Contents - Faperta

Genetic Transformation of Crops for Resistance to Insect Pests 217
Reduction in larval weight (%)
120
100
80
60
40
20
0
Cry 1Ac Cry 1B Cry 1C Cry 1E Cry IIA Buffer
Cry toxins
FIGURE 7.2 Reduction in weight of Helicoverpa armigera larvae fed on artifi cial diet treated with 0.1 and
0.003125 mg of different Cry toxins of Bacillus thuringiensis.
and Diptera. Several of these Bt toxin genes have been used for the genetic transformation
of crop plants.
Cotton
Considerable progress has been made in developing cotton cultivars with Bt genes for
resistance to bollworms, and there is a clear advantage of growing transgenic cotton in
reducing the damage by bollworms and increasing cottonseed yield. The cotton cultivar
Coker 312, transformed with the cry1Ac gene (having 0.1% toxin protein), has shown high
levels of resistance to cabbage looper, Trichoplusia ni (Hubner), tobacco caterpillar, S. exigua,
corn earworm, Helicoverpa zea (Boddie), and tobacco budworm, H. virescens. Cotton bollworm
damage was reduced to 2.3% in fl owers and 1.1% in bolls in the transgenic cotton,
compared to 23% damage in fl owers and 12% damage in bolls in the nontransgenic commercial
cultivar, Coker 312 (Benedict et al., 1996). The cottonseed yield was 1,050 kg ha1 in
Coker 312 compared to 1,460 kg in Bt cotton. Cotton plants with Bt genes are effective
against pink bollworm, Pectinophora gossypiella (Saunders) (Wilson et al., 1992). Survival of
cotton bollworms (H. zea and H. virescens) has been found to be greater on squares and
fl ower anthers than on other fl oral structures in Deltapine 5415 conventional cotton and
transgenic NuCOTN 33B (Cotsaftis et al., 2002). Enzyme-linked immunosorbent assay
(ELISA) indicated that cry1Ac expression varied in different plant parts, but bollworm survival
did not correlate with the protein expression (Greenplate, 1999). Trends in Bollgard II
were similar to Bollgard I (Gore, Leonard, and Adamczyk, 2001).
0.1 μg
0.003125 μg
FIGURE 7.3 Five-day-old Helicoverpa armigera larvae reared on untreated artifi cial diet (A), and the diet treated
with 0.1 mg mL 1 of Cry1Ac (B), and 0.1% commercial formulation (C) of Bacillus thuringiensis.