Heat vs Bt cotton

Evaluating the performance of Bacillus thuringiensis (Bt) cotton in Pakistan has moved far beyond the simple validation of its genetic presence. In recent years, climate change and increasingly erratic weather patterns have transformed the biological response of transgenic crops into a far more complex scientific issue. Fluctuations in day and night temperatures, along with prolonged heatwaves, are increasingly understood to influence Bt gene expression and the plant’s ability to synthesize insecticidal proteins. As a result, modern agronomic perspectives emphasize that Bt cotton efficacy should be assessed through a holistic framework that integrates the 24-hour thermal cycle, gene expression dynamics, environmental stress, and overall crop management practices.

During daytime conditions within an approximate range of 28°C to 35°C, Bt gene expression, particularly Cry1Ac, is generally reported to remain relatively stable across many experimental settings. Under such conditions, cotton plants are able to produce sufficient levels of Bt toxin, often described in literature as varying within a biologically effective range that supports protection against key Lepidopteran pests, including American bollworm and pink bollworm. At this stage, pest pressure is typically reduced, and the plant’s endogenous defense system functions effectively.

When daytime temperatures rise beyond moderate thresholds, generally above 36°C and into the low 40s, cotton plants begin to experience increasing levels of heat stress. This stress is associated with reduced gene activity and a decline in Bt protein synthesis. In many studies, such conditions are linked with a noticeable reduction in toxin expression, which may weaken the plant’s defensive capacity. Under extreme heatwave conditions, particularly when temperatures exceed approximately 43°C, this decline becomes more pronounced. The reduction in Bt protein levels is often associated with disruptions in physiological processes such as nitrogen metabolism, protein synthesis, and oxidative balance, all of which are known to influence overall plant performance under stress conditions.

Nighttime temperatures play a critical role in physiological recovery and metabolic stabilization. When night temperatures remain within a relatively cooler range of about 20°C to 28°C, plants are generally able to recover from daytime stress, allowing partial restoration of metabolic activity and stabilization of Bt gene expression over time. However, when night temperatures remain elevated, typically in the range of 28°C to 32°C, this recovery process becomes less efficient, and plants may remain under sustained stress. In situations where night temperatures exceed approximately 32°C, which are increasingly observed during heatwave events in southern cotton-growing regions of Pakistan, the crop may experience continuous physiological strain with limited recovery potential.

In many cotton-growing regions of Pakistan, prolonged heatwave conditions often involve daytime temperatures reaching the mid to high 40s, combined with elevated night temperatures. Under such circumstances, cotton plants may experience extended periods of thermal stress with limited physiological recovery windows. This persistent stress environment is widely considered to contribute to reduced stability of Bt protein expression, increased pest survival, and accelerated development of pest resistance. Consequently, farmers often report higher reliance on insecticide applications, which can increase production costs and potentially disturb ecological balance in agro-ecosystems.

This climate-related challenge is further compounded by structural issues within the agricultural system, including variability in seed quality, inconsistent genetic purity, and gaps in extension services. Historical observations from severe climatic seasons in parts of southern Punjab highlight how the combination of extreme heat stress and compromised seed quality can negatively affect Cry1Ac expression and overall crop resilience under field conditions.

As Bt expression becomes less stable under environmental stress, pest populations may adapt more rapidly, increasing the risk of resistance development. This often leads to greater dependence on chemical control measures, which may have unintended consequences such as disruption of beneficial insect populations and the emergence of secondary pest outbreaks, including whitefly resurgence. In this context, Bt cotton is increasingly viewed not as a standalone solution but as part of a broader agro-ecological system requiring integrated management.

Ensuring the long-term sustainability of cotton production in Pakistan therefore requires a shift toward integrated approaches that combine climate-resilient irrigation practices, balanced nutrient management, optimized sowing windows, and effective integrated pest management (IPM) strategies. In parallel, advances in biotechnology, including multi-gene stacked traits and CRISPR-based approaches, are being explored globally as potential avenues to improve stress tolerance and stabilize gene expression under challenging environmental conditions.

Ultimately, the long-term performance of Bt cotton in Pakistan is closely linked to the interaction between the 24-hour thermal cycle, genetic stability, and adaptive agronomic practices. Understanding this interaction in the context of a changing climate is increasingly seen as essential for developing sustainable and resilient cotton production systems.