Combining ability for yield and plant phenology in plantain-derived populations

Genetic enhancement of Musa spp. has aimed at producing hybrids with high yield, short stature, fast crop cycling, and disease resistance through interspecific and interploidy crosses. Progeny testing for parental selection has seldom been carried out in Musa and little is known on combining ability and heterosis in this species. A 5 × 5 factorial mating design was used to estimate components of phenotypic variance in 4 x-2 x hybrid populations and to determine the combining ability of their progenitors for yield and associated traits. General combining ability was much greater than specific combining ability for these traits, and, therefore, only little recombinative heterosis could be expected upon crossing. Thus, the 4 x-2 x breeding scheme should aim to accumulate favourable alleles in 4 x and 2 x clones through recurrent selection. Such clones could be used per se or in crosses aimed at restoring the seedlessness character in the progeny due to female sterility in a triploid background. This revised version was published online in August 2006 with corrections to the Cover Date.     

Predicting breeding values of spring barley accessions by using the singular value decomposition of genetic similarities

As pedigree information among parental lines is often incomplete, selection response can be enhanced if a matrix containing genetic similarities is used in the mixed model equations (MME) to predict breeding values. However, a low number of molecular markers may cause this matrix to be singular. This study was conducted to determine if breeding values are still accurate when a singular value decomposition of genetic similarities was performed setting negative singular values to zero. Two‐year data for four traits of 152 spring barley accessions, which were analyzed by 23 SSR markers, were used in the prediction of breeding values. In general, similar values of Akaike Information Criteria and of overall standard error of difference and a Spearman rank correlation coefficient between breeding values ranging from 0.92 to 0.99 were obtained independent of whether the prediction was based on a singular value decomposition of genetic similarities or not. In conclusion, the singular value decomposition of genetic similarities appears to be a suitable method in the case of singular matrices.     

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.     

On the number and size of cross combinations in a breeding programme of self-fertilizing crops

Summary The number and size of crosses in a breeding programme were discussed to the conclusion that the number of crosses rather than the size of a cross should be increased with a given total population size. The advantage due to this manipulation, however, is relatively small when such genotypes as improved for many (twenty-five or more) loci are to be obtained, or when a high proportion (around 0.1 or more) of available combinations have the potentiality of releasing the objective genotypes. In such a case, the ease with which crossing and cultivation can be carried out becomes the decisive factor.     

Low level of selfing found in a sample of crosses in Australian sugarcane breeding programs

In sugarcane breeding programs, parents used in crosses are classified as male or female based on relative amounts of viable pollen produced. Usually the ‘female’ parent produces some pollen, albeit at a lower level than the ‘male’ parent. The possibility of selfing and associated problems have long been recognised by breeders. A high level of selfing may seriously bias estimates of breeding value of parents and affect the reliability of family means for identifying superior crosses. However, there is no reliable information reported indicating the level to which selfing is occurring in sugarcane crosses. The level of selfing was evaluated in eight Australian sugarcane crosses using RAPD markers. The crosses were selected as exhibiting variable levels of performance, as judged by measurements of commercial cane sugar (CCS), cane yield (TCH) and sugar yield (TSH) in plots consisting of random progeny clones. Five to eight male-specific RAPD bands were identified for each cross and used to screen twenty-eight to thirty-eight progeny from each cross. Selfed progeny were identified in each cross on the basis of absence of any male-specific RAPD bands after screening with at least 5 such RAPDs. Levels of selfing ranged from 0 to17.6%, with most of the crosses exhibiting zero or low levels of selfing. Although only a limited number of sugarcane crosses have been studied, this survey suggests that unwanted selfing is not a significant problem in the Australian sugarcane breeding program. This revised version was published online in July 2006 with corrections to the Cover Date.     

