Predicting heterosis for egg production traits in crossbred offspring of individual White Leghorn sires using genome-wide SNP data

Background

The development of a reliable method to predict heterosis would greatly improve the efficiency of commercial crossbreeding schemes. Extending heterosis prediction from the line level to the individual sire level would take advantage of variation between sires from the same pure line, and further increase the use of heterosis in crossbreeding schemes. We aimed at deriving the theoretical expectation for heterosis due to dominance in the crossbred offspring of individual sires, and investigating how much extra variance in heterosis can be explained by predicting heterosis at the individual sire level rather than at the line level. We used 53 421 SNP (single nucleotide polymorphism) genotypes of 3427 White Leghorn sires, allele frequencies of six White Leghorn dam-lines and cage-based records on egg number and egg weight of ~210 000 crossbred hens.

Results

We derived the expected heterosis for the offspring of individual sires as the between- and within-line genome-wide heterozygosity excess in the offspring of a sire relative to the mean heterozygosity of the pure lines. Next, we predicted heterosis by regressing offspring performance on the heterozygosity excess. Predicted heterosis ranged from 7.6 to 16.7 for egg number, and from 1.1 to 2.3 grams for egg weight. Between-line differences accounted for 99.0% of the total variance in predicted heterosis, while within-line differences among sires accounted for 0.7%.

Conclusions

We show that it is possible to predict heterosis at the sire level, thus to distinguish between sires within the same pure line with offspring that show different levels of heterosis. However, based on our data, variation in genome-wide predicted heterosis between sires from the same pure line was small; most differences were observed between lines. We hypothesise that this method may work better if predictions are based on SNPs with identified dominance effects.     

马氏珠母贝3个野生种群及种群间杂交后代遗传多样性的ISSR分析

运用ISSR分子标记技术分析了马氏珠母贝(Pinctada martensii)广西北海(BW)、广东大亚湾(DW)和海南三亚(SW)野生种群及其自繁子一代(BB1、SS1、DD1)和杂交子一代(BS1、BD1、DS1)9个群体各50个个体的遗传多样性.结果表明:3个野生群体遗传多样性分别是0.2585、0.2607和0.2571;3个自繁群体子一代遗传多样性分别是0.2504、0.2545和0.2527,3个杂交子一代遗传多样性分别是0.2747、0.2659和0.2784.种群间杂交增加了子代的遗传多样性,同时增加了杂交子一代与杂交亲本间的遗传距离,而自繁群体的遗传多样性与其来源的野生种群比较,遗传多样性降低.本文指出利用野生群体进行杂交育种应该纯化亲本才能获得杂种优势,人工育苗或选择性育种需要保持足够数量的繁殖亲本以避免遗传多样性降低.     

Maximizing crossbred performance through purebred genomic selection

Background

In livestock production, many animals are crossbred, with two distinct advantages: heterosis and breed complementarity. Genomic selection (GS) can be used to select purebred parental lines for crossbred performance (CP). Dominance being the likely genetic basis of heterosis, explicitly including dominance in the GS model may be an advantage to select purebreds for CP. Estimated breeding values for CP can be calculated from additive and dominance effects of alleles that are estimated using pure line data. The objective of this simulation study was to investigate the benefits of applying GS to select purebred animals for CP, based on purebred phenotypic and genotypic information. A second objective was to compare the use of two separate pure line reference populations to that of a single reference population that combines both pure lines. These objectives were investigated under two conditions, i.e. either a low or a high correlation of linkage disequilibrium (LD) phase between the pure lines.

Results

The results demonstrate that the gain in CP was higher when parental lines were selected for CP, rather than purebred performance, both with a low and a high correlation of LD phase. For a low correlation of LD phase between the pure lines, the use of two separate reference populations yielded a higher gain in CP than use of a single reference population that combines both pure lines. However, for a high correlation of LD phase, marker effects that were estimated using a single combined reference population increased the gain in CP.

Conclusions

Under the hypothesis that performance of crossbred animals differs from that of purebred animals due to dominance, a dominance model can be used for GS of purebred individuals for CP, without using crossbred data. Furthermore, if the correlation of LD phase between pure lines is high, accuracy of selection can be increased by combining the two pure lines into a single reference population to estimate marker effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-015-0099-3) contains supplementary material, which is available to authorized users.     

