International Journal of Horticulture, 2024, Vol.14, No.6, 355-367 http://hortherbpublisher.com/index.php/ijh 362 6.3 Hormone requirements at different stages of the growth cycle The hormone requirements of rapeseed vary significantly at different stages of the growth cycle. During the early stages, auxin and gibberellins are critical for promoting vegetative growth and the transition to reproductive stages. High nitrogen application rates have been shown to enhance auxin biosynthesis, thereby accelerating floral meristem differentiation and increasing seed yield (Hao et al., 2022). Cytokinins play a crucial role in the reproductive development stage of rapeseed, particularly during floral bud differentiation under low-temperature conditions, where their levels rise significantly and then gradually decrease. This hormonal fluctuation is essential for the timing regulation of floral bud development (Tarkowská et al., 2019). During the flowering and pod development stages, the balance of nitrogen and other hormones such as gibberellins and strigolactones becomes crucial. For instance, shading during these stages can disrupt nitrogen dynamics and hormone balance, leading to reduced yield. However, appropriate nitrogen application can mitigate these effects by improving pod wall morphology and carbon metabolism (Javed et al., 2022; Kuai et al., 2023). Additionally, wood vinegar and its compounds, when applied during the seedling and overwintering stages, have been shown to enhance growth, yield, and quality by modulating hormone levels and improving stress resistance (Zhu et al., 2021). 7 Case Studies on Rapeseed Yield and Quality Improvement 7.1 Study on the mechanism of high rapeseed yield in special plateau ecological environments In the Xiangride area of the Qinghai Plateau, with its unique high-altitude and extended daylight ecological environment, an ideal setting is provided for studying the high-yield mechanisms of rapeseed (Brassica napus L.). A study comparing the Qinghai Plateau's Xiangride area (XRD) and the lower-yielding Xining area (XN) found that extended daylight in Xiangride is a key factor for high yield, directly promoting significant increases in thousand-seed weight and silique number by approximately 52.1% and 59.6%, respectively (Xiong et al., 2022). The study showed that seed development in Xiangride begins earlier and lasts longer (Figure 3). Transcriptomic data revealed key yield-related gene expression changes, encompassing processes such as photosynthesis, lipid metabolism, and seed storage protein synthesis. For example, the XTH24 gene, involved in cell wall degradation, was significantly downregulated in Xiangride, whereas genes related to lipid metabolism and oxidation processes showed an upregulation trend. These findings confirm the positive impact of extended daylight on rapeseed yield and provide crucial theoretical support for rapeseed cultivation in high-altitude regions. Figure 3 A proposed working model for rapeseed high yield in the unique plateau habitat (Adopted from Xiong et al., 2022) Image caption: The figure shows that, compared to the Xining region (XN), rapeseed seed development in the Xiangride region (XRD) advances into the late stage earlier, with an enrichment of genes related to storage protein synthesis. The results indicate that longer daylight accelerates the transition to late-stage development, thus extending the seed-filling period and increasing yield, revealing the molecular mechanisms behind the high yield of rapeseed in the unique ecological environment of XRD (Adapted from Xiong et al., 2022)
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