The concept of varietal ability in plant breeding

Summary At the population level, the general varietal ability of a genotype is defined as the expectation of all possible varieties of a given type with this genotype. Specific varietal abilities of order 1, 2, 3..., are defined as interactions from the combined effect of 2, 3, 4... parents in varietal combinations. Genetic effects for varietal value and for the criterion of test are introduced. They allow an expression of the covariance between the value of a genotype according to the testing system and the value of its progeny from random mating in varietal combination. So a general expression of the genetic advance in the varietal value of a population improved by recurrent selection can be given whatever the type of variety and the testing system. The genetic advance is also considered at the level of the varieties. Some examples of prediction formulae for varietal abilities are given for hybrids, synthetics and lines. The problem of prediction of the ability of a genotype to give lines with the best general varietal abilities is also considered.Communication given at the 3rd meeting of the Eucarpia section Biometrics in Plant Breeding, Cambridge, April 4–7, 1978, and in a revised version on the occasion of the Professor Schnell's 65th birthday, Stuttgart, University of Hohenheim, May 19, 1978.     

Impact of plant genetic resources on wheat breeding

This article describes the impact of plant genetic resources on wheat breeding. It defines the important contribution of N.I. Vavilov Institute (St. Petersburg, Russia) to broadening the genetic diversity of new wheat cultivars. Special attention is given to conducting a comprehensive evaluation of intraspecific variability for valuable characters, including: 1) formation of special subcollections, consisting of accessions with useful characters and accessions representing intraspecies diversity for a given character; 2) revealing genetic differences among phenotypically superior accessions; 3) determining a genetic system of intraspecific variability for a given character; 4) formation of a genetic collection; 5) revealing and developing the donors of useful characters. An example using plant height shows that the proposed research approach adequately determines the genetic potential of species and reveals the most effective genes for practical uses. It is assumed that the main sources of genes for breeding Triticum aestivum L. in order of importance will remain: 1) intraspecific diversity of T. aestivum itself; 2) other Triticum species; 3) other genera of the Triticeae Dum. tribe (particularly Aegilops L.); 4) more remote genera of the Poaceae Barnh. botanical family. It is stressed that existing diversity of T. aestivum has been poorly investigated genetically and only partially used by breeders. Properly evaluated, it can provide multiple solutions for traditional and new problems of wheat improvement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genomics-assisted breeding: The next-generation wheat breeding era

Common wheat provides approximately 20% of the total dietary calorie intake of human beings. Recent technological advances in whole-genome sequencing and their application in wheat and its progenitor species provide new opportunities to uncover the genetic variation of wheat traits and to accelerate the traditional breeding (TB) strategies in the context of genomics-assisted breeding (GAB). Integration of TB, marker-assisted selection (MAS) and genomic selection (GS) with high-density SNP markers is expected to accelerate the breeding process and to further enhance genetic gain. With the assistance of the next- or third-generation sequencing technologies and high-throughput phenotyping platforms, GAB can now realistically be considered in the following area: (i) genome sequencing and high-quality assembly to uncover new variations, (ii) whole-genome sequence-based association studies, (iii) gene function (or functional gene) identification and (iv) integration of whole genomic breeding information, utilizing multi-omics data and different breeding strategies. We argue that GAB is becoming the preferred strategy in pursuit of new wheat cultivars with superior traits on high yielding, high nutritional quality, climate-resilience and so on.     

水稻QTL定位在杂种优势理论和杂交稻育种中的应用现状

水稻多数重要农艺性状属于数量性状,因此,数量性状的遗传效应研究对水稻育种具有十分重要的意义。本文就水稻QTL定位在杂种优势基础理论研究中的现状进行了回顾与探讨,同时就定位结果在杂交稻育种中的应用现状展开论述,最后就这些领域的研究进展提出了科学的展望,以期为今后开展杂种优势基础理论研究方式以及杂交育种思路提供一定的帮助和借鉴。     

Achievements and limitations of contemporary common bean breeding using conventional and molecular approaches