Marker-assisted breeding of Xa4, Xa21 and Xa27 in the restorer lines of hybrid rice for broad-spectrum and enhanced disease resistance to bacterial blight

Hybrid rice based on heterosis can significantly increase rice yield compared to inbred rice. Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive bacterial diseases that affect hybrid rice production. To breed a broad-spectrum and high disease resistance to BB in hybrid rice, we introduced the Xa4, Xa21 and Xa27 genes into the restorer lines of Mianhui 725 or 9311 genetic backgrounds and pyramided the three R genes in the progeny derived from the cross between the two lines. A near-isogenic line of the Xa27 gene in the genetic background of 9311 [9311(Xa27)] and another line with the Xa4 and Xa21 genes in the genetic background of Mianhui 725 (WH421) were firstly developed through marker-assisted selection. A new restorer line carrying Xa4, Xa21 and Xa27, designated as XH2431, was selected from the F8 progeny of the cross between 9311(Xa27) and WH421 through marker-assisted breeding and pedigree selection. XH2431 and II You 2431, the hybrids derived from cytoplasmic male-sterile line II-32A and restorer line XH2431, conferred high resistance to all 23 Xoo strains collected from 10 countries. XH2431 restored the fertility of II-32A to the normal level in the F1 generation. In addition, II You 2431 showed good agronomic traits under greenhouse conditions. The development of XH2431, 9311(Xa27) and WH421 provides a set of restorer lines with broad-spectrum and enhanced resistance to BB for hybrid rice.     

DNA fingerprint variability within and among parental lines and its correlation with performance of F1 laying hens

Genetic diversity within and among nine pure lines of Beijing White Leghorn chickens was determined by DNA fingerprinting using human ministatellite probes 33.6 and -globin 3HVR, as well as bacteriophage M13. Within lines similarity coefficients ranged from 0.497 to 0.628, significantly higher than that within a sample of white chicken from a local market. Relationships among lines were established by clustering analysis based on inter-line coefficients of difference calculated from DNA fingerprints of pooled DNA. A complete diallel crossing among the nine pure lines was conducted. By using linear correlation analysis, it was found that the maximum distance between parental lines was positively correlated with egg number, egg production, survival rate and their corresponding heterosis percentages within a pair of reciprocal crosses. Similar relationships were found where only the higher of the reciprocal crosses were used in the analysis. It was also shown that similarity coefficients within a sire line or dam line were positively correlated with 40-week egg number and its heterosis percentage and the heterosis percentage for 40-week egg production, but negatively correlated with the 40-week survival rate of the cross-bred populations.     

Heterosis is common and inbreeding depression absent in natural populations of Arabidopsis thaliana

The importance of genetic drift in shaping patterns of adaptive genetic variation in nature is poorly known. Genetic drift should drive partially recessive deleterious mutations to high frequency, and inter‐population crosses may therefore exhibit heterosis (increased fitness relative to intra‐population crosses). Low genetic diversity and greater genetic distance between populations should increase the magnitude of heterosis. Moreover, drift and selection should remove strongly deleterious recessive alleles from individual populations, resulting in reduced inbreeding depression. To estimate heterosis, we crossed 90 independent line pairs of Arabidopsis thaliana from 15 pairs of natural populations sampled across Fennoscandia and crossed an additional 41 line pairs from a subset of four of these populations to estimate inbreeding depression. We measured lifetime fitness of crosses relative to parents in a large outdoor common garden (8,448 plants in total) in central Sweden. To examine the effects of genetic diversity and genetic distance on heterosis, we genotyped parental lines for 869 SNPs. Overall, genetic variation within populations was low (median expected heterozygosity = 0.02), and genetic differentiation was high (median F_ST = 0.82). Crosses between 10 of 15 population pairs exhibited significant heterosis, with magnitudes of heterosis as high as 117%. We found no significant inbreeding depression, suggesting that the observed heterosis is due to fixation of mildly deleterious alleles within populations. Widespread and substantial heterosis indicates an important role for drift in shaping genetic variation, but there was no significant relationship between fitness of crosses relative to parents and genetic diversity or genetic distance between populations.     

