Plant Genetic Resources Laboratory, Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Punjab, Pakistan.
Muhammad Nawaz Shareef University of Agriculture, Multan, Punjab, Pakistan.
Transgenic Res. 2019 Apr;28(2):199-212. doi: 10.1007/s11248-019-00114-9. Epub 2019 Feb 21.
Transgenic cotton expressing the toxin Cry1Ac from Bacillus thuringiensis L. (Bt) is widely cultivated in Pakistan after its formal approval in 2010. The exposure of the local target pests to the Cry1Ac endotoxin for this duration might have changed the baseline susceptibility. To probe the status of resistance in one of the main target pests, Helicoverpa armigera, field-collected larvae were reared in the lab for conducting leaf fed bioassays. Twenty-six cotton accessions collected from farmers, including 25 Bt-cotton and one non-Bt, were tested to quantify the level of Cry1Ac, an insecticidal crystalline protein (ICP), in leaves of lower, middle and upper canopies of plants. The concentration of ICP was tested through Enzyme-linked Immunosorbent Assay and found significantly variable (P < 0.01) between and within accessions. The highest mean expression was observed in Accession-2 and Accession-4, while the lowest in Accession-21 and Accession-19. Among fresh leaf tissues from different parts of the plant, the highest mean expression was recorded at 60 days after sowing in upper canopy leaves of cotton accessions, which decreased in lower parts of the plant with the lowest mean expression in lower canopy leaves. Laboratory bioassays, to calculate lethal dose, for H. armigera showed that LD and LD were 0.62 μg/g and 1.59 μg/g of fresh tissue weight, respectively. A strong positive correlation also exists between the levels of Cry1Ac protein and insect mortality (r = 0.84). These findings suggested the future risk of cultivation of Bt cotton, carrying single Cry1Ac gene, in Pakistan, as resistance surging in H. armigera against Cry protein. These results may also have significant implications for the resistance management in Bt crops, especially cotton, in future.
转 Bt 基因抗虫棉在 2010 年正式获得批准后，在巴基斯坦得到广泛种植。当地靶标害虫在这段时间内持续接触 Cry1Ac 内毒素，可能已经改变了其基线敏感性。为了研究主要靶标害虫之一棉铃虫的抗性现状，我们从农民那里收集了 26 个棉花品种（系），包括 25 个 Bt 棉花和 1 个非 Bt 棉花，用于进行室内叶喂生物测定，以量化叶片中的 Cry1Ac 含量。Cry1Ac 是一种杀虫晶体蛋白（ICP），我们通过酶联免疫吸附试验（ELISA）检测叶片中 ICP 的浓度，发现品种（系）之间和品种（系）内的浓度存在显著差异（P < 0.01）。最高的平均表达量出现在品种（系）2 和品种（系）4 中，而品种（系）21 和品种（系）19 中表达量最低。在来自植株不同部位的新鲜叶片组织中，棉株中上部冠层叶片的表达量最高，随着植株下部的下降而降低，下部冠层叶片的表达量最低。在棉铃虫的实验室生物测定中，计算致死剂量，LD50 为 0.62μg/g 和 1.59μg/g 的新鲜组织重量。Cry1Ac 蛋白水平与昆虫死亡率之间也存在很强的正相关关系（r = 0.84）。这些发现表明，在巴基斯坦，未来种植携带单一 Cry1Ac 基因的 Bt 棉花可能会面临棉铃虫对 Cry 蛋白产生抗性的风险。这些结果对于未来 Bt 作物（特别是棉花）的抗性管理也具有重要意义。
