BIOTECHNOLOGY AND MOLECULAR BIOLOGY IN PRACTICAL HORTICULTURE

Article number

520_1

Pages

17 – 44

Language

Abstract

The possibility of transforming crop plants became realistic more than 20 years ago (reviewed in Walden and Wigender, 1995). The first procedures, based on vectors derived from Agrobacteria, were followed by other more species-specific methods and at present almost all crop plants can be transformed.
The technology has revealed powerful.
One example is sufficient: the Bt toxin, in the different versions active against Lepidoptera, Diptera and Coleoptera, when expressed in planta has the capacity to control insect pests (Fischoff et al., 1987; Perlack et al., 1993; Armstrong et al., 1995; Wünn et al., 1996). According to Krattiger (1997) the Bt genes have the potential to substitute almost one third of the 8,100 million US dollars necessary to chemically control the insect pests.
A large part of the first wave of transgenic crops currently cultivated, are Bt insect resistant.
Their success demonstrates that agricultural productivity will be improved in the future in a contest of more safe and sustainable farming systems (James, 1997). Horticultural crops seem to follow the trend. Solanum melongena was transformed with a Bt cryIII class gene and transgenic plants were fully resistant to Leptinotarsa decemlineata first- and third-instar larvae (Iannacone et al. 1997). Similarly, synthetic cryIIIA Bt plants were resistant to neonate larvae of the same insect (Jelenkovic et al. 1998, Arpaia et al. 1997). A synthetic cryIAb gene coding for Bt, again transferred to eggplant, resulted in a significant insecticidal activity against the larvae of the fruit borer Leucinodes orbonalis (Kumar et al. 1998). Tomato Bt plants exhibit resistance against Spodoptera exigua, Heliothis virescens and Manduca sexta (Van der Salm et al., 1994). Fruit trees like persimmon transgenic for cryI were found resistant to Plodia interpunctella and Monema flavescens (Tao et al., 1997), while apple and cranberry have been also transformed for the same purpose (Cheng et al., 1994, Serres 1993).

Other toxins are now offered as alternatives to the Bt protein.
These are chitinase, lectins, and alpha -amylase-inhibitors (Gatehouse et al., 1996; Ishimoto et al., 1996; Schroeder et al., 1995), proteinase-inhibitor II (Duan et al., 1996; Thomas et al., 1995), cystatin (Irie et al., 1996), and cholesterol-oxidase (Purcell et al., 1993). The transformation of strawberry with cystatin cDNA clones controls the Coleoptera pest black vine weevil Otiorynchus sulcatus. An efficient control of this insect by plant cystatin-expressing transgenic strawberry plants is therefore potentially possible, but a correct targeting of the inhibitors in the plant cell using appropriate signal peptides could be necessary (Michaud et al., 1995). Insecticidal effects of three plant-derived genes, those encoding snowdrop lectin, bean chitinase and wheat alpha-amylase, were investigated and compared with effects of the cowpea trypsin inhibitor gene CpTI. Resistance was assayed by exposing the plants to larvae of the tomato moth, Lacanobia oleracea. Plants expressing the lectin showed an enhanced level of resistance (Gatehouse et al. 1997). A cDNA encoding the alpha-amylase inhibitor from the seeds of the common bean was transformed into pea.
The development of pea weevil larvae was blocked at an early stage.
Seed damage was minimal and seed yield was not significantly reduced in the transgenic plants (Schroeder et al., 1995). The cowpea trypsin inhibitor gene was transformed into Brassica oleracea var. capitata. Insect-tolerance of the transgenic plants to Pieris rapae L. was observed by testing the plants in the laboratory (Fang et al., 1997a). New strategies are being proposed which address the problem of insect control, like the expression in planta of antibodies against insect gut proteins, the