Variation in Broccoli Cultivar Phytochemical Content under Organic and Conventional Management Systems: Implications in Breeding for Nutrition

Organic agriculture requires cultivars that can adapt to organic crop management systems without the use of synthetic pesticides as well as genotypes with improved nutritional value. The aim of this study encompassing 16 experiments was to compare 23 broccoli cultivars for the content of phytochemicals associated with health promotion grown under organic and conventional management in spring and fall plantings in two broccoli growing regions in the US (Oregon and Maine). The phytochemicals quantified included: glucosinolates (glucoraphanin, glucobrassicin, neoglucobrassin), tocopherols (δ-, γ-, α-tocopherol) and carotenoids (lutein, zeaxanthin, β-carotene). For glucoraphanin (17.5%) and lutein (13%), genotype was the major source of total variation; for glucobrassicin, region (36%) and the interaction of location and season (27.5%); and for neoglucobrassicin, both genotype (36.8%) and its interactions (34.4%) with season were important. For δ- and γ- tocopherols, season played the largest role in the total variation followed by location and genotype; for total carotenoids, genotype (8.41–13.03%) was the largest source of variation and its interactions with location and season. Overall, phytochemicals were not significantly influenced by management system. We observed that the cultivars with the highest concentrations of glucoraphanin had the lowest for glucobrassicin and neoglucobrassicin. The genotypes with high concentrations of glucobrassicin and neoglucobrassicin were the same cultivars and were early maturing F1 hybrids. Cultivars highest in tocopherols and carotenoids were open pollinated or early maturing F1 hybrids. We identified distinct locations and seasons where phytochemical performance was higher for each compound. Correlations among horticulture traits and phytochemicals demonstrated that glucoraphanin was negatively correlated with the carotenoids and the carotenoids were correlated with one another. Little or no association between phytochemical concentration and date of cultivar release was observed, suggesting that modern breeding has not negatively influenced the level of tested compounds. We found no significant differences among cultivars from different seed companies.

有机农业需要能够适配有机作物管理体系、无需使用合成农药的栽培品种，以及营养价值得以优化的基因型材料。本研究涵盖16项试验，旨在对比23个西兰花栽培品种在有机与常规种植管理下、于美国两个西兰花主产区（俄勒冈州与缅因州）的春播与秋播地块中，所积累的与健康促进相关的植物化学物（phytochemicals）含量。本次定量分析的植物化学物涵盖：硫代葡萄糖苷（glucosinolates）、生育酚（tocopherols）以及类胡萝卜素（carotenoids），其中具体包括萝卜硫苷（glucoraphanin）、芸苔素葡糖苷（glucobrassicin）、新芸苔素葡糖苷（neoglucobrassicin），δ-、γ-、α-生育酚，以及叶黄素（lutein）、玉米黄质（zeaxanthin）、β-胡萝卜素（β-carotene）。
就萝卜硫苷（变异贡献占比17.5%）与叶黄素（13%）而言，基因型是总变异的主要来源；对于芸苔素葡糖苷，产区（36%）以及地点与季节的交互作用（27.5%）是主要影响因素；而新芸苔素葡糖苷的变异则同时受基因型（36.8%）及其与季节的交互作用（34.4%）主导。对于δ-与γ-生育酚而言，季节对总变异的贡献最大，其次为地点与基因型；总类胡萝卜素的变异则以基因型（8.41%~13.03%）为最大变异来源，同时其与地点、季节的交互作用同样具有影响。整体而言，种植管理体系对植物化学物含量无显著影响。
本研究发现，萝卜硫苷含量最高的栽培品种，其芸苔素葡糖苷与新芸苔素葡糖苷的含量往往最低。芸苔素葡糖苷与新芸苔素葡糖苷含量较高的基因型对应同一批栽培品种，均为早熟F1杂交种。生育酚与类胡萝卜素含量较高的栽培品种则为开放授粉品种或早熟F1杂交种。本研究明确了各植物化学物含量更高的特定产区与种植季节。
园艺性状与植物化学物之间的相关性分析显示，萝卜硫苷与类胡萝卜素呈负相关，而各类胡萝卜素之间彼此相关。未观测到植物化学物含量与栽培品种育成日期之间存在显著关联，这表明现代育种并未对受试化合物的含量产生负面影响。不同种子公司提供的栽培品种之间未出现显著差异。