Combining ability and heterosis under pest epidemics in a broad-based global wheat-breeding population

Wheat breeders rarely apply population improvement schemes or select parental sources according to combining ability and heterotic patterns. They rely on pedigree selection methods for breeding new cultivars. This experiment was undertaken to assess the advantages of using diallel crosses to define combining ability and understand heterosis in a broad‐based wheat‐breeding population across different environments affected by yellow rust. Sixty‐four genotypes derived from a full diallel mating scheme were assessed for grain yield in two contrasting growing seasons at two locations for two consecutive years. Parental genotypes showed significant combining ability for grain yield that was affected by yellow rust and genotype‐by‐environment (GE) interactions, both of which affected heterosis for grain yield. Significant GE interactions suggested that decentralized selection for specific environments could maximize the use of this wheat germplasm. Cultivar effects and specific heterosis were the most important factors influencing grain yield. Some crosses capitalized on additive genetic variation for grain yield. This research shows the power of available quantitative breeding tools to help breeders choose parental sources in a population improvement programme.     

Comparison of intra- and inter-pool crosses in faba beans (Vicia faba L.). II. Genetic effects estimated from generation means in Mediterranean and German environments

Genetic diversity between parents is important for hybrid breeding and for maximum usefulness of a cross in pure line breeding. However, wide crosses may suffer from poor adaptation in the target environments and recombination losses owing to disruption of favourable epistatic gene combinations. In this study we investigated the importance of various gene effects for different traits in the parents and generations F¹ to F⁵ derived from 99 intra- and inter-pool crosses among 20 lines of the Minor, Major, and Mediterranean germplasm pools of faba bean in Mediterranean and German environments. Yield performance of parental inbreds and progenies of crosses in different selfing generations was high in the region of adaptation of the respective germplasm pool. Heterosis for yield was greatest in interpool crosses of Minor × Mediterranean germplasm, amounting to 106% in Mediterranean and 72% in German environments. Interpool crosses exhibited significantly greater heterosis compared with intrapool crosses in both mega-environments. Generation means analysis revealed the importance of additive gene effects and dominance × dominance epistasis in Mediterranean and German environments. Dominance effects and additive × additive epistasis for yield were negligible in most crossing groups. Since intrapool crosses of Mediterranean germplasm in Mediterranean environments and crosses of Minor and Major germplasm in the German environments were most promising, we suggest crosses among adapted germplasm for hybrid breeding and for establishing new base material in line breeding in faba bean.     

Linkage analysis among loci for RAPDs, isozymes and some agronomic traits in Brassica campestris L.

Common bean, Phaseolus vulgaris L. is intercropped or relay cropped with maize in many Andean highlands of Colombia and Peru. Breeding beans for the target multiple cropping systems is essential for the development of productive and sustainable agriculture for the Andean smallholders. Outline of the breeding programme should follow the farming system approach with the establishment of on-farm trials and early farmers involvement. Bean breeding is oriented to minimize intercrop competition and to stabilize complementarity with maize. Genetic traits needed for improved varieties are divided as follows : traits not interacting with the cropping systems, traits specific to intercrops and traits related with socioeconomic and seed quality aspects. Screening, prebreeding and recombination nursery are better made under sole cropping while varietal improvement and on-farm trials are conducted under the target multiple cropping systems. Breeding schemes may involve recurrent, pedigree and bulk hybrid selection. The given application concerns the genetic improvement of P. coccineus, P. polyanthus and interspecific hybrids of P. vulgaris for both simultaneous and relay intercropping in Colombia and Peru. Earliness, cold tolerance, resistance to fungus diseases (mainly Ascochyta leaf blight and anthracnosis) and seed yield potential were the major objectives of the bean improvement programme. Priority has been given to the exploitation of the large diversity available in the secondary gene pool of common bean. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Phenotypic recurrent selection in ideotype breeding of pinto beans