鸡杂种与纯种间CIDH基因的差异表达及其与杂种优势的关系

运用银染mRNA差异显示技术进行鸡杂种优势分子遗传机理研究。在检测白洛克肉鸡(EE)和丝毛乌骨鸡(CC)纯种及其正反交杂种间的mRNA差异表达情况时,发现一个只在杂种表达的475bp的cDNA片段:CE15A15。经过反向Northern印记杂交和RT-PCR验证,发现该片段在杂种中表达增强。序列比对结果表明该片段与鸡部分cDNA序列(ID:AW198493)的相似程度高达97％,而这一序列又相似于墨西哥野鼠的细胞质异柠檬酸脱氢酶(CIDH)基因(ID:AF048831),说明CI15A15为鸡CIDH基因的部分cDNA。表型数据的统计分析表明,丝毛乌骨鸡(CC)和白洛克肉鸡(EE)正反交杂种(CE、EC)的活重和屠体性状与同期纯种相比都具有负优势,而脂肪性状则具有不同程度的正优势。由于CIDH直接参与了动物机体脂肪酸合成代谢,由此推断,该cDNA片段在鸡纯种和杂种中的差异表达可能与杂种优势形成有关。     

Theory of nucleus breeding schemes with overlapping generations

Summary Explicit methods are derived for estimating steady-state genetic responses and genetic differences between nucleus and base progeny crops in open nucleus breeding schemes which utilize genetic differences between progeny groups with parents of different ages or between age groups. Explicit methods are also given for estimating proportions which should be selected from the different nucleus and base selection groups so as to maximise genetic responses under each of a range of selection methods. Some basic differences between selection programmes utilizing genetic differences between progeny groups with parents of different ages and those utilizing genetic differences between age groups in nucleus breeding schemes are summarized.     

落羽杉与墨西哥落羽杉3个杂交后代品系的生长和杂种优势分析

以落羽杉〔Taxodium distichum(Linn.)Rich.〕和墨西哥落羽杉(T.mucronatum Tenore)及其3个杂交后代品系'中山杉405'('Zhongshansha 405')、'中山杉406'('Zhongshansha 406')和'中山杉407'('Zhongshansha 407')2年生盆栽扦插苗为研究对象,对株高和地径的年增长量、总叶面积、株高和地径的增长量动态变化、株高和地径的生长期进行了比较分析,并根据地径增长量分析了3个杂交后代品系的杂种优势.结果表明:3个杂交后代品系的年株高增长量介于父本与母本之间但无显著差异,而三者的年地径增长量和总叶面积则明显高于父本和母本.墨西哥落羽杉与3个杂交后代品系的株高和地径生长期均一致,分别为5月11日至10月5日和6月1日至11月9日;而落羽杉的株高和地径生长期分别为5月11日至8月10日和6月8日至11月16日.5月份至10月份,墨西哥落羽杉的株高持续增长,而3个杂交后代品系的株高不连续增长,落羽杉的株高则在8月10日之后停止生长;生长初期和生长末期,3个杂交后代品系的地径增长量均高于父本和母本;秋季3个杂交后代品系均能快速进行地径生长,而此时父本和母本的地径增长量均下降.除夏季的少数时间段外,'中山杉405'在整个生长季都表现出明显的杂种优势,而'中山杉406'和'中山杉407'在整个生长季总体上表现出杂种优势,且它们的杂种优势最大值均出现在生长后期,说明供试的3个杂交后代品系在秋季也能快速生长.研究结果显示:供试的3个杂交后代品系均遗传了落羽杉地径生长迅速和墨西哥落羽杉株高生长期长的特性,秋季3个杂交后代品系的地径和株高增长量总体上均高于父本和母本,表现出明显的杂种优势.     

DNA markers and crossbreeding scheme as means to select sires for heterosis in egg production of chickens

Genotypes for 24 microsatellite markers, dispersed across the chicken genome, were used to predict progeny performance and heterosis for egg production (number and mass) in 'layers' (egg-type chickens). These markers were used to evaluate genetic distance between each of 39 sires sampled from two-layer male-lines; Rhode Island Red (RIR) and White egg Leghorn (Leghorn), and a DNA pool of 30 randomly sampled females from a Brown-egg female line (Silver). Each sire was analysed for egg production across months in the laying period and cumulatively in each of three subperiods; onset (2 month), mid (9 month) and late (1 month). The average Reynolds' genetic distance between Leghorn sires and the Silver female line (theta;=0.6) was significantly higher than that between RIR sires and the Silver female line (theta;=0.5). Neither performance nor heterosis values in the RIR sire's daughters were associated with genetic distance values between sires and the Silver female line. On the other hand, performance as well as heterosis values of Leghorn's daughters were positively associated with genetic distance. This association was particularly evident in the mid-subperiod. If 25% of the most genetically distant Leghorn sires from the Silver female line had been selected in a single generation on the basis of DNA markers information only, average egg production of the crossbred daughters would have been improved by about nine eggs (3%). In principle, further improvement is possible if selection to increase genetic distance between the parental lines is carried on.     

