Leibniz Institute of Vegetable and Ornamental Crops, Theodor-Echtermeyer-Weg 1, 14979, Großbeeren, Germany.
Present address: Erfurt Research Centre for Horticultural Crops, University of Applied Sciences Erfurt, Kühnhäuser Straße 101, 99090, Erfurt, Germany.
BMC Genet. 2020 Dec 7;21(1):147. doi: 10.1186/s12863-020-00954-z.
Up to now, diploid and triploid cultivars were reported for the ornamental crop Hydrangea macrophylla. Especially, the origin of triploids and their crossing behaviors are unknown, but the underlying mechanisms are highly relevant for breeding polyploids.
By screening a cultivar collection, we identified diploid, triploid, tetraploid and even aneuploid H. macrophylla varieties. The pollen viability of triploids and tetraploids was comparable to that of diploids. Systematic crosses with these cultivars resulted in viable diploid, triploid, tetraploid and aneuploid offspring. Interestingly, crosses between diploids produced diploid and 0 or 1-94% triploid offspring, depending on the cultivars used as pollen parent. This finding suggests that specific diploids form unreduced pollen, either at low or high frequencies. In contrast, crosses of triploids with diploids or tetraploids produced many viable aneuploids, whose 2C DNA contents ranged between the parental 2C values. As expected, crosses between diploid and tetraploid individuals generated triploid offspring. Putative tetraploid plants were obtained at low frequencies in crosses between diploids and in interploid crosses of triploids with either diploid or tetraploid plants. The analysis of offspring populations indicated the production of 1n = 2x gametes for tetraploid plants, whereas triploids produced obviously reduced, aneuploid gametes with chromosome numbers ranging between haploid and diploid level. While euploid offspring grew normally, aneuploid plants showed mostly an abnormal development and a huge phenotypic variation within offspring populations, most likely due to the variation in chromosome numbers. Subsequent crosses with putative diploid, triploid and aneuploid offspring plants from interploid crosses resulted in viable offspring and germination rates ranging from 21 to 100%.
The existence of diploids that form unreduced pollen and of tetraploids allows the targeted breeding of polyploid H. macrophylla. Different ploidy levels can be addressed by combining the appropriate crossing partners. In contrast to artificial polyploidization, cross-based polyploidization is easy, cheap and results in genetically variable offspring that allows the direct selection of more robust and stress tolerant polyploid varieties. Furthermore, the generation of polyploid H. macrophylla plants will favor interspecific breeding programs within the genus Hydrangea.
迄今为止，已报道观赏作物绣球花存在二倍体和三倍体品种。特别是，三倍体的起源及其杂交行为尚不清楚，但潜在机制对多倍体的培育具有重要意义。
通过筛选一个品种集，我们鉴定出了二倍体、三倍体、四倍体，甚至非整倍体绣球花品种。三倍体和四倍体的花粉活力与二倍体相当。与这些品种进行系统杂交可得到有活力的二倍体、三倍体、四倍体和非整倍体后代。有趣的是，二倍体之间的杂交产生了二倍体和 0 或 1-94%的三倍体后代，具体取决于用作花粉亲本的品种。这一发现表明，特定的二倍体形成减数分裂前的花粉，频率要么低，要么高。相比之下，三倍体与二倍体或四倍体的杂交产生了许多有活力的非整倍体，其 2C DNA 含量在双亲 2C 值之间。如预期的那样，二倍体和四倍体个体之间的杂交产生了三倍体后代。在二倍体之间的杂交和三倍体与二倍体或四倍体的种间杂交中，以较低频率获得了推定的四倍体植株。后代群体的分析表明，四倍体植物产生了 1n=2x 的配子，而三倍体显然产生了染色体数量在单倍体和二倍体水平之间的减数分裂前的、非整倍体配子。虽然正常生长的是二倍体后代，而非整倍体植株在后代群体中表现出发育异常和巨大的表型变异，这很可能是由于染色体数量的变化。随后与种间杂交中获得的假定二倍体、三倍体和非整倍体后代植物进行杂交，产生了有活力的后代，发芽率为 21%至 100%。
存在形成减数分裂前花粉的二倍体和四倍体，允许有针对性地培育绣球花多倍体。通过结合适当的杂交伙伴，可以处理不同的倍性水平。与人工多倍化相比，基于杂交的多倍化简单、廉价，并产生遗传上可变的后代，允许直接选择更健壮和更能耐受胁迫的多倍体品种。此外，绣球花多倍体植物的产生将有利于绣球属内的种间杂交计划。
