New strategies for increasing heterozygosity in crops: Vicia faba mating system as a study case

Our research assesses the feasibility of using artificial selection on pre-mating floral traits to modify the mating system of faba bean (Vicia faba). This analysis considered two synthetic populations, which were derived from different genetic pools and had undergone five years of multiplication. For these populations, we identified floral and inflorescence traits that influence outcrossing per plant and examined the relative importance of these traits in governing yield. Codominant isozyme loci and the mixed-mating model were used to estimate the multilocus female outcrossing rate. A maternal half-sib design was used to evaluate the additive genetic component of floral and inflorescence traits, yield and yield components. Multiple regression was used to assess the effects of floral and inflorescence traits on outcrossing and yield and components of yield. The two populations exhibited mixing mating. Self-fertilization appears to result from the action of pollinating bees, so that its incidence could be modified by selection on floral and inflorescence traits that affect pollination. Floral and inflorescence traits affected individual differences in outcrossing unequally, with most variation being associated with the numbers of displayed flowers and inflorescences. Variation among plants in reward traits and in shape, although statistically significant, had limited and inconsistent influences on individual differences in outcrossing. Yield and its components varied strongly with aspects of floral display and, to a lesser extent, floral design, except for seed weight. Overall, our results imply that both outcrossing and yield could be enhanced by selection for plants that produce more inflorescences, each with relatively few flowers.     

Inter-accession variation in floral morphology in radish (Raphanus sativus L.)

We investigated variation in floral morphology among 36 accessions of radish (Raphanus sativus L.). We found wide, continuous inter-accession variation in 15 traits related to the size of the floral organs and the stigma position relative to the anthers of long stamens. A principal-component analysis of the 15 floral traits also showed wide variation among accessions. A large proportion of this variation was accounted for by lengths of stamens and the petal tube. In addition, the phenotypic stabilities with respect to the macro-environment (as affected by different sowing dates) and the micro-environment (among the flowers within a plant) differed between traits. Correlation analyses using all traits suggest the existence of genetic linkages or pleiotropies among floral organs. Our results indicate that floral morphologies varied greatly among radish accessions and they could be affected by the macro- and micro-environment. To explore the relationship between floral morphology and pollination efficiency, we compared the number of pollen grains deposited on the stigmas in the presence and absence of insect pollinators using three accessions with very different floral morphology. Because an accession with a higher stigma position than anthers might avoid self-pollination and an accession with a large stigma size received more pollen grains, floral morphology may affect pollination efficiency. Because the effect of pollination efficiency on seed production is well known, our results suggest that radish floral morphology affects seed production through its effect on pollination efficiency.     

蚕豆异交率相关因素研究及应用进展

蚕豆是常异花授粉作物,异交率一般为20%~30%,最高可达84%。媒介昆虫、气候条件、地理因素、种植密度、品种基因型、花序的小花数量及小花结构特点、田间环境等都对异交率产生影响,媒介昆虫是异交发生的主要途径。异交会导致种质一致性的丧失,给资源的保存利用、品种繁育和应用基础研究等带来一定阻碍,但同时异交又是群体遗传多样性保障和杂种优势利用的重要条件。本文从异交率、异交媒介、异交影响因素及异交率的应用研究4个方面总结蚕豆异交率研究和应用情况,并对今后研究方向进行展望。     

Selection in Faba Bean for Tolerance to Broomrape, Orobanche crenata Forsk.

Six populations of faba bean (Vicia faba L.) were developed through various selection schemes to examine the influence of selection In improving tolerance to Orobanche crenata (Forsk.) in local faba bean stocks. All populations trace their origin to 209 farmers’ seed lots that were collected from Egypt. The entries of each population were grown during the 1982/1983 season in the Orobanche nursery located at Giza in Egypt. Comparison among means of the selected, populations showed that more progress in improving Orobanche tolerance could be achieved from combined selection between and within lots. Between-lots selection was less efficient than single-plant selection. Results, of this study show that considerable progress could be achieved from selection for Orobanche tolerance in local faba bean germplasm. There was sufficient residual genetic variation in the selected populations to expect substantial progress from further selection for most tolerance traits.     