Use of molecular markers in reciprocal recurrent selection of maize increases heterosis effects

We examined the effect of incorporation of molecular markers on variability between and within populations in order to maximize heterotic effects and longevity of a maize reciprocal recurrent selection program. Molecular variability was quantified by inter-simple sequence repeat (ISSR) markers between and within the maize populations Cimmyt and Piran?o in the 10th cycle of a reciprocal recurrent selection program. Forty-two S(1) progenies of each population were analyzed, these being families of full-sibs selected according to their agronomic traits. Thirteen primers were selected, which produced 140 bands; 114 of them were polymorphic and 26 monomorphic. Based on UPGMA grouping analysis and by genetic distances, it was possible to identify "contaminant" progenies. These progenies belong to the Piran?o or Cimmyt groups, but cluster in the opposite heterotic group. Identification of "contaminant" progenies is relevant for selection, because, besides identifying genotypes that should be eliminated at the recombination stage, it allows increased heterosis expression in crosses between more genetically distinct individuals. After the elimination of the "contaminant" progenies and those that were allocated between the heterotic groups, a new statistical analysis was carried out, which demonstrated increased genetic distances between the populations. It was concluded that the application of molecular markers in reciprocal recurrent selection programs allows the optimization of the monitoring of genetic variability within and between populations, favoring recombination between more distant progenies, besides ensuring increased longevity of the reciprocal recurrent selection program.     

Combined genetic analysis of partial blast resistance in an upland rice population and recurrent selection for line and hybrid values

The CNA-IRAT 5 upland rice population has been improved for 4 years by recurrent selection for blast resistance in Brazil. In order to predict the efficiency of recurrent selection in different test systems and to compare the relative advantage of hybrids versus pure line breeding, a combined genetic analysis of partial blast resistance in the CNA-IRAT 5 population was undertaken. A three-level hierarchical design in inbreeding and a factorial design were derived from the base population. Partial blast resistance of lines and hybrids was evaluated in the greenhouse and in the field by inoculation with one virulent blast isolate. The means and genetic variances of the hybrids and lines were estimated. Genetic advance by recurrent selection was predicted from estimates of variance components. The inheritance of partial blast resistance was mainly additive but non-additive effects were detected at both levels of means and variances. Mean heterosis ranged from 4%–8% for lesion size and lesion density to 10–12% for leaf and panicle resistance. High dominance or homozygous dominance variances relative to additive variance and negative covariance between additive and homozygous dominance effects were estimated. A low frequency of favourable alleles for partial resistance would explain the observed organisation of genetic variability in the base population. Recurrent selection will efficiently improve partial blast resistance of the CNA-IRAT 5 population. Genetic advance for line or hybrid values was expected to be higher testing doubled haploid lines than S1 lines, or than general combining ability. Two components of partial resistance assessed in the greenhouse, lesion size and lesion density, could be used as indirect selection criteria to improve field resistance. On the whole, hybrid breeding for partial blast resistance appeared to be slightly more advantageous than pure line breeding.     

Hybrid wheat: quantitative genetic parameters and consequences for the design of breeding programs

Key message

Commercial heterosis for grain yield is present in hybrid wheat but long-term competiveness of hybrid versus line breeding depends on the development of heterotic groups to improve hybrid prediction.

Abstract

Detailed knowledge of the amount of heterosis and quantitative genetic parameters are of paramount importance to assess the potential of hybrid breeding. Our objectives were to (1) examine the extent of midparent, better-parent and commercial heterosis in a vast population of 1,604 wheat (Triticum aestivum L.) hybrids and their parental elite inbred lines and (2) discuss the consequences of relevant quantitative parameters for the design of hybrid wheat breeding programs. Fifteen male lines were crossed in a factorial mating design with 120 female lines, resulting in 1,604 of the 1,800 potential single-cross hybrid combinations. The hybrids, their parents, and ten commercial wheat varieties were evaluated in multi-location field experiments for grain yield, plant height, heading time and susceptibility to frost, lodging, septoria tritici blotch, yellow rust, leaf rust, and powdery mildew at up to five locations. We observed that hybrids were superior to the mean of their parents for grain yield (10.7 %) and susceptibility to frost (?7.2 %), leaf rust (?8.4 %) and septoria tritici blotch (?9.3 %). Moreover, 69 hybrids significantly (P < 0.05) outyielded the best commercial inbred line variety underlining the potential of hybrid wheat breeding. The estimated quantitative genetic parameters suggest that the establishment of reciprocal recurrent selection programs is pivotal for a successful long-term hybrid wheat breeding.     

