遗传距离在不同环境条件下变化的研究

本文研究利用北方春小麦区35份品种(系)为材料,通过两年、两地及不同试验处理,研究了春小麦10个数量性状的遗传距离及聚类分析在不同试验处理中的变化。结果表明:遗传距离D~2值是反映品种在一定条件下数量性状综合指标之间的差异;D~2值在不同年份、地点、试验处理中有明显的变化,并无一定的规律性;聚类结果是品种表型聚类;不同处理的聚类结果不一致;D~2值和聚类结果与品种的亲缘关系、地理来源无必然的联系;当不同的试验处理水平所造成的小生态环境相近时,两处理D~2值间存在着显著的正相关,否则,不存在相关关系。在一定生态环境条件下测得的D~2值,只有在与其相近的环境条件下才具有指导意义。此外,依据遗传距离D~2值指导选配亲本具有一定的局限性;1.类间品种杂交可能导致品种近亲繁殖;2.类内品种不杂交会遗漏掉有益杂交组合。     

基于卫星通讯与Internet相结合的远程教育系统模式

介绍了现代远程教育的一般概念和远程教育的演变过程,以及当前国内外现代远程教育的发展动向;文章分析了我国目前远程教育技术领域中基于卫星通讯与Intemet相结合的远程教育系统模式,以及这种系统模式的构成和采用的技术标准.     

浅谈面向对象数据库的技术和发展

面向对象数据库把面向对象的方法和数据库技术结合起来,使得数据库的分析、设计最大程度地与人们对客观世界的认识相一致,是数据库技术中巨大的进步。概述了面向对象数据库的特征、优势及其重要技术,并对这一技术进行了展望。     

西气东输山区管道施工的管理与实践

以西气东输管道工程19标段为例,介绍了山区管道施工的总体计划、不同地段施工方案和各项施工工序的内容及其相互间的组织协调关系.针对山区段管道施工中存在的主要问题,并根据管道施工安全和质量保证体系的要求,提出了平原地段管道实行沟上焊接,山区地段管道全部采用沟下焊接的施工方案.南留沟峡谷和坂河峡谷管道施工的实践表明,轻型轨道运管法比较适宜在山区管道施工中应用.     

Genetic distance and its association with heterosis in peas

Summary The relationship between the genetic distance of parents and both the heterosis of F₁ hybrids and the variance of F₅ lines was investigated in 72 crosses of pea (Pisum sativum L.). The genetic distance between each pair of parents was estimated, using isozyme (GDi), morphological (GDm) or quantitative (GDq) markers and finally a combination of isozyme and morphological markers (GDi+m). GDm was poorly correlated with the other measures of genetic distance, which in turn were strongly correlated with each other. Genetic distance was moderately correlated with the level of heterosis for yield over midparent in the F₁ generation, with the highest correlation obtained from GDi+m. GD was not significantly correlated with heterosis for yield over the better or best parent but it was significantly correlated with all three measures of heterosis for pods per plant and hundred seed weight. There was no correlation between genetic distance and the level of heterosis for yield and total dry matter in the F₂ generation, but GDi, GDi+m and GDq were predictive for the level of inbreeding depression in grain yield and total dry matter. When parents were high in genetic distance, crosses produced highly transgressive segregants for basal branches per plant, hundred seed weight, harvest index and onset of flowering. Genetic distance between parents was thus a useful measure for predicting a portion of hybrid performance and also of the variance of derived inbred lines. It was concluded that when choosing parents for a cross, consideration should be given to their genetic distance as well as their overall adaptation and their yield. There is considerable potential for optimising choice of parental combinations in the development of improved pea cultivars.     

Associations among widely used French and U.S. maize hybrids as revealed by restriction fragment length polymorphisms

Summary Eighty DNA Restriction Fragment Length Polymorphism (RFLP) clones were used as probes to profile 47 hybrids of maize (Zea mays L.) that are of widespread usage in France and 49 hybrids that are either in common usage or are new releases in the U.S. The objectives were to 1) investigate the degree to which RFLPs provide unique characterization of hybrids; 2) show associations among hybrids using both cluster and principal coordinate analyses; 3) measure the ability of RFLPs to show associations among hybrids that reflect those to be expected on the basis of pedigree; and 4) compare the patterns and extent of genetic diversity among French hybrids with that found among a set of widely used U.S. hybrids.RFLPs showed all French hybrids to have different profiles, however, 3 hybrids were very similar with more than 90% of their profiles in common. Twenty-seven U.S. hybrids showed this level of similarity with one or more U.S. hybrids. High correlations (r=0.93, 0.94) were found for pedigree distance versus RFLP distance between pairs of French and of French and U.S. hybrids, respectively. Similar levels of correspondence for rank correlations between RFLP and pedigree data were also found. Similar groupings of hybrids were shown by two cluster analysis methods and by principal coordinate analysis. Inclusion of hybrids in cluster groupings was supported by observation of raw distance data for selected hybrids and their nearest neighbors. Most hectarage in France is planted to hybrids that fall within 2 related groups of germplasm on the basis of RFLP data. Minimum distance standards could promote breeders to surmount the challenge of introducing elite yet diverse germplasm into agriculture.     

