Agronomic performance and Asiatic corn borer resistance of tropical converted transgenic corn hybrids containing the truncated Cry!A(b) gene (Bt-11) in Davao City, Philippines

Field evaluation of four experimental hybrid versions of Bt-11 maize namely, NK5447BBA, NK5447BBB, NK5447BBC and NK5447BBE protected by Cry1A(b) gene under natural Asiatic corn corer (ACB) (Ostrinia furnacalis guenee) infestations was done during the 2004 wet season and 2004-2005 dry season in Davao City, Philippines. The objectives of the trials were done to verify the efficacy of Bt-11 observed under greenhouse condition against the ACB, and to evaluate the agronomic performance of the hybrid versions that contain Bt-11. The experimental Bt-11 maize hybrids were compared with the approved Bt corn hybrids (DK818YG) and their isogenic hybrids (DK818 and NK5447), DK9051 and NK8840. Results showed that Bt-11 was effective in protecting maize against ACB under natural field infestation. At vegetative stage, leaf feeding damage was significant only during the wet season trial. It showed low damage to non-Bt maize and no-damage to Bt maize. At harvest, the check entry showed low to moderate damage of the ears, tassels and stalks, while the Bt-11 maize hybrids and DK818YG showed little to no damage. Ears and tassels damage were significantly different during the wet season trial among the Bt and non-Bt corn entries. On the other hand, the number of holes in the stalks were significantly different among Bt and non-Bt corn entries across the two trials. Among the four experimental hybrid versions of Bt-11 NK5447, versions NK5447BBB was the best in terms of overall agronomic characteristics. The average yield of NK5447BBB (9.1 t/ha-wet season, 5.3 t/ha-dry season) was slightly higher than that of NK5447 isogenic non-Bt hybrid (8.3 t/ha- wet season, 5.9 t/ha- dry season) and was not significantly different from the highest yielding entry, DK818YG (9.9 t/ha-wet season, 5.7 t/ha-dry season). The presence of 32 species of arthropods in the experimental field, both in Bt and non-Bt corn entries, was an indication of neutral effect of Cry1A(b) protein on non-target species.