Compatibility between wild and cultivated common bean (Phaseolus vulgaris L.) genotypes of the Mesoamerican and Andean gene pools: Evidence from the inheritance of quantitative characters

The extent and distribution of incompatibility between gene pools (Mesoamerican and Andean) and evolutionary classes (wild, landrace and bred) of the common bean (Phaseolus vulgaris) was explored by seeking anomalous values of highly heritable quantitative traits in the progeny of crosses. Clear incompatibility (no progeny or sterile or deformed progeny) was shown by 28 crosses in a 12-parent wild × bred diallel cross, and 37 crosses in a 12-parent landrace × bred diallel cross. Incompatibility was particularly common in the progeny of certain genotypes, but was not consistently associated with the division between gene pools or evolutionary classes. When crosses showing clear incompatibility were eliminated from the data, days to flowering, number of seeds per pod, log (weight per seed) and seed roundness in the F₁ generation gave a good fit to an additive-dominance model, confirming that there is no overall tendency to incompatibility between the gene pools. There was a division between the gene pools with regard to log (weight per seed), as expected, but there was no such division, with regard either to the means of the parent lines or the distribution of the statistics V _r and W _r (which indicate the distribution of dominant alleles between genotypes), for the other quantitative variables. Differences between reciprocal crosses were strikingly widespread, and appeared generally to be due to cytoplasmic effects or cytoplasmic × nuclear interactions rather than maternal effects, indicating that the direction in which a cross is made may have a perceptible effect on the progeny that can be obtained from it. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Number and size of cross progenies from a constant total number of plants manageable in a breeding program

Summary This short paper discusses the optimum number of crosses and size of progenies for a given total population size to minimize the risk of not finding any favourable genotype in the breeding material. It is shown that the number of crosses must generally be as large as possible. In special situations it may be advantageous to include also less promising crosses instead of enlarging the progenies of more promising crosses.     

Interspecific hybridization in <Emphasis Type="Italic">Sarcococca</Emphasis> supported by analysis of ploidy level,genome size and genetic relationships

Knowledge of ploidy level differences, genome size and genetic relationships between species facilitates interspecific hybridization in ornamentals. For Sarcococca (Buxaceae) only limited (cyto)genetic information is available. The aim of this study was to determine the genome size and chromosome number and to unravel the genetic relationships of a breeder’s collection using AFLP marker analysis. Based on these results, interspecific crosses were made and the efficiency and hybrid status was verified. Two groups of diploid plants (2n = 2x = 24) were observed, with either a genome size of 4.11–4.20 or 7.25–9.63 pg/2C. All the tetraploid genotypes (2n = 4x = 48) had genome sizes ranging from 7.91 to 8.18 pg/2C. In crosses between parents with equal ploidy level and genome size a higher crossing efficiency (on average 58% of the hybridizations resulting in fruits) and more true hybrids (on average 96% of the offspring) were obtained compared to crosses between plants with different genome size and ploidy level (on average 23% fruits and 24% hybrids, respectively). In none of the cross combinations, the ploidy level or genome size was found to be a complete hybridization barrier, although unilateral incongruity was found in some cross combinations. Distant genetic relationships did not hamper the hybridization within Sarcococca genotypes. Our findings will contribute to a more efficient breeding program and a faster achievement of hybrids with an added value.     

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.     

四向杂交设计QTL分析的极大似然方法

四向杂交（four-way cross）设计是指4个纯系亲本参与杂交衍生分离群体的一种交配设计。尽管国际上已经提出基于四向杂交设计的迭代重新加权最小平方（iteratively reweighed least squares，IRWLS）QTL作图方法，但该方法忽略了双侧标记基因型内QTL基因型的混合分布特性，当QTL位置和标记的位置不重合时作图精度较低。本文根据四向杂交设计的数量遗传模型，发展出基于四向杂交设计和混合分布理论的QTL作图的极大似然估计方法。首先利用染色体上所有标记基因型联合计算该染色体上任一假定位置QTL的条件概率，然后根据混合分布理论建立基于EM算法实现的QTL作图的极大似然估计方法。以计算机模拟数据研究了QTL遗传力、样本容量和分子标记信息含量3个因素对方法的影响，结果表明,（1）在QTL的被发现能力上，标记信息不完全的四向杂交设计仅略低于信息完全时的四向杂交设计；（2）随着QTL遗传力、样本容量和标记信息含量的增大，QTL位置以及效应估计值的准确度和精确度逐步提高。     

