Aktivitas Residu Protein Cry1Ac Pada Lahan yang Ditanami Kapas Transgenik-Bt di Bajeng dan Soppeng, Sulawesi Selatan
The persistence in soil of Cry1Ac protein originating from transgenic Bt-cotton was determined using bioassay against the cotton bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae). Transgenic Bt-cotton (Bollgard) and nontransgenic cotton (Delta Pine) were planted at two field sites in South Sulawesi, i.e. in Bajeng and Sopeng. Soil samples were collected from each plot at the two field sites at 0, 1, 3, and 5 months after planting, and at one-month intervals after harvest for three months. Soil suspension from each sample was mixed with agar based diet (1 g soil/20 ml soil-diet mixture) then was presented to neonate larvae of H. armigera. Two reference standards were used, i.e. pure Cry1Ac protein (0.165 x 104 to 1.436 x 105 ng per ml of the proteindiet mixture) and non-Bt-soil spiked with Cry1Ac protein (0.11 x 104 to 9.573 x 104 ng per ml of the soil-diet-mixture). Larval mortality was recorded at 7 days of treatment. In both reference standards, mortality of H. armigera larvae occurred in a concentrationdependent fashion, i.e. larval mortality increased with the increase in Cry1Ac protein concentration, with LC50 of 0.95 x 104 and 1.65 x 104 ng/ml, respectively, for the pure protein and spiked non-Bt-soil standards. Result of the bioassay of soil samples from the field sites showed the residues from both transgenic cotton soils did not cause any mortality (0%) in the test insects. This indicates that the concentrations of Cry1Ac residue in soil at the study sites were very low (in the second standard, Cry1Ac at a concentration of 0.33 x 104 ng/ml caused about 10% larval mortality).
KEY WORDS: Transgenic-Bt, Cry1AC, Kapas, Sulawesi Selatan, Helicoverpa armigera