitonogamy. Moreover, daily displays often involved one floral form and mixed-formed with unequal ratios of left- and right-styled flowers also reducing opportunities for geitonogamy. Therefore variation in daily floral display in these two Monochoria species suggests that the impact of monomorphic enantiostyly in promoting geitonogamy will be reduced by small display sizes, or through simulating dimorphic enantiostyly.

Duplications inCYC‐like Genes from Dipsacales Correlate with Floral Form

Flower symmetry is of special interest in understanding the evolution and ecology of angiosperms. Evidence from the Antirrhineae (within the lamiid clade of Asteridae) indicates that several TCP gene family transcription factors, especially CYCLOIDEA (CYC), play a role in specifying dorsal identity in the corolla and androecium of monosymmetric (bilateral) flowers. We examine the evolution of this gene family in Dipsacales, representing the campanulid clade of Asteridae, in relation to evolutionary shifts in floral symmetry and stamen abortion. We identify three major forms of CYC‐like genes in Dipsacales. We identify the position of additional gene duplications by comparing each of the three gene trees to a well‐supported Dipsacales phylogeny. We infer duplications in two of the major gene lineages along the line leading to the Caprifoliaceae correlated with the origin of monosymmetric flowers. There are no duplications or losses associated with major shifts in stamen number. However, there are several additional duplications within the Caprifoliaceae, especially in the Morinaceae, possibly related to calyx monosymmetry and/or stamen reduction. Within the protein‐coding sequences, we identify a new conserved region—the ECE region—that appears to be present across known angiosperm sequences. There are major changes in length and in the presence or absence of the ECE region in the Dipsacales, indicating changes in gene function. These studies expand our understanding of the evolution of CYC‐like genes in angiosperms and provide a new system for studying the role of this gene family in determining floral form.

THE SYMBOLISM OF JADE IN CLASSIC MAYA RELIGION

The Classic Maya esteemed jadeite not only for its preciousness and beauty but also as stone of great symbolic import. This paper examines the religious significance of jade and certain types of jade artifacts among the Classic Maya. In this study, I note that the Classic Maya ascribed a number of meanings to jade, including maize, centrality, and rulership, as well as a material embodiment of wind and the vitalizing breath soul. Because of its close relationship to the breath spirit, jade was an important component of funerary rites and the ritual conjuring of gods and ancestors. Carved in floral form, jade earspools were considered supernatural sources or passageways for the breath spirit, frequently portrayed as a bead or a serpent emerging from the center of the jade flare. A common Classic Maya death expression,och b'ih, pertains directly to resurrection of the soul through the symbolism of earspools. Many of the symbolic meanings and imagery found with Classic Maya jade also appears with other cultures of ancient Mesoamerica, including Teotihuacan, Xochicalco, and the contact-period Aztec. Rather than being wholly of Classic Maya origin, many aspects of this jade symbolism and related artifacts can be also found among the earlier Middle Formative Olmec.

FLORAL SPECIALIZATION WITHOUT TRADE-OFFS: OPTIMAL COROLLA FLARE IN CONTRASTING POLLINATION ENVIRONMENTS

Most models of floral specialization assume that adaptations to a particular type of pollinator incur a fitness trade-off in reduced effectiveness of others. To examine this assumption and characterize the form of trade-offs, I manipulated floral form in Dudleya greenei (Crassulaceae), a species that is pollinated by hummingbirds, bumble bees, and other insects. Existing pollination literature predicts that pollination by hummingbirds should favor narrower flowers than pollination by bumble bees. When hummingbirds alone visited experimental populations, narrow flowers indeed performed best by most measures. Hummingbirds showed a slight preference for flowers of intermediate width but deposited more pollen per visit and more pollen overall, and they exported more dye (a pollen analogue) as corolla flare decreased. Bees were more effective than birds at pollinating wide flowers but did not generate overall performance trade-offs. Bees also preferred flowers of intermediate width and deposited more pollen per visit and more pollen overall as corolla flare decreased, but the overall efficiency with which bumble bees exported dye was independent of corolla flare. This demonstrates that phenotypic specialization for hummingbirds might evolve without trading-off the effectiveness of bumble bees. However, both birds and bees tended to transfer dye most efficiently between like phenotypes, suggesting that the form of selection and presence of trade-offs may be frequency dependent in natural populations.

