杨树三倍体选育研究进展

杨树三倍体具有速生,纤维长等特点,是速生短周期纸浆材的首选树种,本文从发现树天然三倍体,人工培养杨树三倍体,特别是采用杂交,筛选天然2n花粉,人工诱导2n配子方法培育三倍体等方面,对杨树三倍体的育种研究现状进行了综述,指出了杨树三倍体育种的发育方向及意义。     

杨树抗冻性的研究现状

杨树是世界上广泛栽培的重要造林树种之一,我国是世界上杨树资源丰富的国家。杨树具有速生丰产、实用性强、无性繁殖能力强,且基因组较小等特点,现已成为研究林木生理和基因工程研究的模式植物。本文概述了国内外有关杨树抗冻性的生理生化性质及其指标、天然杂种的选择以及人工杂交选育种等方面研究现状,并展望了杨树基因工程在杨树抗冻性遗传改良中的应用前景。此外,对今后如何开展杨树抗冻改良育种的研究提出了一些设想。     

杨树抗冻性的研究现状

杨树是世界上广泛栽培的重要造林树种之一,我国是世界上杨树资源丰富的国家,杨树具有速生丰产、实用性强、无性繁殖能力强,且基因组较小等特点,现已成为研究林木生理和基因工程研究的模式植物。本文概述了国内外有关杨树抗冻性的生理生化性质及其指标、天然杂种的选择以及人工杂交选育种等方面研究现状,并展望了杨树基因工程在杨树抗冻性遗传改良中的应用前景,此外,对信后如何开展杨树抗冻改良育种的研究提出了一些设想。     

三倍体杨树核型分析

对4种三倍体杨树核型进行了比较分析,三倍体毛白杨核型为：2n=3x=57=1M 31m 10sm 15st;三倍体I-214为：2n=3x=57=2M 33m(2SAT) 10sm(1SAT) 10st(3SAT) 2t;三倍体武黑1号为：2n=3x=57=2M 38m(4SAT) 14sm(2SAT) 3st;三倍体廊坊3号为：2n=3x=57=35m 10sm(1SAT) 10st(2SAT) 2t(1SAT)。结果显示三倍体毛白杨核型与三倍体黑杨核型有显著不同,表明它们的基因组结构不同,起源各异。     

鱼类人工多倍体育种的研究进展

鱼类多倍体育种是鱼类育种最热的领域之一。本文概述了鱼类人工多倍体育种研究的进展情况,包括鱼类人工多倍体育种的方法和人工多倍体鱼类可育性等方面。鱼类人工多倍体育种的方法主要有物理、化学和生物学方法,三倍体鱼预期是不育的,四倍体是可育的,但目前两性可育的四倍体的报道还很少。本文还对人工多倍体鱼的生物学意义作了简单的阐述。本文旨在为对今后进一步开展鱼类人工多倍体育种研究提供参考。     

麦类作物多胚的研究

对高原602双胚苗的细胞学进行了研究,有3种类型2n-2n、2n-3n和2n-n,出现频率分别为0．16％、0．02％和0．02％。在2n-2n型里,又发现了形态上的差异,即2n（顶芒）-2n（长芒）。对单倍体育种和三倍体的起源进行了讨论。     

乌鳢三倍体诱导及其生长

采用热休克抑制第二极体排放的方法诱导乌鳢(Channa argus)三倍体,以探索人工诱导乌鳢三倍体的理想热休克条件。采用DNA含量测定法和红细胞核大小鉴定法对获得的鱼苗倍性进行鉴定,同时对普通二倍体乌鳢群体与三倍体群体的生长差异进行了比较研究。结果表明,(1)热休克法适宜诱导条件为,(28±0.5)℃培育水温授精后4 min,在水温42℃条件下持续处理3 min,三倍体诱导率最高,达到87.69%;(2)三倍体与二倍体DNA含量差异极显著(P0.01),其比值为1.50︰1.00;(3)三倍体和二倍体在红细胞核长径、红细胞核体积、红细胞核面积等6项指标上存在极显著差异(P0.01);与二倍体相比,三倍体红细胞体积和核体积分别是其1.69倍和1.60倍;(4)在4月龄与8月龄,三倍体的体长和体重比二倍体稍高,但两者差异不显著(P0.05)。本实验结果为进一步开展乌鳢倍性育种奠定了基础。     