Inheritance of characters determining growth and development of tomato (Lycopersicon esculentum Mill.) under low energy conditions

Summary Diallel crosses were made between 15 tomato genotypes with varying performance under a low energy regime. It appeared that differences between genotypes for 11 vegetative and generative plant characters are determined mainly by additive genetic variation. For breeding cultivars adapted to low energy conditions, crossing genotypes with a high GCA for weight of trusses and fruits (WTF) and genotypes with a high GCA for weight of vegetative plant parts (WVP) seems most promising. Complications may arise from the negative correlation between GCA values for WTF and WVP, and the strong positive correlation between GCA values for fruit number and WTF, causing small fruits.     

Triple Test Cross Analysis in F2 Populations of Four Promising Crosses of Field Pea

The components of genetic variation were studied in four F₂ crosses (PG₃× 5064, T₁₆₃× B.V., T₁₆₃× Arkel and 5064 × ED) for quantitative characters such as days to flowering, plant height, pod number, seed number, test weight and yield/plant. The overall epistasis (T type) was, in general, a major contributor for genetically controlling the expression of the characters in all the- four crosses except for the character seed number in crosses 1 and JV, where the j + l component at epistasis played a significant role in determining the expression of this attribute:. Though the ‘j + l’ component of the epistasis was significant, it was relatively less important than the ‘i’ type epistasis. Both the additive and dominance components of the genetic variation were highly significant for all the trans studied in all die four sets of crosses. The expression of the dominance was directional only for a few characters in certain crosses. The degree of dominance lies in the partial range, and heritability estimates obtained were high for most of the trails. The possible application of cross prediction in the isolation of superior recombinant inbred lines in pea is discussed.     

大豆杂种产量相关的位点及等位变异分析

选用来源于中国黄淮和美国的熟期组II~IV的8个大豆品种, 按Griffing方法II设计, 配成28个双列杂交组合, 包括8个亲本共计36份材料。选用300个SSR标记, 对8个大豆亲本进行全基因组扫描, 利用基于回归的单标记分析法, 对大豆杂种产量和分子标记进行相关性分析, 估计等位变异的效应和位点的基因型值, 剖析杂种组合的等位变异。结果表明, 300个SSR标记中有38个与杂种产量显著相关, 分布于17个连锁群上, 其中D1a和M等连锁群上较多, 有8个位于连锁定位的QTL区段内(±5 cM)。单个位点可分别解释杂种产量表型变异的11.95%~30.20%。杂种的位点构成中包括有增效显性杂合位点、增效加性纯合位点、减效加性纯合位点和减效显性杂合位点4部分, 其相对重要性依次递减。从38个显著相关的SSR标记位点中, 遴选出Satt449、Satt233和Satt631等9个优异标记基因位点, Satt449~A311、Satt233~A217和Satt631~A152等9个优异等位变异, 以及Satt449~A291/311、Satt233~A202/207和Satt631~A152/180等9个优异杂合基因型位点。这些结果为理解杂种优势的遗传构成和大豆杂种产量聚合育种提供了依据。     

甘薯配合力分析的若干问题

首次将不完全双列杂交(NCⅡ)模式,结合甘薯遗传特点应用于甘薯育种。根据4年试验结果,提出了可行的试验方法、群体规模和评定指标;并就高淀粉、高产育种亲本选配中的若干问题提出了看法。     

Evidence suggests that Mycosphaerella pinodes infection of Pisum sativum is inherited as a quantitative trait

