Transgenic Tropical Maize with cryLAb and cryLAc Genes from Microprojectile Bombardment of Immature Embryos

Maize has been one of the prime targets for genetic manipulation in monocotyledonous grains. The first demonstrations of progress were the successful production of transgenic plants by microprojectile bombardment (Klein et al. 1989; Fromm et al. 1990; Gordon-Kamm et al. 1990; Genovesi et al. 1992; Walter et al. 1992; Frame et al. 1994; Wan et al. 1995, Brettschneider et al. 1997); then successful hygromycin (Walters et al. 1992), bialaphos (Spencer et al. 1990), and glyphosate (Howe et al. 1992) selection of stable transformants, and recent Agrtobacterium — mediated gene insertion in maize plants (Ishida et al. 1996). Most studies on maize transformation have utilized genotypes adapted to temperate zones (Fromm et al. 1990; Gordon-Kamm et al. 1990; Walter et al. 1992; Armstrong et al. 1995) and plants regenerated from these lines were shown to transmit the recombinant DNA to their progeny. Little or no attention, however, has been focused on the transformation potential of maize germplasm and inbred lines adapted to tropical and subtropical regions. Production of genetically transformed plants depends both on the ability to integrate foreign genes into target cells and the efficiency with which plants are regenerated from genetically transformed cells. Embryogenic calli and plant regeneration were obtained from 50% of tropical and subtropical lines, 87% of midaltitude lines, and 75% of highland lines tested (Bohorova et al. 1995) and type II callus with high potential for plant regeneration from tropical maize was produced (Prioli and Silva 1989; Carvalho et al. 1997). These studies serve as the basis for developing transgenic technology for maize inbreds adapted to tropical conditions.