Essential oil content and quality of rose-scented geranium

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GENERAL INTRODUCTION

Worldwide there are about 3000 plant species which are known for their essential oil production (Lintu, 1995). However, approximately only 300 of these species are commercially important to date (Lintu, 1995) and among these is rose-scented geranium (Pelargonium capitatum × P. radens), which belongs to the family Geraniaceae and genus Pelargonium. The genus Pelargonium L’ Herit comprises about 250 species and these are distributed throughout the world such as in South Africa, Australia, Madagascar, the Middle East, other parts of Africa, Europe and Asia. The centre of origin for this genus is South Africa; about 600 wild scented geranium species are known to be native to the Cape Province of South Africa (Weiss, 1997; Lis-Balchin, 2002).
Botanically, rose-scented geranium is a male sterile, erect and perennial aromatic shrub, with a multi-harvest, high value, commercially important essential oil (Weiss, 1997; Lis-Balchin, 2002). It is a highly fragrant shrub, about 1 to 1.3 m in height, with soft, green to grey-green stem, which becomes woody and dark with age. Leaves are always fragrant with a rose essence, lobed with 5 to 7 palmate, which grow opposite to each other from the stem. The inflorescence is pink and flowering is in spring and early autumn. The root system is extensively spread and is believed to penetrate below 30 cm, especially under stress conditions (Weiss, 1997; van Wyk & Gericke, 2000; Demarne, 2002; Lis-Balchin, 2002; Miller, 2002).

Secondary metabolites and plants

Plants are known to be super chemists due to their ability to synthesize more complex compounds than animals (Salisbury & Ross, 1992; Rost et al., 1998). They synthesize chemical compounds which are more than what is required for their growth in quality and quantity (Rost et al., 1998). In the plant kingdom, certain plant species are known for the synthesis of two metabolic products. These are primary and secondary metabolites. Secondary metabolites are organic compounds that are synthesized by plants through metabolic pathways (Fig. 2.1) but not essential for normal growth and development of the plant. The nomenclature secondary metabolite, secondary products or natural products was given in order to separate them from the primary compounds, i.e. compounds which have a significant role in development of plants such as sugar phosphates, amino acids and amides, proteins, nucleotides, nucleic acids, chlorophyll and organic acids (Salisbury & Ross, 1992; Taiz & Zeiger, 2002). For many years they were believed to be waste products of metabolic processes. Then in the nineteenth and early twentieth century a study of these compounds was initiated by organic chemists who were interested in their extraction for medicinal drugs, poisons, flavours and industrial materials (Taiz & Zeiger, 2002). Recently, the magnitude of these compounds in plants was discovered and some are known to play important roles as attractants in the interaction of plants and other organisms (e.g. in pollination) and some are antibiotics or toxins against pathogens and herbivores (Rost et al., 1998; Taiz & Zeiger, 2002).

Historical background and geographic distribution of rose-scented geranium

Rose-scented geranium (Pelargonium capitatum × P. radens) belongs to the family Geraniaceae and genus Pelargonium. The genus Pelargonium L’ Herit comprises about 250 species and these are distributed throughout the world such as in South Africa, Australia, Madagascar, the Middle East, other parts of Africa, Europe and Asia. The centre of origin for this genus is South Africa; about 600 of wild scented geranium species are known to be native in the Cape Province of South Africa (Weiss, 1997; Lis-Balchin, 2002). The first discovery was in 1672 (P. cucullatum) from Table Mountain. When the British controlled the Cape of Good Hope, South Africa, the interest on the genus augmented and it was introduced in most British colonized areas.
The easy to grow characteristics of the plant also contributed towards its spreading (Weiss, 1997; Lis-Balchin, 2002). The genus Pelargonium contains 15 subgenera (sections) which include the subgenus Pelargonium with about 25 species and the species in this subgenus are characterised by variegated or fragrant leaves. Of the 25 species, only four cultivars (P. graveolens, P. odoratissimum, P. capitatum and P. radens) are believed to have the potential for essential oil production. With species from South Africa, by the year 1690, a cross breeding between the species was started in England, at a botanical garden known as Kew Garden and resulted into the commercially important essential oil producing cultivar Rose, a hybrid between P. capitatum × P. radens (Wiess, 1997; Lis-Balchin, 2002).