Susceptibility of Faba Bean (Vicia faba L.) to Heat Stress During Floral Development and Anthesis

Experiments were conducted over 2 years to quantify the response of faba bean (Vicia faba L.) to heat stress. Potted winter faba bean plants (cv. Wizard) were exposed to temperature treatments (18/10; 22/14; 26/18; 30/22; 34/26 °C day/night) for 5 days during floral development and anthesis. Developmental stages of all flowers were scored prior to stress, plants were grown in exclusion from insect pollinators to prevent pollen movement between flowers, and yield was harvested at an individual pod scale, enabling effects of heat stress to be investigated at a high resolution. Susceptibility to stress differed between floral stages; flowers were most affected during initial green‐bud stages. Yield and pollen germination of flowers present before stress showed threshold relationships to stress, with lethal temperatures (t₅₀) ?28 °C and ~32 °C, while whole plant yield showed a linear negative relationship to stress with high plasticity in yield allocation, such that yield lost at lower nodes was partially compensated at higher nodal positions. Faba bean has many beneficial attributes for sustainable modern cropping systems but these results suggest that yield will be limited by projected climate change, necessitating the development of heat tolerant cultivars, or improved resilience by other mechanisms such as earlier flowering times.     

Controls over pollination and ovule fertilization in Vicia faba

Summary Variation in the frequencies of pollination and ovule fertilization was generated among faba bean (Vicia faba L.) genotypes in experiments which compared self-and open-pollination, natural and extended photoperiods, presence and absence of honey bees and a range of plant populations.There was a near-1:1 relationship between the frequencies of pollination of stigmas and the fertilization of at least one ovule within the pistil. Pollination was the major barrier to fertilization of the pistil, and ovules, since no mechanism was evident in the style to prevent pistil fertilization. The frequency with which single ovules were fertilized in pollinated pistils fell as their distance from the stigma increased, and averaged 83.5% overall.The frequency of pollination was most influenced by the level of autofertility possessed by the genotype, and the activity of pollinators. Provision of honey bees to plants in caged plots showed that high levels of pollination could be achieved under open-pollinated conditions, but this was also influenced by autofertility. Increasing plant population in the field had only a small effect on pollination, but extending photoperiod caused the levels and timing of self-pollination in three genotypes to vary.Large differences were found among genotypes in their early stigma receptivity, that is, the frequency of stigmas found to be pollinated at the erect standard stage, prior to the flower opening and being visited by bees. The implications of early stigma receptivity for producing new cultivars were discussed.     

Genetic variability of faba bean genotypes for chocolate spot (<Emphasis Type="Italic">Botrytis fabae</Emphasis>) resistance and yield

Faba bean (Vicia faba L.) has high utility as a food and soil fertility improving crop. One of the major fungal pathogens of faba bean is Botrytis fabae, the causative agent of chocolate spot. The disease affects significantly the leaf, stem, pod and seed of faba bean compromise its productivity in the smallholder farming sector. Nonetheless, there are limited resistant/tolerant faba bean varieties available and disease control technology options. Therefore, it was prudent to evaluate faba bean landraces for chocolate spot resistance. Fifty landraces together with ten improved varieties were evaluated both in the field and in the greenhouse under natural and artificial inoculation with previously selected aggressive Botrytis fabae isolate (Iso-016) from West Gojjam, in Ethiopia. There were highly significant differences (p?<?0.001) among the landraces for reaction to the disease and agronomic traits. Significant positive correlation was recorded between reaction of genotypes in the field and greenhouse disease data. The overall mean disease epidemics varied from 92.5 to 697.5 for the area under disease progress curve (AUDPC). The highest level of resistance was found in the ICARDA lines, ILB-4726, ILB-938 and BPL-710. Of all 18 landrace collections displayed significantly lower disease reaction than the susceptible check. However the resistance was moderate. The selected eighteen landraces will be recommended for use in breeding for chocolate resistance. Overall, resistance was highly heritable, suggesting that phenotypic selection can be exploited to improve chocolate spot resistance in faba bean varieties.     

