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.     

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.     

Selection for yield in early generations of self-fertilizing crops

Summary If a breeder is to apply selection to a cross-population of a self-fertilizing crop and wishes to maximize his chances of finding a productive genotype, he will have to introduce yield tests in the F₃ lines. Should he not do so because of his intention to work on many populations simultaneously, his tests would be considerably less accurate and the finding of a favourable combination more or less a matter of mere chance.Bulk breeding will result in genetic drift or numbers of plants too large to manage, or in a combination of both.Application of the Single Seed Descent for quantitative characteristics causes such a genetic drift, that the method is not to be recommended.Multiple crosses (double-crosses) to improve quantitative characteristics require populations of a size, that cannot be realized and/or selected. This type of crosses is more suited for cases in which qualitative characteristics form the breeding goals and when it is impossible to obtain the favourable combination using only two varieties.Genic recessive male sterility may be a means to raise large progenies. In the F₃ it confuses the issue of yield of fruits or seeds, which is highly vulnerable in any case. In the F₂ its significance for finding the proper recombinant is very low.     

The Effect of Photoperiod Insensitivity on the Salt Tolerance of Amphiploids between Bread Wheat (Triticum aestivum) and Sand Couch Grass (Thinopyrum bessarabicum)

From the crosses (6 × triticale ‘Lasko’× AARR) בLasko’ one plant with 56 chromosomes was obtained. The selfed progenies showed reduction of somatic chromosome number. A reciprocal cross of hyperploid introgressive plants with ‘Lasko’ indicated similar transmission rates of additional chromosomes through female and male gametes. The degree of initial reduction is of great importance for the number of succeeding generations needed to reach the hexaploid level. With regard to the output of introgressive lines of practical breeding importance, it is necessary to continue and to promote the recombination processes between donor and recipient genetic information for as long as possible. An interruption of recombination by beginning selection too early leads to the loss of genetic variability in the progenies.     

混合选择与系谱选择对大豆杂交材料定向选择效果比较的研究

通过多年的系统试验,证明对大豆杂交早期世代的材料,用混合选择法针对成熟期、株高、结莢习性,以及种粒大小等性状进行定向的选择,效果并不次于系谱选择法,但却简便易行。大豆杂交材料经过数代的定向混合选择,便形成为能适应当地条件与要求的优良生态类型。在这个基础上,再用个体选择法进行选择,能较有保证地选育出高产优质抗性強的优良品系。     

Optimum number of crosses and progeny per cross in breeding self-fertilizing crops. I. General approach and first numerical results

Summary Based on maximization of selection response, Peek (1986) proposed methodology for determining the optimum number of crosses and progeny per cross in breeding self-fertilizing crops. By this method the total selection response is obtained by adding the individual responses from the two steps of selection: selection between crosses and selection within crosses. In this paper, Peek's approach has been generalized for finite or nonnormal populations. Optimum numbers of crosses are determined by testing capacity, number of selected crosses, number of selected lines from each selected cross, and heritability.In the case selection of the best line from the best cross, the optimum number of crosses increases monotonically with increasing testing capacity (for any given fixed heritability). For increasing heritabilities, however, the optimum number of crosses exhibits relatively flat maxima (for any given fixed testing capacity). These maxima are located at intermediate or sub-intermediate heritabilities.For varying numbers of selected crosses and selected lines from each selected cross the main results are: The optimum number of crosses i) increases with increasing testing capacity, ii) increases with increasing number of selected crosses and iii) decreases with increasing number of selected lines from each selected cross.     

Reciprocal recurrent selection applied to Coffea canephora Pierre. III. Genetic gains and results of first cycle intergroup crosses

Breeding of the allogamous Coffea canephora species in Côte d'Ivoire is based, from 1984 onward, on a reciprocal recurrent selection scheme exploiting the good performance of crosses between two genetically distinct populations (‘Guinean’ and ‘Congolese’). Results are presented here on intergroup cross progenies evaluated on individual plant basis over a six year period in three fully randomized trials planted in 1985 and 1986. Yields of the bi-parental crosses varied from 16 to 1407% of the mean of the two commercial clonal cultivars and the most productive crosses were also the most vigourous. Selection of individual trees and cross progenies, based on a combined individual-family index, was carried out for high yield, good vigour of young plants and moderate canopy diameter of adult trees. Expected genetic gains, as estimated in relation to the mean of all crosses, for selection of 5% of the best trees, were high for yield (over 60%), moderate for young plant vigour (14 to 18%), and, as intended, low for canopy diameter. In addition, selection by independent culling for leaf rust resistance and bean weight was carried out. As a result, 6 promising crosses with yield similar or higher than those of the control cultivars, were selected as candidates for commercial use, as well as 65 individual trees, within 19 different crosses. Expected genetic gain for yield for these selected trees is about 60% compared to the average yield of the most productive control clone. Continuation of the programme is discussed, with specific attention to further progress expected for quality traits.     

