Hybrid breeding of rice via genomic selection

Hybrid breeding is the main strategy for improving productivity in many crops, especially in rice and maize. Genomic hybrid breeding is a technology that uses whole‐genome markers to predict future hybrids. Predicted superior hybrids are then field evaluated and released as new hybrid cultivars after their superior performances are confirmed. This will increase the opportunity of selecting true superior hybrids with minimum costs. Here, we used genomic best linear unbiased prediction to perform hybrid performance prediction using an existing rice population of 1495 hybrids. Replicated 10‐fold cross‐validations showed that the prediction abilities on ten agronomic traits ranged from 0.35 to 0.92. Using the 1495 rice hybrids as a training sample, we predicted six agronomic traits of 100 hybrids derived from half diallel crosses involving 21 parents that are different from the parents of the hybrids in the training sample. The prediction abilities were relatively high, varying from 0.54 (yield) to 0.92 (grain length). We concluded that the current population of 1495 hybrids can be used to predict hybrids from seemingly unrelated parents. Eventually, we used this training population to predict all potential hybrids of cytoplasm male sterile lines from 3000 rice varieties from the 3K Rice Genome Project. Using a breeding index combining 10 traits, we identified the top and bottom 200 predicted hybrids. SNP genotypes of the training population and parameters estimated from this training population are available for general uses and further validation in genomic hybrid prediction of all potential hybrids generated from all varieties of rice.     

Preliminary research of the RAPD molecular marker-assisted breeding of the edible basidiomycete Stropharia rugoso-annulata

Summary The average RAPD molecular genetic distance was proposed as a criterion in selecting monokaryotic parents for cross breeding and predicting the performance of hybrids of the mushroom Stropharia rugoso-annulata. Three groups of cross pairs or hybrids were recognized based on the average RAPD genetic distance of the monokaryotic parental population. The RAPD-based molecular genetic distance significantly correlated with hybrid mycelial growth rate and mycelial growth heterosis, and their determination coefficients were 0.9237 and 0.8464 respectively. One of the hybrids in group I showed more vigorous mycelial growth in different pH conditions, incubation temperatures, carbon and nitrogen sources, and higher mushroom yield compared with its dikaryotic parent. These results suggested that RAPD-based molecular genetic distance of the monokaryotic parents might be a suitable criterion for selecting monokaryotic parents and predicting the performance of hybrids in mushroom cross breeding.     

Inheritance of resistance against northern leaf blight of maize using conventional breeding methods

Maize (Zea mays L.) is one of the important cereal crops along with wheat and rice worldwide. The purpose of this study was to use classical genetic approaches to assess the resistance of various maize parents and hybrids to the northern corn leaf blight (NCLB) disease in two different locations in Egypt. Eight parents, 28 F1, and 2 check hybrids were evaluated. The analysis of variance showed high significant variations between maize parents and their hybrids for the studied parameters and NCLB disease, besides there are significant variations between both locations. Results of maize parents showed that Sids 63, Giza 602, and Giza 628 cultivars exhibited the highest values and were resistant to NCLB in both locations comparing with Nubaria 39 and Gemmiza 18 that were susceptible to NCLB disease. Concerning the maize hybrids, analysis of variance and mean squares of growth characters in both locations indicated high significant variations between the maize hybrids including the check hybrids. When combined between the two locations for current parameters against NCLB, the data pointed that the Sakha location values for maize hybrids were much closed to the combining data in parents and the hybrids detected high resistance to this disease comparing with Nubaria location. All tested maize lines (38 lines), including parents and hybrids were classified as follows, two lines were rated as 1 (highly resistant), three were rated as 2 (resistant), sixteen were rated as 3 (moderate resistant), eight were rated 4 (moderately susceptible) and nine were rated 5 (susceptible). The data explaining that the crossing between high resistant maize cultivars produced high levels of resistance to NCLB disease. Therefore, our results verified that classical breeding could efficiently increase the resistance levels of maize germplasm against NCLB disease by developing new cultivars with superior performance in terms of grain yield, disease resistance and grain quality.     

