Reproductive diversity and strategies for breeding in St. John's wort (Hypericum perforatum L.)

St. John's wort (Hypericum perforatumL.) is a medicinal crop plant that reproduces by apomixis. To study the reproductive diversity within the initial breeding material, 656 plants from 92 accessions of the species were analysed by flow cytometric seed screening (FCSS) and compared to 66 plants of cv. ‘Topaz’ as a control. Among plants from the 92 accessions, 16 were obligate sexuals, nine were obligate apomicts and all remaining ones were facultative apomicts. Among controls, there were six obligate and 60 facultative apomicts. Tests of reproductive pathways indicated that, in the investigated collection, all apomictic plants were tetraploid and all sexual plants were diploid. A strategy for a cross breeding program in St. John's wort is illustrated by crossing one diploid obligately sexual mother plant with six tetraploid facultative apomicts. All 91 F₁ progeny obtained were triploid with 58% being obligate sexuals and 42% facultative apomicts. To quantify the different routes of seed formation within facultatively apomictic individuals, the reproductive pathways were reconstructed from about 30 single seeds from each of five tetraploid and two triploid plants using FCSS. The frequency of seed formed by apomixis ranged from 54% to 67% among four tetraploid genotypes. One triploid and two tetraploids formed 23% to 73% of the so-called B_III hybrids (fertilization of unreduced eggs) and one triploid was obligately sexual. The results show that while the mode of reproduction in H. perforatum is highly variable, tetraploid obligate apomicts as well as diploid and triploid obligate sexuals can be selected as starting material for breeding purposes. This revised version was published online in July 2006 with corrections to the Cover Date.     

平邑甜茶多胚现象研究

平邑甜茶具有产生多胚种子,萌发多实生苗的能力.平邑甜茶的种胚数最大为三.随着种子的生长发育多胚种子的逐渐下降,而单胚种子的比率逐渐上升.种子完全成熟时,三胚的种子完全消失,双胚种子的比例为0.61%-0.86%.     

玉米异位双胚与同位双胚籽粒的来源及其无融合生殖性

本文报道了在玉米自交系A上发现的异位双胚粒和同位胚粒的来源与无融合生殖性．结果指出:1．异位双胚粒是一个异位单胚粒和一个正常单胚粒或者两个异位单胚粒在籽粒形成过程中合二为一形成的子房融合籽粒；2．同位双胚粒是合子胚在胚胎发育过程中一分为二裂生形成的孪生双胚籽粒；3．以紫胚玉米的紫胚等当代直感性状为标记性状测定了异位双胚粒与同位双胚粒的无融合生殖性，结果显示，异位双胚粒和同位双胚粒均不是无融合生殖体．     

Variation in important pasture grasses. II. Cytogenetic and reproductive variation

Abstract

The chromosome numbers and reproductive variation of seven important pasture grasses from South Africa are compared. This comparison indicates that all these species form polyploid complexes, all reproduce both sexually and either apomictically or vegetatively, and some form of hybridization or cross‐fertilization occurs in each species. The ecological success of these species can, therefore, be attributed to the fact that they combine the advantages of polyploidy and apomixis and, at the same time, bypass the disadvantages with their hybridization potential.     

冬小麦无融合生殖系研究初报

通过对上万份材料的筛选、鉴定、转化、处理,获得Am92372,Am871131,Am87-6072等3个兼性无融合生殖材料。     

小麦双胚苗类型及后代观察初报

对小麦与天蓝偃麦草杂交诱导后代筛选的36个双胚苗株系进行形态特性分类.共有6种,即双鞘同步型.双鞘异步型,单鞘同步型.单鞘一叶重叠同步型.单鞘一叶共生同步型、单鞘异步型,小麦双胚苗二代再现双苗率极小,三代双胚苗两苗系再现频率分别为0.823%和0.139%.二代分离奇异,三代按株系趋向整齐.双胚苗及后代去雄套袋有不同程度的自主结实特性.是有性和无性基因型细胞的嵌合体,双苗特性可通过有性或无性过程传递给后代,无性的表达可能需特定的环境条件.双胚苗是选择兼性或专性无融合生殖的一个中间型桥梁材料.     