中国苹果授粉研究现状

苹果是中国最重要的栽培果树,然而目前其单产和优果率较低、果实品质较差,严重制约了中国苹果在国际市场上的竞争力。尽管人工授粉可以提高产量,但目前人工授粉成本不断增加;传粉昆虫对大幅提高苹果产量,尤其增加优质果率方面有着不可替代的作用,但目前自然界传粉昆虫数量严重不足,无法满足苹果产业规模化发展的需求。大力推广蜜蜂、壁蜂授粉技术,深入研究切叶蜂、土中筑巢蜂等苹果野生传粉昆虫的人工驯养技术是确保苹果产业可持续发展的重要途径;同时,科学配置授粉树也是提高苹果坐果率、优质果率、改善苹果品质的关键。本研究综述了苹果花部特征、传粉方式、传粉昆虫种类以及影响苹果授粉效果的因素等,并对今后开展苹果授粉的研究提出了几点建议,以期为提高中国苹果产量和品质提供一些思路。     

不同传粉方式对子莲授粉效果的影响

[目的]子莲是一种基础产量比较低的植物,需要依赖传粉者的活动才能完成胚珠受精,授粉优劣是直接影响子莲产量与质量的重要因素。[方法]中华蜜蜂和意大利蜜蜂都是理想的授粉昆虫,各有其独特的生物学特性,在抗逆性、采集积极性和采集偏好性等生物学特性方面均存在不同差异。应用意蜂和中蜂为大田子莲授粉,对其采集活动方式与授粉效果进行了对比研究。[结果]1、活动方式结果表明：它们的采集行为相似,但活动方式不同,在夏季高温天气,意蜂较中蜂的采集工作时间要长,因此具有更高的授粉效益。2、授粉效果结果表明：与产量相关的子莲单粒重、接籽率;与商品性相关的莲子纵、横径4项指标,意蜂授粉组与中蜂授粉组之间差异不显著,但与自然授粉组和无虫媒授粉组之间差异显著。其中,意蜂授粉组的平均接籽率最高为87.82%,较自然授粉组和无虫媒授粉组接籽率分别提高33.27%和79.10%;自然授粉组莲子平均单粒重最大达3.68g,显著高于其他授粉类型;无虫媒授粉组较其他授粉组莲子果型最小。同时,与产量相关的子莲蓬粒总重,意蜂授粉组与其他授粉组之间,均差异显著,较中蜂授粉组、自然授粉组和无虫媒授粉组蓬粒总重分别提高25.88%、37.67%和665.50%。[结论]据此得出意蜂与中蜂具有类似的授粉效果,都能够完成授粉任务,意蜂较中蜂授粉能够获得较高的子莲产量,并显著优越于自然授粉与无虫媒授粉方式, 从而产生更高的授粉效益。     

How to maintain improved cultivars

Improved cultivars loose their identity and healthiness unless maintained properly. Contaminating and degrading forces, such as outcrossing, volunteer plants, mixing, natural selection, mutation and seed-borne diseases, are at the root of this. Maintenance selection can prevent this deterioration. How it is carried out depends on the reproduction system of the crop. Crops are therefore classified into four categories; typical cross-pollinating crops, self-pollinating crops with a substantial amount of outcrossing, typical self-pollinating crops with little outcrossing, and the vegetatively reproduced crops. Generally some of the “breeder seed” is used to plant a small plot with spaced plants. A fair number of healthy plants of the cultivar type is selected and the seed is harvested per plant. The progenies of the selected plants are grown in small plots. Non-uniform or deviating plots and plots with a seed-borne disease are removed. The seed of the progenies that are healthy, uniform and similar (and so of the cultivar type) are harvested per progeny to be tested next season on larger plots. The same selection is applied and only the seed of the progenies that are healthy, uniform and similar are harvested together to produce the “breeder seed”. The details of this maintenance selection vary with the reproduction system, the multiplication rate of the crop and the possibilities available to the breeder. Seven crops, potato, common bean, barley, wheat, faba bean, quinoa and maize are discussed here as they represent the different reproduction systems and multiplication rates, while being important Andean food crops.     