宁夏农牧交错带土地利用变化对土壤质量的影响

在宁夏盐池县分别选取农田、弃耕地、天然草地、人工柠条林地和杨树林地5种土地利用类型作为研究样地,测定土壤理化性质指标,采用土壤质量综合技术指标,阐明中国北方典型农牧交错带土地利用变化对土壤质量的影响规律。结果表明：(1)土壤粗砂粒表现为弃耕地和天然草地显著高于农田、人工柠条林地和杨树林地(P<0.05),土壤细砂粒表现为杨树林地显著高于农田、弃耕地、天然草地和人工柠条林地(P<0.05),土壤极细砂粒和土壤黏粉粒均表现为农田和人工柠条林地显著高于弃耕地、天然草地和杨树林地(P<0.05)。土壤含水量、土壤pH值和土壤电导率表现为农田显著高于弃耕地、天然草地、人工柠条林地和杨树林地(P<0.05)。土壤有机碳含量表现为弃耕地和柠条林地显著高于农田、天然草地和杨树林地(P<0.05)。土壤全氮含量表现为农田显著高于弃耕地、天然草地、柠条林地和杨树林地(P<0.05)。(2)不同土地利用类型的土壤质量指标之间存在显著相关性(P<0.05)。其中,杨树林地各评价指标之间的相关系数最高,天然草地次之,农田、柠条林地较低,而弃耕地最低。(3)土壤质量综合得分大小顺序为：农田>弃耕地>0>草地>柠条林地>杨树林地。研究表明,对水浇农田实行保护性耕作和精细管理,并且农田弃耕后自然恢复成草地,有利于宁夏农牧交错带沙地土壤质量改善,但天然草地和人工林建设样地土壤质量较差。     

离体培养柑桔小胚获得三倍体植株

三倍体植株因不能进行正常的减数分裂,常产生败育的胚囊和花粉;又因柑桔属植物具有单性结实的能力,因而人工培育三倍体植株已成为获得无核柑桔品种的一条重要途径。在柑桔属植物中,获得三倍体主要有三条途径:(1)通过胚乳离休培养诱导三倍体植株;(2)四倍体品种同二倍体品种杂交,获得三倍体;     

人工三倍体新桑品种嘉陵20号的AFLP分析

利用AFLP分子标记技术, 从DNA水平对人工三倍体新桑品种嘉陵20 号(2n=3x=42) 及其亲本以及与嘉陵20号同亲本的2 个三倍体(2n=3x=42) 桑树材料与10 个二倍体(2n=2x=28) 桑树材料进行了遗传背景分析。获得了它们的指纹图谱、遗传距离及遗传相似系数, 并绘制出了它们的UPGMA聚类图。研究结果发现: 嘉陵20 号的母本7920 (2x;♀) 与父本西庆四号(4x; ♂) 间的相似系数为0 6612。这为今后更具强大杂交优势和多倍体优势的新型人工三倍体新桑品种选育时杂交亲本的选择与组配提供了较有用的参考依据。     

2n egg formation in Populus × euramericana (Dode) Guinier

Three synthetic triploid seedlings were derived from a cross between maternal parent Populus × euramericana (Dode) Guinier and Populus nigra var. italica (Moench.) Koehne via embryo rescue by treating female floral buds with colchicine at certain developmental stages before and after pollination, and identified by flow cytometric analyses. A total of 21 microsatellite primers were used to infer the ploidy of gametes forming the hybrids and the underlying meiotic mechanism. The results suggest that 2n eggs originated from the maternal poplar, contributing the extra haploid genome in the triploids. In addition, first division restitution (FDR) 2n eggs were produced in the maternal tree according to the marker genotypes of these triploids. Cytological analyses of megasporogenesis revealed that meiosis of the maternal parent was asynchronous. This cytological evidence suggests that 2n eggs result from FDR after treatment with colchicine, as a portion of megaspore mother cells (MMCs) were within the first division at the post-pollination stage. These results aid in understanding the mechanism of 2n egg formation in poplar and make the utilization of 2n eggs in polyploid poplar breeding more effectively.     

