Genetic Transformation of Geraniums
The florist’s geranium (Pelargonium × domesticum) is a favorite house plant, available in many varieties. Other Pelargonium species are commercially important for geranium oil. These plants are known as scented geraniums and the principal ones are: P. gra
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PELLEGRINESCHI 1
1 Introduction The florist's geranium (Pelargonium x domesticum) is a favorite house plant, available in many varieties. Other Pelargonium species are commercially important for geranium oil. These plants are known as scented geraniums and the principal ones are: P. graveolens, P. jragrans, P. odoratissimus, P. capitatum, P. quercifolia, P. citrosum, and P. abrotaniolium. The remaining families of the Geraniales order are of less economic importance; some are, however, important locally for food (as oil for seasoning or tuber production) and ornamental planting. An example of these is the "hardy geraniums", hundreds of whose varieties are collected by gardeners and amateurs for their easy growth (e.g., Geranium robertianum or G. psillostemon). Numerous investigations have been conducted on various aspects of micropropagation (see Cassells 1992) and the in vitro production of geraniin, tannins, and other secondary metabolites, and the literature has been recently reviewed by Ishimaru and Shimomura (1995). The principal aims of this chapter on the genetic transformation of geraniums are related to improvements in the ornamental characteristics of the florist geranium, such as a compact canopy, a change in the flower colors, and, for the scented geraniums, an increase in the production and quality of essential oils (Pellegrineschi et al.
1994).
2 Methods and Factors in Geranium Genetic Transformation 2.1 Agrobacterium-Mediated Transformation Successful genetic transformation of geranium mediated by Agrobacterium is dependent on a number of factors related to both the plant and the bacteria, which can be manipulated to increase transformation events.
lBiotechno!ogy Research Unit, IITA, Oyo Road, PMB 5320, Ibadan, Nigeria
Biotechnology in Agriculture and Forestry, Vol. 38 Plant Protoplasts and Genetic Engineering VII (ed. by Y.P.S. Bajaj) © Springer·Veriag Berlin Heidelberg 1996
A. Pellegrineschi
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2.1.1 Bacterial Material The type of bacterial strain used is one of the most important factors in obtaining a good transformation percentage range. It has been reported by several authors (De Cleene and De Ley 1976, 1981; Chilton et al. 1982; Bouzar et a1.1993) that virulence and effective host range differ in the Agrobacterium strains. This is true also of Geranium, where it has been found that a different percentage of transformed tissue can be obtained (hairy roots) depending on the Agrobacterium strain used (Fig. 1). To test the efficiency of the transformation capacity of Agrobacterium in Pelargonium, five wild-type strains of A. rhizogenes were used as inocula: A4, HRI, 8196, A4RSI, and A4RSNT. The bacteria were grown at 28°C for 48 h on AP medium (Petit et al. 1983) without antibiotics. Before inoculation of plant material, frozen Agrobacterium stocks were transferred to fresh medium for two subcultures to reestablish normal growth. All Pelargonium species tested in vitro were susceptible to the A. rhizogenes strain HRi. The first hairy roots were visible 10 days after inoculation. On subse
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