Genetic aspects of resistance to cocoa swollen-shoot virus in Ghana

The inheritance of resistance in cocoa to infection with cocoa swollen-shoot virus was studied in seed inoculation experiments with progenies of Upper Amazon, Trinitario and West African Amelonado parents. In an eight parent diallel cross grown in two seasons and in six male × female factorial experiments, general combining abilities were much more important than specific combining abilities. The diallel cross revealed significant maternal effects but there was little evidence of specific reciprocal differences. Estimates of general combining abilities corresponded with expectation and were positively correlated with maternal effects, the latter indicating that tester parents should be used as males. The results from scaling tests with hybrids between selections from the River Nanay (a Peruvian tributary of the River Amazon) and Amelonado fitted a model with additive resistance; there was no evidence of dominance. Attempts to obtain stronger sources of resistance by hybridisation and selection were unsuccessful. In three crosses the resistance of individual seedlings was compared with that of the parents using test crosses but no evidence of transgressive segregation was obtained. In further experiments seedings of two hybrids between contrasting parents were heavily inoculated with virus so that few healthy survivors remained. Test crosses showed that these survivors and randomly selected seedlings of the same parentage did not differ as resistance sources.     

Genetic parameters of intra- and inter-specific hybrids of Eucalyptus globulus and E. nitens

Intra-specific hybrids within Eucalyptus nitens and E. globulus were compared directly with inter-specific E. nitens × globulus using common parents. Diameter (age 2, 4, 6, 10 years) and Pilodyn (age 6 years) were used as indirect measures of growth and wood density, respectively. Genetic parameters were estimated for all cross types and traits. A direct comparison of the general combining ability with the general hybridising ability was made. Heterosis was estimated for intra- and inter-specific hybrids. The intra-specific hybrids in both species exhibit intermediate heritabilities and levels of additive genetic variance. The inter-specific F1 E. nitens × globulus exhibited high incidence of abnormalities at young ages and high levels of later age mortality. The mean performance of surviving inter-specific F1 hybrids was generally intermediate for all traits, to varying degrees, between the parental intra-specific crosses, and there is little evidence for significant heterosis. Different provenances of E. globulus may exhibit different responses to hybridisation. In this case, the inter-specific F1 hybrids, using Taranna E. globulus, appear to perform worse on average than those using King Island provenance for growth traits. There is evidence that specific hybrid families are produced that outperform most of the pure species families for one or other of the traits examined; however, there is no reliable quantitative genetic method of predicting which parents should be used.     

双单杂交技术选育亮盖灵芝与白肉灵芝优良性状杂交子

以亮盖灵芝Ganoderma lucidum和白肉灵芝G. leucocontextum为亲本,采用亮盖灵芝异核体双核菌丝与通过原生质体单核化获得的白肉灵芝单核体进行双单杂交,最终获得34株杂交子。采用ISSR技术对34株杂交子及亲本进行DNA多态性聚类分析,杂交子主要分为两个类群。对杂交子进行生长速度和灵芝酸含量对比,筛选到4株优质杂交子。进一步进行杂交子及亲本间HPLC指纹图谱对比,发现4株杂交子中有3株HPLC指纹图谱在具备两个亲本特征灵芝酸的同时,还有低极性灵芝酸的产生。     

Features of the F1 hybrids of Hystrix longe-aristata and two Japanese Elymus species

Hybrids between species of Elymus and Hystrix were obtained by the embryo-rescue technique. The two Elymus species E. ciliaris and E. yezoensis were used in combinations with H. longe-aristata. All three species involved are indigenous to Japan. The hybrids had mainly a single spikelet per node like the Elymus parents, and the spikelets had few florets as in Hystrix. The microsporogenesis of the hybrids was highly anomalous, and the hybrid plants were completely sterile. In combination with E. yezoensis the anther development was inhibited at an early stage and microsporocytes were not found. The results indicate that the two genera are distantly related.     

Olfactory neuron responsiveness and pheromone blend preference in hybrids between Ostrinia furnacalis and Ostrinia nubilalis (Lepidoptera: Crambidae)

The olfactory receptor neuron (ORN) and behavioral responses of hybrids between the Asian corn borer (ACB), Ostrinia furnacalis, and the E-strain European corn borer (ECB(E)), Ostrinia nubilalis were examined and compared to the parental populations. In hybrids and both parents, the large-spike-size ORN was capable of responding to all four pheromone components of ACB and ECB, despite differences in which compounds elicited the greatest spike frequency in each population. There was a small-spiking ORN more narrowly tuned to the minor pheromone components in both ACB and ECB(E). In hybrids the homologous small-spiking ORN was tuned primarily to the ECB(E) minor pheromone component, with some responsiveness to the ACB minor component. Both species and all the hybrids had an intermediate spike-size ORN tuned primarily to their common behavioral antagonist. Dominance of responsiveness to the ECB(E) versus the ACB minor pheromone component on the small-spiking ORN may explain the greater tendency of hybrids to fly upwind to the ECB(E) pheromone blend than the ACB blend. This finding points toward a distinct evolutionary role for this ORN in allowing a pheromone shift.     