Effectiveness of early generation selection under two plant densities in faba bean (Vicia faba L.)

The effectiveness of early generation selection under low and high plant density was evaluated in faba bean (Vicia faba L.). For this, the faba bean cv. 'Polycarpe' was pollinated by eight higher yielding cultivars of different origin. The F₁'s and F₂'s together with 'Polycarpe' and the pollinator with the highest yielding ability (cv. 'Effe') were evaluated under high plant density with adjacent controls and under low plant density in a honeycomb design. It was found that the eight hybrids had a different ranking at low than at high plant density for both generations (F₁and F₂). Hybrid Pol.x A-58 had the best combined yield performance in the F₁and F₂under high and hybrid Pol.x A-37 under low plant density. Application of individual plant selection in the F₂and F₃generation of the two crosses (Pol.x A-58 and Pol.x A-37), under both low plant density according to UNR-O honeycomb design and high plant density using a moving average, resulted in the selection of four groups with 20 selected F₃plants each. Within each group, equal numbers of seeds from each plant were mixed to establish four mixtures. These mixtures together with two controls ('Polycarpe' and 'Effe') were evaluated in a randomized complete block design (22 plants/m²) in one location for two years. It was found that the material selected continuously under low plant density had a significantly higher yield than the material selected under high plant density. In addition, the material selected from Pol.x A-37 (H₁R₂) under high plant density had a lower mean yield than that selected continuously under low plant density (H₁H₂). Their average yield over years was significantly higher than the yield of the material selected from Pol.x A-58 under both plant densities. Furthermore, the material selected from Pol.x A-58 under low plant density, had a significantly higher mean yield over years than its sibs selected under high plant density. It was concluded that honeycomb selection at low plant density can be used effectively for early generation selection in faba bean.     

Expected levels of heterozygosity in autotetraploid progeny populations

Summary A breeding program aimed at improving the seed yield in bean for processing was started. Six parents divergent in a range of agronomical characters were crossed according to diallel mating design. Cluster analysis performed on the composite cross population evidenced divergence between F1 hybrids and to maximize genetic recombination, the most different F1 hybrids were intercrossed. A Factor analysis was performed on 7 morphological and yield-determining traits of 15 hybrids F1 and parents. Three Factors, representing patterns of variables interpreted as productivity per plant, growth factor, and branching-productivity, were extracted. These results evidenced the inverse relationship between seed yield components (seeds/pod, pods/plant, and hundred seed weight): i.e. the selection for either variable is detrimental to the other. It may be possible to break this association if the plant construct assures high sink to satisfy all plant requirements: tall and large plants bearing numerous nodes, leaves and reproductive structures. Moreover, the selection practiced simultaneously on the yield components positively affected the seed yield trait. An index of selection and response to selection were estimated on the segregant populations. The realized gain in seed/yield reached after one cycle of selection (C1) was 6.5 g, about 20% over the base population (C0). The expected gain from selection based on the superior 5% plants in C2 families was 25.5% and approached the realized gain. The result of this paper gives evidence to support that the seed yield can be improved by an adequate selection intensity and selection index can be very useful when it is faced with the improvement of several traits at the same time.     