细胞质雄性不育系在大豆常规育种中的应用研究

提高育种效率是育种家追求的育种手段之一,大豆细胞核雄性不育系已被应用于轮回选择育种中,但细胞质雄性不育系能否应用于常规大豆育种程序还未曾有报导。此研究以13个细胞质雄性不育系和9个恢复系配制15个杂交组合,利用苜蓿切叶蜂授粉,通过对其后代的选择与鉴定,选育出4个高产、优质大豆新品系。探讨了该方法的育种效率、组合选配与后代选择问题以及杂种优势与后代表现的关系。研究结果显示,该方法能显著提高育种效率,为细胞质雄性不育系在常规大豆育种中的应用开辟了新的途径。     

Number of crosses and population size for participatory and classical plant breeding

In the breeding of self-pollinating crops, crossing creates variation upon which selection is exerted. If the value of crosses cannot be predicted then this uncertainty means that many crosses need to be made. However, since there is a limit to the capacity of a breeding programme, more numerous crosses result in each cross having a small population size, fewer progenies in later generations and a lower probability of recovering good genotypes from each cross. Published theory on the optimum number of crosses in a plant breeding programme, for a predominantly self-pollinating crop, usually assumes that all crosses are equal value. This overestimates the number of crosses required. When the optimum size of a population in a favourable cross is considered, theory predicts that very large populations are desirable. The required population size is even larger if linkage of loci controlling different traits is also considered. Hence, in an inbreeding crop, one possible strategy is to select a small number of crosses that are considered favourable and produce large populations from them to increase the probability of recovering superior genotypes. In an out breeding crop, the analogy is a few composites with large population sizes. This low-cross-number strategy is ideally suited to the particular constraints and advantages of participatory plant breeding. Such an approach, although not essential, may still be advantageous in classical breeding. When a breeding programme is based on few crosses, which parents are chosen is crucial and farmer participatory methods are highly effective in narrowing the choice. Modified bulk population breeding methods, and recurrent selection are desirable strategies in the participatory plant breeding of self-pollinating crops when combined with a low-cross-number approach. This revised version was published online in August 2006 with corrections to the Cover Date.     

An efficient method to produce segregating populations in quinoa (Chenopodium quinoa)

Quinoa offers a promising alternative for staple food, considering its outstanding nutritional value and tolerance to abiotic stresses. To develop breeding programmes in quinoa, a reliable crossing method for increasing the genetic variation is required. In the following study, we aimed to develop segregating populations in quinoa. We tested the efficiency of three different crossing methods (hand emasculation, warm water emasculation and no emasculation). Moreover we developed a two-stage selection strategy based on morphological traits and molecular markers for the selection of hybrid plants. We reported hand emasculation to be the most efficient crossing method, followed by warm water emasculation and no emasculation. Our results demonstrated that crosses in quinoa can be successfully performed, despite its complicated flower structure and high self-pollination rate. Additionally, we developed 30 segregating populations from crosses between accessions of different origins with varying phylogenetic relationship, which offers a promising perspective for quinoa breeding programmes in the future.     

Proof of concept to unmask the breeding value of genetic resources of barley (Hordeum vulgare) with a hybrid strategy

Broadening the genetic base of elite breeding programmes is crucial for further breeding success. The absence of major adaption genes, however, often masks the grain yield breeding value of genetic resources. We assessed the ability of a hybrid strategy to provide unbiased performance estimates of 21 barley genetic resources. By crossing them to elite tester lines, 25 three-way hybrids were produced and evaluated together with a part of their parents and eight elite hybrids for important agronomic traits in replicated field trials in four environments. The phenotypic data analyses revealed that the hybrid strategy facilitated to identify promising resources by substantially improving lodging resistance. Combining genotypic data for 5,562 SNPs with the phenotypic data highlighted the potential to boost the diversity of the elite breeding pool via targeted introgression of genetic resources into the male and female heterotic pools. We propose an application of the hybrid strategy for genetic resources of entire genebank collections and to use genome-wide predictions to support a targeted choice of accessions with high value for barley breeding.     