Prediction of heterosis in crosses between inbred lines of Drosophila melanogaster

Summary The aim of the experiment was to determine if the estimated genetic distance between two populations could be used to predict the amount of heterosis that would occur when they were crossed. Eight lines of known relatedness to each other were produced by eight generations of sib mating and sub-lining. This produced lines that varied in coefficient of coancestry from zero to 0.78. Fourteen reciprocal crosses of these lines were used to measure heterosis for larval viability and adult fecundity. Gene frequencies at six polymorphic enzyme loci were used to estimate the genetic distances between lines, which were then compared with the known degrees of coancestry. The estimated genetic differences were poorly correlated with the known coancestry coefficients (r=0.4), possibly due to the small number of loci typed. Also genetic distances were only about 1/3 of what was expected. Selection acting on blocks of genes linked to the enzyme loci probably prevented the expected increase in homozygosity. Coancestry coefficient was correlated with heterosis (r=0.44–0.71). This level of correlation implied differences in heterosis among parent lines with the same level of coancestry. This variability is expected if a small number of loci explain most of the heterosis. The average level of heterosis was less than expected after eight generations of sib mating. This is most likely due to selection opposing the increase in homozygosity caused by inbreeding. The combination of these two imperfect correlations resulted in no significant correlation between genetic distance estimated from markers and heterosis.     

Influence of parentage upon growth in Ostrea edulis: evidence for inbreeding depression

Genetic variability for growth was analysed in three populations of Ostrea edulis, selected for resistance to the protozoan parasite Bonamia ostreae. This study was undertaken first to determine the potential for selection for growth in populations that have never been selected for this character, and second to estimate heterosis versus inbreeding depression. Growth was monitored in culture for 10 months. The selected populations (namely S85-G3, S891-G2 and S89W-G2), their crossbred population and a control population were composed of full-sib families whose parents were already genotyped using five microsatellite markers. This genotyping allowed the estimation of genetic relatedness among pairs of parents. The parents' relatedness was then correlated with the growth performance of their offspring within each of the three populations, and inbreeding depression was estimated. The population effect for growth was highly significant, with the crossbred population having the highest growth rate, followed by S891-G2 and S89W-G2, S85-G3 and the control population. The within-populations family effect was also highly significant, indicating, as well as the high value for heritability at the family level (between 0.57 and 0.92), that a potential for a further selection for growth still exists within the three populations. Estimates of inbreeding depression (relative to the mean, for complete inbreeding) were high (1 for S891-G2, 0.44 for S89W-G2 and between 0.02 and 0.43 for S85-G3), which correlates with the apparent heterosis for growth observed in the crossbred population. These results are discussed in the context of the future management of the selected populations.     

Line and crossing effects in a diallel mating system with highly inbred lines of White Leghorn chickens

Summary Seven highly inbred lines of White Leghorn chickens were used in a near complete diallel mating plan during eight years. The lines originated from three different base populations selected for egg weight. Average inbreeding coefficients of parents of chicks hatching in successive years were 0.75, 0.80, 0.84, 0.86, 0.89, 0.91, 0.93 and 0.94. The composition of line, specific combining ability and reciprocal effects and their estimated values are given. These effects were estimated for age at first egg (AFE), average weight of all eggs laid to 40 weeks (EW40), body weight at 40 weeks (BW40), number of eggs to 40 weeks (EP40) and number of eggs between 41 and 60 weeks (EP60). Records of 3247 hens surviving to 40 weeks and of 3133 birds to 60 weeks could be used. Large differences between line effects could be found in all traits. They were only partly due to the preceding selection in the base populations. All specific combining effects were in the expected direction, negative for AFE and positive for EW40, BW40, EP40 and EP60. Recovery of inbreeding depression inflated these effects rather substancially. Average heterosis, defined as the relative superiority of a line combination over the mid parent value, was –11.3%, 5.8%, 7.8%, 45.1% and 35.8% for AFE, EW40, BW40, EP40 and EP60 respectively. One line showed a relative superiority in AFE of -19.3% compared to about –7.9% for all other combinations. Reciprocal or sex-linked effects were generally smaller in all traits than specific combining effects, they were considerably smaller in AFE, EP40 and EP60. General reciprocal effects could be found for several lines in one or more traits. Offspring of two lines, when used as sire lines, showed a negative correlation between reciprocal effects of egg weight and body weight.     