The inheritance of bean size,pod size and number of beans per pod in cocoa (Theobroma cacao L.), with a note on bean shape

Studies have been made on the F₁ and F₂ generations of crosses between the Amazon clones Nanay 32, Parinari 7, and Parinari 35. There is wide variation in size from pod to pod on a tree, and this is largely paralleled by variation in bean number, bean size remaining relatively constant. However in some trees bean size increases in the largest pods, bean number remaining constant. It appears that if a pod is too small for the inherent number of beans to be present at their inherent size, the number of beans which develop is reduced so that their inherent size is attained; if the pod is larger than is required for the full number of beans to attain their inherent size the beans may increase in size above the inherent value. Thus if the average bean size in a sample of pods taken from a tree indicates the inherent bean size reasonably accurately it is likely that the inherent bean number will be relatively underassessed, and conversely if the observed bean number indicates the inherent number relatively accurately it is likely that the observed bean size will overassess the inherent size. Scatter-diagrams may therefore be more informative than averages.Bean number and bean size are strongly inherited but the difficulties described above tend to obscure the pattern. In the Pa7 x Na32 F₁ progeny inherent bean sizes are low and probably relatively constant while inherent bean numbers vary widely; in consequence inherent bean numbers are well indicated by samples of pods taken from the trees, and inheritance of bean number in the F₂ progenies is very clear while inheritance of bean size is not. In contrast, in the F₁ of Pa35 x Na32, there is clear segregation in bean size while bean numbers are relatively high and constant; inheritance of bean size in the F₂ progenies is clear while the evidence of inheritance of bean number is weaker.The average pod weight of a progeny seems to be determined by the inherent bean size and the inherent bean number.Bean breadth and bean thickness tend to be negatively correlated. It is suggested that where the number of ranks of beans in a pod is high relative to the length of the pod and the inherent bean size, the beans, lacking room for expansion in thickness, tend to increase in breadth so as to attain the inherent size. Short fat pods may therefore tend to contain broad, thin, plate-like beans.     

Agronomic performance of crosses between Nordic and exotic barleys

Exotic germplasm may be useful for the improvement of agronomic performance of barley breeding material. This study was conducted in order 1) to evaluate if it is possible to improve performance of Nordic barley breeding material by utilizing exotic germplasm sources (unadapted landraces and H. spontaneum), 2) to evaluate incorporation of exotic germplasm into a genetic base widely adapted to the agro-ecological conditions of the extreme Scandinavian north as well as to the base adapted to the conditions of the south of this geographical region, and 3) to evaluate whether an index composed of several traits corresponded to 'breeder's phenotypic evaluation' of the progenies. Earliness, straw length, number of ears/plant, yield/plant, seed shattering, persistence of awns and an index computed from these traits were studied in Swedish and Finnish 4-way crosses along with their adapted parents. Most of the crosses headed earlier than their adapted parents and none of the crosses outyielded the adapted parents. The most favorable frequency distributions for the index were found in the crosses with only cultivated barleys as parents. Transgressive segregates were also found in progenies with H. spontaneum parents. Incorporation of exotic barleys was most successful into the local genetic base. Comparisons between indices and breeder's phenotypic evaluation suggested reconsideration of evaluation methods early in parent development.     

三种不同类型大豆及其杂种后代主要农艺性状的配合力分析

利用具有明显差异的3种不同进化类型的大豆，采用双列杂交方式配制类型内及类型间共15个杂交组合。结果表明，不同类型大豆主要农艺性状的一般配合力明显不同。秣食豆在株高、节间长、分枝数、单株荚数和单株粒数等性状上具有增效作用；在粒茎比和收获指数等性状上具有减效作用。亚有限类型大豆则有降低株高和节间长度，提高     

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.     

