Heterosis in relation to genetic divergence and specific combining ability in groundnut (Arachis hypogaea L.)

Summary The frequency and magnitude of heterosis were examined in relation to genetic divergence among parents in two diallel cross experiments in groundnut. The parents were grouped into clusters based on their diver-gence. The range, mean and standard deviation of the intra-and inter-cluster divergence were used to define four divergence classes. The frequency of heterotic crosses and the magnitude of heterosis for yield and its components were found to be higher in crosses between the parents in intermediate divergence classes than extreme ones. The results agreed well with the overall status of the specific combining ability of these crosses.     

Interspecific Oryza Sativa L. X O. Glaberrima Steud. progenies in upland rice improvement

Fertile interspecific progenies between Oryza sativa L. and O. glaberrima Steud. were produced through backcrossing and doubled haploid breeding (DHB). Backcrossing with the O. sativa parents increased fertility and helped combine the O. sativa and O. glaberrima features. The use of DHB to generate a large proportion of doubled haploids from interspecific F₂ hybrids, helped overcome constraints associated with the conventional breeding of these species, such as: (1) slow fixation of the lines, (2) frequent partial sterility of the progenies and (3) low recovery of useful recombinants. Although true interspecific progenies between O. sativa and O. glaberrima were generally rare, their occurrence in some populations was as high as 30%. Some progenies combined the high yield potential of O. sativa, a result of high spikelet number caused by secondary branches on the panicle, with useful traits of O. glaberrima such as rapid leaf canopy establishment and high N responsiveness. The progenies partly inherited the O. glaberrima parents' high specific leaf area (SLA) during early growth, theoretically improving competitiveness with weeds, and from the O. sativa parents the rapid decrease in SLA towards the reproductive stage, theoretically allowing for high leaf photosynthetic rates and high grain yield. Research is in progress to develop new interspecific plant type concepts for resource poor, weed prone upland rice environments in West Africa. This revised version was published online in July 2006 with corrections to the Cover Date.     

Integration of breeding and technology into diversification strategies for disease control in modern agriculture

While diversity for resistance has been recognised for more than 60 years as a key factor in disease management, and diversification strategies such as cultivar mixtures and multilines are described and advocated in almost every plant pathology textbook, the general view in modern agriculture is that diversity would be too difficult and expensive to implement. In addition, difficulties in marketing the produce are emphasised. The question thus arises if and how such strategies can be designed to find a place in modern agriculture. Considering the general ecological benefits of diversification and the possible economical benefits for growers and society, several possible approaches to the solution of actual and perceived problems in modern agriculture are discussed. An important route towards achieving diversity would be to integrate it into the breeding process. Selection criteria would include inducibility of resistance and competitive ability, in order to produce diversified varieties able to adapt both to unpredictable environmental conditions (especially climatic) and to changing pest and pathogen populations through co-evolution. Evolutionary breeding methods such as composite crosses and modern landraces and some of the legal problems associated with these approaches are discussed. Technical solutions are integral to the future use of diversification strategies and range from more or less simple adjustments to machinery for planting and harvesting to devices designed for separation of the harvested products.     

龙眼正反交杂种后代果实经济性状遗传倾向研究

以晚熟龙眼‘立冬本’、‘苗翘’正反交的54个杂种后代单株为材料,研究了正反交杂种后代的单果重、果形指数、果肉厚度、核重、可食率、可溶性固形物含量等果实经济性状的遗传倾向。结果表明：正反交杂种后代单果重有趋小的倾向,果肉厚度和可溶性固形物含量有超亲的倾向,果核重、可食率呈趋中的倾向,果形指数变异小,趋于近圆形。流汁程度和果肉质地在后代中表现受母本的影响大。其它性状受‘立冬本’品种特性影响较大,倾向于果梗软韧、果实排列较紧密、皮青褐色、汁液多。正反交后代均存在超亲子代,表现出一定的杂种优势。     

Nonhost plant species as donors for resistance to pathogens with narrow host range. II. Concepts and evidence on the genetic basis of nonhost resistance