Chromosome-level genome assembly of a triploid poplar Populus alba ‘Berolinensis’

Many recent studies have provided significant insights into polyploid breeding, but limited research has been carried out on trees. The genomic information needed to understand growth and response to abiotic stress in polyploidy trees is largely unknown, but has become critical due to the threats to forests imposed by climate change. Populus alba ‘Berolinensis,’ also known “Yinzhong poplar,” is a triploid poplar from northeast China. This hybrid triploid poplar is widely used as a landscape ornamental and in urban forestry owing to its adaptation to adverse environments and faster growth than its parental diploid. It is an artificially synthesized male allotriploid hybrid, with three haploid genomes of P. alba ‘Berolinensis’ originating from different poplar species, so it is attractive for studying polyploidy genomic mechanisms in heterosis. In this study, we focused on the allelic genomic interactions in P. alba ‘Berolinensis,’ and generated a high-quality chromosome-level genome assembly consisting of 19 allelic chromosomes. Its three haploid chromosome sets are polymorphic with an average of 25.73 nucleotide polymorphism sites per kilobase. We found that some stress-related genes such as RD22 and LEA7 exhibited sequence differences between different haploid genomes. The genome assembly has been deposited in our polyploid genome online analysis website TreeGenomes ( https://www.treegenomes.com ). These polyploid genome-related resources will provide a critical foundation for the molecular breeding of P. alba ‘Berolinensis’ and help us uncover the allopolyploidization effects of heterosis and abiotic stress resistance and traits of polyploidy species in the future.     

Genetic identification of 91 poplar cultivars based on SSR markers

Accurate genetic identification and relationship analysis of poplar cultivars is necessary to establish commercial poplar plantations and select suitable breeding strategies. In this study, 91 poplar cultivars belonging to four sections (Aigeiros, Tacamahaca, Populus and Turanga) and inter/intra-sectional hybrids were genotyped using 18 polymorphic simple sequence repeat (SSR) markers. In total, 222 alleles were amplified with an average of 12.3 alleles per marker. The mean polymorphic information content and power of discrimination were 0.706 and 0.813, respectively. Five SSR markers (ORPM_103, ORPM_247, GCPM_1048, GCPM_1255 and LG_X_19) constituted a core fingerprint and were sufficient to identify all the tested cultivars. With some notable exceptions, cultivars of the same species generally clustered together in cluster (UPGMA) and ordination (PCO) analyses. Flow cytometry indicated that 11 poplar cultivars were triploid. Among these, seven had three alleles at some loci, suggesting that SSR markers could indicate the ploidy level to some extent. This study provides useful genetic information for the identification and protection of poplar cultivars in China and offers a guideline for the selection of poplar crossing parents based on ploidy level and genetic relationships.     

三倍体白杨杂种无性系指纹图谱的构建

目的:构建三倍体白杨杂种无性系指纹图谱,鉴定三倍体白杨杂种无性系。方法:分离纯化三倍体白杨杂种DNA模板,采用扩增片段长度多态性(AFLP)分子标记技术构建三倍体白杨杂种无性系指纹图谱。结果:从64对引物组合中筛选出M-CTA/E-CAG、M-CAC/E-CCA、M-ACT/E-CTC和M-CTT/E-CTG等4对多态性较高的引物组合,并应用该引物组合对21个三倍体白杨杂种无性系进行了AFLP分析,构建了21个三倍体白杨杂种无性系指纹图谱。结论:构建无性系指纹图谱是鉴别三倍体白杨杂种无性系的有效方法,能够有效鉴别21个三倍体白杨杂种无性系。本研究为品种鉴定及新品种权保护奠定了基础。     

Multilocus half-tetrad analysis and centromere mapping in citrus: evidence of SDR mechanism for 2n megagametophyte production and partial chiasma interference in mandarin cv 'Fortune'

The genetic structure of 2n gametes and, particularly, the parental heterozygosity restitution at each locus depends on the meiotic process by which they originated, with first-division restitution and second-division restitution (SDR) being the two major mechanisms. The origin of 2n gametes in citrus is still controversial, although sexual polyploidisation is widely used for triploid seedless cultivar development. In this study, we report the analysis of 2n gametes of mandarin cv 'Fortune' by genotyping 171 triploid hybrids with 35 simple sequence repeat markers. The microsatellite DNA allele counting-peak ratios method for allele-dosage evaluation proved highly efficient in segregating triploid progenies and allowed half-tetrad analysis (HTA) by inferring the 2n gamete allelic configuration. All 2n gametes arose from the female genitor. The observed maternal heterozygosity restitution varied between 10 and 82%, depending on the locus, thus SDR appears to be the mechanism underlying 2n gamete production in mandarin cv 'Fortune'. A new method to locate the centromere, based on the best fit between observed heterozygosity restitution within a linkage group and theoretical functions under either partial or no chiasmata interference hypotheses was successfully applied to linkage group II. The maximum value of heterozygosity restitution and the pattern of restitution along this linkage group would suggest there is partial chiasma interference. The implications of such a restitution mechanism for citrus breeding are discussed.     

