Department of Plant Breeding (IVP), Agricultural University Wageningen, Wageningen, The Netherlands.
Theor Appl Genet. 1991 Oct;82(5):645-56. doi: 10.1007/BF00226804.
The level and mode of 2n megaspore formation was studied in full-sib diploid potato clones with either normal or desynaptic (ds-1ds-1) meiosis. Cytological analysis revealed that functional 2n megaspores produced by normal and desynaptic clones originate exclusively from 'second division restitution (SDR)' and 'first division restitution (FDR)', respectively. SDR 2n megaspores resulted from the omission of the second meiotic division following chromosome doubling after anaphase I, whereas FDR 2n megaspores resulted from a direct equational division of univalent chromosomes at anaphase I (pseudohomotypic division). Comparative data strongly indicated that the observed mechanisms of SDR and FDR 2n megaspore formation are extremes of a continuum that is being brought about by common genes for precocious chromosome division. Depending on the relative timing of cell cycle and chromosome division, this precocious chromosome division may impose postreductional (SDR) or prereductional (FDR) 'restitution' of the sporophytic chromosome number under normal synaptic and desynaptic conditions, respectively. The observed frequencies of 2n megaspores closely correlated with seed set, following pollination by tetraploid varieties and by desynaptic diploid clones with exclusive FDR 2n pollen formation. Up to 54.0 and 21.5 seeds/ fruit were obtained from normal synaptic (SDR) and desynaptic (FDR) progeny, respectively. The high frequency of segregants with either SDR or FDR 2n megaspore formation (78.0 and 45.2%, respectively) supports the hypothesis that sexual polyploidization is the driving force behind the origin and evolution of polyploid Solanum species. The present identification of diploid potato clones with consistent FDR 2n megaspore formation extends the opportunities for direct transfer of enhanced diploid germ plasm to tetraploids, and particularly advocates the feasibility of 2x(ds-1; FDR)×2x(ds-1; FDR) breeding schemes in cultivar development and the production of relatively vigorous and uniform true potato seed (TPS) varieties. Its potential value and limitations for breeding and the experimental induction of diplosporic apomixis are discussed.
研究了具有正常减数分裂或去联会（ds-1ds-1）的同卵双生二倍体马铃薯克隆体中的 2n 大孢子形成的水平和模式。细胞学分析表明，正常和去联会克隆体产生的功能 2n 大孢子分别仅源自“第二次分裂还原（SDR）”和“第一次分裂还原（FDR）”。SDR 2n 大孢子是由于后期 I 之后的染色体加倍后第二次减数分裂缺失而产生的，而 FDR 2n 大孢子是由于后期 I 时单价染色体的直接均等分裂（拟同源分裂）产生的。比较数据强烈表明，观察到的 SDR 和 FDR 2n 大孢子形成机制是由早熟染色体分裂的共同基因引起的连续体的极端。根据细胞周期和染色体分裂的相对时间，这种早熟的染色体分裂可能会在正常突触和去联会条件下分别对孢子体染色体数进行减数后（SDR）或减数前（FDR）“还原”。观察到的 2n 大孢子频率与四倍体品种授粉后以及仅形成 FDR 2n 花粉的去联会二倍体克隆体的种子结实密切相关。从正常突触（SDR）和去联会（FDR）后代中分别获得了高达 54.0 和 21.5 粒/果实。具有 SDR 或 FDR 2n 大孢子形成的分离个体的高频率（分别为 78.0%和 45.2%）支持了性多倍体化是多倍体茄属物种起源和进化的驱动力的假设。目前鉴定出具有一致 FDR 2n 大孢子形成的二倍体马铃薯克隆体，为将增强的二倍体种质直接转移到四倍体中提供了更多机会，特别是提倡了 2x（ds-1；FDR）×2x（ds-1；FDR）育种方案在品种开发和生产中相对健壮和均匀的真薯种子（TPS）品种的可行性。讨论了其在育种和二倍体无融合生殖的实验诱导中的潜在价值和局限性。