鲜食葡萄杂交后代果肉质地表型遗传分析

为得到参试品种果肉脆度的遗传传递力指数和估算组合传递力及狭义遗传力,用‘瑰宝’作测试品种,计算每个参试品种的遗传传递力指数,用亲子回归系数估算法,计算不同组合脆肉性状的组合传递力和狭义遗传力。统计分析结果表明：‘瑰宝’作父本时,3个品种的脆肉性状遗传传递力指数为‘秋红’最大,‘奥山红宝石’次之,‘玫瑰香’最小;‘瑰宝’作母本时,其后代果肉脆度与父本关系较大,7个品种的脆肉性状遗传传递力指数从大到小依次为‘秋红’、‘皇家秋天’、‘粉红太妃’、‘粉红葡萄’、‘无核白鸡心’、‘达米娜’、‘玫瑰香’;通过不同杂交组合的组合传递力比较发现,软肉品种和特脆品种杂交＞脆肉品种和较脆品种杂交＞较脆品种和软肉品种杂交,亲子回归系数估算,葡萄脆肉质地的狭义遗传力h²＝0.9816,说明脆肉性状遗传能力较强。葡萄品种脆肉性状的遗传力和杂交组合传递力的估算对葡萄育种选择选配亲本有指导意义。     

Wheat breeding assisted by markers: CIMMYT’s experience

Significant progress has been made in the characterization of loci controlling traits of importance using molecular markers. A number of markers are currently available in wheat for genes of interest to the breeders. Markers can be used to better characterize parental material, thereby improving the efficiency and effectiveness of parental selection for crossing and to track genes in segregating progenies through the selection process. Although a number of breeding programs are using molecular markers at modest levels, the costs associated with marker assisted selection (MAS) are frequently cited as the main constraint to their wide-spread use by plant breeders. However, this is likely to change when user-friendly, high-throughput, automated marker technologies based on single nucleotide polymorphisms become available. These evolving technologies will increase the number of available markers, and will improve the efficiency, throughput, and cost effectiveness of MAS, thereby making it more attractive and affordable to many breeding programs. This article examines the extent to which molecular markers have been used at the International Maize and Wheat Improvement Center (CIMMYT) in applied wheat breeding and reviews the limited publicly available information on MAS from other wheat breeding programs. As markers are currently available for relatively few traits, we believe that MAS must be integrated with ongoing conventional breeding to maximize its impact. When used in tandem with phenotypic selection, MAS will improve response to selection for certain traits, thereby increasing rates of genetic progress.     

矮秆超大穗小麦亲本与多抗丰产小麦主要农艺性状的配合力评价及遗传分析

为了进一步挖掘矮秆超大穗小麦亲本在遗传育种中的应用潜力,为小麦高产、超高产育种选择优良亲本和最优杂交组合提供理论依据,选用5个矮秆超大穗小麦品种（系）作为父本,8个多抗丰产小麦品种（系）作为母本,按NCII遗传交配设计,采用8×5不完全双列杂交法,配制了40个杂交组合,对小麦亲本及杂种F1的株高、主穗长、单株穗数、结实小穗数、主穗粒数、主穗产量、单株产量、千粒重8个性状进行了考察,并在基因型方差分析显著的基础上进行了配合力评价及遗传力分析。结果表明：父本中A1、A3、A4是综合性状优良的亲本,其多数性状的一般配合力均较高,特别是穗长、主穗粒数、结实小穗数、主穗产量、单株产量的一般配合力高,而株高的一般配合力效应值较低,是很理想的矮秆超大穗多粒亲本材料。母本中B5、B6单株穗数一般配合力较高,株高的一般配合力效应值较低,可作小麦高产杂交育种的矮秆多穗型亲本使用。结合特殊配合力效应分析：组合B5×A3单株穗数、主穗产量、单株产量、千粒重特殊配合力效应最高,株高特殊配合力效应较低,可作为的矮秆、多穗、粒重高且高产的重点杂交组合。B2×A4主穗长、单株产量、单株穗数特殊配合力效应都较高,而株高特殊配合力效应低,可作为矮秆大穗高产的重点杂交组合。遗传力分析表明：单株产量、千粒重、主穗长、主穗产量皆在70%以上,表明这4个性状的广义遗传力较大,受环境影响较小,而狭义遗传力的分析除主穗长、主穗粒数、主穗产量、株高大于50%,其余4个性状均低于50%,说明受环境影响大,不宜早期选择,应该适当推迟选择的代数。     