Comparison of PCR-based molecular marker analyses of Musa breeding populations

Progress in the breeding of plantain and banana has been restricted by the complex genetic structure and behaviour of cultivated polyploid Musa. Genetic improvement has been hindered due to the large amount of space required for growth and maintenance of plant populations, in addition to the long growth cycle and the low levels of fertility and seed viability characteristic of cultivated genotypes. Molecular marker assisted breeding has the potential to dramatically enhance the pace and efficiency of genetic improvement in Musa. This study was conducted to compare different PCR-based marker systems (RAPD, VNTR and AFLP) for the analysis of breeding populations generated from two diverse Musa breeding schemes. All three assays detected a high level of polymorphism between parental genotypes and within progeny populations. As expected, AFLP assays had by far the highest multiplex ratio while VNTR analysis detected the highest levels of polymorphism. AFLP analysis of a full-sib tetraploid hybrid population confirmed previous reports based on VNTR analysis, of a high frequency of recombination during 2n (3x) gamete formation by a triploid plantain landrace. In addition, both VNTR and RAPD analyses of a full-sib triploid hybrid population suggested a high frequency of homoeologous recombination during n (2x) gamete formation by tetraploid hybrids. In general, there was a poor correlation between estimates of genetic similarity based on different types of marker. The implications of these findings for the molecular breeding of Musa crops are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Variation in pollen formation and its cytological mechanism in an allotriploid white poplar

Variation in pollen formation and its cytological mechanism in an allotriploid white poplar were investigated by the squashed technique and indirect immunofluorescence. Besides 0.5% stuck pollen grains, this allotriploid produced regularly spherical pollen grains. It was estimated that 90.3% of pollen grains were viable. Diameters of the viable spherical pollen grains ranged from 23.2 to 72.9 μm, with a bimodal frequency distribution. Numerous meiotic abnormalities were found, including highly irregular chromosome pairing, lagging chromosomes and chromosome bridges, micronuclei, and multiple spindles, which indicate highly genetic imbalance of this allotriploid. Some micronuclei triggered minispindle formation in metaphase II and participated in cytokinesis to form microcytes in sporads. Abnormal orientation of metaphase II spindles contributed to production of dyads and triads, which produced unreduced microspores. However, parallel orientation of spindles was not necessary for dyad formation, because an organelle band positioned in the equatorial region prevented the spindles from coalescing. Some microsporocytes exhibited a complete or partial absence of cytokinesis, which resulted in the formation of monads and the increased frequency of dyads and triads. The perspective of this triploid in the polyploid breeding program of white poplar is discussed.     

Genetic diversity among Korean bermudagrass (Cynodon spp.) ecotypes characterized by morphological, cytological and molecular approaches

The genus Cynodon comprises ten species. The objective of this study was to evaluate the genetic diversity of Korean bermudagrasses at the morphological, cytological and molecular levels. Morphological parameters, the nuclear DNA content and ploidy levels were observed in 43 bermudagrass ecotypes. AFLP markers were evaluated to define the genetic diversity, and chromosome counts were made to confirm the inferred cytotypes. Nuclear DNA contents were in the ranges 1.42-1.56, 1.94-2.19, 2.54, and 2.77-2.85 pg/2C for the triploid, tetraploid, pentaploid, and hexaploid accessions, respectively. The inferred cytotypes were triploid (2n = 3x = 27), tetraploid (2n = 4x = 36), pentaploid (2n = 5x = 45), and hexaploid (2n = 6x = 54), but the majority of the collections were tetraploid (81%). Mitotic chromosome counts verified the corresponding ploidy levels. The fast growing fine-textured ecotypes had lower ploidy levels, while the pentaploids and hexaploids were coarse types. The genetic similarity ranged from 0.42 to 0.94 with an average of 0.64. UPGMA cluster analysis and principle coordinate analysis separated the ecotypes into 6 distinct groups. The genetic similarity suggests natural hybridization between the different cytotypes, which could be useful resources for future breeding and genetic studies.