Before likely sources of resistance in pea to Mycosphaerella pinodes can be exploited in a breeding program, the inheritance of genetic mechanisms governing the variation in resistance need to be understood. Disease responses were first examined in a diallel cross of nine Pisum sativum genotypes. An analysis of variance of parental and F₁ data detected significant additive and dominance variation but no reciprocal effects. Gene interactions were not significant in leaves with the exception of the line JI 252 and there was no association detected between the frequencies of dominant or recessive alleles and parental disease response. In stems, the slope of the regression line of the covariance if array members with their non recurrent parent on the variance of an array was significantly different from one and the additive-dominance model was therefore rejected. The non-significance of interactions among genes determining disease response in leaves was supported by the triple test cross analyses. These analyses showed that the narrow-sense heritability of disease response was higher in crosses involving SA 1160 than in the cross Wirrega × Austrian Winter. These crosses are likely to generate inbred lines more resistant to M. pinodes infection than either parent. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mid-parent heterosis and combining ability of European corn borer resistance in maize

Success in breeding maize resistant to the European corn borer has been limited, with the exception of leaf feeding resistance. The inheritance of resistance to leaf, sheath-collar and ear damage in four maize germplasms and their six F₁ crosses was evaluated by diallel analysis. Plants in a completely randomized design were artificially infested at the whorl, anthesis or full silk stage of plant development and were evaluated in the field for insect damage. A damage index based on size, number and location of lesions was calculated for each stage. Stowell's Evergreen (susceptible) had a mean damage index three to six times that of Maiz Amargo (resistant) at the whorl stage and the progeny plants were more resistant than the susceptible parent. Maiz Amargo and its crosses had significantly lower mean indices than Stowell's Evergreen for sheath-collar damage in Year 1 but not Year 2. Zapalote Chico, Maiz Amargo and their cross were significantly less damaged than other genotypes at the full silk stage. Heterosis values indicated an increase in resistance of crosses over the midparent average at all three stages of development. General combining ability (GCA) was highly significant for all types of damage, but specific combining ability was significant only for leaf damage. Based on estimates of GCA, Maiz Amargo was the best source of resistance to leaf and sheath-collar damage and both Zapalote Chico and Maiz Amargo would be good parents for ear damage resistance. Results suggest that resistance at different plant development stages can be combined.     

Investigations on the breeding behaviour of aneuploids of guava

Summary The breeding behaviour of aneuploids of guava (Psidium guajava L.) such as trisomic, tetrasomic, and higher aneuploids has been studied. Reciprocal crosses between aneuploids and diploids indicated less than 100% crossability. The aneuploids when used as male parents crossed less frequently than as female parents and certain aneuploids crossed more readily than others. Differences were observed in fruit size, fruit weight, and seed number in the reciprocal crosses.The extra chromosome was found to be transmitted through both the egg cell and the pollen. However, the frequency of transmission was greater through the egg cell than the pollen. As high as 26% transmission of extra chromosomes were obtained through the egg cell. There was no clear cut difference between trisomics and higher aneuploids with regard to the frequency of transmission of extra chromosomes.     

A comparison of progeny from diallel crosses of diploid potato with regard to the frequencies of 2n-pollen grains

Summary Selection of diploid potato genotypes that produce high frequencies of 2n-pollen grains in different environments is an important requirement for analytic breeding as well as for true potato seed production. In this context, quantitative estimates of 2n-pollen formation were made in two type of diploid potato populations. One population set consisted of the progeny from diallel crosses of five well-known diploid potato clones (A=US-W 5293.3, B=US-W 5295.7, C=US-W 5337.3, D=US-W 7589.2 and E=772102-37). Another population set was obtained by pollinating three genotypes of Solanum phureja, IvP35, IvP48 and IvP101 with clones A, C and E. It was observed that the behaviour of the parental clones with respect to 2n-pollen grains formation in different environments, such as in Europe and China, was stable. The correlation coefficient between means of 2n-pollen grains frequency of combinations and percentage of genotypes with more than 5% 2n-pollen grains in a given combination were estimated and that between mean and maximum frequency of 2n-pollen grains formation in each combination. The results showed that the former coefficients were significant wheareas the latter were not. The combining ability analysis revealed variation in 2n-pollen grains formation between families. Specific combining ability (SCA) effects contributed much more than general combining ability (GCA) to the variation in 2n-pollen grains formation. The broad-sense heritability of 2n-pollen grains formation was estimated to vary between 0.45 and 0.53 and the narrow-sense heritability was calculated to be 0.15 and 0.20 in the two types of populations. This means that additive variance was relatively low. Two to four genes were estimated to control the inheritance of 2n-pollen grains formation.     

