Performance of converted Bt corn, hybrids against asiatic corn borer, Ostrinia furnacalis Guenee under limited field release condition

The performance of three locally adapted corn hybrids converted for cryIAb gene expression from Bacillus thuringiensis var. Kurstaki were evaluated under limited field release condition in the Agroseed Research Station at Lagao, General Santos City [South Cotabato, Philippines]. The objective of the field test is to verify the resistance reaction of these materials observed under containment. Condition against the corn borer, Ostrinia furnacalis Guenee and compare its performance against the non-Bt counterpart and local checks. Natural infestation was augmented by artificially infesting about to hatch corn borer eggmass at the rate of one eggmass per plant at the early vegetative stage, 15 neonate larvae to the silk of the ear to insure uniform infestation. All other safety guidelines required by the National Committee on Biosafety of the Philippines (NCBP) were rigorously followed. From the leaf feeding damage evaluated for three rating periods and stalk and ear damage rating, results showed that the Bt hybrids exhibited highly resistant reaction. Significantly lower counts in the number of entrance holes and length of tunnel in the stalk, number of entrance holes and length of tunnel in the ear and the number of larvae and pupa recovered from plants sampled 90 days from planting on the Bt corn entries. Similarly, lower incidence of Diplodia ear rot and Fusarium ear rot were noted on the harvested ears as a result of no borer damage on the ears. The trial also demonstrated the high specificity of the protein only against the corn borer since many beneficial insect particularly Green lacewing, spiders and coccineled beetle were abundant both in the Bt and non-Bt plots. Corn aphid incidence were higher on the Bt plots since the plants appeared more healthy compared to non-Bt plots because of borer damage. Yield was significantly higher on the Bt corn ranging from 7.1 to 8.5 tons/ha compared to the non-Bt which ranged from 4.4 to 5.1 tons per hectare. The susceptible check, Supersweet yielded only 1.44 tons