Phylogeny of Amorpheae (Fabaceae: Papilionoideae)

The legume tribe Amorpheae comprises eight genera and 240 species with variable floral form. In this study, we inferred a phylogeny for Amorpheae using DNA sequence data from the plastid trnK intron, including matK, and the nuclear ribosomal ITS1, 5.8S, and ITS2. Our data resulted in a well-resolved phylogeny in which the tribe is divided into the daleoids (Dalea, Marina, and Psorothamnus), characterized by generally papilionaceous corollas, and the amorphoids (Amorpha, Apoplanesia, Errazurizia, Eysenhardtia, and Parryella), characterized by non-papilionaceous flowers. We found evidence for the paraphyly of Psorothamnus and for the monophyly of Dalea once D. filiciformis is transferred to monophyletic Marina. Errazurizia rotundata is more closely related to Amorpha than to the other errazurizias, and Eysenhardtia is supported to be monophyletic. The monotypic Parryella and Apoplanesia are placed within the amorphoids. Among Papilionoideae, trnK/matK sequence data provide strong evidence for the monophyly of Amorpheae and place Amorpheae as sister to the recently discovered dalbergioid clade.

Evolution of zygomorphy in monocot flowers: iterative patterns and developmental constraints

SummaryHere we explore morphological transitions among monocot flowers and discuss them in terms of modification of existing structures. Monocot flowers are typically arranged in five whorls (carpels, inner and outer stamens, inner and outer tepals), and are radially symmetrical, constructed around a 3‐fold axis of rotational symmetry that delineates three planes of bilateral symmetry. Differential development of one or two of the three organs within a whorl inevitably emphasizes one plane of symmetry, by eliminating the other planes, rendering the whorl zygomorphic. Zygomorphy (monosymmetry) has evolved more than once in monocotyledons. Stamen suppression is a widespread aspect of zygomorphy and conforms to two broad categories of pattern. In the more frequent Pattern 1, 1–3(−5) adaxial stamens (both inner and outer) are either reduced in size or entirely suppressed. Pattern 2 involves loss, reduction or modification of at least the outer abaxial stamen. Pattern 2 often characterizes groups that are phylogenetically embedded within Pattern 1 clades, perhaps indicating that this pattern results from loss of function or overexpression of the same genes involved in establishment of Pattern 1. Heterotopy has been an important evolutionary phenomenon among Zingiberales (some stamens becoming petaloid) and perhaps grasses (petals possibly becoming sepaloid). Heterochrony is the most frequent cause of more subtle changes in the degree of bilateral symmetry shown by monocot flowers by enhancing (peramorphosis) or retarding (paedomorphosis) individual organs within specific whorls. Contents Summary 25 I. Introduction 28 II. Background 27 III. Asparagales 28 IV. Commelinids: ZHC clade 29 V. Commelinids: Poales 32 VI. Conceptual transitions among floral forms revisited 34 VII. Examples from monocot flowers 37 VIII. Specific cases of ontogenetic transitions between contrasting floral morphs 39 IX. Conclusions 40 Acknowledgements 42

Flower Development: Initiation, Differentiation, and Diversification

Flowering is one of the most intensively studied processes in plant development. Despite the wide diversity in floral forms, flowers have a simple stereotypical architecture. Flowers develop from florally determined meristems. These small populations of cells proliferate to form the floral organs, including the sterile outer organs, the sepals and petals, and the inner reproductive organs, the stamens and carpels. In the past decade, analyses of key flowering genes have been carried out primarily in Arabidopsis and have provided a foundation for understanding the underlying molecular genetic mechanisms controlling different aspects of floral development. Such studies have illuminated the transcriptional cascades responsible for the regulation of these key genes, as well as how these genes effect their functions. In turn, these studies have resulted in the refinement of the original ideas of how flowers develop and have indicated the gaps in our knowledge that need to be addressed.