Common bean (Phaseolus vulgaris L.) improvement programs have been successful using conventional breeding methods to accomplish a wide array of important objectives. Specific achievements include the extension of range of adaptation of the crop, the development of cultivars with enhanced levels of disease and pest resistance and breeding lines that possess greater tolerance to drought. The most effective breeding method depends on the expression and inheritance of the trait to be selected and the target environment. Many bean improvement programs use molecular markers to facilitate cultivar development. In fact, several recent germplasm releases have used molecular markers to introgress and or pyramid major genes and QTL for disease resistance. Related species (P. coccineus and P. acultifolius) via interspecific hybridizations remain an important albeit long-term source for resistance to economically important diseases. Slow progress has been made in the improvement of traits such as adaptation to low soil fertility and tolerance to high levels of soluble Al in the soil using conventional breeding methods. The inability to directly measure root traits and the importance of genotype × environment interaction complicate the selection of these traits. In addition, symbiotic relationships with Rhizobium and mycorrhiza need to be taken into consideration when selecting for enhanced biological N fixation and greater or more efficient acquisition of soil P. Genomic examination of complex traits such as these should help bean breeders devise more effective selection strategies. As integration of genomics in plant breeding advances, the challenge will be to develop molecular tools that also benefit breeding programs in developing countries. Transgenic breeding methods for bean improvement are not well defined, nor efficient, as beans are recalcitrant to regeneration from cell cultures. Moreover, if issues related to consumer acceptance of GMOs cannot be resolved, traits such as herbicide tolerance in transgenic bean cultivars which would help farmers reduce production costs and decrease soil erosion will remain unrealized.     

Repetitive cycling and simple recurrent selection in traditional barley breeding programs

Summary A critical examination of three representative barley development programs from three barley producing areas of the world reveals that the evolution of each can be explained by the concepts of simple or phenotypic recurrent selection. Typically, each has utilized only 13 to 16 separate genetic sources in their program. Most of the sources were introduced over 50 years ago and have been progressively recombined through a simple recurrent selection process. The time period required for selection, testing, and reincorporation of improved genetic recombinants into the breeding program, or the completion of a cycle of recurrent selection, ranged from 6.5 to 10.5 years. If the major operative force in barley breeding is recurrent selection, then additional attention should be given to increasing the genetic base and reducing the time required to complete cycles of selection.     

Estimation of parental value for varieties used in plant breeding

A method to estimate variety value directly in a plant breeding process is proposed. The approach is based on frequencies of variety progenies succeeding in breeding trials. The number of crossing combinations is demonstrated to estimate parental breeding values (PBV) more effectively than the number of lines. Because of the possibility of significant sexual effects the parental breeding value is estimated by the square mean of the female and male variety breeding values. For adequate PBV estimation, all the varieties tested should involve an equal number of crossing combinations as male and female parents. The Latin square principle can be used for planning such crosses. The results of barley breeding programmes are used as an example for the application of the proposed method. It is shown that the PBV estimates obtained in a current breeding cycle allow the effectiveness of the following cycles to be increased by better planning of the subsequent crosses.     

Feasibility of breeding male-sterile populations for use in developing interpopulation hybrids of pearl millet

Inter‐population hybrids of pearl millet, Pennisetum glaucum (L.) R. Br., have a substantial grain yield advantage over open‐pollinated varieties that makes them an appropriate and economically viable proposition for many African agricultural situations, provided that stable male‐sterile populations can be developed for use as seed parents. The objective of this research was to examine the feasibility of breeding stable male‐sterile populations, using the d₂ dwarf version of Nigerian Composite NCD₂ and the A₄ cytoplasmic‐nuclear male sterility system as a test case. Results showed that two cycles of recurrent selection for sterility maintenance ability led to the development of a fully effective maintainer version of NCD₂. There was no significant difference between the original C₀ cycle bulk and the C₃ cycle bulk (developed from the third and final cycle of recurrent selection) for grain yield and other agronomic traits. The male‐sterile population at the third backcross stage, developed from the maintainer version of NCD₂, had as high a level of stable male sterility as the A¹ system commercial inbred male‐sterile line 841A₁. Thus, it is concluded that with the use of the A₄ cytoplasmic male‐sterile system, it would be possible rapidly to develop a maintainer version of any population without detrimental effects on grain yield and agronomic traits. Male sterility of populations developed from these maintainers will be highly stable, paving the way for their effective utilization as seed parents in breeding inter‐population hybrids.     