双列杂交设计的主-微位点组遗传分析方法研究

数量性状遗传研究通常以双亲本杂交后代为对象,而作物育种中常涉及多个具有优良性状的亲本作为有利基因的供体,因此有必要研究多个材料间的遗传关系,以便从中选择最佳亲本组合,这对杂种品种选育尤其重要。本研究在以往位点组分析方法的基础上,将其扩展为主基因＋多基因遗传模型框架下双列杂交设计的主－微位点组遗传分析方法,将微位点组从原来的剩余部分中分离出来。该方法针对双列杂交设计的主位点组和微位点组及其与环境互作的统计遗传模型提出了主位点组检测与效应估计和微位点组效应估计的逐步选入回归法;因模拟实验发现逐步选入回归法的F测验有偏,提出了F测验的调整方法。利用模拟方法评估了遗传率、主位点组个数、增效基因型频率、主位点组间相似性和微基因效应等因素与方法功效的关系。然后通过模拟实验数据和油菜实际试验数据的分析验证了所提方法的应用效果。本研究建立的双列杂交设计的主－微位点组遗传分析方法为杂种品种的亲本选配提供了方法和理论依据。     

Plant breeding interpretations of the effects of bulk breeding on four populations of beans (Phaseolus vulgaris L.)

Summary The effect of bulk breeding on yield and its components was studied in two high-yielding and two low-yielding bean crosses until the F₆ generation. It was found that bulk breeding on the whole did not alter the mean values in the high-yielding crosses, but that there was a steady increase in the mean values of the low-yielding crosses with generation. As well as mean values the use of variance as a determinant of cross potential was also studied. It was found for characters markedly influenced in their expression by the environment, of which grain yield is the prime example, that progeny variance did not differ significantly from parental variance. It was concluded that interplant competition was the factor of the environment responsible for this effect.     

优质高产稳产型水稻新品种垦优2000的选育及利用

垦优2000是以中国首批优质米品种“京越1号”为骨干亲本,与两个优良性状互补的品种杂交配组,育成的水稻新品种。突出特点是既保持了河北省品种株型优良,丰产性好的特性又提高了品质性状。适宜冀东、冀中等一季稻区种植。高产栽培的关键在于早播早插调控合理的群体和注重后期的肥水管理。     

Agronomic performance of anther‐derived doubled haploid and single seed descent lines in crosses between primary and secondary winter triticale

Octoploid (8x) and hexaploid (6x) primary triticales (xTriticosecale Wittm.) can be used as crossing parents with secondary 6x triticales to enlarge the genetic basis of a breeding programme or introgress traits. Doubled haploid (DH) production permits to develop homozygous lines more rapidly from a segregating generation than other breeding methods such as single seed descent (SSD). Both anther‐derived DH and SSD lines were produced from reciprocal cross‐combinations between 8x and 6x primary and 6x secondary triticales. Field experiments of DH and SSD lines were conducted in three environments as two‐replicate lattices to measure seven agronomic traits. A tendency for higher grain yield, taller plants and a higher 1000‐kernel weight of SSD lines compared with DH lines was found. Significant genetic variation for all traits in both breeding methods was revealed, indicating their suitability to select superior genotypes. Hexaploid and even more so 8x primary triticales can profitably be included as crossing parents in a commercial breeding programme. In such crosses, the primary triticales should be used as the male parents if followed by DH method.     

