Beyond Bt cotton

For Pakistan, the future of cotton cannot be defined by Bt technology alone. Bt cotton has provided an important biological tool against specific target bollworm species, but cotton productivity is governed by a much broader interaction among genotype, temperature, water availability, soil conditions, nutrient supply, pest and disease pressure and crop management.

This distinction has become increasingly important as Pakistan’s cotton-growing environment becomes hotter and increasingly water-limited. Extreme heat, particularly during the May to July period, has emerged as a persistent constraint. Maximum temperatures in many cotton-growing areas exceed 40°C and can rise considerably higher under extreme conditions. At the same time, limited water availability can intensify the stress imposed by high temperatures. Future cotton breeding therefore needs to address heat and drought as interconnected environmental stresses rather than treating them as separate challenges.

Research observations indicate that as temperatures rise within the approximate range of 32°C to 36°C, pollen viability, successful fertilization and boll retention in cotton can begin to decline. Beyond this range, these effects may become progressively more severe, with consequences for reproductive success and yield.

Future climate projections also point towards increasing thermal stress across Pakistan’s warmer regions. According to certain estimates, summer temperatures could increase by approximately 1.6°C to 1.8°C by 2050. In several areas of Punjab and Sindh, daily maximum temperatures during May to August could reach 46°C to 47°C.

The concern is therefore not simply whether a cotton plant can survive extreme heat. The more important question is whether it can continue to flower, achieve successful fertilization, retain bolls and maintain yield and fiber quality under those conditions.

A heat-tolerant variety should consequently not be defined merely by its ability to survive at 45°C or above. From an agronomic perspective, meaningful heat tolerance should be assessed through pollen viability, successful fertilization, flower and boll retention, boll setting, seed-cotton yield and fiber quality, particularly during the flowering and boll-setting stages when the crop is highly sensitive to heat.

If a plant survives extreme temperatures but loses most of its flowers and bolls, describing it as a commercially successful, high-yielding heat-tolerant variety would be misleading.

Drought tolerance is equally complex. A desirable variety should not merely survive under limited water availability. It should maintain root development, plant water status, photosynthetic activity, water-use efficiency, reproductive retention and yield at acceptable levels despite water stress.

This is particularly relevant to Pakistan because heat and water scarcity frequently occur together. A breeding program that evaluates drought tolerance only under water-limited conditions without considering high temperature may fail to capture the conditions experienced by farmers in the field. For this reason, future breeding programs should place greater emphasis on screening germplasm under combined heat and drought stress.

The first requirement is to identify cotton germplasm capable of maintaining superior physiological and agronomic performance under heat and limited water availability. Systematic screening of domestic and exotic germplasm can help identify promising genotypes and breeding lines with desirable heat and drought tolerance traits.

However, final yield alone is not an adequate screening criterion. Breeding programs should also examine physiological and biochemical indicators such as: flower and boll retention, pollen viability, photosynthetic efficiency, plant water status, canopy temperature, stomatal behavior, cell membrane stability, relative water content, water-use efficiency and root development.

These indicators can help identify the physiological mechanisms that allow particular genotypes to maintain performance under stress.

Pakistan’s research institutions have already generated valuable evidence in this area. Institutions including NIAB, CCRI Multan, NIA Tando Jam and AARI have used parameters such as Cell Membrane Thermostability, Pollen Viability, Anther Dehiscence, Relative Water Content and Photosynthesis in heat and drought tolerance studies.

These studies have demonstrated differences among genotypes in their ability to withstand heat and water stress. Some genotypes have also shown better root development and water-use efficiency under drought conditions.

Research under combined heat and drought stress deserves particular attention because it more closely reflects the conditions faced by cotton growers. However, promising experimental results should not automatically be considered suitable for commercial deployment. They need to be validated through multi-location and multi-year field trials.

A critical scientific distinction must also be maintained. Heat tolerance, drought tolerance and pest resistance are separate genetic and physiological traits.

A genotype may tolerate high temperatures but remain highly susceptible to whitefly. Another may perform relatively well under limited water availability but lack adequate resistance against pink bollworm.

The objective of future breeding should therefore be to develop multi-trait cultivars in which high yield potential, desirable fiber quality, heat tolerance, drought tolerance and resistance to major pests and diseases are brought together within a suitable genetic background.

This is a much more demanding objective than simply developing a variety with one desirable trait. It requires a breeding strategy that recognizes the interaction among multiple traits rather than selecting each trait in isolation.