Breeding the common bean (Phaseolus vulgaris L.) for resistance to bean common mosaic virus: alternatives to backcrossing

A series of field experiments was undertaken in order to determine whether resistance to bean common mosaic virus (BCMV) could be incorporated into genotypes of the common bean (Phaseolus vulgaris L.) suitable for cultivation in Zimbabwe without recourse to backcrossing. Six inbred genotypes carrying the resistance-conferring alleles at the loci I and Bc-3 were crossed with five locally-adapted inbred genotypes. The first experiment comprised F₃ progeny rows, each derived from a single unselected F₂ plant, the second, F₃ bulks selected for resistance, and the third, a comparison of selected and unselected F₂-derived F₄ lines. The number of days to flowering and to maturity, the incidence of mosaic and necrosis symptoms, seed yield and seed size were recorded. There was evidence that late flowering and maturity were associated with BCMV resistance in some crosses, though not strongly enough to present an obstacle to plant breeding. The incidence of virus symptoms and seed yield were influenced by genetic factors additional to the major resistance genes, and variation in seed yield was present not only between bulk populations of crosses, but also between single-row plots of lines within crosses. This indicates that early-generation selection for yield in the presence of BCMV, even among progeny selected for BCMV-resistace, is likely to be effective. However, the variation in yield among F₄ lines was least in the highest-yielding crosses, which may represent a limit to successful selection for yield. Seed size was partly under additive genetic control, but there was also evidence of non-allelic interactions. There was no association between large seed size, preferred by consumers, and susceptibility to BCMV in the progeny, indicating that the association between these characters in the parent lines is fortuitous and will not present an obstacle to plant breeding. It is noted that a considerable amount of useful genetic information can be obtained without recourse to elaborate crossing schemes, provided that unselected progeny are included in experiments as controls. The evidence presented indicates that resistance to BCMV can be combined with appropriate values of maturity date, yield and seed size without the need for backcrossing.     

Inheritance of Corolla Size, Number of Stamens and Percentage of Plants with Petaloid Stamens in Evergreen Azaleas (Rhododendron Subsect. obtusa)

Research has been carried out on the inheritance of corolla size, number of stamens and percentage of plants with petaloid stamens (double flower) in evergreen azaleas (Rhododendron Subsect. obtusa). For this purpose two incomplete diallel crosses were used. The first one included seven species and one cultivar and the second diallel 13 cultivars. In both diallels for all three characters the GCA mean squares were high. Also, the positive correlation between the parental values and the GCA estimates for flower size and number of stamens indicates that the expression of these characters is mainly determined by additive gene action. A negative correlation was found between GCA estimates for die n number of stamens and the percentage of plants with petaloid stamens. When breeding azaleas with large double flowers, parents can be directly selected on the basis of these characters since additive genetic variance dominates. As no genetic correlations were found between corolla size and number of stamens (percentage of plants with petaloid stamens) the breeding will not be hampered by unfavourable linkage of genes for these characters.     

Genotypic variation for competitive ability in spring wheat

Herbicides are the primary method of weed control for crop production in developed countries. For economic and environmental reasons alternative control strategies are being devised. One of these strategies is the development of competitive crop cultivars. The objectives of this research were to establish whether spring wheat (Triticum aestivum L.) genotypes differed in competitive ability and if those differences were related to specific growth characteristics. Sixteen genotypes of spring wheat were grown under simulated weed competition conditions at Saskatoon, Canada over a 3–year period. Four high and four low tillering genotypes from each of two crosses (Neepawa/M1417 and Ingal/M1417) were studied. Weeds consisted of cultivated oat (Avena saliva cv. ‘Waldern’) and oriental mustard (Brassicajuncea cv. ‘Cutlass’) sown at two densities (48 and 96 seeds/m² per weed species). Seedling establishment, ground cover, and seed yield for the three species were determined, as was wheat tiller number, spike number, maximum height, leaf area index, leaf orientation, and flag leaf length and size. Significant (P = 0.001) weed rate by genotype interactions involving changes in genotype rank were detected for wheat grain yield, indicating that the 16 wheat genotypes differed in competitive ability. Wheat grain yield reductions averaged over the two weed densities ranged from 45% to 59%. The highest-yielding genotypes under weed-free conditions were not necessarily the highest yielding under weedy conditions. Genotypes which suffered smaller yield reductions were more effective in suppressing weed growth. Although competitive genotypes were generally taller than non-competitive genotypes, other traits such as large seedling ground cover and flag leaf length were associated with wheat yield under competitive conditions.     