玉米自交系间遗传距离与产量杂种优势,杂种产量的关系

以13个玉米自交系及其按双列杂交配制的78个单交种为材料,研究性状选择、亲本选择对遗传距离与产量杂种优势、杂种产量关系的影响,结果表明:(1)当性状数较少时,遗传距离与产量杂种优势、杂种产量的关系因性状的不同而异;当性状数较多时,遗传距离与产量杂种优势、杂种产量的关系为抛物线,受性状影响较小;(2)当所选亲本材料的遗传差异较大时,遗传距离与产量杂种优势的关系为抛物线;当所选亲本材料的遗传差异较小时,遗传距离与产量杂种优势的关系为直线或不相关。     

Asymmetries,heterosis, and phenotypic profiles of red junglefowl,White Plymouth Rocks,and F<Subscript>1</Subscript> and F<Subscript>2</Subscript> reciprocal crosses

During the domestication of farm animals, humans have manipulated genetic variation for growth and reproduction through artificial selection. Here, data are presented for growth, reproductive, and behavior traits for the red junglefowl, a line of White Plymouth Rock chickens, and their F₁ and F₂ reciprocal crosses. Intra- and intergenerational comparisons for growth related traits reflected considerable additive genetic variation. In contrast, those traits associated with reproduction exhibited heterosis. The role of sexual selection was seen in the evolution of prominent secondary sexual ornaments that lend to female choice and male-male competition. The large differences between parental lines in fearfulness to humans were only mitigated slightly in the intercross generations. Whereas, overall F₁ generation heterosis was not transferred to the F₂, there was developmental stability in the F₂, as measured by relative asymmetry of bilateral traits. Through multigenerational analyses between the red junglefowl and the domestic White Plymouth Rocks, we observed plasticity and considerable residual genetic variation. These factors likely facilitated the adaptability of the chicken to a broad range of husbandry practices throughout the world.     

Exploitation of heterosis for carotenoid content in African marigold (<Emphasis Type="Italic">Tagetes erecta</Emphasis> L.) and its correlation with esterase polymorphism

African marigold (Tagetes erecta L.), a major source of carotenoids, is also grown as a cut flower and a garden flower in addition to being grown for its medicinal values. We studied gene action, combining ability and heterosis, aiming at genetic improvement of T. erecta for enhanced carotenoid content in petals, and report for the first time that heterosis can be exploited for total carotenoids and its commercially important fractions. Total content of carotenoids and lutein appears to be governed by dominance (or non-additive) gene action, while content of xanthophyll esters is governed by both additive and dominance (or non-additive) gene actions. Specific combining ability variance was predominant for all the three traits. General and specific combining abilities and heterosis were highly significant. Heterobeltiosis was also positive. General combining ability (GCA) variances were not significantly correlated to performance per se. There was also no correlation between performance per se of normal petalled pollen parents and the performance of crosses made between male-sterile (female) and male-fertile (pollen) parents. These findings suggest that carotenoid content should not be the only criterion considered in the selection of parental lines. Studies on esterase in seeds and peroxidase in seedlings revealed a relatively high level of polymorphism in esterase with a total of 14 isoforms, whereas peroxidase showed low polymorphism. Similarity indices between different parental combinations, calculated based on seed esterase polymorphism, showed a significant negative correlation (r = -0.479, P = 0.05) with heterosis for carotenoid content. This indicates that the selection of parents with wider variation in their esterase profiles may possibly be exploited for genetic enhancement of carotenoids in T. erecta.     

针茅水孔蛋白基因多态性分析及其地理分布

以分布于内蒙古的草甸草原(森林草原)、典型草原、荒漠草原上的7种针茅属植物为材料,利用聚合酶链反应-单链构象多态性(PCR-SSCP)方法,分析了水孔蛋白基因的外显子1和内含子1的遗传多态性.结果表明:外显子1有AA、BB和CC 3种基因型,内含子1有DD、EE、FF和GG 4种基因型;种间存在基因多态性,种内没有多态性,所有种均表现出遗传的单态性和100%的纯合度.从基因型地理分布看,AA基因型在草甸草原、森林草原、典型草原及荒漠草原区的针茅种上均有分布,BB、CC基因型只分布在荒漠草原区的针茅中;DD基因型分布于草甸草原、森林草原及典型草原区的针茅属植物中,荒漠草原区分布有EE、FF、GG等3种基因型.荒漠草原区的植物是旱生程度最强的一类草原群落,该区的3种针茅具有丰富的遗传多态性.