大鹅观草与蛇河披碱草属间杂种的细胞遗传学研究

Cytogenetic study on intergeneric hybrids between Roegneria grandis and Elymus wawawaiensis

关键词:  大鹅观草  蛇河披碱草  属间杂种  染色体配对  亲缘关系

Key words:   Roegneria grandis  Elymus wawawaiensis  intergeneric hybrid  chromosome pairing  homology

摘要:

为探讨大鹅观草(Roegneria grandis,2n=4x=28)的染色体组组成,为其正确的分类处理提供细胞学依据。该研究通过人工远缘杂交,成功获得3株大鹅观草与蛇河披碱草(Elymus wawawaiensis,2n=4x=28)属间杂种F₁植株。杂种植株形态介于两亲本之间,不育。亲本及杂种经I₂-IK溶液染色后进行花粉育性检测,结果显示Roegneria grandis和Elymus wawawaiensis的花粉可育,育性高达94.6%和90.5%; 杂种F₁不育。花粉母细胞减数分裂中期I染色体配对结果显示,亲本花粉母细胞配对正常,均形成14个二价体,以环状二价体为主,Roegneria grandis有频率很低(0.04/细胞)的单价体出现; 杂种F₁平均每个花粉母细胞形成6.46个二价体,变化范围为5～8; 在观察的83个花粉母细胞中,有35.2%的花粉母细胞形成了7个二价体,形成6个二价体的细胞占42.59%,较少细胞形成8个二价体; 平均每个细胞形成14.66个单价体,变化范围为10～18; 平均每细胞观察到0.14个三价体; 杂种花粉母细胞染色体构型为14.66 I+6.46 II+0.14 III; 平均每细胞交叉数为9.83,C值为0.35。结果表明:(1)R. grandis与Elymus wawawaiensis有一组染色体组同源的St染色体组,另外一组染色体组不是St或者H染色体组,Roegneria grandis的染色体组组成不是StSt^g;(2)较低频率的三价体(平均0.14个/细胞),可能是由于R. grandis的St和Y染色体组间具有一定的同源性,也可能是染色体易位等原因导致,对于Y染色体组的起源还需深入地研究;(3)在不同地理来源的披碱草属和鹅观草属物种中St染色体组同源性不同,R. grandis与来自于北美的Elymus lanceolatus与E. wawawaiensis的St染色体组较与分布于亚洲的E. sibiricus和E. caninus的St染色体组同源性反而更高,其原因还需要进一步地研究。

Abstract:

To investigate the genomic constitution of Roegneria grandis(2n=4x=28)and to provide cytological evidence for the taxonomic treatment of R. grandis, artificial distant hybridization between R. grandis and Elymus wawawaiensis(2n=4x=28)was carried out. Three F₁ hybrid plants were obtained successfully. The general morphological appearance of the intergeneric F₁ hybrid was intermediate between the Roegneria grandis and Elymus wawawaiensis. For estimation of pollen fertility study, pollen grains of hybrids were examined after staining in I₂-IK solution. Pollen grains of parental species were highly fertile. The percentage of stained pollen grains of Roegeria grandis reached 94.6%, and 90.5% pollen grains of Elymus wawawaiensis were fertile. Pollen grains of the hybrid between Roegeria grandis and Elymus wawawaiensis were sterile. Chromosome pairing at meiosis metaphase I(MI)of Roegeria grandis and Elymus wawawaiensis and their F₁ hydrid were analyzed. Meiosis of the parental tetraploid species was quite regular with 14 bivalents. Most of them were ring bivalents. A low frequency of univalent(0.04/cell)was observed in Roegeria grandis. Chromosome pairing at meiosis metaphase I(MI)was observed in 83 MI cells in the F₁ hybrid. Meiotic pairing in the F₁ hybrid averaged 6.46 bivalents per cell, varying from 5 to 8. 7 bivalents occurred in 35.2% of the MI cells, 42.59% of the MI cells had 6 bivalents, and 8 bivalents were observed in several MI cells. All the metaphase I cells contained unpaired chromosomes,ranging from 10 to 18,with a mean of 14.66 univalents per cell. 0.14 trivalents per cell were observed. The meiotic configurations of the F₁ hybrid were 14. 66 I+6.46 II+0.14 III. The chiasmata per cell were 9.83 with C value of 0.35. The results were as follows:(1)Roegeria grandis and Elymus wawawaiensis shared a homologous St genome. The other genome of Roegeria grandis was not St or H genome. The genome constitution of R. grandis was not StSt^g genome;(2)A low frequency of trivalents(averaged 0.14 per cell)were observed in the F₁ hydrid. They can probably be attributed to structural rearrangements between chromosomes of R. grandis and Elymus wawawaiensis, or a certain degree of homoeology between the St and Y genomes in these species. Further study needs to be done to investigate the oringin of Y genome;(3)The homology of St genome of Elymus species from different geographical origins with the St genome of Roegeria grandis was different. Elymus lanceolatus and E. wawawaiensis were from north America, and E. sibiricus and E. caninus were from Asia. The homology of St genome of Roegeria grandis with the St genome of Elymus species from north America was higer than that with the St genome of Elymus species from Asia. The reason remained to be discussed in the future.