BACKGROUND The ornamental crop Hydrangea macrophylla develops highly attractive lacecap (wild type) or mophead inflorescences. The mophead trait, which is mostly favored by consumers, is recessively inherited by the INFLORESCENCE TYPE locus (INF). If lacecap cultivars are crossed with mophead cultivars, then either 50% or all progenies develop lacecap inflorescences, depending on the zygosity at the INF locus. For most cultivars, the zygosity at the INF locus is unknown. Furthermore, the determination of the inflorescence type in offspring populations is time-consuming, because seedlings flower the first time in the 2nd year after sowing. Within this study, we aimed to develop DNA-based markers that allow to determine the zygosity at the INF locus of prospective parental plants and to predict the inflorescence phenotype of seedlings already in the non-flowering stage. RESULTS By crossing a mophead and a lacecap cultivar of H. macrophylla, we produced a pseudo-backcross F1 population consisting of 422 plants. These plants segregated into 279 lacecap, 73 mophead, 3 intermediate and 67 non-flowering plants, differing significantly from the expected 1:1 segregation ratio. Surprisingly, 75% of these plants were triploid, although both parents were diploid. We found that the lacecap parent produced unreduced pollen, which induced the formation of triploids. 380 randomly selected F1 plants were genotyped by genotyping-by-sequencing (GbS). Using a genome assembly of cultivar 'Sir Joseph Banks', we performed subsequently a bulk sequence analysis with pooled GbS data of diploid versus mophead plants. We identified directly 2 markers tightly linked with the INF locus, each of them explaining 99.7% of the inflorescence phenotype. Using a collection consisting of 56 diploid, triploid or tetraploid H. macrophylla varieties, we detected 6 sequence variants for one of these markers. Two variants were associated with the mophead phenotype. Furthermore, we found by marker analysis a co-segregation between the mophead and the non-flowering trait, which indicates a major flowering time locus next to the INF locus. CONCLUSION Through bulk sequence analysis of pooled GbS data from diploid and polyploid F1 plants, we identify rapidly tightly linked markers for the inflorescence type, a dominant-recessively inherited trait in the non-model plant species H. macrophylla.

中文翻译：

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通过绣球的二倍体和三倍体F1植物的基因分型来快速鉴定花序类型标记。

背景技术观赏植物八仙花（Hydrangea macrophylla）发育出高度吸引人的花边（野生型）或mo头花序。黑头特征，最受消费者青睐，是隐性基因位点（INF）隐性遗传的。如果lace带品种与mo子品种杂交，则取决于INF基因座的合子性，要么50％或所有后代都会产生lace带花序。对于大多数品种，INF位点的合子性是未知的。此外，确定后代种群的花序类型非常耗时，因为幼苗在播种后的第二年首次开花。在这项研究中，我们旨在开发基于DNA的标记，这些标记可以确定预期的亲本植物在INF位点的合子性，并预测已经处于非开花期的幼苗的花序表型。结果通过杂交大叶H的mo头和a带品种，我们产生了由422种植物组成的假回交F1群体。这些植物被隔离为279个带帽73，73个mo子，3个中间花和67个非开花植物，与预期的1：1隔离比明显不同。出人意料的是，这些植物中有75％是三倍体的，尽管两个亲本都是二倍体的。我们发现lace带亲本产生未还原的花粉，从而诱导三倍体的形成。通过测序基因分型（GbS）对380个随机选择的F1植物进行基因分型。使用品种“约瑟夫·班克斯（Sir Joseph Banks）”的基因组装配，我们随后使用二倍体植物与拖头植物的汇总GbS数据进行了大序列分析。我们直接鉴定了2个与INF基因座紧密相连的标记，每个标记解释了99.7％的花序表型。使用由56个二倍体，三倍体或四倍体H. macrophylla变种组成的集合，我们为这些标记之一检测了6个序列变体。拖头表型有两个变异。此外，我们通过标记分析发现拖把头和非开花性状之间存在共隔离，这表明主要的开花时间基因座位于INF基因座旁边。结论通过对来自二倍体和多倍体F1植物的GbS数据的大序列分析，我们确定了花序类型的快速紧密连锁的标记，