Cotton, one of the world’s most crucial crops for textile production and edible oil, faces unprecedented challenges. Rising global temperatures, pest invasions, and the demand for higher-quality fibers have pushed traditional breeding methods to their limits.

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For decades, developing a new cotton variety took over ten years due to the plant’s long generation cycle of approximately 130 days. A groundbreaking 2025 study in Theoretical and Applied Genetics by Hebei Agricultural University introduces speed breeding in cotton, reducing the cycle to 71–85 days and enabling up to five generations annually.

Understanding the Need for Speed Breeding in Cotton

Cotton’s traditional breeding cycle is slow and labor-intensive. Farmers and researchers typically wait 130 days for a single generation to mature, and developing a new variety with desired traits like drought tolerance or pest resistance can take over a decade.

This timeline is unsustainable given the urgent threats of climate change and a global population projected to reach 10 billion by 2050. For instance, pests like bollworms and diseases like Fusarium wilt are becoming more aggressive, while consumers demand softer, more durable cotton fabrics.

Speed breeding, a technique that manipulates environmental conditions to accelerate plant growth, has already succeeded in crops like wheat and rice.

However, cotton’s sensitivity to light cycles it’s a short-day plant that flowers when nights are long—made it resistant to existing speed breeding methods.

To overcome this, researchers optimized two key processes light spectrum conditions and immature embryo culture. Their work not only shortened breeding cycles but also improved the efficiency of introducing new traits like higher fiber yield.

How Light Spectrum Optimization Accelerates Growth

Light plays a critical role in plant development, especially for cotton. The research team designed a custom LED lighting system to mimic natural sunlight while emphasizing wavelengths that trigger faster flowering.

The system combined four types of light red (660 nm), far-red (730 nm), white (6,500 K), and cold white (13,000 K). Red light boosts photosynthesis and biomass production, while far-red light inhibits proteins like phytochrome B, which delay flowering in short-day plants.

Cold white LEDs added blue light to strengthen stems and leaves without generating excess heat.When tested on two cotton varieties—JSh929 (early-maturing) and ND601 (mid-early)—the results were remarkable.

Under optimized light, JSh929 produced flower buds in just 19 days (compared to 32 days under traditional lighting) and flowered at 45 days. Similarly, ND601 showed buds at 21 days and flowers at 46 days, cutting 18 days off its usual cycle.

Microscopic analysis of shoot tips revealed that floral development began earlier under the custom LEDs, with key flowering genes like GhFT and GhSOC1 peaking three days sooner than in control groups.

Immature Embryo Culture: Skipping the Wait for Seeds

Another bottleneck in traditional cotton breeding is the long wait for seeds to mature—typically 50–60 days after pollination. To bypass this, the team refined a technique called immature embryo culture.

Instead of waiting for seeds to fully develop, they harvested embryos just 25–30 days after pollination and nurtured them in a nutrient-rich liquid medium.The process involved two stages. First, embryos were placed in a liquid medium (L-mAUH) containing growth hormones like auxins and cytokinins.

Shaking the embryos at 40 rotations per minute ensured even nutrient distribution, stimulating root growth within 12 hours. Next, the embryos were transferred to a solid medium (mAUH) with balanced nutrients like potassium nitrate and iron.

This step supported the development of cotyledons (seed leaves) and true leaves.The results were striking 90% of embryos grew cotyledons within six days, and 94.5% developed true leaves by day 14.

The seedlings also had robust root systems, eliminating the need for grafting a labor-intensive step in traditional methods. Survival rates after transplanting exceeded 90%, proving the reliability of this approach.

Combining Light and Embryo Culture for Five Generations a Year

By integrating light optimization and embryo culture, the team created the Integrated Speed Breeding Technique 2.0 (ISBT2.0). This system reduced the average generation cycle to 79.5 days (ranging from 71–85 days), allowing breeders to achieve up to five generations annually.

To validate its practicality, the researchers used ISBT2.0 to introduce the iaaM gene a bacterial gene that enhances fiber yield and quality into a high-yielding cotton variety called JND24.

Using marker-assisted selection (MAS), they identified plants carrying the iaaM gene early in the growth cycle.GUS staining, a visual marker, turned the petioles of genetically modified plants blue, enabling rapid screening. PCR tests later confirmed the gene’s presence.

Within 1.5 years, the team developed BC₄F₃ progeny (fourth-generation hybrids) with a 3.5% increase in lint percentage (fiber yield) and improved micronaire values. Genomic analysis showed these plants retained 98.2% of the original JND24 genetic background, ensuring stability while enhancing desired traits.

The Science Behind Faster Flowering and Stronger Fibers

The success of speed breeding hinges on understanding cotton’s biology. For example, GhFT and GhSOC1 are genes that act as master switches for flowering. GhFT, produced in leaves, travels to the shoot tip to initiate flowering, while GhSOC1 integrates environmental signals like light and temperature.

Under optimized light, both genes peaked three days earlier than usual, directly linking molecular changes to faster bud formation.Similarly, the iaaM gene works by increasing auxin levelsa hormone that promotes cell elongation.

In modified cotton plants, auxin levels rose by 25%, leading to longer, finer fibers. This genetic tweak not only boosted lint percentage but also improved micronaire values, making the cotton softer and more suitable for high-end textiles.

Implications for Farmers and the Textile Industry

The implications of speed breeding are profound. For farmers, faster breeding cycles mean quicker access to varieties resistant to pests, droughts, or diseases. For instance, integrating Bt genes (for insect resistance) into elite cotton strains could take just 2 3 years instead of a decade.

Challenges and the Path Forward

Despite its promise, speed breeding faces hurdles. The initial cost of LED systems and climate-controlled facilities ranges from $50,000 to $100,000, putting them out of reach for small-scale breeders. Additionally, embryo culture requires sterile lab conditions and expertise in molecular biology.

To address these challenges, the researchers advocate for public-private partnerships to subsidize costs and training programs. Future innovations could integrate AI to automate light and temperature adjustments or expand the technique to crops like soybeans and hemp.

Conclusion:

Speed breeding in cotton is more than a technical achievement—it’s a lifeline for a struggling industry. By shortening breeding cycles and enhancing precision, this technology empowers scientists to tackle climate change, pests, and market demands head-on.

For farmers, it promises resilient varieties; for consumers, sustainable textiles. As research continues, the fusion of speed breeding with gene editing and AI could redefine global agriculture, ensuring cotton remains a cornerstone of economies and cultures worldwide.

References:

Wang, G., Sun, Z., Yang, J. et al. The speed breeding technology of five generations per year in cotton. Theor Appl Genet 138, 79 (2025). https://doi.org/10.1007/s00122-025-04837-8

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