Family selection in plant breeding

Summary Plant breeding programmes rarely take explicit practical account of the two sources of genetic variance, namely between and within full-sib families, even though existence of these two sources of variation has long been recognised. This paper refers to inbred and clonal crops, not to outbred, seed-propagated species. Theory suggests that the two variances should be of similar size, sometimes very similar. Good comparisons have never been made because variance within families is laborious to estimate. It is proposed that sets of families be assayed as to means in formal trials and only the best few, judged against standards as having potential for superior segregates, should be exploited thoroughly. The calculation as to approximate equality of genetic variances between and within families is important. The vast majority of families should probably be discarded without further ado, and at considerable economy. Sensible decision-making requires an economic component in order to exploit the trade-off between the cost of the initial trial and families discarded without further cost. The object of this paper is a critical review of practical principles, not a general review of a large and diffuse literature.     

CHA杂种小麦灌浆优势规律研究

以4个CHA杂种及其亲本和CK为材料, 采用数学模型分析、 相关分析、 通 径分析等方法, 研究了CHA杂种灌浆优势及其动态规律和与气象因子的关系, 结果表明 , (1) 4个CHA 杂种籽粒干物质积累动态过程均存在杂种优势, 最终干物质积累均存在 超亲优势, 最终干物质超亲优势形成过程有灌浆全期形成、 灌浆中后期形成和灌浆后期     

A model calculation approach towards the optimization of a standard scheme of seed‐parent line development in hybrid rye breeding

The importance of hybrid rye (Secale cereale L.) breeding has steadily increased over the last decades. This paper presents results of model calculations aiming to optimize the number of candidates, testers to assess combining ability and test locations at each selection stage of a standard scheme of seed‐parent line development. Two variants of the scheme differing in the number of stages and the cycle length are investigated. Optimization criterion is the expected selection gain per year under the restriction of a fixed budget. Prediction of selection gain rests on quantitative–genetic and economic parameters estimated from breeders’ data. Optimization covers different genetical and economical situations. Results show that the optimum number of testers to assess combining ability depends on the relative amount of dominance variance. The efficiency of a breeding scheme strongly increases with decreasing cycle length. A larger budget should mainly be used to increase the number of candidates at all selection stages. Recommendations for practical breeding schemes are given. We conclude that model calculations are a valuable tool for the optimization of breeding schemes.     

Participatory plant breeding with maize in Mexico and Honduras

Maize is a staple food crop in many developing countries. However, if seven major maize producing countries are excluded from this group, data indicate that only 34% of the maize area is planted with improved seed despite considerable effort invested in maize breeding. This has led researchers to investigate other options, such as farmer-participatory plant breeding, for delivering the benefits of plant breeding knowledge and technology to farmers in developing countries. This paper describes short-term results from participatory maize breeding studies in Mexico and Honduras. Results from three selection cycles in Mexico suggest that stratified mass selection without pollination control, with selections carried out by researchers in farmers' fields, may be effective at improving yield in farmers' local varieties. In Honduras, mass selection with pollination control, where selections were done by collaborating farmers in their own fields on their own varieties, showed trends (non-significant) towards yield improvement. Farmer selection seemed to offer the greatest yield benefit over experiment station selection on the farm with the lowest yield potential, suggesting that farmer-participatory approaches may be most advantageous in marginal environments where experiment station conditions differ most dramatically from farmers' conditions. These studies highlighted the importance of seed systems knowledge in designing participatory plant breeding programs. For cross-pollinated crops, they also highlighted the need to balance progress from selection and demands on farmers' time and labor in choosing breeding methods. Further work is needed to investigate farmer-participatory breeding approaches that can address post-harvest traits. This revised version was published online in August 2006 with corrections to the Cover Date.     

Subset selection in plant breeding practive

Summary Selection decisions in variety testing should partly be based on statistical motives. Useful tools for this are subset selection procedures. These procedures can also be used when the performed experiment has an incomplete block design or when a series of regional trials is studied. Various selection rules serve different selection goals, but they all need so-called selection constants. Often, these constants have to be approximated by computer simulation. For this simulation, and also for the execution of the selection rules, software has been developed and is available. Some practical adjustments and modifications of subset selection in plant breeding practice are proposed. Finally, a case study of selection in sugar beet is presented.     