壁蜂与蜜蜂对棉花胞质雄性不育系的传粉特性比较

为了筛选适用于棉花胞质雄性不育系授粉的蜂种,2013―2014年以蜜蜂为对照,在网室内进行壁蜂对棉花胞质雄性不育系授粉试验,观察壁蜂和蜜蜂在棉花花朵上的生物学特性,并进行田间性状的统计分析。结果表明:壁蜂的适应性较好,受天气影响较小,但温度超过35℃后访花活动明显减少;壁蜂在不育系和保持系上的单花停留时间极显著大于蜜蜂。壁蜂授粉与蜜蜂授粉,在单株结铃数、单铃籽粒数和衣分上差异极显著,单株果枝数、铃重差异显著。蜜蜂授粉较壁蜂授粉平均制种产量高,但壁蜂制种成本低。改进田间管理措施以及采用多次适时释放壁蜂的方式,壁蜂授粉将会在棉花胞质雄性不育系授粉中发挥更大作用。     

Phenotypic recurrent selection in common bean (Phaseolus vulgaris L.) based on performance of S2 progenies

Summary The effect of a recurrent selection procedure for improving seed yield per plant was evaluated in common bean. Progress was registered after three cycles of recurrent selection with S2 progeny evaluation performed on the grain yield/plant. Gain from selection was estimated by field testing 45 random S2 lines from each of the C0, C1 and C2 populations. Response to selection for seed yield/plant was 6 g from C0 to C1 and 4.4 g from C1 to C2. The seed yield improvement was due principally to an increase in pods/plant; little contribution was provided by the 1000-seed weight and seeds/pod traits. Broad-sense heritability and genotypic variance for grain yield remained high in all cycles which suggests further gain from additional selection cycles. Grain yield/plant is significantly correlated to pods/plant and seeds/pod traits in all cycles, indicating that plants with favourable combinations of these traits could be identified. The proposed recurrent selection procedure appears to be effective in improving the population and extracting superior genotypes for varietal development.     

Variation in traits affecting nodulation of common bean under intercropping with maize and sole cropping

Common bean (Phaseolus vulgaris L.), an important food crop in Europe, America, Africa and Asia, is thought to fix only small amounts of atmospheric nitrogen. It contributes significantly to the sustainability of traditional cropping systems because of the predominance of small-scale farmers who cultivate beans in those areas. The objectives of this work were to evaluate bush bean varieties under common agronomic cropping systems and to evaluate breeding lines under low N-fertility sole cropping and intercropping systems. The purpose of the study was to characterize the genotype and cropping system's variability in symbiotic and plant characters and to identify the most suitable genotypes to establish an effective symbiosis with indigenous strains of Rhizobium. No significant differences among the bush bean varieties evaluated under typical fertilization practices were observed for N₂-fixation and plant traits except for seed nitrogen. Significant differences among the bean lines studied under low N-fertilization conditions were detected for plant growth,plant component and N₂-fixation traits. A significant interaction of bean genotype x cropping system was found for number of nodules per plant and nodule moisture on the bush bean varieties studied, and for days to emergence, days to flowering, end of flowering, shoot length, root dry weight and shoot nitrogen on the bean lines evaluated. Nodulation parameters were correlated positively with the yield components, shoot and root parts and duration of flowering, and correlated negatively with seed crude protein, pod and seed dimensions and seed dry weight. These observations indicate that it may be possible to increase both the symbiotic N₂-fixation and seed yield through plant breeding. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of morpho-physiological, phenological and reproductive behaviour in protogynous lines of Indian mustard [Brassica juncea (L.)]

Understanding the relationship between floral and reproductive traits are critical to understand the evolution of plant species in brassica and need for selecting lines as parental lines in hybrid seed prodcution. The protogyny nature of Brassica species are characterized based on the variations in floral morphology, protogyny interval, stigma receptivity, pollen biology, compatibility and seeds set. The variation in stigma morphology features (stigma exsertion prior to anthesis) and protogyny interval (ranged from 8 to 10 days) formed phenotypically distinct. Studies on stigma receptivity and pollen viability revealed significant variability and found to be at its peak up to 3 days after anthesis and reduced drastically thereafter. Compatibility crosses and post pollination events such as pollen deposition on the surface of the stigma and culminating with the entry of the pollen tube into the embryo sac, was rapid and completed within 2 days after pollination, whereas in in-compatible cross not even single pollen was germinated on stigmatic surface and consequently no pollen tube growth even after sixth day of pollination. In compatible crosses average seed set ranged from 3 to 8 seeds per pod from cross pollination and no seed set in self. The investigation revealed that variation exists for protogyny interval, stigma receptivity and compatibility in the protogynous lines of Indian mustard and this can be exploited for the production of hybrids without emasculation.     