Research on some characters in black currant progenies

Populations derived from selfs and crosses of a small number of black currant varieties with the variety Consort were analysed for various characters, viz. vigour, number of flowers, flowering time, ripening time, fruit-set, strig-length and berry size. Flowering began in the third growing year. In the next year the bushes could be assessed to best advantage. The results of the evaluations are:

1. 1.
   The vigour of the selfed progenies showed, with the exception of Consort, a clear inbreeding depression as compared with the hybrid populations.     
   
   

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。     

Cytometric and morphometric identification of diploid, tetraploid and pentaploid plants derived from Actinidia arguta (2n = 4x) crossed with A. deliciosa (2n = 6x)

Interspecific crosses between Actinidia arguta (In = 4x) and A. deliciosa (2n = 6x) were carried out in order to transfer cold resistance from a wild to the cultivated kiwifruit species. Of the 65 progenies obtained and analysed by flow cytometry, 16 were diploid, one was tetraploid and 48 were, as expected, pentaploid. Morphologically, the diploids can be distinguished from the pentaploids by their longer lamina. The existence of 5x progenies confirms the existence of gene flow between A. arguta and A. deliciosa, whereas the existence of 2x and 4x progenies provides evidence for parthenogenesis within the Actinidia genus following an interspecific cross. The study demonstrates the utility of flow cytometry for genomic analysis of progenies derived from interspecific crosses. Possible uses of both sexual and parthenogenetic progenies in the breeding and genetics of kiwifruit are discussed.     

Evaluation of globe artichoke and related germplasm for resistance to artichoke latent virus

Summary A total of 280 globe artichoke (Cynara scolymus L.) clones were assessed for reaction to naturally occurring artichoke latent virus (ALV) in field trials. Also, the reaction of 17 seed progenies of crosses which produced ALV-resistant clones in the field, 20 self progenies of parental genotypes common to these crosses, self progenies of 17 artichoke cultivars, and 7 accessions ofC. cardunculus andC. syriaca were evaluated in the glasshouse following mechanical inoculation with ALV. The local and systemic presence of ALV, and the relative virus content in infected plants were determined by ELISA.All cultivars and most of the otherC. scolymus material tested (clones and seed progenies) proved to be highly susceptible to ALV. Ten progenies were less susceptible to mechanical inoculation as shown by the moment the virus could be detected, and a slow rate of accumulation of viral antigen. Some plants in two seed progenies possessed apparently a high resistance as could be concluded from the failure of ALV to spread or to multiply in plant.Accessions ofC. cardunculus andC. syriaca were also highly susceptible to ALV. However, an interspecific hybridC. cardunculus x C. syriaca presented the highest level of resistance, the plants remained free of local and systemic infection. Ratios of resistant to susceptible plants in self progenies of resistant plants suggested that this resistance was dominant.     

应用双单倍体克服籼粳交的不亲和性初探

通过对籼粳交Ｆ１体细胞愈伤组织的秋水仙素处理和四倍体花药培养，建成了水稻四倍体诱导及双单倍体分解系统。应用这一系统获得了４４个籼粳交组合的双单倍体及其自交４后代。对这些双单倍体及其后代的遗传分析表明，籼粳交育性可能受寡基因控制，双单倍体途径通过改变正常的世代交替过程，能部分克服籼粳交的不育性及倾籼或倾粳的偏态分离，并具有比Ｆ２更丰富的遗传多样性。在双单倍体一代群体中，育性正常的植株约占４０％，这是     

Untersuchungen zur Leitbündelstruktur der Ackerbohne (Vicia faba L.)

Investigations on the vessel structures of broad beans ( Vicia faba L.)
The number of vessels was observed in the fruit bearing axes of some varieties from Vicia faba Minor, Equina and Major during flowering. These investigations were also made on some F₂- progenies of crosses from minor × equina and Paucijuga × Eufaba and on some topflower plants.
The varieties of Minor and Equina had about 12 vessels on the base of the axis, these diminished to the top of the axis 3 or 4 vessels just before the last flower. The varieties of Major had 12 vessels on the base of the axis too, but these diminished faster because of the smaller number of flowers on the axis. In Paucijuga the number of vessels on the base of the axis was only 3 to 4. Plants of Paucijuga had only 2 or 3 flowers per axis.
Progenies from crosses between Minor × Equina had more vessels on the base of the axis, probably due to a heterotical inheritance. In progenies from crosses between Paucijuga × Eufaba an intermediate inheritance was found in the number of flowers per axis and in the number of vessels.
Due to the investigations on a comprehensive material it is probable that the described vessel structure exists in most broad beans. This structure is complex arranged and modifyable. With this organization it is quite unprobable that the vessel structure will be a yield reducing factor.     