Summary Plant growth habit (type) plays a major determining role in the acceptance of a dry bean cultivar by commercial growers. Under the threat of wet fall conditions in the midwestern U.S., growers show a preference for upright plant types-I and II over the more prostrate type-III growth habit of commercial pinto cultivars. The prostrate habit creates considerably more risk of harvest losses and potential of white mold (Sclerotinia sclerotiorum) development during a wet growing season.The breeding strategy being utilized to develop better adapted pinto bean cultivars for the humid midwest is based on the concept of ideotype breeding which has been successfully applied to small seeded navy and black beans. A system of phenotypic recurrent selection using S₁ selection is being followed in order to recombine desirable traits from two diverse germplasm pools. One germplasm pool possesses the desirable architectural plant form and disease resistance traits of the small-seeded types while the medium-seeded germplasm source possesses the desirable seed size, shape and color characteristics of the pinto class. Since a repulsion phase linkage appears to exist between type-II architecture (architype) and medium seed size (40 g/100 seeds), recurrent selection is shown to be the most effective procedure for breaking up undesirable linkage groups and for increasing the frequency of desirable genes, thus enhancing the chance for the desirable genetic recombinations to occur.Journal Article No. 11667 of the Michigan Agricultural Experiment Station.     

Growth habit and gene pool effects on inheritance of yield in common bean

Summary To satisfy farmer and consumer preferences, breeding efforts to increase yield potential in common bean must take into account the interrelated effects of growth habit, seed size, maturity, and gene pool on yield expression in segregating populations. To examine the relationships among these traits, a genetic study was conducted to determine the effect of growth habit on yield and seed size in crosses among five bean lines from diverse gene pools. Two parental bean lines had determinate, type I growth habits and large seed size typical of the Neuva Granada-Andean gene pool. Two other lines were tropical Mesoamerican types with type II growth habits and small seed size; and the fifth line, G13625, a landrace of the Jalisco gene pool from the Mexican highlands, had a type IV climbing growth habit and medium seed size. Individual F₂ plants from each cross and parental lines were evaluated for growth habit and yield component traits under high input field conditions. The following season, the evaluations were repeated on random F₃ plants. Of the five parental lines, only G13625 showed significant GCA effects for yield in both the F₂ and F₃ generations. Improved yielding ability of G13625 progeny was associated with an increased expression of climbing bean growth habit traits: guide length, climbing ability, node number on main stem, and plant height. Crosses between Andean x Mesoamerican and Andean x Jalisco genotypes, as well between growth habit type I (Andean x Andean) and between type II (Mesoamerican x Mesoamerican) had very low parent-offspring heritability values for yield. Yield heritability was only significant for crosses between Mesomerican x Jalisco gene pools. An apparent simple genetic control of growth habit modification towards semi-climbing and climbing types is proposed as the major reason for increased yields in these crosses. No genetic linkage between genes controlling growth habit and seed size was detected which might restrict the development of high yielding large-seeded type II lines.     

Breeding tepary bean (Phaseolus acutifolius) for drought adaptation: A review

Tepary bean (Phaseolus acutifolius A. Gray) is a relatively higher drought-tolerant crop than common bean (P. vulgaris), serving as genetic resource for food and genetic enhancement of related legumes. Tepary bean production is hampered by cultivation of low yielding and abiotic stress-susceptible cultivars. Targeted selection of agronomic, physiological and biochemical traits that maximizes yield gains using Phaseolus gene pool is useful to develop stress-tolerant and high-performing genotypes. The objective of this review is to provide breeding progress made regarding tepary bean improvement for drought adaptation. Agronomic, physiological and biochemical traits utilized for selection of drought-tolerant genotypes are highlighted. Genetic and genomic resources developed for tepary bean or closely related species such as common bean useful for genetic analysis and breeding are discussed. Opportunities and challenges to facilitate breeding of tepary bean genotypes with improved abiotic stress adaptation are highlighted. This will enable development of drought-tolerant tepary bean genotypes targeting selection of agronomic, physiological and biochemical traits. Use of genetically related and complementary Phaseolus species and marker-assisted selection method is key to developing drought-tolerant genotypes.     