中国超级杂交稻育种研究的进展与策略探讨

介绍了中国超级杂交稻育种的目标,技术路线和育种理论,综述了中国超级杂交稻育种研究的概况,以及在亲本选育,品种选育和分子育种技术等方面取得的进展,阐述了通过加强水稻种质资源的创新与利用,扩大亲本遗传差异,提高水稻生物学产量,改善水稻生理机能等技术策略,选育出综合性状优良的超级杂交稻新组合,进一步提高中国超级杂交稻产量水平     

Decentralized selection and participatory approaches in plant breeding for low-input systems

Heterogeneous environments make it difficult to apply consistent selection pressure because often it is difficult to identify a single or a few superior genotypes across all sets of conditions. However, when the target system is characterized by heterogeneity of environmental stress, varieties developed in high-yielding conditions may fail to satisfy farmers’ needs. Although this type of system is often found in marginal environments of developing countries, heterogeneous environmental conditions are also a feature of organic and low-external-input systems in developed countries. To meet the needs of these systems, breeding programs must decentralize selection, and although decentralized selection can be done in formal breeding programs, it is more efficient to involve farmers in the selection and testing of early generation materials. Breeding within these target systems is challenging, both genetically and logistically, but can identify varieties that are adapted to farming systems in marginal environments or that use very few external inputs. A great deal has been published in recent years on the need for local adaptation and participatory plant breeding; this article reviews and synthesizes that literature.     

水稻籼爪交和粳爪交杂种优势的研究Ⅱ.农艺性状的杂种优势分析

研究了籼爪交和粳爪交杂种在长沙、三亚的农艺性状和干物质产量的杂种优势.在长沙的籼爪交杂种在结实率和每穗实粒数方面具有负向超亲优势,在每穗实粒数、结实率、单株粒重和理论产量方面存在负向对照优势,其余性状均为正向优势;粳爪交杂种在千粒重和结实率方面存在负向超亲优势,其余性状为正向超亲优势, 在始穗期、秆高和单     

Participatory plant breeding research: Opportunities and challenges for the international crop improvement system

This paper describes the current state of international plant breeding research and explains why the centralized global approach to germplasm improvement that was so successful in the past is today being transformed by the incorporation of decentralized local breeding methods designed to better incorporate the perspective of end users into the varietal development process. It describes international breeding efforts for major crops and identifies factors that have contributed to the success of the international breeding system; discusses shortcomings of the global approach to plant breeding and explains why future successes will depend critically on researchers' ability to incorporate the knowledge and preferences of technology users; reviews a number of farmer participatory research methods that are currently being tested by plant breeding programs throughout the developing world; describes synergies that can potentially be achieved by linking centralized global and decentralized local breeding models; and discusses technical, economic, and institutional challenges that will have to be overcome to integrate end user-based participatory approaches into the international plant breeding system. This revised version was published online in August 2006 with corrections to the Cover Date.     

Organic varieties for cauliflowers and cabbages in Brittany: from genetic resources to participatory plant breeding

Plant breeding for organic agriculture (OA) was stimulated when it came under the European Organic Agriculture Regulation (2092/91) in 2004. In Brittany, the need for specific varieties for organic farming arose early for the Brassica species because of the unsuitability of most of the modern varieties to the principles of OA. Moreover, the private sector of plant breeding finds it economically difficult to satisfy the demands of OA. The aim of the present study is to provide varieties and seed for organic farmers for two vegetable Brassica crops, and to show how genetic resources can contribute to this purpose in the framework of a Participatory Plant Breeding (PPB) programme. The emergence of PPB in Brittany is the result of several concomitant and favourable circumstances: the will of the professionals (represented by IBB, Inter Bio Bretagne), their organization (an experimental station, the PAIS, Plateforme Agrobiologique d’IBB à Suscinio), the research initiative in INRA and the availability of genetic resources. From genetic resource observations, our experience showed several breeding situations: reviving a traditional activity (Roscoff cauliflower and local cabbages), extending tradition (autumn cauliflower), diversifying production by new introductions (coloured cauliflowers), and creating new forms of population varieties (broccoli and coloured cauliflowers). Farmers have taken charge of population breeding by mass selection and the PAIS, with INRA scientific support, has taken up innovative selection and the improvement of varieties completing the farmers’ initiatives. The PAIS remained the central point for information and for providing the seed for trials. Seed production will be managed in a collective way. Until now, the exchange of seed remained an experimental dimension of PPB. French seed legislation represents a limitation on the development of seed exchange by PPB.