Hunan hybrid cotton cultivars, particularly Xiangzamian No. 3 and Xiangzamian No. 8, are widely cultivated in the main cotton-producing regions of the Yangtze River Basin. Several Chinese companies are actively involved in developing F1 generations of Xiangza cotton varieties. To meet the growing demand from developers and farmers for high-quality Xiangza cotton, it is essential to rapidly and efficiently propagate the parent lines while ensuring seed quality. This ensures the purity, quality, and quantity of the final products.
Cotton is a highly cross-pollinated crop, and under natural conditions, it is prone to outcrossing, leading to biological mixing, mechanical contamination, and genetic variation. If proper measures are not taken during the multiplication of parent lines, hybridization and mutation can occur over time, reducing the value of the hybrid variety. In the breeding process of hybrid cotton, especially when large quantities of parents are being produced for seed, strict control over contamination and inferior plants is crucial. Only by maintaining high purity and quality can the hybrid advantages be fully utilized.
In the case of large-scale cultivation of Xiangzamian parents, improper management or inadequate anti-contamination measures can result in the production of completely different "parents," which would significantly reduce the application value of Hunan hybrid cotton varieties.
The key technical measures for cultivating Xiangza cotton varieties include:
1. **Establishment of Parental Propagation Areas**: All Xiangzamian cotton varieties should be grown in contiguous, concentrated areas. Large-scale planting around the same region must use the same Xiangzamian variety, with a minimum isolation distance of 500 meters. This helps reduce biological mixing and prevents cross-contamination, ensuring pure and high-quality seeds.
2. **Improving Seedling Cultivation Techniques**: Enhancing the propagation efficiency of seedlings is an important method for increasing yield. Traditionally, Hunan has used transplantable rice seedlings for cotton, but current practices involve small seedlings with limited nutrient capacity. These small seedlings often have poor root development and suffer damage during transplanting, lowering survival rates. For Xiangzamian cotton, seedlings should be larger—7–7.5 cm in diameter, 10 cm long, and with 600 g of soil per pot. This allows better root growth, stronger seedlings, and improved survival after transplanting, promoting early and vigorous growth.
3. **Optimizing Planting Density**: Spacing plants appropriately can maximize seed production with fewer seeds. Currently, large-scale cotton farming in Hunan uses a density of 3,500–4,000 plants per 667 square meters. However, for Xiangza cotton, the recommended density is 1,500–2,000 per 667 square meters. This reduces seed usage by half, doubles the area, and increases harvest volume. Sparse planting also improves light exposure, enhances plant development, and supports better fertilizer and water management, leading to more bolls, reduced shading, and fewer damaged fruits.
Author: Hunan Cotton Research Institute
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