Bt technology remains an important component of cotton protection, but experience shows that it cannot be regarded as a universal solution to all cotton production challenges.

In Pakistan, pink bollworm infestation and damage have been reported even in varieties carrying Cry1Ac and Cry1Ac + Cry2Ab traits. Some double-gene varieties have provided relatively better protection, but complete control has not been consistently achieved.

Long-term reliance on a single or limited number of Bt traits, combined with continuous Bt cultivation and selection pressure on pest populations, raises concerns about the evolution of resistance in field populations.

The appropriate response is not to abandon Bt technology. It is to place it within a broader genetic and pest-management strategy.

Proven Bt traits should be incorporated into elite genetic backgrounds that already possess desirable yield potential, fiber characteristics and resilience to abiotic stresses. At the same time, resistance monitoring, appropriate refuge strategies and Integrated Pest Management should remain integral components of cotton production.

Non-target pests, particularly whitefly, require their own integrated management strategy because Bt traits designed against specific bollworm species do not provide equivalent protection against sucking pests.

Genetics alone cannot explain cotton performance under field conditions. Soil plays a fundamental role in determining how effectively a genotype can express its potential.

Soil structure, organic matter, water-holding capacity, nutrient availability, salinity, pH and drainage influence root development, water uptake and nutrient utilization. During extreme heat, poor soil water retention or a root system weakened by salinity and degraded soil structure can intensify heat and water stress.

A critical distinction is therefore necessary. Good soil conditions do not make a variety heat-tolerant. Rather, appropriate soil and land management provide the conditions under which a genetically superior plant can express its potential.

Conversely, even an elite genotype may fail to deliver its potential under poor soil conditions, inappropriate irrigation or nutrient imbalance.

Climate resilience in cotton is therefore not purely a genetic issue. It is the outcome of the interaction between genetics and the production environment.

Modern genetic and molecular tools can significantly accelerate the breeding process. Identification of quantitative trait loci, or QTLs, associated with heat and drought tolerance, together with molecular markers, marker-assisted selection and genomic approaches, can improve the efficiency of identifying and selecting desirable traits.

However, molecular techniques cannot replace field testing.

The presence of a genetic marker or candidate gene does not, by itself, demonstrate agronomic success. The associated trait must consistently translate into improved yield, reproductive performance and fiber quality under actual field conditions.

The most effective breeding system will therefore integrate genetic, physiological, edaphic and agronomic indicators rather than relying on any single source of information.

Pakistan needs a more comprehensive framework for evaluating new cotton varieties. The interaction among Genotype × Environment × Soil × Management (G × E × S × M) provides such a framework.

A variety that performs exceptionally well at an experimental station may perform very differently under the high-temperature conditions of Southern Punjab or Sindh. Differences in soil type, temperature, humidity, water availability, sowing date, plant density and crop management can substantially alter genotype performance.

Consequently, promising varieties should undergo multi-location, multi-soil and multi-year testing under diverse management conditions.

Particular attention should be given to environments where extreme heat and water deficits occur simultaneously because these conditions more closely represent the actual production challenges faced across Pakistan’s cotton belt.

The purpose of such testing should not be limited to identifying varieties that survive stress. The real objective should be to identify cultivars that maintain flower and boll retention, yield and fiber quality under stress.

That is the difference between a stress-tolerant phenotype and a genuinely climate-resilient commercial cultivar.

Pakistan’s future cotton breeding strategy cannot remain confined to a single genetic trait.

The breeding objective should be to develop cultivars that combine:

High yield potential + desirable fiber quality + heat tolerance + drought tolerance + resistance to major pests and diseases + adaptability to diverse soils and environments. Bt technology can remain an important component of this genetic package. But its long-term value will depend on how effectively it is combined with improved genetics, resistance management, Integrated Pest Management and appropriate crop management.

The ultimate target should be a cotton variety that does not merely survive a hotter and drier environment, but continues to produce commercially viable yields and acceptable fiber quality under those conditions.

For Pakistan, this requires a shift from single-trait thinking towards an integrated breeding framework based on Genotype × Environment × Soil × Management (G × E × S × M).

Such an approach can provide a stronger scientific pathway towards cotton cultivars capable of maintaining reproductive performance, yield and fiber quality under current climatic pressures while preparing the crop for an increasingly hot, dry and unpredictable future.