Molecular genetic diversity within and among German ecotypes in comparison to European perennial ryegrass cultivars

Perennial ryegrass (Lolium perenne L.) is the most important grass species for temperate grassland agriculture. The level and distribution of genetic variation in gene bank ecotype collections is still largely unknown but of great interest for the planning of breeding programmes. The objectives of this study were to (i) assess the molecular variance and population structure of German ecotypes at the regional and population level, (ii) assign ecotypes to germplasm pools and (iii) compare the relationship between German ecotypes and previously‐investigated European cultivars of perennial ryegrass, A total of 22 ecotypes originating from three geographic areas in Germany. each with a sample size of 20 individual plants, were investigated with 156 polymorphic RAPD markers. Genetic distance among ecotypes ranged from 0,27 to 0.48, An analysis of molecular variance (AMOVA) revealed a much larger variation within populations (71%) than among them (29%). Ecotypes from North Germany were significantly different from those of South and Middle Germany. Thus, two distinct germplasm pools could be identified. The 22 ecotypes and 22 previously investigated cultivars shared 98% of the molecular variance.     

Genetic relationships between Sicilian wild populations of Brassica analysed with RAPD markers

Brassica comprises very variable species, both morphologically and genetically. Among these species, the Sicilian populations of Brassica sect. Brassica, species related to kale crops form a complex group. The genetic relationships among 15 populations occurring in Sicily and one from Calabria, representing the existing diversity, have been investigated using random amplified polymorphic DNA (RAPD) markers. This assay, carried out with 22 arbitrary primers, generated 236 polymorphic fragments, 21 of which were specific for single populations (mainly Brassica insularis, Brassica incana and Brassica macro‐carpa). Jaccard's genetic distances were computed and the phylogenic tree was established using the UPGMA algorithm. The dendrogram obtained showed four branches grouping: (1) B. incana populations; (2) B. insularis and B. macrocarpa, occurring in small islands around Sicily; (3) B. rupestris populations; and (4) B. villosa populations. Within B. rupestris, only B. rupestris subsp. brevisiliqua was clustered in the B. villosa group. The classification obtained is discussed with regard to the morphological, ecological and geographical data.     

Indica-Japonica differentiation of paddy rice and its relationship with heterosis

The Indica‐Japonica differentiation of three photoperiod‐sensitive and/or thermosensitive genetic male‐sterile rice (PGMS or TGMS, respectively) lines and 47 male parental lines from seven ecotypes were studied for their restriction fragment length polymorphism marker data to determine which ecotype crosses with the three PGMS and/or TGMS lines could lead to higher yield potential, and to estimate the relationship between the Indica‐Japonica differentiation of parents and heterosis in grain yield and its components. The results indicated that hybrids derived from ‘N422s’ and the early‐middle ripening Indica varieties from southern China, and hybrids between ‘Pei'ai64s’ and three Japonica ecotypes, including North‐eastern Japonica varieties, restoring lines of Japonica hybrid rice and north China Japonica varieties, showed the highest grain yields. There was less variation of yield among the F1s between ‘108s’ and the seven ecotypes than among the other F₁s. Highly significant positive correlations between heterosis of the F₁ yield and genetic distance of the parents were detected, although the correlation between F₁ yield performance and genetic distance did not reach a significant level. Considerable variation of correlation between heterosis and genetic distance was also detected in the Indica × Indica crosses and Indica × Japonica crosses. There was much higher correlation (r = 0.63) between the F₁ yield performance and the genetic distance of parents in the Indica × Indica crosses than in the others. It is proposed that a genetic distance of 0.4‐0.8 between the two parents of hybrid rice might be appropriate not only for F₁ performance, but also for heterosis.     

传统双高油菜与双低油菜最佳隔离距离的分析

[目的]确定双高油菜与双低油菜的最佳隔离距离。[方法]以双高油菜蓉油4号为中心,在其周围200m范围内种植华杂5号,开放授粉,用纸层析法测定芥酸含量,研究不同距离下双高油菜对双低油菜芥酸含量的影响。[结果]不同间隔距离下,华杂5号的芥酸含量受影响程度不同,随隔离距离的变化呈现一定的规律性。4m处华杂5号百粒受影响率的为28.25,此后,随着间隔距离增加,芥酸受影响程度逐渐减小。32m处百粒受影响率降为5.00,64m处为1.30,接近于0,而128m时完全无影响,即芥酸上升率随间隔距离增加而逐渐减少。[结论]双高油菜对双低油菜芥酸含量的影响随隔离距离的增大而减小。隔离距离至少32m以上,最好64m以上。