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 involved in the development of F1 hybrid generations of Xiangza cotton varieties. To meet the growing demand from breeders and farmers for high-quality Xiangza cotton, it is essential to rapidly and efficiently propagate the parent lines while ensuring seed quality. This guarantees the purity, quality, and quantity of the final products.
Cotton is a highly cross-pollinated crop, making it prone to biological mixing, mechanical contamination, and natural mutations in the field. If proper measures are not taken to prevent contamination and remove inferior plants, even the best hybrid parent lines can produce hybrids and mutants after several years of propagation. In the breeding process of hybrid cotton parents, especially when large quantities are needed for seed production, strict control over purity is crucial. Only by maintaining high genetic purity can the hybrid vigor be effectively utilized. In large-scale cultivation of Xiangzamian parents, poor management or insufficient isolation can lead to the production of completely different "parents," which would significantly reduce the value of Hunan hybrid cotton varieties.
The key technical measures for cultivating Xiangza cotton varieties include:
1. **Establishing a Parental Propagation Area**: All Xiangzamian cotton cultivars should be grown in contiguous plots. Large-scale planting around the same area must use the same variety, with a minimum isolation distance of 500 meters to minimize cross-pollination and ensure variety purity.
2. **Improving Seedling Breeding Techniques**: Traditional methods of transplanting rice seedlings have evolved into more efficient systems. However, current practices often involve small seedlings with limited root development, leading to transplant shock and lower survival rates. For Xiangzamian cotton, seedlings should be larger—7–7.5 cm in diameter, 10 cm long, with 600 grams of soil per pot. This promotes better root growth, stronger seedlings, and higher transplant survival rates.
3. **Optimizing Planting Density**: The current density for large-scale cotton production in Hunan is 3,500–4,000 plants per 667 square meters. However, for Xiangza cotton breeding, the recommended density is 1,500–2,000 plants per 667 square meters. This reduces seed usage by half, doubles the production area, and increases yield potential. Lower density also improves light exposure, enhances plant growth conditions, and allows for better fertilization and irrigation management. It helps increase boll numbers, reduce shading, and improve overall productivity.
Author: Hunan Cotton Research Institute
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