The Comparative Biology of Mirror‐Image Flowers

Enantiostyly, the deflection of the style to the left or right side of the floral axis, is a sexual polymorphism reported from at least 10 angiosperm families in both monocotyledons and dicotyledons. To investigate variation in the enantiostylous condition, we examined sex‐organ reciprocity and the arrangements of left‐ and right‐styled flowers in 15 enantiostylous species from eight genera in six families. Enantiostyly can be expressed at three distinct levels of structural organization. In “monomorphic enantiostyly,” individual plants produce both floral forms, either mixed within an inflorescence or segregated between left‐ and right‐styled inflorescences. In “dimorphic enantiostyly,” plants are exclusively left‐ or right‐styled and this condition is a genetic polymorphism. Enantiostyly is most commonly associated with the reciprocal deflection of a pollinating anther (“reciprocal enantiostyly”), although there is a continuum in stigma‐anther position, ranging from no reciprocal anther to complete reciprocity. Comparative analyses of a composite phylogeny of the monocotyledons indicate that in this group enantiostyly has evolved at least 11 times, often simultaneously with the gain of heteranthery. Both concentrated changes and maximum likelihood tests indicated that heteranthery and the loss of nectaries are significantly associated with the presence of enantiostyly, indicating a syndrome of traits where pollen is the main reward and anthers are divided into two functions: pollination and nutrition. The association of enantiostyly with heteranthery, the loss of nectaries, and the reciprocal placement of a pollinating anther suggest that the polymorphism functions to increase the precision of cross‐pollen transfer and to reduce interference of stigmas and anthers within or between flowers on the same plant.

Floral Development in the Nymphaeales

Numerous phylogenetic analyses and recent paleobotanical findings continue to support the inclusion of Nymphaeales as basal or near‐basal extant angiosperms. The distinctive differences in floral morphology and habit between non‐Nymphaealian taxa of the ANITA grade compared with water lilies, nevertheless, remain perplexing. In this investigation, scanning electron microscope observations on Brasenia (Cabombaceae), Nuphar, Nymphaea, Ondinea, Victoria, and Euryale (Nymphaeaceae) are added to the observations of earlier investigations to enhance our understanding of early floral evolution and shifts in floral ontogeny and to contribute new data for improved cladistic analyses. The enlargement of flowers and amplification of floral parts distinctive in Nymphaeaceae is based on continuing surface area enlargement of the floral apex, allowing numerous organs to be produced acropetally in distinctive parastichies, compared with the ring meristem found in some primitive eudicots (Nelumbonaceae, Papaveraceae) that increase floral organ number but in dense pulses or clusters without clear order. The smaller flowers of the Cabombaceae and their lower number of floral organs are now regarded as more typical of the ancestral angiosperm flower. One may conclude that changes in the size of the floral apex and its geometric conformation alter flower size, number of parts, and phyllotaxy. The ebracteate condition and herbaceous, aquatic habit of Nymphaeales when compared with Archaefructus, a recently discovered herbaceous aquatic angiosperm from the Upper Jurassic/Lower Cretaceous that is proposed as a new basal angiosperm family, continue to question the relationship of early angiosperms to the aquatic habitat. Is the ebracteate state significant, and how did the shift to aquatic habitats impact floral form of early angiosperms?

AN OPTIMISED PROTOCOL FOR ROSE TRANSFORMATION APPLICABLE TO DIFFERENT CULTIVARS

The production of cut-flower roses makes a substantial contribution to the global floriculture industry. Breeding programmes are driven by consumer requirements for novel and improved phenotypes, coupled to optimum production, disease and pest resistance. Traditionally, new cultivars have been developed through sexual hybridisation. However, this process is time consuming and by introducing one agronomically useful trait another may be eliminated. For example, improvement of floral form and production over many decades has resulted in the loss of scent from many modern rose cultivars. The introduction of specific genes into known rose cultivars could facilitate the generation of new cultivars with improved agronomic traits, without the problems associated with conventional breeding. Plant phenotype, yield and resistance to pests and diseases are characteristics that can be manipulated on an individual basis. In the present investigation, Agrobacterium tumefaciens-mediated transformation of embryogenic callus from a number of rose cultivars was optimised using the beta-glucuronidase (gus; uidA) gene. Stable integration of the transgene was confirmed at each stage of somatic embryogenesis and in regenerated plants. An optimised protocol was used to deliver potentially agronomically useful transgenes into cultivars with the aim of improving flower production, disease resistance or reintroducing scent into those cultivars in which it was absent. Results indicate that the manipulation of individual traits by genetic engineering in existing cultivars shows considerable promise and may be an adjunct in the future to conventional breeding.