Transformation of Somatic Embryos of Fruit Trees and Grapevine

Abstract

The major objectives of most fruit improvement programmes include breeding for desirable growth habit, resistance to biotic and abiotic stress factors, and high quality and extended shelf life of fruits. Incorporation of genes that govern these economic attributes in the popular fruit cultivars is difficult through conventional breeding and takes years to achieve. Therefore, improvement of elite fruit cultivars through direct gene transfer without gross shuffling of the genome is an economically viable strategy to improve fruit trees and vines within a relatively short period. Genes from any organism can now be transferred and expressed in fruit crops, but the efficiency of transformation, integration and expression of foreign genes and regeneration of transgenic plants from transformed cells are still unpredictable (Owens, 1995; Birch, 1997). Both transformation and regeneration are less efficient in fruit trees and vines than in many herbaceous crops (Scorza, 1991; Schuerman and Dandekar, 1993). Agrobacterium and the biolistic gun are two methods used to transform plant cells. Agrobacterium-mediated transformation has been successfully used in apple, pear, citrus and mango, while the biolistic gun is preferred for papaya. Both Agrobacterium and biolistic gun are used for grape transformation. Adventitious shoot morphogenesis and somatic embryogenesis are the two pathways of plant regeneration in cultured plant cells. Transgenic plants of apples and pears are regenerated by transforming adventitious shoots in leaf cultures (Schuerman and Dandekar, 1993; Mourgues et al., 1996; Scorza et al., 1998), whereas transgenic grapes, mangoes and papayas are produced from transformed somatic embryos (see reviews by Gray, 1995; Litz et al., 1995; Oliviera et al., 1996; Srinivasan and Scorza, 1997). Transgenic citrus plants are produced from adventitious shoots of internode sections of seedlings (Moore et al., 1992; Cervera et al., 1998).