Region-specific yield optimization strategies for rapeseed (Brassica napus L.) in the middle Yangtze Basin across the 30°N latitude

To elucidate the effects of major climatic factors and key agronomic traits on yield formation of winter rapeseed in the middle Yangtze Basin, this study takes the 30°N latitude as a geographical boundary to systematically compare the ecological adaptability and yield-determining factors of winter rapeseed between northern and southern regions. The objective is to provide a theoretical foundation and practical guidance for optimizing regional line selection and precision cultivation. Four representative growing seasons, characterized by distinct climatic conditions—namely warm and dry, cold and humid, and years with strong climate variability—were selected (2006-2007, 2009-2010, 2016-2017, and 2019-2020). Field experiments were conducted across six national winter rapeseed regional trial stations located north and south of the 30°N line. Comprehensive agronomic data were collected for all tested lines, and corresponding monthly climate data were compiled. The impacts of climatic factors on yield, as well as variations in agronomic traits and their synergistic contributions to yield, were analyzed using multiple statistical methods. Results showed that the northern region (north of 30°N) experienced lower winter temperatures, a greater diurnal temperature range, relatively reduced precipitation, and less sunshine during early growth stages, but more sunshine during later stages. In contrast, the southern region (south of 30°N) was relatively warmer, with higher rainfall and reduced sunlight during late growth stages. On average, the northern region achieved significantly higher yields than the southern region by 779.1 kg hm^-2 (<italic>P </italic>&lt; 0.01). It also exhibited higher yield per plant and more siliques per plant, although it faced higher disease pressure. Stepwise regression analysis indicated that yield in the northern region was mainly influenced by April precipitation, while in the southern region it was primarily affected by December sunshine duration and March precipitation. Path analysis further revealed that yield in the north was directly determined by yield per plant and seed number per silique. In the south, yield was more dependent on the combined effects of yield per plant and thousand-seed weight, and the negative impact of excessive branching and seed size needed to be managed. Broadly adapted lines such as 0112, 9ZYYP27, and Keleyou 4 performed well across both ecological zones, while lines such as Hua 68P25, Yuhua 7, and Yueyou 577 showed strong region-specific adaptability. Significant ecological divergence exists across the 30°N boundary in terms of climatic resources, yield components, and dominant agronomic traits. Regional patterns of light, temperature, and water availability significantly influence yield formation mechanisms. It is recommended that the northern region focus on optimizing early-season light utilization and enhancing resistance to late-season waterlogging, prioritizing lines with <italic>Sclerotinia</italic> stem rot resistance, and high yield per plant with strong seed number and weight. For the southern region, emphasis should be placed on optimizing mid-to-late season light use and developing lines with high photosynthetic efficiency, waterlogging resistance, high yield per plant, more seeds, and elevated oil content. A regional deployment strategy combining “broad adaptability and specific adaptation” is proposed to synergistically advance precision breeding and efficient cultivation, thereby promoting high and stable yields and green, sustainable development of winter rapeseed in the middle Yangtze Basin.