Inheritance of slow rusting to stem rust in wheat

Summary The inheritance of the slow rusting character was studied on F₅ progenies from seven spring wheat cultivars (Triticum aestivum) crossed in all possible combinations without reciprocals. The cultivars and their progenies were evaluated for slow rusting in 1974 and 1975 in epidemics of Puccinia graminis f. sp. tritici, races 15 and 151, and traces of other races. Slow rusting varied significantly among the parents and among the F₅ progeny of each cross. Transgressive segregation occurred in each cross, i.e. some progeny rusted more slowly than the parents and some faster. In crosses with both Idaed 59 and Kenya 58 the progeny distributions were skewed towards slow rust development but the distributions in the other crosses were normal. The genetic control of slow rusting was predominantly additive, and narrow sense heritability was approximately 80 percent. The number of segregating genes having an effect on slow rusting was estimated to be 2 to 12 pairs depending on the cross. Correlation between slow rusting and maturity was usually negative but in most crosses the relationship was small.Contribution No. 9624 from the Agricultural Experiment Station, University of Minnesota, St. Paul, Minnesota 55108.     

粳稻杂种劣势的遗传及表型特性分析

杂种优势是自然界的一种普遍现象,但在杂交水稻育种实践中也时常发现杂种劣势现象,为了更好地阐明杂交育种理论和揭示品种本质有必要对杂种劣势的遗传机理进行更深层次的研究。本研究旨在通过两个韩国粳稻品种(Aranghyangchalbyeo和Sanghaehyangheolua)及其正反交后代(F1,F2)特性的比较,解析水稻杂种劣势的表型、类别及其遗传模式。形态学分析表明,正反交F1植株的劣势表现均明显、稳定且不受环境影响,主要农艺性状的中亲劣势值均为负值,其中F1的株高、分蘖数和结实率与亲本相比显著降低(P<0.01);F1劣势表现从发芽后第5d开始,地下部的劣势表现比地上部更为明显。细胞组织结构观察表明,分蘖盛期F1劣势植株叶片发育正常,而其根部气腔发育较亲本迟缓,从而阻碍了地上部与地下部的通气情况,因此也影响了整个植株的正常生长。遗传学分析发现,该劣势组合成熟期F2群体中正常与劣势植株呈现7:9的分离,结合分蘖盛期该F2群体株高的分离模式,推断该杂种劣势的表型是由两个互补的显性基因控制。该研究结果为揭示杂种劣势的多样性及分子遗传机制提供了新思路。     

Adaptive properties of Picea abies progenies are influenced by environmental signals during sexual reproduction

Summary Several independent tests have shown that climate and weather during sexual reproduction influence the adaptive properties of the Picea abies progenies. This phenomenon is expressed in seed orchards established by moving parent trees, propagated as grafts, from north to south, from high to low elevation, or from outdoor to indoor greenhouse conditions. The progenies exhibit delayed flushing in the spring, later growth cessation of leader shoots in the summer, delayed bud-set, higher frequency of lammas shoots and delayed development of frost hardiness in the autumn compared to progenies reproduced in the colder native environment. The altered performance is persistent. We have found no effect on progenies of photoperiod and temperature treatments given to the males during meiosis and pollen production. However, when crosses were made in early spring (March), inside a heated greenhouse (short day, high temperature), the progenies are less frost hardy during cold acclimation than progenies from identical crosses performed in late spring (May; long day high temperature) in the greenhouse. The most hardy offspring were from crosses performed under outdoor conditions in May (long day, low temperature). These results indicate that some stages in reproduction, such as female meiosis, pollen tube growth, syngamy and early embryo development, are sensitive to temperature and/or photoperiod which then alter the phenotypic performance of the offspring. The most likely explanation is the existence of a regulatory mechanism affecting the expression of genes controlling adaptive traits. If this is true, it must have implications for the genetic interpretation of provenance differences in Norway spruce.