Farmers’ participation and breeding for durable disease resistance in the Andean region

In the Andean region, the Preduza project and its partners combined breeding for durable disease resistance using locally adapted cultivars and farmer participatory methods. The approach taken resembles participatory variety selection (PVS). Farmers participated in the selection of advanced materials, rather than finished cultivars. This paper describes this approach and reports experiences with farmers–breeders collaboration. As breeders involved farmers as participants, they learned more about the most important criteria of male and female farmers for preferred cultivars in the marginal environments of Andean cropping systems. This approach encouraged the use of locally adapted cultivars (often landraces), made the breeders less dependent on foreign materials, and has resulted in selection and development of new wheat, barley, common bean, quinoa, potato and maize cultivars. Breeding programmes based on crossing locally adapted cultivars followed by selection by the breeders in the early phases of the breeding programmes and by participatory selection with the farmers in the more advanced stages of the breeding programmes appeared successful. It became clear that breeders must be well acquainted with the farmer preferences such as the requirements for specific agronomic, storage, processing and marketing traits. Over a period of five years the centralized formal breeding approach predominantly based on material produced by the international institutes was replaced by decentralized breeding approaches based largely on local germplasm with extensive farmer participation.     

Combining ability of common bean (Phaseolus vulgaris) genotypes for root traits across diverse environments

Root system architecture is important for common bean (Phaseolus vulgaris) adaptability to diverse environments. Beans employ complex adaptive root mechanisms for coping with multiple stresses in production environments. Understanding genetic control of root traits is central to improvement of common bean for adaptation to marginal environments. The objectives of this study were to (i) determine combining ability of root and agronomic traits and (ii) estimate the heritability and genetic correlation of root and agronomic traits in common bean. Four bean lines with superior root traits were crossed with four locally adapted varieties in a North Carolina II mating scheme to generate 16 crosses. The 16 F₁s were selfed and advanced to F₂ generation. Eight parents and their F₂ progenies were evaluated in an alpha-Lattice design with two replications. General and specific combing ability mean squares were significant (p ≤ .05) for all traits measured. General predictability ratios ranged from .47 to .68 across locations suggesting that both additive and non-additive gene action modulate root traits and seed yield. Positive and significant (p ≤ .05) phenotypic and genetic correlations revealed significant association between root traits and yield. Moderate to high heritability estimates of between .43 and .67 were realized. Such estimates point to possible deployment of a successful selection programme. Genotype AFR398 displayed significant positive GCA effects among its crosses for both root and agronomic traits hence a potential candidate genotype for inclusion in a bean genetic improvement programme for marginal environments.     

Phenotypic variation in a core collection of common bean (Phaseolus vulgaris L.) in the Netherlands

Forty accessions, forming a core collection of mainly bush type of the common bean (Phaseolus vulgaris L.) germplasm in the Netherlands, were evaluated for 14 qualitative and quantitative traits at the Agricultural University, Wageningen (WAU), the Netherlands in 1992. These and an additional 117 Dutch accessions, mainly collected in private home gardens, were also evaluated for phaseolin seed protein pattern, and morphological and agronomic traits at the International Center for Tropical Agriculture (CIAT, Spanish acronym), Cali, Columbia between 1987 and 1997. Multivariate and principal component analyses at both WAU and CIAT indicated existence of one large group with no discernable patterns among Dutch common bean collections of landraces, garden forms and cultivars. However, when phaseolin, an evolutionary, biochemical marker, was used as an initial classification criterion followed by use of morphological markers, the two major gene pools; Andean and Middle American with two races in each (Chile and Nueva Granada in Andean, and Durango and Mesoamerica in Middle American) were identified. The Andean gene pool was predominant (136 of 157 accessions), especially the race Nueva Granada (126 accessions) characterized by the bush determinate growth habit type I and T phaseolin. The new core collection comprised 31 accessions. Bean races Chile, Durango, and Mesoamerica were represented by 10, 7, and 14 accessions, respectively. Of the 9 French or snap bean accessions six possessed characteristics of race Mesoamerica and three belonged to Durango race. Occurrence of these and a large number of other recombinants strongly suggested considerable hybridization and gene exchange between Andean and Middle American gene pools, thus blurring the natural boundaries and forming a large single group of common bean germplasm in the Netherlands. The inter-gene-pool recombinants of both dry and French beans should be of special interest to breeders for use as bridging-parents for development of broad-based populations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geographical distribution of the DL1 and DL2 genes causing hybrid dwarfism in Phaseolus vulgaris L., their association with seed size,and their significance to breeding