Female fertility of potato (Solanum tuberosum ssp. tuberosum) dihaploids

Summary Results of testcrosses and seed set data of the dihaploid breeding program at the Potato Research Institute in Gross Lüsewitz, Germany, indicate that the low level of female fertility could hinder success in crossing work. With the objective to reveal major components of female fertility, the behavior of 47 outstanding potato dihaploids (S. tuberosum ssp. tuberosum, 2n=2x=24) was assessed in testcrosses over a period of 3 years. Analysis of variance was carried out for the traits: number of seed per berry (S/B), number of intact seed per berry (IS/B), and number of non-germinable seed per berry (NGS/B). Significant sources of variation included cross combinations, years, and cross combination-year interactions. More than 20 S/B were obtained in 25.4% of all cross combinations performed over 3 years using up to three pollinators. Berry set was not correlated to seed set, but was in general determined by the pollinator used. The number of seedless berries (SLB/F) was related to neither total berry set nor seed production. The trait S/B remained stable over different years, and thus it deemed to be most useful as a measure of the level of female fertility in practical breeding work. Selection for female fertility in early generations of a breeding program is recommended to avoid limitations in the production of variability via sexual recombination.     

Marker-based screening of maize inbred lines using support vector machine regression

The phenomenon of heterosis is widely used in hybrid breeding programmes, despite the fact that no satisfactory molecular explanation is available. Estimators of quantitative genetic components like GCA and SCA values are tools used by the plant breeder to identify superior parental individuals and to search for high heterosis combinations. Obtaining these estimators usually requires the creation of new parental combinations and testing their offspring in multi-environment field trials. In this study we explore the use of ɛ-insensitive Support Vector Machine Regression (ɛ-SVR) for the prediction of GCA and SCA values from the molecular marker scores of parental inbred lines as an alternative to these field trials. Prediction accuracies are obtained by means of cross-validation on a grain maize data set from the private breeding company RAGT R2n. Results indicate that the proposed method allows the routine screening of new inbred lines despite the fact that predicting the SCA value of an untested hybrid remains problematic with the available molecular marker information and standard kernel functions. The genotypical performance of a testcross hybrid, originating from a cross between an untested inbred line and a well-known complementary tester, can be predicted with moderate to high accuracy while this cannot be said for a cross between two untested inbred lines.     

AFLP增效和减效位点预测杂交水稻产量性状模型构建

选用13个水稻不育系和19恢复系按NCⅡ设计配制2套半双列杂交组合,分别用每套组合F1产量性状对该套亲本AFLP多态性位点(总位点)进行筛选,获得阳性、增效和减效三类位点。分别用基于总位点、阳性、增效和减效4类位点的亲本遗传距离构建AFLP标记预测模型,对另一套组合产量性状进行预测。结果表明:(1)总位点中只有少数为阳性位点。与总位点相似,阳性位点用于产量性状预测时,预测值与实际值的相关系数(以下简称为预测系数)太低;(2)而单独利用增效或减效位点,以及同时利用该2类位点(构建二元模型),3类预测效果均大大提高,其中增效位点对结实率,增效或减效位点,及同时利用增效和减效位点对单株产量,4个预测系数在0.6以上,可以用于指导水稻育种;(3)利用2套组合均筛选到的共同增效和减效位点的预测也达到较高水平,其中4个预测系数在0.5以上,因其所使用的预测位点数大大减少,应用更为有利。     

Production of Doubled Haploids by Anther Culture and Wheat X Maize Method in a Wheat Breeding Programme

Utilization of the doubled haploid method of breeding usually shortens the time to cultivar release, and methods of haploid production need evaluation in a breeding programme. Thirty-eight different three-way crosses were tested for anther culture response. On average 5.8 percent of the anthers cultured produced calli. Three crosses were found recalcitrant for callus induction. Overall, the anther culture method produced 0.6 plantlet per 100 anthers cultured. Five crosses with an average of 5.8 and 2.8 percent of anthers producing calli and plantlets, respectively, were compared using anther culture and wheat × maize crosses. Non-responsive genotypes for callus induction and plantlet formation in the anther culture method proved to be good parental material in wheat × maize crosses. The average percentages of embryo formation and plantlet production in wheat × maize crosses were 10.3 and 4.7, respectively. Anther-derived plants were cytologically unstable, whereas all the plants regenerated from wheat × maize crosses were haploids (n = 21 chromosomes). The chromosome numbers of the polyhaploids were doubled with a colchicine treatment. Improvement of the two haploid production methods to facilitate their efficient use in a breeding programme is discussed.