高粱的光合特性和杂种优势

从杂交高粱及其亲本的PEP羧化酶、丙酮酸磷酸二激酶、NADP-苹果酸酶和NAD-苹果酸脱氢酶活性比较了它们的光合碳代谢特性,也比较了它们在光合强度、CO_2补偿点和产量指标上的差异,分析了不同组合的杂种的叶面积和产量构成因素在各生育期的变化。高产的杂交种比其亲本有较高的关键酶活性、高光合强度和低的CO_2补偿点,其光合特性具有超亲优势,并在这些优势和增加体内物质向穗内分配的基础上增加了穗粒数。     

吉林省部分玉米种质资源抗玉米弯孢菌叶斑病鉴定研究

玉米弯孢菌叶斑病主要是由弯孢菌（Curvularia lunata）引起的侵染性病害。近年来,该病害在我国玉米主产区发生面积逐年扩大,已成为玉米重要病害之一。本文研究了吉林省主要玉米杂交种和自交系抗病性差异,结果表明：玉米杂交种间以及自交系间抗病性差异明显;吉63、黄早4、自330、丹9046、丹9041、铁7922、掖478、沈5003、丹340和E28等一批应用多年的种质资源均为感病类型（MS-HS）;而新选育的各类群一些种质和具有热带、亚热带血缘的78599等一些外来种质资源均为抗病类型（R～HR）。杂交种的抗病性与双亲的抗病性有密切关系;玉米杂交种苗期较抗病,抽丝期极为感病,这表明杂交种抗性随植株生长而递减。     

Expression of anatomical leaf traits in homoploid hybrids between deciduous and evergreen species of Vaccinium

We investigated the anatomical expression of leaf traits in hybrids between evergreen Vaccinium vitis‐idaea and deciduous V. myrtillus. We compared parents from four populations with their respective F1 hybrids and tested whether (i) transgression can be the source of novel anatomical traits in hybrids; (ii) expression of transgressive traits is more probable for traits with similar values in parents and intermediate for more distinct values, as predicted by theory; and (iii) independent origin of hybrids leads to identical trait expression profiles among populations. We found that anatomical leaf traits can be divided into four categories based on their similarity to parents: intermediate, parental‐like, transgressive and non‐significant. Contrary to the common view, parental‐like trait values were equally important in shaping the hybrid profile, as were intermediate traits. Transgression was revealed in 17/144 cases and concerned mainly cell and tissue sizes. As predicted by theory, we observed transgressive segregation more often when there was little phenotypic divergence, but intermediate values when parental traits were differentiated. It is likely that cell and tissue sizes are phylogenetically more conserved due to stabilising selection, whereas traits such as leaf thickness and volume fraction of the intercellular spaces, showing a consistent intermediate pattern across populations, are more susceptible to directional selection. Hybrid populations showed little similarity in expression profile, with only three traits identically expressed across all populations. Thus local adaptation of parental species and specific genetic background may be of importance.     

Recent natural hybridization between two allopolyploid wheatgrasses (Elytrigia, Poaceae): ecological and evolutionary implications

BACKGROUND AND AIMS: Natural hybridization was investigated between two predominantly allohexaploid wheatgrasses, weedy Elytrigia repens and steppic E. intermedia, with respect to habitats characterized by different degrees of anthropogenic disturbance. METHODS: Using flow cytometry (relative DNA content), 269 plants from three localities were analysed. Hybrids were further analysed using nuclear ribosomal (ITS1-5.8S-ITS2 region) and chloroplast (trnT-F region) DNA markers in addition to absolute DNA content and chromosome numbers. KEY RESULTS: Weedy E. repens was rare in a steppic locality whereas E. intermedia was almost absent at two sites of agricultural land-use. Nevertheless, hybrids were common there whereas none were found at the steppic locality, underlining the importance of different ecological conditions for hybrid formation or establishment. At one highly disturbed site, > 16 % of randomly collected plants were hybrids. Hexaploid hybrids showed intermediate genome size compared with the parents and additive patterns of parental ITS copies. Some evidence of backcrosses was found. The direction of hybridization was highly asymmetric as cpDNA identified E. intermedia as the maternal parent in 61 out of 63 cases. Out of nine nonaploid cytotypes (2n = 9x = 63) which likely originated by fusion of unreduced and reduced gametes of hexaploids, eight were hybrids whereas one was a nonaploid cytotype of E. repens. The progeny of one nonaploid hybrid demonstrated gene flow between hexaploid and nonaploid cytotypes. CONCLUSIONS: The results show that E. repens and E. intermedia frequently cross at places where they co-occur. Hybrid frequency is likely influenced by habitat type; sites disturbed by human influence sustain hybrid formation and/or establishment. Hexaploid and nonaploid hybrid fertility is not negligible, backcrossing is possible, and the progeny is variable. The frequent production of new at least partially fertile cyto- and genotypes provides ample raw material for evolution and adaptation.     