Botanical description of rose-scented geranium

The genus Pelargonium L’Herit is one of the indigenous plants to South Africa; contains 15 subgenera and among this the subgenus Ciconium, Dibrachya and Pelargonium can be mentioned (Weiss, 1997). As described by Van der Walt (1985), the species from the subgenus Pelargonium are characterised by highly branched stems, aromatic or multicoloured leaves and most woody shrubs or sub-shrubs. Rose-scented geranium belongs to the subgenus Pelargonium and it is male sterile with haploid somatic number of 2n = 77.
It is an erect and perennial aromatic shrub, with a multi-harvest, high value, commercially important essential oil (Weiss, 1997; Lis-Balchin, 2002). It is a hybrid between P. capitatum and P. raden. It is a highly fragrant shrub, about 1 to 1.30 m in height, with soft, green to grey-green stem, which become woody and dark with age. Leaves are always fragrant with a rose essence, lobed with 5 to 7 palmate, which grow opposite to each other from the stem. The inflorescence is pink and flowering is in spring and early autumn. The root system is extensively spread and is believed to penetrate below 30 cm especially under stress conditions (Weiss, 1997; van Wyk & Gericke, 2000; Demarne, 2002; Lis-Balchin, 2002).

Propagation and planting

In literature, rose geranium is described as male-sterile and, therefore, can not produce seeds. This is due to its unusual chromosome number (x = 11; ‘2n’ = 7x = 77) and hybrid characters (Weiss, 1997; Lis-Balchin, 2002). Therefore, the only means to propagate this plant is by asexual method, mostly stem cuttings (LisBalchin, 2002). Stem cuttings from the terminal as well as the hard stem cuttings can propagate geranium and both cuttings were found to produce similar essential oil (Rajeswara Rao, 1999). Top cuttings root best followed by medial and basal cuttings in sand. Rooted cuttings, suckers or splits are also reported to be equally effective to stem cuttings even though they require a longer time to grow. Vegetative propagation through tissue culture is also possible and an effective method of producing large numbers of plants, but it is not mostly used because it is expensive compared to other propagation methods (Brown & Charlwood, 1986: Yue et al., 1993; Satyakala et al., 1995).

TABLE OF CONTENTS :

• PAGE
• LIST OF TABLES
• LIST OF FIGURES
• LIST OF SYMBOLS AND ABBREVIATIONS
• ABSTRACT
• CHAPTER
  • 1 GENERAL INTRODUCTION
  • 2 LITERATURE REVIEW
  • 2.1 Introduction
  • 2.2 Secondary metabolites and plants
  • 2.3 Historical background and geographic distribution of rosescented geranium
  • 2.4 Botanical description of rose-scented geranium
  • 2.5 Cultivation of rose-scented geranium
  • 2.6 Essential oil content and quality of rose-scented geranium
  • 3 RESPONSE OF ROSE-SCENTED GERANIUM HERBAGE YIELD, ESSENTIAL OIL YIELD AND OIL COMPOSITION TO CONVENTIONAL AND ORGANIC NITROGEN FERTILIZERS
  • 3.1 Introduction
  • 3.2 Materials and methods
  • 3.3 Results and discussion
  • 3.4 Conclusions and recommendations
  • 4 TIME OF NITROGEN FERTILIZER APPLICATION ON REGENERATED ROSE-SCENTED GERANIUM BIOMASS YIELD, ESSENTIAL OIL YIELD AND OIL COMPOSITION
  • 4.1 Introduction
  • 4.2 Materials and methods
  • 4.2.1 Re-growth trend
  • 4.2.2 Time of nitrogen topdressing vs. re-growth cycle
  • 4.3 Results and discussion
  • 4.3.1 Fresh herbage re-growth trend and plant growth parameters
  • 4.3.2 Time of nitrogen topdressing vs. re-growth cycle
  • 4.4 Conclusions and recommendations
  • 5 INFLUENCE OF SEASON ON NITROGEN FERTILIZATION OF ROSE-SCENTED GERANIUM AND THE ESTIMATION OF FOLIAR NITROGEN STATUS USING SPAD- CHLOROPHYLL METER
  • 5.1 Introduction
  • 5.2 Materials and methods
  • 5.3 Results and discussion
  • 4.4 Conclusions and recommendations
  • 6 HERBAGE YIELD, ESSENTIAL OIL YIELD AND OIL COMPOSITION OF ROSE-SCENTED GERANIUM AS INFLUENCED BY LIMING
  • 6.1 Introduction
  • 6.2 Materials and methods
  • 6.3 Results and discussion
  • 6.4 Conclusions and recommendations
  • 7 GENERAL DISCUSSION, CONCLUSIONS AND
  • RECOMMENDATIONS
  • RESEARCH OUTPUTS RESULTED FROM THIS PROJECT
  • LITERATURE CITED
  • APPENDIX

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Rose-scented geranium (Pelargonium spp.) herbage yield, essential oil yield and composition as influenced by nitrogen nutrition and liming