Contents - Faperta

Genetic Engineering of Entomopathogenic Microbes for Pest Management 269
TABLE 8.4
Genetically Modifi ed Commercial Bacillus thuringiensis Products for Pest Control
Bt Strain Product Target Insect References
Aizawai recipient, kurstaki
donor
Kurstaki recipient, aizawai
donor
Agree, Design
(transconjugant)
Condor, Cutlass
(transconjugant)
strains that produce crystals, but the crystals remain encapsulated in the mother cell
(Lereclus et al., 1995; Bravo et al., 1996).
Several commercial products (Table 8.4) and novel strains of Bt have also been developed
through genetic engineering (Table 8.5). The shuttle vector pHT3101 and its derivative
pHT408 bearing a copy of a cryIAa delta-endotoxin gene have been transferred into several
Bt subspecies through phage CP-54Ber-mediated transduction (Lecadet et al., 1992). In
Cry and Cry native recipients, the introduction of the cryIAa gene resulted in the
formation of large bipyramidal crystals that were active against P. xylostella. Transductants
displaying dual specifi city have been constructed by using new isolates LM63 and LM79,
which have larvicidal activity against Phaedon cochleariae (Fab.) and Leptinotarsa decemlineata
(Say). It was not possible to introduce pHT7911 into B. thuringiensis subsp. entomocidus,
aizawai, or israelensis by transduction. However, electroporation was successful, and transformants
expressing the toxin gene cryIIIA carried by pHT7911 showed high levels of
expression of the cloned gene. CP-54Ber-mediated transduction has been found to be useful
for introducing cloned crystal protein genes into Bt, creating strains with new combinations
of genes. Sudarsan et al. (1994) studied the colonizing ability of a transcipient strain
of B. megaterium carrying a lepidopteran-specifi c cryIAa gene of B. thuringiensis var. kurstaki
strain HD1 in the phyllospheres of various economically important plants. The transcipient
strain remained on the leaves of cotton and okra for more than 28 days, but its survival
in phyllospheres of mulberry, groundnut, chickpea, tomato, and rice was limited to about
3 to 5 days. The persistence of B. thuringiensis was extremely short (4 days) on all the crop
plants tested. Bacillus polymyxa (Prazmowski) colonizes the crop better than Bt (Sudha,
Jayakumar, and Sekar, 1999). Inoculation with B. polymyxa in rice plants increased the shoot
and the root growth. The cry1Ac gene expressed in B. polymyxa (BP113) showed toxic effects
against fi rst-instar larvae of yellow stem borer of rice, Scirpophaga incertulas (Walk.).
The Alternative Delivery Systems for Bt Toxins
Lepidoptera
(Bt-resistant Plutella
xylostella)
Baum et al. (1999); Navon (2000),
Joung and Cote (2000)
Lepidoptera Baum et al. (1999); Navon (2000);
Joung and Cote (2000)
Kurstaki CRYMAX, Leptinox Lepidoptera Baum et al. (1999); Navon (2000);
Joung and Cote (2000)
Kurstaki recipient Raven Lepidoptera,
Coleoptera
d-endotoxin encapsulated in
Pseudomonas fl uorescens
MVP, MATTCH,
M-Trak (CellCap ® )
Lepidoptera,
Coleoptera
Baum et al. (1999); Navon (2000);
Joung and Cote (2000)
Joung and Cote (2000)
In addition to traditional formulations, alternative means of delivery, including endophytic
bacteria such as Leifsonia (Clavibacter) xyli Davis et al. (Lampel et al., 1994), have been used to
deliver the toxins to the target insects (Gelemter and Schwab, 1993). Plant-colonizing bacteria
such as Pseudomonas fl uorescens Migula, P. cepacia Burkholder, Rhizobium leguminosarum