Summary Dwarlism in F₁ hybrids has been observed in over 100 crosses of dry beans (Phaseolus vulgaris L.) at the Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia. In each cross, one parent always had small seeds and the other parent either medium or la ge ones. This apparent incompatibility between the two groups of germplasm was controlled by two complementary, dominant genes: DL₁ and DL₂. Smallseeded bean lines carried gene DL₁ and originated in Brazil, Colombia, Guatemala, and Mexico; medium for large-seeded bean lines carried gene DL₂ and were from Bolivia, Brazil, Chile, Colombia, Turkey, The United States, and West Germany. Thes two genes have probably played an important role in the evolution of dry bean forms of different seed sizes by serving as a genetic barrier or isolating mechanism, thus limiting free genetic recombination between the two germplasm groups.Apparent differences in the adaptiveness and yielding ability of the two groups of bean germplasm, smallys, medium- and large-seeded, and some breeding implications for manipulation of the genes causing F₁ hybrid dwarfism were also discovered.     

Inheritance of angular leaf spot resistance in common bean line BAT 332 and identification of RAPD markers linked to the resistance gene

The existence of genetic variability for angular leaf spot (ALS) resistance in the common bean germplasm allows the development of breeding lines resistant to this disease. The BAT 332 line is an important resistance source to common bean ALS. In this work we determined the inheritance pattern and identified RAPD markers linked to a resistance gene present in BAT 332. Populations F₁, F₂,BCs and BCr derived from crosses between BAT 332 and cultivar Rudá were used. Rudá is a commercial cultivar with carioca type grains and susceptible to ALS. The resistance of BAT 332 to race 61.41 of the pathogen was confirmed. Segregation analysis of the plants indicated that a single dominant gene confers resistance. For identification of RAPD markers linked to the resistance gene, bulk segregant analysis (BSA) was used. Two RAPD markers,OPAA07₉₅₀ and OPAO12₉₅₀, linked in coupling phase at 5.10 and 5.83 cM of this gene, respectively, were identified. These molecular markers are important for common bean breeders and geneticists as source of genetic information and for marker assisted selection in breeding programs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selection potential for seed yield from intra- and inter-racial populations in common bean

Common bean populations from crosses between lines of different races are thought to be more promising for selection of high yield potential than those from intra-racial crosses. Three distinct diallel crosses were made to test this hypothesis and to determine the possibility of substituting diallel crosses for multivariate techniques that estimate genetic divergence. The crosses were between races Mesoamerica × Mesoamerica, Mesoamerica × Durango and Jalisco, and Mesoamerica × Nueva Granada. The parents and the resulting F₄ populations were evaluated at Lavras-MG, Lambari-MG and Patos de Minas-MG, Brazil. The diallel analysis of seed yield was done and the genetic divergence estimated by Mahalanobis distance. Estimates of general and specific combining ability indicated that some inter-racial populations were more promising for selection to increase seed yield than intra-racial populations. However, due to their undesirable seed color and size, and growth habit, especially in a short term breeding program, the chances of obtaining high yielding lines with an acceptable bean is reduced. Genetic divergence was not a good measure to choose the parents because usually, the most divergent groups included were not adapted lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