Different flooding responses in Rorippa amphibia and Rorippa sylvestris, and their modes of expression in F1 hybrids

The river floodplain species Rorippa amphibia, Rorippa sylvestris, and their hybrid Rorippa x anceps were studied here, with the aim of identifying potential species differences with respect to flooding tolerance, and of assessing their expression in F1 hybrids. Parents and their F1 hybrids were subjected to three flooding treatments mimicking natural conditions, and growth-related and leaf morphological traits were compared. In contrast to R. sylvestris, R. amphibia responded to waterlogging by forming specialized roots, and its growth was not reduced. These traits were dominantly expressed in hybrids. Both species and the hybrids established shoot growth over 2 wk of complete submergence. Only in R. sylvestris was this not at the expense of root biomass, suggesting that R. sylvestris can photosynthesize underwater. Rorippa sylvestris also showed a hyponastic response. Hybrids were intermediate to the parents in this respect. This study shows that phenotypic expression of parental traits in F1 hybrids is mostly additive, but can also be dominant. This suggests that a large overlap in habitat use of parents and hybrids is likely. If such an overlap occurs, the main evolutionary consequences of hybridization in Rorippa will be the introgression of genes, as the hybrids are fully fertile.     

用SSR标记鉴定大豆杂交组合F1的方法研究

为建立鉴定大豆杂种的方法,采用亲本间有多态性的3对SSR引物,对148个耐盐与盐敏感大豆品种正反交F1植株进行分子鉴定,结果表明,有81．8％的F1为真杂种,且3对多态性SSR引物检测结果一致;在亲本基因型纯合的情况下,采用1对在亲本间有多态性的SSR引物即可对F1真伪进行准确判断;亲本间分子量差异大的SSR位点可用高浓度琼脂糖电泳进行快速鉴定。利用该方法对2007年参加国家大豆区试的大豆杂交种品系H02—286的50粒种子进行纯度鉴定,进一步验证了SSR标记检测杂种真伪的可行性。     

曲穗草属天然杂种的鉴定及形成研究

本研究通过形态学、细胞学、系统发育分析等方法对小麦族曲穗草属(Campeiostachys)的两株疑似天然杂种进行鉴定,探究其可能的亲本及杂种形成机制.结果显示:两株天然杂种在形态上与短芒曲穗草(Cam-peiostachys breviaristata(Keng)Y.H.Zhou,H.Q.Zhang et C.R.Y...     

木兰科5个种间杂种减数分裂行为观察

对木兰科5个二倍体人工杂交后代的减数分裂行为进行观察。结果表明,各杂交F1代的减数分裂行为基本正常,在减数分裂中期I有个别二价体提前分开形成单体;中期I还存在异型二价体,说明杂交亲本间（种间）都有一定的遗传分化,但这种变异仅停留在基因水平上;后期I偶有染色体桥出现。杂种F1代的减数分裂过程基本正常,能形成生活力正常的生殖孢子。可预期的是自然界中木兰科属内种间的自然二倍体杂种可自行繁衍,经过一定繁衍周期后,即可形成具有相对稳定种群的新种。     

Frequency-dependent fitness of hybrids between oilseed rape (Brassica napus) and weedy B. rapa (Brassicaceae)

Fitness of interspecific hybrids is sometimes high relative to their parents, despite the conventional belief that they are mostly unfit. F(1) hybrids between oilseed rape (Brassica napus) and weedy B. rapa can be significantly more fit than their weedy parents under some conditions; however, under other conditions they are less fit. To understand the reasons, we measured the seed production of B. napus, B. rapa, and different generations of hybrid plants at three different densities and in mixtures of different frequencies (including pure stands). Brassica napus, B. rapa, and backcross plants (F(1) ♀ × B. rapa) produced many more seeds per plant in pure plots than in mixtures and more seeds in plots when each was present at high frequency. The opposite was true for F(1) plants that produced many more seeds than B. rapa in mixtures, but fewer in pure stands. Both vegetative and reproductive interactions may be responsible for these effects. Our results show that the fitness of both parents and hybrids is strongly frequency-dependent and that the likelihood of introgression of genes between the species thus may depend on the numbers and densities of parents and their various hybrid offspring in the population.     