Summary It is commonly argued that wild plant species with a very high level of resistance to a micro-organism which is pathogenic on a crop species would be useful donors of resistance. Whether this principle is true if the wild species is a distinct nonhost, remains to be proved. It is assumed that nonhost resistance, if not based on avoidance, rests on a poor adaptation of the micro-organism to general defence mechanisms in the plant. No basic compatibility is achieved. Major-genic hypersensitive host resistance would, according to the concept, be superimposed on basic compatibility. The defence reaction is switched on if a resistance allele recognizes a specific avirulence factor produced by the pathogen. The frequency of the resistance allele would depend on the selection pressure exerted by the pathogen population.In contrast to these concepts, there is evidence that nonhost resistance, at least to formae speciales, rests on an extremely high allele frequency of effective major genes for resistance, rather than on a complex of genes that play part in a general defence system. Especially the high allele frequency and the durability of the nonhost resistance are in conflict to what would be expected if the concepts hold true. It is concluded that part of the theoretical concepts needs to be revised or extended to reconcile them with the evidence. A major-genic base for nonhost resistance would be very interesting from the breeder's point of view, because transfer of such a resistance to a crop would be less hard to accomplish than that of more complex inherited defence systems.     

大豆亲本杂交方式对后代的遗传变异及品系产量表现的影响 Ⅰ.单交与双交的比较研究

1985—1990年用两套亲本的单、双交组合为材料,比较后代表现及选择效果,以明确双交是否较单交更优越。结果表明:单、双交组合F_2代的株高、主茎节数、单株荚数、单株粒数、百粒重、单株粒重的平均表现、标准差及变异系数无大差异。双交组合多数性状的变异幅度处在两个单交组合之间。除第二套组合双交的主茎节数同时显著少于两个单交外,其余性状均未能同时达到显著水平。按相同育种目标入选的高世代品系在生育期、抗倒伏、抗病性方面,双交均可获得与单交相似的选择效果。两个单交组合与相应的双交组合的F_4、F_5品系平均产量、20％高产品系平均产量、前二名高产品系平均产量的差异未能达到显著水平。看来,对产量进行选择,双交并不比单交更优越。     

浅谈公路桥涵台背回填施工质量控制

本文作者结合工程实践，对公路桥涵台背回填施工工艺及质量控制进行了全面论述，提出了具体措施。     

Dental bridging as a treatment for large oral fistulae in two horses

Chronic orocutaneous, oronasal, or orosinus fistulae can be challenging to repair. This report describes placement of a dental bridge as a treatment for oral fistulae and outcome in two horses. A 12-year-old, Westphalian gelding was presented for nasal discharge because of an oromaxillary fistula after dental repulsion of the Triadan 209 4 years earlier. The second case, a 5-year-old Oldenburg mare was presented for an orocutaneous fistula 7 weeks after dental repulsion of the Triadan 208. Both were treated by placing an 8-shaped cerclage wire, inserted through the rostral and caudal interdental spaces and crossing at the level of the missing tooth. Polymethylmethacrylate (PMMA) was then used to seal the fistula. No significant complications occurred during or after the surgery. In both cases clinical signs did not recur. In the first case the dental bridge is currently (5 years after the intervention) in place. In Case 2 the construction was removed after 1.5 years and the fistula had healed completely. This case report suggests that placing a dental bridge composed of cerclage wire and PMMA should be considered as an easy, noninvasive and efficient way to manage large oromaxillary or orocutaneous fistulae.     

‘京白梨’与‘鸭梨’正反交后代果实性状遗传倾向研究

 以‘京白梨’与‘鸭梨’及其正反交后代为材料,研究了果实性状的遗传倾向。结果表明：‘京白梨’与‘鸭梨’杂交后代果实性状大多为多基因控制的数量性状。杂种后代果实有变小的趋势,平均遗传传递力为77.14%,平均变异系数为38.26%。果实可溶性固形物与可溶性糖都呈升高的趋势,后代平均超高亲率分别为97.25%和35.28%。正反交后代果实硬度均呈增大的趋势,平均遗传传递力为123.81%。可滴定酸有增加的趋势,平均变异系数为51.1%。果实维生素C的遗传正反交倾向不同。果实石细胞有明显增多的趋势,后代平均遗传传递力达到了182.62%。     

应用细胞质雄性不育系构建甘蓝型油菜三交杂种

在测交一代保持不育系不育特性的品种（系）称为临时保持系；将回交３－４代仍能保持不育系不育特性的品种（系）为永久保持系．前者较多，后者较少。临时保持系的研究和三交杂种的应用结果表明；三交杂种方法是克服细胞质雄性不育系微量花粉的有效途径．两个强优势的三交杂种的产量比中油８２１增产１２％以上，一个比相应的单交杂种增产２．２％，一些三交杂种的抗性得到改良。