Ploidy manipulation in guinea grass (Panicum maximum Jacq., Poaceae) utilizing a Hybridization-supplemented Apomixis-components Partitioning Approach (HAPA)

Ploidy manipulations are achieved by utilizing unreduced gametes, somatic chromosome doubling or haploidization. Apomixis, the asexual mode of reproduction through seeds, involves two of these phenomena viz., apomeiosis (unreduced embryo-sac formation) and parthenogenesis (fertilization-independent embryogenesis). The two components when partitioned may yield high frequencies of triploids and haploids, and thus, serve as a tool to manipulate ploidy levels when appropriately supplemented with hybridization schemes. Utilizing this H ybridization-supplemented A pomixis-components P artitioning A pproach (HAPA), the largest ploidy series in a crop plant was generated in guinea grass ( Panicum maximum Jacq.). Eighty-nine diverse guinea grass accessions were characterized for their reproductive capacities to identify tetraploid (2 n  = 4 x  = 32) accession(s) with high apospory but reduced parthenogenetic capacity, thereby producing a high frequency of hexaploid seeds. Seeds from accession IG 04-164 were utilized to produce a ploidy series by appropriately combining partitioned apomixis components and hybridizations in two seasonal cycles. We successfully obtained plants representing ploidies 3 x, 4 x , 5 x , 6 x , 8 x and 9 x , all derived from a single 4 x progenitor. Production methodology, reproducibility and utilization of HAPA in cytogenetic and molecular studies are discussed.     

无融合生殖——无性种子的形成过程

 无融合生殖是一种通过种子进行无性繁殖的过程。目前国际上通用的无融合生殖概念是指二倍体无融合生殖,即发生在被子植物胚珠中的不经减数分裂和受精作用而产生种子的生殖方式。尽管目前已在被子植物52个科的400多种植物中发现了无融合生殖植物,但作物中普遍缺乏无融合生殖特性。本文介绍了无融合生殖的发生类型,对无融合植物的分布情况以及近年来国内外新发现的无融合生殖种进行了归纳和整理,总结了无融合生殖的遗传学控制和分子机理研究方面的最新进展,对无融合生殖在农业中的应用和生态学意义等问题进行了讨论。     

植物无融合生殖研究的现状及进展

介绍了植物无融合生殖在选育无融合生殖品种及育种材料方面的成果;概述了植物无融合生殖在胚胎学、遗传学及生殖特性,杂种优势固定途径及无融合生殖材料选育途径等方面研究的现状和趋势。      

应用胚珠切割及子房透明技术观察无融合生殖甜菜M14胚囊发育

介绍了一种快速简便观察分析无融合生殖甜菜胚囊发育过程的制片法。通过剥离胚珠,并对胚珠珠孔端进行再次切割和分离,经过固定和脱水,用冬青油整体透明及丁香油封片,在OLYMPUS—BX51型荧光显微镜下通过荧光技术观察发育中的胚囊产生自发荧光,可分辨出胚囊的内部结构。用FPA和4％戊二醛两种固定液效果不同．后者效果更佳。     

一种提取悬铃叶苎麻（ B. tricuspis （Hance） Marino）花序RNA的方法

应用改良CTAB法提取苎麻属野生种悬铃叶苎麻（Boehmeri．tricuspis（Hance）Marino）的花序RNA，通过1．2％琼脂糖凝胶电泳，测定分析260nm和280nm处的吸光值发现，应用该法提得的RNA完整性好，得率高；对其反转录产物进行AFLP分析表明，每一特定引物组合均能产生稳定清晰的条带，且在各引物间有差异。认为所提RNA符合分子生物学实验要求。另外，本文还对提取RNA过程中应注意的一些事项进行了讨论。     

人工创造植物无融合生殖的研究进展

对人工创造植物无融合生殖的各种途径进行了总结 ,对创造植物无融合生殖的方法进行了比较分析 ,认为植物体细胞杂交法是目前最好的选择。提出了两种用生物工程技术创造植物无融合生殖方法的设想 ,并对其应用前景进行了展望。     

Review of Pennisetum section Brevivalvula (Poaceae)

Section Brevivalvula is one of five sections in the large tropical grass genus Pennisetum. It belongs to the tertiary genepool of P. glaucum (L.) R. Br., pearl millet, and consists of six morphological taxa: P. atrichum Stapf & Hubb., P. hordeoides (Lam.) Steud., P. pedicellatum Trin., P. polystachion (L.) Schult., P. setosum (Swartz) L. Rich. and P. subangustum (Schum.) Stapf & Hubb., which together form a polyploid and agamic complex. Four euploid (x = 9) and twelve aneuploid chromosome levels have been found till now; the polyploids are apomictic, while diploid populations of P. polystachion and P. subangustum are considered sexual. This revised version was published online in July 2006 with corrections to the Cover Date.     

Breeding for apomixis in potato: Pursuing a utopian scheme

Summary Apomictic propagation in potato holds a great promise for the new technology of growing potatoes from botanical seeds in stead of tubers. It is explained that apomixis results from the combination of abnormal meiosis, abnormal fertilization and parthenogenesis.An ideal scheme is given for growing potatoes from true seeds. This scheme remains utopian when autonomous apomixis is not available. Autonomous apomixis occurs when the reduction division is lacking (no gene recombination, no reduction of chromosome number) and the resulting 2n egg cell develops parthenogenetically without fertilization of the central nucleus. The first best approach is pseudogamous apomixis, which differs from autonomous apomixis in the necessity of fertilization of the central nucleus. Second best is the parthenogenetic development of 2n eggs, since these have originated through an abnormal type of reduction division. This type is characterized by the lack of formation of a reduction cell wall and fusion of the two spindles at metaphase II of meiosis (first division restitution).Apomixis in the narrow sense, either pseudogamous or autonomous, is defined. It has not been found in potato species or species hybrids. On the basis of our knowledge about characteristic features of existing apomictic species, about genetics and evolution of apomixis and about the occurrence of particular elements of apomixis in potato the possibility of introducing apomixis into potato from existing elements is discussed along with methods to induce missing elements. Some tentative approaches are suggested which in the long run may lead to the detection of potato genotypes with apomictic propagation.Edited version of a paper presented at the 19th Planning Conference of the International Potato Center (CIP) in Manila, Philippines in September 1979 on production of potatoes from true seed. Published with the consent of CIP.     

Regeneration and somaclonal variation in apomictic Paspalum dilatatum Poir

Summary In an attempt to incorporate variation into a uniform obligate apomict, plants of apomictic common dallisgrass, Paspalum dilatatum Poir., were regenerated from callus derived from immature inflorescences. Plants developed through both organogenesis and embryogenesis. A total of 682 regenerants were produced and more than 400 were transplanted into a field nursery and screened for somaclonal variation. Eventually 20 regenerants were selected, increased, and planted into a replicated nursery along with normal common dallisgrass. The characteristics examined were maturity date, plant height, number of racemes per inflorescence, number of spikelets per raceme, pubescence, stigma and anther color, ergot resistance, seed germination, seed set, pollen stainability, method of reproduction, and chromosome number. There were differences among the regenerants and between them and common dallisgrass for all traits except chromosome number, stigma and anther color, and ergot resistance. One of the more important regenerants had significantly higher seed set than common dallisgrass. All regenerants reproduced by aposporous apomixis but some exhibited a high degree of abortion while others had more aposporous embryo sacs per ovule than common dallisgrass. These findings demonstrate that common dallisgrass can be regenerated through tissue culture and that somaclonal variation is expressed in some of the regenerants, even though some of the altered traits are deleterious.