Plant genetics affects arthropod community richness and composition: evidence from a synthetic eucalypt hybrid population

To examine how genetic variation in a plant population affects arthropod community richness and composition, we quantified the arthropod communities on a synthetic population of Eucalyptus amygdalina, E. risdonii, and their F1 and advanced-generation hybrids. Five major patterns emerged. First, the pure species and hybrid populations supported significantly different communities. Second, species richness was significantly greatest on hybrids (F1 > F2 > E. amygdalina > E. risdonii). These results are similar to those from a wild population of the same species and represent the first case in which both synthetic and wild population studies confirm a genetic component to community structure. Hybrids also acted as centers of biodiversity by accumulating both the common and specialist taxa of both parental species (100% in the wild and 80% in the synthetic population). Third, species richness was significantly greater on F1s than the single F2 family, suggesting that the increased insect abundance on hybrids may not be caused by the breakup of coadapted gene complexes. Fourth, specialist arthropod taxa were most likely to show a dominance response to F1 hybrids, whereas generalist taxa exhibited a susceptible response. Fifth, in an analysis of 31 leaf terpenoids that are thought to play a role in plant defense, hybrids were generally intermediate to the parental chemotypes. Within the single F2 family, we found significant associations between the communities of individual trees and five individual oil components, including oil yield, demonstrating that there is a genetic effect on plant defensive chemistry that, in turn, may affect community structure. These studies argue that hybridization has important community-level consequences and that the genetic variation present in hybrid zones can be used to explore the genetic-based mechanisms that structure communities.     

Inefficiency of genetic recombination in hybrids between Escherichia coli and Salmonella typhosa

An Escherichia coli Hfr strain in which three negative chromosomal alleles (leu(-), arg(-), and mtl(-)) were closely linked to three positive alleles (ara(+), rha(+), and xyl(+), respectively) was employed in matings with a Salmonella typhosa recipient. The detected expression of the negative E. coli alleles in S. typhosa hybrids selected for receipt of an associated positive E. coli marker was used to determine the occurrence of haploid S. typhosa recombinants, as distinguished from stable partial diploid hybrids. At the same time, the inheritance patterns and segregation behavior of the positive alleles provided indicators of the occurrence of partial diploid hybrids. Examination of both positive and negative markers inherited by ara(+), rha(+), and xyl(-) selected S. typhosa hybrid classes indicated that relatively short E. coli chromosomal segments (generally about 4 min or less in length) were involved in recombination (haploidy), whereas rather extensive E. coli genetic segments were conserved in the diploid state. S. typhosa hybrids selected for receipt of the ara(+) marker showed a 52% incidence of leu(-) haploidy, which is probably close to being an accurate measure of recombination at the site of the ara(+) allele. S. typhosa hybrids selected for receipt of the rha(+) or xyl(+) markers showed only a 20% incidence of arg(-) or mtl(-) haploidy, respectively, but both of these hybrid classes exhibited a higher incidence of conservation of extensive E. coli diploid segments than did the ara(+) selected class. Remating of haploid S. typhosa hybrids with recombinant xyl(+)mtl(-) or rha(+)arg(-) regions resulted in higher frequencies of hybrid recovery than were observed in the initial matings. However, there was a higher incidence of partial diploidy and a lower incidence of haploidy among the hybrids obtained from these rematings.     

马铃薯杂种F1的SSR鉴定

为选育抗黑痣病、高产优质的马铃薯新品种,选用引进品种‘大西洋’分别与‘陇薯6号’、‘陇薯7号’杂交,获得了杂种F1代,利用SSR标记技术对‘大西洋’与‘陇薯6号’的42个杂种F1、‘大西洋’与‘陇薯7号’的9个杂种F1单株进行了鉴定。从59对SSR引物中筛选出2对在亲本间存在差异、扩增稳定、条带清晰的引物S184和STM1049,用于‘大西洋’ב陇薯6号’杂种F1、‘大西洋’ב陇薯7号’杂种F1及其亲本的基因组DNA扩增。SSR带型分析显示,杂种F1的SSR带型呈双亲互补型、缺失型、父本型和母本型4类,依据带型特征鉴定出供试的51个马铃薯杂种F1单株均为真杂种,表明SSR分子标记技术用于马铃薯杂种真实性鉴定是可行的。该研究可为进一步开展马铃薯杂交后代目标性状优异株系选育提供依据。