绿豆单株产量与主要农艺性状的灰色关联度分析

为探讨绿豆主要农艺性状对单株产量影响的主次关系，以15 个绿豆品种为试验材料，采用灰色关联度分析法，对绿豆7 个农艺性状与单株产量的关联度进行统计分析。结果表明：各性状因子与单株产量的关联度由高到低排序为单株荚数、株高、主茎节数、百粒重、单荚粒数、主茎分枝、生育期。因此，在山西高产绿豆新品种选育时，应首先注重单株荚数和株高。     

Variation in floral scent compounds recognized by honeybees in Brassicaceae crop species

Floral scent attracts pollinators. We investigated the floral scent compounds recognized by pollinators in six Brassica crop species, including allogamous species with different genomes and autogamous species with two parental genomes and radish (Raphanus sativus). Biologically active compounds recognized by honeybees were screened from all floral compounds by combined gas chromatography–electroantennogram analysis and their profiles were determined by gas chromatography–mass spectrometry. Fourteen of the 52 compounds were active. All accessions had more than two active compounds, but the compounds greatly differed between the two genera. On the basis of similarities in whether active compounds were presence or absence, their amount and their composition ratio, we divided the Brassica accessions into three to five groups by cluster analyses. Most groups were composed of a mixture of allogamous and autogamous species sharing same genome, indicating that the variation depended on genome, not species. These results suggest that all species require pollinator visits for reproduction, despite their different reproductive systems. However, the inter-genus and intra-specific variations shown by the multiple groups within a species might cause different visitation frequencies by pollinators between genera and among accessions within a species, resulting in insufficient seed production in some accessions or species.     

Significance of Seed Source on Grain Yield in Faba Beans (Vida faba L.) and Dry Peas (Pisum sativum L.)

In order to investigate the significance of seed source on yield and related characters 47 seed lots of seven faba bean varieties and 24 seed lots of five dry pea varieties were tested in three series of field trials. The grain yield of the faba bean varieties tested was considerably modified by seed source, whereas only small and nonsignificant effects of seed source were found in dry peas. In general, seed sources with a high thousand grain weight, a high protein content, high portions of undamaged and healthy seeds, and in faba beans a high degree of cross-fertilization exhibited superior grain yields. Production of high-performance seed proved to be the most difficult for the large-seeded and white-flowered faba bean varieties. Based on a tabular summary on factors affecting effects of seed source problems of seed production in both grain legumes and their impact on yield are discussed.     

Shortening the generation cycle in faba bean (Vicia faba) by application of cytokinin and cold stress to assist speed breeding

The aim of this study was to reduce the length of the breeding cycle for faba bean by accelerating seed setting. We examined the mode and time of exogenous 6-benzylaminopurine (BAP) (cytokinin) application, and cold treatments and their combinations in two faba bean genotypes. Acropetal node number of pod and seed set and pollen viability were recorded during the experiments. Application of BAP improved pollen germination. The application of 10^–5 M BAP 4 days after flowering increased seed set at the lower nodes. Cold treatment (8/4°C day/night for 2 days) after the onset of flowering induced the formation of more pods and faster pod set compared to the non-cold treatment. The time to first seed was significantly reduced, and pollen viability was increased in plants exposed to cold treatment. Increased pollen viability also showed a significant positive correlation with seed setting. The combinations of 10^–5 BAP and cold treatment together had similar and independent effects. These results will accelerate plant breeding in faba bean by providing additional tools for reducing generation time.