Genomics,genetics and breeding of common bean in Africa: A review of tropical legume project

Common bean (Phaseolus vulgaris L.) is an important legume crop worldwide. The International Centre for Tropical Agriculture (CIAT) and its national partners in Africa aim to overcome production constraints of common bean and address the food, nutrition needs and market demands through development of multitrait bean varieties. Breeding is guided by principles of market‐driven approaches to develop client‐demanded varieties. Germplasm accessions from especially two sister species, P. coccineus and P. acutifolius, have been utilized as sources of resistance to major production constraints and interspecific lines deployed. Elucidation of plant mechanisms governing pest and disease resistance, abiotic stress tolerance and grain nutritional quality guides the selection methods used by the breeders. Molecular markers are used to select for resistance to key diseases and insect pests. Efforts have been made to utilize modern genomic tools to increase scale, efficiency, accuracy and speed of breeding. Through gender‐responsive participatory variety selection, market‐demanded varieties have been released in several African countries. These new bean varieties are a key component of sustainable food systems in the tropics.     

春玉米主要穗部性状配合力及遗传参数分析

选育具有高配合力的优良自交系是育种工作的基础,为更好的了解北方早熟春玉米区玉米(Zea mays L.)自交系的配合力表现和性状遗传规律,为杂交种组配和种质改良提供亲本和育种策略,选用在生产及种质改良中常用的12个玉米自交系,按双列杂交模式设计组配杂交组合, 以完全随机区组设计进行试验,对主要穗部性状进行鉴定,按照改良griffingⅣ 双列杂交分析方法对数据进行处理。试验表明一般配合力和特殊配合力效应在亲本间存在显著差异。穗粗、容重、籽粒行数等性状遗传力较高,主要受加性效应控制。而产量、穗重主要受非加性基因控制,易受环境因素影响。K12、丹340和黑选169对提高产量的效应明显,P138在提高后代容重方面优势显著,含有地方种质的早熟材料龙抗118、大粒黄可以显著提高后代穗部长度。     

Sources of resistance to angular leaf spot (Phaeoisariopsis griseola) in common bean core collection, wild Phaseolus vulgaris and secondary gene pool

Angular leaf spot (ALS) is one of the most devastating diseases of common bean (Phaseolus vulgaris L.) in tropical and subtropical countries. The causal fungus, Phaeoisariopsis griseola(Sacc.) Ferr. is highly variable and a diverse source of resistance genes is required to manage this disease. We evaluated a common bean core collection,primary and secondary gene pools and lines derived from inter-specific crosses of P. vulgaris and P. coccineus or P. polyanthus (secondary gene pool) for resistance to angular leaf spot. Of the 1441 accessiones in the core collection, only 2.2% were resistant to both Andean and Mesoamerican races of P. griseola, 28% were resistant only to Andean and 9% to Mesoamerican races. Of the 32 resistant accessions, 68%originated from Bolivia, Colombia,Guatemala and Mexico. More accessions from these countries should be examined for P. griseola reaction. Very few wild P. vulgaris accessions (4%), were resistant to ALS. In contrast, high levels of resistance (62%) were found in the secondary gene pool. Among the 1010 lines from inter-specific crosses, 109 lines were highly resistant. These genotypes from the primary and secondary common bean gene pools resistant to Andean and Mesoamerican races of P. griseola offer a potential for developing broad and durable ALS resistance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heterosis and combining ability of seven maize germplasm populations