标记辅助选择育种中QTL基因型的多点联合推断

传统的育种方法对数量性状的选择存在很大难度,现代分子标记技术为实现控制数量性状基因的准确选择提供了有效的技术手段。目前分子标记辅助选择实践仅是对标记基因型的选择,而非直接对QTL基因型进行选择。尽管标记基因型容易获得,但标记基因型通常并非QTL基因型,除非有关的QTL恰巧在标记座位。因此,如何鉴别QTL的基因型成为分子标记辅助选择的关键。QTL基因型通常需要通过分子标记基因型进行推断,由于标记信息的不完全或缺失,使得对个体QTL基因型的鉴别会发生困难。本文在四向杂交设计的基础上,结合贝叶斯理论和马尔可夫链原理,提出一种通用的QTL基因型多点联合推断方法,该方法能够很方便地处理显性标记和缺失标记,同时结合标记信息和表型数据联合推断QTL基因型的条件概率。模拟研究发现,表型数据选择的效果较差,其选择的个体QTL基因型基本上都是错误的,而应用本文所论述的方法,将表型数据与标记数据相结合选择,对QTL基因型的判断正确,且推断的把握性很高。     

Partial resistance in lettuce to downy mildew (Bremia lactucae). 2. Differential interactions between plant genotypes and fungus races and the relationship of latent period,infection frequency and number of infected leaves with the level of partial resistance

Summary In three experiments differential interactions between lettuce genotypes and Bremia lactucae races were investigated and also the influence of latent period, infection frequency and number of infected leaves on the level of resistance.In experiment 1 very significant differential interactions were observed mainly caused by two plant genotypes (PIVT 82 and PIVT 315) and race NL 7. In experiments 2 and 3 differential interactions were absent or of minor importance. Results suggest that partial resistance often was of a race-non-specific character. Latent period appeared to be a major component of resistance in the lettuce-Bremia lactucae relationship. It determines the onset of the next cycle of spore production and is also indicative of fungus growth in host tissue. Compared with infection frequency and number of infected leaves, latent period shows a small error variation and can efficiently be measured. The closeness of the relationship of the number of primary infections and the number of infected leaves with resistance level varied, depending on the experiment. The above three components appeared to be associated but the degree of the association varied. The variable behaviour of the three components suggests that they are governed by different genes.For the level as well as for the complexity and durability of the resistance, accumulation of as many components of resistance as possible is desirable. Therefore, in parents all such components should be analysed before crosses are carried out to improve resistance level. In the final products of crossing and selection the relative importance of components should also be investigated to determine whether an increased resistance level results from additional effects of the parents on one component (e.g. latent period) or from accumulation of different components in a plant genotype.Students at the Agricultural University Wageningen     

Efficient application of in vitro anther culture for different European winter wheat (Triticum aestivum L.) breeding programmes

The efficiency of our anther culture protocol was tested with high‐ and low‐responding genotypes, ‘Svilena’ and ‘Berengar’, and 93 F₁ winter wheat crosses in 2010 and 2011. Based on data for these genotypes, the effect of genotype influenced the number of embryo‐like structures, regenerated plantlets and green plantlets, while the number of albino plantlets was affected by genotype, year and environmental factors. Although genotype also influenced the production of green plantlets from breeding crosses, with green plantlets per 100 anthers ranging from 0.04 to 28.67, the average regeneration rate over all crosses was 5.3 green plantlets/100 anthers, which resulted in a total of 11 416 well‐rooted green plantlets. The survival rate of green plantlets following acclimatization was 97.21% in 2010 and 96.34% in 2011. In this study, the phenomenon of albinism and genotype dependency did not hinder the production of more than five thousand green plantlets each year. In our experiments, anther culture proved to be an efficient method in winter wheat breeding programmes with lower costs than alternative technologies.