BACKGROUND Heading time is an important adaptive trait in durum wheat. In hexaploid wheat, Photoperiod-1 (Ppd) loci are essential regulators of heading time, with Ppd-B1 conferring photoperiod insensitivity through copy number variations (CNV). In tetraploid wheat, the D-genome Ppd-D1 locus is absent and generally, our knowledge on the genetic architecture underlying heading time lacks behind that of bread wheat. RESULTS In this study, we employed a panel of 328 diverse European durum genotypes that were evaluated for heading time at five environments. Genome-wide association mapping identified six putative QTL, with a major QTL on chromosome 2B explaining 26.2% of the genotypic variance. This QTL was shown to correspond to copy number variation at Ppd-B1, for which two copy number variants appear to be present. The higher copy number confers earlier heading and was more frequent in the heat and drought prone countries of lower latitude. In addition, two other QTL, corresponding to Vrn-B3 (TaFT) and Ppd-A1, were found to explain 9.5 and 5.3% of the genotypic variance, respectively. CONCLUSIONS Our results revealed the yet unknown role of copy number variation of Ppd-B1 as the major source underlying the variation in heading time in European durum wheat. The observed geographic patterns underline the adaptive value of this polymorphism and suggest that it is already used in durum breeding to tailor cultivars to specific target environments. In a broader context our findings provide further support for a more widespread role of copy number variation in mediating abiotic and biotic stress tolerance in plants.

中文翻译：

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Ppd-B1的拷贝数变异是硬粒小麦抽穗期的主要决定因素。

背景技术抽穗时间是硬质小麦的重要适应性状。在六倍体小麦中，Photoperiod-1（Ppd）基因座是抽穗时间的重要调节剂，Ppd-B1通过拷贝数变异（CNV）赋予光周期不敏感性。在四倍体小麦中，缺乏D基因组Ppd-D1基因座，通常，我们对抽穗期背后的遗传结构的了解落后于面包小麦。结果在这项研究中，我们采用了328种欧洲硬质小麦基因型，对五个环境下的抽穗时间进行了评估。全基因组关联映射确定了六个推定的QTL，2B染色体上的主要QTL解释了26.2％的基因型变异。已显示此QTL对应于Ppd-B1处的拷贝数变异，针对该拷贝存在两个拷贝数变异。较高的拷贝数赋予了较早的前进方向，并且在低纬度易受热和干旱影响的国家中更为频繁。另外，发现对应于Vrn-B3（TaFT）和Ppd-A1的另外两个QTL分别解释了基因型变异的9.5％和5.3％。结论我们的结果表明，Ppd-B1的拷贝数变异是欧洲硬粒小麦抽穗期变化的主要来源，但其作用尚不明确。观察到的地理格局突显了这种多态性的适应性价值，并表明在杜伦麦育种中已经将其用于根据特定目标环境定制品种。在更广泛的背景下，我们的发现为拷贝数变异在介导植物的非生物和生物胁迫耐受性中发挥更广泛的作用提供了进一步的支持。