Contents - Faperta

90 Biotechnological Approaches for Pest Management and Ecological Sustainability
Schwarzbach, and Fischbeck, 1983). Recent reports on the duration of induced resistance in
host-pathogen systems have been documented in barley (Pelcz and Wolffgang, 1986), cotton
(Liu, Chen, and Wang, 1990), and cucumber (Dalisay and Kuc, 1995). Insect herbivory
has been shown to induce resistance in soybean plants (Lin, Kogan, and Fischer, 1990;
Fischer, Kogan, and Paxton, 1990; Lin and Kogan, 1990) against the soybean looper,
Pseudoplusia includens (Walker) and the Mexican bean beetle, E. varivestis. Cross-resistance
to P. includens due to previous Cerotoma trifurcata (Forster) injury in the form of induced
resistance is benefi cial to the plant. Bean leaf beetle, C. trifurcata herbivory also affects
larval growth rates and reduced the suitability of foliage to the corn earworm, H. zea in
soybean (Felton, Summers, and Mueller, 1994).
Chemically induced expression systems or “gene switches” enable temporal, spatial, and
quantitative control of genes introduced into plants or those that are already present in the
plants to impart resistance to insects. This approach has provided opportunities for management
of development of resistance in insect pest populations in transgenic crops. In addition
to insect or pathogen attack, resistance can also be induced by suboptimal concentrations of
potassium iodide, copper, and herbicides. Effectiveness of the chemical injury inducer
Actigard in providing resistance to various insect pests and pathogens in the tomato has
been demonstrated by Inbar et al. (1998). Induced resistance against E. varivestis lasted three
days after damage in soybean (Underwood, 1998). Proteinase inhibitors and oxidative
enzymes such as polyphenol oxidase, peroxidase, and lipoxygenase persist for at least
21 days after induction in damaged tomato leafl ets (Stout, Workman, and Duffey, 1996).
A wide range of inducible genes has been identifi ed in plants based on endogenous
chemical signals, such as phytohormones, responses to insect and pathogen attack, or
wounding. The best-studied system utilizes the PR1-a promoter from tobacco, which is
induced during systemic resistance response following pathogen infection (Uknes et al.,
1993). The PR1-a mRNA levels can also be induced by exogenous application of salicylic
acid or 1,2,3-benzothaidiazole-7-carbothioic acid S-methyl ester (BTH) (Ward et al., 1991;
Gatz, 1997). The latter has been commercialized as a plant immunization chemical.
However, PR1-a use may be limited due to its responsiveness to exogenous signals such as
pathogens, UV-B, and pollutants (Gatz, 1997). Safeners used for detoxifi cation of certain
herbicides also induce a range of metabolic enzymes, such as glutathione-S transferase and
cytochrome P 450 ( Jepson, Martinez, and Sweetruan, 1998). Safener-induced cDNA clones
(In 2-2 and GST-27) have been isolated from maize and Arabidopsis. These promoters can be
induced by M-(aminocarbonyl)-2-chloro benzenesulfonamide and the herbicide sulfonylurea.
Tetracycline and lactose represser operator systems from Escherichia coli Escherich have
also been used to control gene expression ( Jepson et al., 1994). Tetracycline (TetR) repressor
protein has been used to regulate the expression from CaMV 35S promotor (Gatz and
Quail, 1998). Another system in yeast uses a copper-dependent transcriptional activation
system, which consists of ace1 gene encoding a metalloresponsive factor expressed constitutively.
Activation of the reporter gene (ace1) is achieved in the presence of copper (Mett,
Lochhead, and Reynolds, 1993). Copper has traditionally been used as a fungicide, but
application of copper for activation of the reporter gene may not be ideal in all crops.
Another transcriptional activation system (Alc) is based on ethanol (Caddick et al., 1998).
The AlcR transcription factor interacts with ethanol or related inducers. It has a low activity,
rapid and reversible induction, and suffi ciently high levels of induction to generate
phenotypic effects. Glucocorticoid receptor (GR) (Wang et al., 1997) and ecdysone receptor
(Wing, Slawecki, and Carlson, 1988; Jepson, Martinez, and Sweetruan, 1998) also have the
potential for use as switches for inducible resistance to insects.
Octadecanoid and the salicylic acid pathways are involved in the induced attraction of the
parasitoid wasp, Cotesia rubecula (Marshall) by Arabidopsis thaliana (L.) Heyn. infested with