Understanding the combining ability and heterosis of available germplasm is a prerequisite for successful maize improvement and breeding. The objectives of this study were to analyze the combining ability and heterosis of seven representative maize germplasm populations, and further, to evaluate their potential utility in germplasm improvement. A total of 21 crosses were made among these seven populations in a complete diallel without reciprocals. The parental populations and 21 crosses were evaluated for days to silking (DS), ear height (EH), and grain yield (GY) in the Northeast and Yellow and Huai River maize growing areas in China in 2012. Csyn5, Csyn7, Cpop.11, and Cpop.12 had desirable general combining ability (GCA) effects for DS and EH in both the Northeast China mega-environment (NCM) and the Yellow and Huai River Regions of China mega-environment (YHCM). Cpop.11 possessed a favorable GCA effect for GY in the NCM, as did Csyn5, Cpop.17, and Cpop.18 in the YHCM. Csyn6 and Csyn7 exhibited tremendous yield-enhancing potential in both mega-environments. Additionally, six combinations including Csyn7 × Csyn6, Csyn5 × Csyn6, Cpop.11 × Cpop.18, Cpop.12 × Cpop.17, Csyn7 × Cpop.17, and Csyn5 × Csyn7 exhibited better specific combining ability effects for GY, yield performance, and mid-parent heterosis in the appropriate mega-environment. These results indicated that the seven populations would be very useful for the improvement of related agronomic traits, and the six candidate combinations possessed great potential for further improvement and utilization.     

The Nutritive Value and Yield of Alfalfa in Relation to Nitrogen Fertilization on Sulphur Industry Reclaimed Lands

The aim of this study was to determine the direction and magnitude of change in morphological and agronomical characters of spring barley ( Hordeum vulgare L.) in Germany over a period of 80 years and to assess the value of various strategies for further crop improvement. Old and new two-rowed cultivars, eight in each case, were tested together with their F₂ intra-group diallel crosses in a field trial at Braunschweig-Völkenrode in 1994. New parents and their crosses showed a higher dry matter grain and total biomass yield, a lower plant height, and a higher harvest index as compared to the respective old germplasm. The annual genetic gain in grain yield was estimated at 0.15%. The superior grain yield of the new germplasm was attributable to the higher number of ears per plant and the larger kernel weight. The F₂ mid-parent heterosis in grain yield was 7.6 and 7.2 % for the old and new crosses, respectively. The differences between the two types of crosses were nonsignificant except for the higher heterosis for plant height in the new crosses. General combining ability effects were significant for all characters in both types of crosses, whereas specific combining ability effects were significant in a few cases only. In the new crosses, a significant positive correlation was found between grain yield and straw yield (r = 0.52), whereas no such association was observed between grain yield and harvest index. For further gain in grain yield, improvement of the straw yield is more promising than increasing harvest index.     

水稻株型的研究进展

水稻第三次产量的突破将可能产生于理想株型与优势利用相结合的超高产育种，笔者综述了水稻理想株型的形态特征、株型的相关栽培生理、株型遗传与育种、与植株形态建成相关的分子生物学等方面的研究现状，并讨论了存在的问题，展望了今后的研究发展方向。     

Potential for wild species in cool season food legume breeding

Wild species which are crossable to cultivated pea, lentil, and chickpea have been collected and are maintained in major germplasm collections throughout the world. Wild species of Vicia crossable to the cultivated faba bean have not been found. The primary, secondary, and tertiary gene pools of the cool season food legumes represent potential genetic diversity that may eventually be exploited in cultivated types to overcome biotic and abiotic stresses. Technical difficulties in obtaining hybrids beyond those within the primary gene pool is a major obstacle. Reproductive isolation, embryo breakdown, hybrid sterility, and limited genetic recombination are major barriers to greater use of wild germplasm. Conventional crossing has been successful in producing interspecific hybrids in Lens, Cicer and Pisum and those hybrids are being evaluated for desired recombinants. In vitro culture of hybrid embryos has been successful in overcoming barriers to wider crosses in Lens. The successful transfer of genes from wide sources to cultivated types can be assisted by repeated backcrossing and selection designed to leave behind undesired traits while transferring genes of interest. Molecular marker assisted selection may become a valuable tool in the future use of wild species. In general, too little is known about the possible genetic variation available in wild species that could be valuable in developing resistance to biotic and abiotic stresses. Current efforts on the use of wide hybridization in the cool season food legumes are reviewed and discussed.