无融合生殖核桃果实矿质营养变化研究

[目的]了解无融合生殖核桃果实的矿质营养水平。[方法]用原子吸收分光光度仪测定不同时期果实中7种矿质元素含量。[结果]在所测矿质元素中,除Cu、Zn元素外,无融合生殖果实中K、Ca、Mg、Fe、Mn诸元素含量均低于对照 除Fe元素外,其他各元素在无融合生殖果实中的含量在年周期中都呈下降趋势,且无融合生殖果实比对照下降的要多。[结论]无融合生殖果实比自然授粉受精果实矿质营养水平低,致使其不能正常生长发育成熟。     

异源三倍体甜菜（VVC）无融合生殖的研究

 通过栽培甜菜与白花甜菜杂交,获得了真实杂种VC88-1（VVCC,2n=36）。用栽培甜菜对其回交,合成了异源三倍体甜菜（VVC,2n=27）,它具有无融合生殖特性。异源三倍体甜菜具有两个物种的形态特征,表现为中间型,更偏向野生种。植株繁茂,叶片平展深绿色,根形不整有岔根,木质化较强。细胞学检查有丝分裂中期可清晰判定两个物种的染色体,构成独特的9长18短核型。经过几年观察选育已经选育出传递率在80%以上的无融合生殖系9个,并判定为兼性无融合生殖。利用石蜡切片研究了无融合生殖的发生过程,观察到卵细胞等8核胚囊及胚胎发育全过程,认定异源三倍体甜菜胚囊发育为蝶须型,是属于有丝分裂型的二倍体孢子生殖的无融合生殖类型。讨论了异源三倍体甜菜进一步利用的可能性。     

苎麻属系统学研究进展

苎麻是我国重要的纤维植物,栽培历史悠久。但苎麻属植物的系统学研究较少,严重落后于其它经济作物。本文从栽培苎麻的起源、演化关系、染色体基数及苎麻属起源、无融合生殖4个方面概述了苎麻属植物的系统学研究成果,并提出存在的问题和今后的研究方向。     

二十一世纪水稻育种新战略Ⅱ．利用远缘杂交和多倍体双重优势进行超级稻育种

本文论述了远缘杂交和多倍体化结合利用基因组间和多倍本杂种优势，开创水稻育种新途径的策略。纵观水稻育种的历史，无论是常规杂交育种，还是杂交稻育种，其研究战略都是建立在有性生殖和二倍体基础上的，归根结底，都是利用栽培稻同一基因组（A基因组）内优良基因的重组以及从野生稻向栽培稻引入少数优良基因。从作物进化趋势看，水稻是二倍体，基因组小、DNA含量低、染色体小，增加基因组数，提高倍性水平，利用异源多倍体杂种优势将是水稻育种新途径。针对同源四倍体水稻结实率低的关键问题，可采取拉大亲缘关系距离、减少多价体形成，应用广亲和、无融合生殖基因等措施，从遗传机理上提高多倍体水稻结实率。按三步实施战略：一、选用极端类型籼粳稻、爪哇稻，诱导亚种间杂种多倍体；二、诱导亚洲栽培稻和非洲栽培稻以及非洲野生稻种间杂种多倍体；三、诱导AA基因组的栽培稻与其它不同基因组野生稻（BB、CC、BBCC、CCDD、DD、EE、FF、GG、HHJJ）的种间多倍体。在实施过程中发挥一特殊基因材料的特殊作用，如广亲和基因对于克服籼粳杂种一代不育性、特别是雌败育的作用，无融合生殖缺乏减数分裂发生和受精过程对于克服染色体配对分离而导致的杂种败育的作用，以及类似于小麦中存在的抑制部分同源染色体配对的Ph基因对于防止水稻异源多倍体的基因组间部分同源性配对形成多价体、染色体桥、落后染色体等现象的作用，为选育异源多倍体水稻、无融合生殖水稻提供可靠保证。近三年的实践已经初获良好的结果，利用无融合生殖水稻品系籼粳交，亚洲稻与美洲稻杂交已获得杂种优势明显、结实率高达85％的优良多倍体株系，为实现这一育种新战略打下了良好基础。