, Narahashi 1-363, Higashiyamato, Tokyo, 207-0031, Japan.
Department of Mathematics and Natural Sciences, College of Arts and Sciences, Tokyo Woman's Christian University, Tokyo, 167-8585, Japan.
J Plant Res. 2021 Mar;134(2):195-208. doi: 10.1007/s10265-021-01255-x. Epub 2021 Feb 9.
Phegopteris decursivepinnata includes diploids, tetraploids, and triploid hybrids based on x = 30. We obtained polyploid progeny from triploid hybrids through selfing and crossing experiments. Triploids occasionally formed well-filled spores. The mean occurrence frequencies of well-filled and germinated spores were 2.8% and 0.8%, respectively. Viable spores that succeeded in germinating were regarded as unreduced, triploid spores, because the resulting gametophytes yielded triploid (2n = 86-92) and hexaploid (2n = 170-184) progeny in both isolated and mixed cultures of gametophytes. The triploid and hexaploid progeny likely arose apogamously and sexually, respectively. One of the hexaploid progeny yielded hexaploid sporophytes (2n = 169-180) in the mixed culture of its gametophytes. Artificial crossing between triploid and diploid sporophytes produced tetraploid (2n = 116, 120) and pentaploid (2n = 145-150) progeny that likely arose through the mating of 3x gametes from the triploid with both 1x and 2x gametes from the diploid, respectively. Unreduced spore formation was confirmed in diploid sporophytes. The tetraploid progeny formed viable spores at a frequency of 63-75%. Triploid hybrids of this species are thus expected to produce new triploids, tetraploids, and hexaploids in nature. The wide range of variation in chromosome numbers of hexaploid progeny suggests that viable spores from parental triploid hybrids had unreduced chromosomes, whose numbers, however, deviated considerably from those of the hybrids. This chromosome deviation of viable spores may result from errant movements of chromatids of univalents when unreduced dyads form in meiosis. Downward chromosome deviation from the chromosome number of the parental hybrids may affect the developmental progress of viable spores more tolerantly than upward chromosome deviation.
蹄盖蕨属包括基于 x=30 的二倍体、四倍体和三倍体杂种。我们通过自交和杂交实验从三倍体杂种中获得了多倍体后代。三倍体偶尔会形成饱满的孢子。饱满孢子和萌发孢子的平均出现频率分别为 2.8%和 0.8%。成功萌发的有活力的孢子被认为是未经减数分裂的三倍体孢子，因为由此产生的配子体在配子体的单独和混合培养中产生了三倍体（2n=86-92）和六倍体（2n=170-184）后代。三倍体和六倍体后代可能分别通过无配子生殖和有性生殖产生。六倍体后代之一在其配子体的混合培养中产生了六倍体孢子体（2n=169-180）。三倍体和二倍体孢子体之间的人工杂交产生了四倍体（2n=116、120）和五倍体（2n=145-150）后代，这些后代可能是由三倍体的 3x 配子与二倍体的 1x 和 2x 配子交配产生的。在二倍体孢子体中证实了未经减数分裂的孢子形成。四倍体后代形成有活力的孢子的频率为 63-75%。因此，该物种的三倍体杂种有望在自然界中产生新的三倍体、四倍体和六倍体。六倍体后代的染色体数目变化范围很广，这表明来自亲本三倍体杂种的有活力的孢子具有未经减数分裂的染色体，但其数量与杂种有很大的偏差。这些有活力的孢子的染色体偏差可能是由于减数分裂过程中未减数二联体形成时单价体的染色单体错误移动所致。与向上的染色体偏差相比，向下的染色体偏差从亲本杂种的染色体数偏离可能更能容忍有活力的孢子的发育进程。
