Evaluation of Brassica oleracea var. italica germplasm

Worldwide, broccoli (Brassica oleracea var. italica) is among the most economically important, nutritionally rich, and widely-grown vegetable crops. To explore the genomic basis of the dramatic changes in broccoli morphology in the last century, we evaluated 109 broccoli or broccoli/cauliflower intermediates for 24 horticultural traits. Genotype-by-sequencing markers were used to determine four subpopulations within italica: Calabrese broccoli landraces and hybrids, sprouting broccoli, and violet cauliflower, and to evaluate between and within group relatedness and diversity. While overall horticultural quality and harvest index of improved hybrid broccoli germplasm has increased by year of cultivar release, this improvement has been accompanied by a considerable reduction in allelic diversity when compared to the larger pool of germplasm. Two landraces are the most likely founding source of modern broccoli hybrids, and within these modern hybrids, we identified 13 reduction-in-diversity genomic regions, 53 selective sweeps, and 30 (>1 Mbp) runs of homozygosity. Landrace accessions collected in southern Italy contained 4.8-fold greater unique alleles per accessions compared to modern hybrids and provide a valuable resource in subsequent improvement efforts. This work broadens the understanding of broccoli germplasm, informs conservation efforts, and enables breeding for complex quality traits and regionally adapted cultivars.

全球范围内，西兰花（ Brassica oleracea var. italica ）不仅是经济价值极高的作物，其营养价值亦十分丰富，且种植范围广泛。为了探究西兰花形态在近一个世纪内的显著变化背后的基因组基础，本研究对109个西兰花及其与花椰菜杂交种进行了24个园艺性状的评估。通过基因分型测序标记，确定了 italica 中的四个亚种群：卡劳雷西兰花地方品种和杂交种、松花西兰花以及紫花菜花，并评估了各组群间的相关性和多样性。尽管改良杂交种种质在品种发布年份的整体园艺品质和收获指数有所提升，但这种改善伴随着与种质库相比的等位基因多样性的显著减少。两个地方品种最可能是现代西兰花杂交种的基础来源，在这些现代杂交种中，我们发现了13个多样性减少的基因组区域、53个选择性清洗以及30个（>1 Mbp）的纯合子连锁区域。在意大利南部收集的地方品种，每个品种所含的独特等位基因数量是现代杂交种的4.8倍，并为后续的改良工作提供了宝贵的资源。本研究拓展了对西兰花种质资源的理解，为保护工作提供了信息，并促进了复杂品质性状和区域适应性品种的育种工作。