Using yield quantitative trait locus targeted SSR markers to study the relationship between genetic distance and yield heterosis in upland cotton (Gossypium hirsutum)

The objective of this study was to examine the relationship between heterosis and genetic distance in upland cotton (Gossypium hirsutum L.). Heterosis in the different environments was evaluated and the relationship between heterosis and genetic distance (GD) was determined based on SSR markers for yield quantitative trait loci (QTL). Yields of seed cotton and lint showed a linear relationship with mid‐parent heterosis (MPH) and better‐parent heterosis (BPH). The variation in heterosis for other traits and their correlation with GD may be due to environmental factors or the effort of QTLs tested in the present study may vary in different environments. The present findings provide a foundation for heterotic grouping of parental lines and breeding of new cotton hybrids with improved seed cotton yield. This study calls for more research with stable QTLs as well as advance molecular marker techniques may be used in predicting yield heterosis in a more precise and reliable manner.     

杂交水稻产量及农艺性状杂种优势分析

为探讨杂种优势与双亲值、双亲一般配合力（GCA）、组合特殊配合力（SCA）、双亲遗传距离的关系,利用10个不育系和10个恢复系,按不完全双列杂交配制100个组合,对杂交水稻产量及农艺性状的杂种优势进行了分析,探索杂种优势的预测方法。结果表明：杂种一代的超亲优势和对照优势主要体现在穗长、每穗总粒数、每穗实粒数几个性状上,其具有正向超亲优势组合的比例分别达到61.0%、66.0%和53.0%,具有正向对照优势的比例分别为62.0%、78.0%和79.0%,结实率性状具有正向对照优势的比例也达到58.0%。杂种优势与父母本值、父母本平均值、高亲值、低亲值及父母本差值都有较为密切的关系,超亲优势与高亲值在8个性状上都极显著相关;对照优势与母本值、父母本平均值、高亲值都呈显著或极显著正相关。杂种优势与SCA和亲本的GCA效应值密切相关,特别是对照优势与SCA和双亲的GCA都呈显著或极显著正相关,同时与父母本的GCA之差和之和都有较大的关系。杂种优势与遗传距离的关系比较复杂,当遗传距离在5~5.5范围内,双亲的距离越远,杂种优势越强。     

Marker-assisted increase of genetic diversity in a double-low seed quality winter oilseed rape genetic background

Generation of novel genetic diversity for maximization of heterosis in hybrid production is a significant goal in winter oilseed rape breeding. Here, we demonstrate that doubled haploid (DH) production using microspore cultivation can simultaneously introgress favourable alleles for double‐low seed quality (low erucic acid and low‐glucosinolate content) into a genetically diverse Brassica napus genetic background. The DH lines were derived from a cross between a double‐low quality winter rapeseed variety and a genetically diverse semisynthetic B. napus line with high erucic acid and high glucosinolates (++ quality). Twenty‐three low‐glucosinolate lines were identified with a genome component of 50–67% derived from the ++ parent. Four of these lines, with a genome component of 50–55% derived from the ++ parent, also contained low erucic acid. Heterosis for seed yield was confirmed in test‐crosses using these genetically diverse lines as pollinator. The results demonstrate the potential of marker‐assisted identification of novel genetic pools for breeding of double‐low quality winter oilseed rape hybrids.     

以半冬性甘蓝型油菜为亲本增强春性甘蓝型油菜杂种优势

以春性恢复系与半冬性品种(系)杂交后选育的16份新春性恢复系及其4个亲本系[2个半冬性甘蓝型油菜品种(系)和2个春性甘蓝型恢复系]、2个春性甘蓝型不育系为材料, 利用SSR、SRAP和AFLP分子标记技术分析材料间的遗传差异, 同时利用以上2个春性不育系分别与12个新春性恢复系和1个春性亲本恢复系Ag-5进行NCII双列杂交, 测定其杂种优势及杂种表现。16份新恢复系中除931和帐23外, 其余的14份新恢复系与2个不育系的遗传距离均大于其春性亲本恢复系与相应不育系的遗传距离, 说明导入半冬性品种遗传成分能扩大春性恢复系与不育系间的遗传差异; 配制的26个杂交组合中, 其双亲中不育系所对应保持系单株产量为高亲值的组合有15个, 其中13个组合单株产量超亲优势都强于所对应不育系与亲本恢复系Ag-5所配杂交组合, 说明导入半冬性品种遗传成分可增强甘蓝型春油菜杂种优势; 12个新恢复系分别与2个不育系所配24个组合中18个组合的单株产量都分别超过所对应不育系与亲本恢复系Ag-5所配杂交组合, 说明导入半冬性品种遗传成分能提高甘蓝型春油菜杂种的产量; 新恢复系与2个不育系杂交后代的抗病性均强于其亲本恢复系与相应不育系杂交后代的抗病性, 说明导入半冬性品种遗传成分能提高春性甘蓝型油菜杂交种抗菌核病的能力。研究结果表明, 半冬性甘蓝型油菜品种可能为春油菜杂交育种提供有价值的遗传资源。     

Relationship between heterosis and genetic distance based on morphological traits and AFLP markers in pepper

Genetic diversity is considered as one of the criteria for the selection of parents for hybrid breeding. The present study was undertaken to evaluate genetic divergence among seven pepper cultivars and to assess the relationship between heterosis and parental genetic distance. Twenty‐one F₁ hybrids and seven parents were evaluated for 15 morphological characters in a greenhouse and in the field. The parents were examined for DNA polymorphisms using six amplified fragment length polymorphism (AFLP) primer combinations. Cluster analysis using two genetic distance measures grouped the seven parents differently. Mid‐parent and high‐parent heterosis was observed for most characters. Most hybrids outperformed the parental lines for fruit yield, earliness and plant height. Morphological and AFLP‐based distance measurements were efficient enough to allocate pepper genotypes into heterotic groups. The correlations of morphological distances with mid‐parent heterosis were significant for days to flowering and maturity, suggesting earliness can be predicted from morphological distances of parental lines. However, the correlations of AFLP‐measured genetic distances with mid‐ and high‐parent heterosis were non‐significant for all characters, except for fruit diameter, and proved to be of no predictive value.     

Genetic analysis of rapeseed self-incompatibility lines reveals significant heterosis of different patterns for yield and oil content traits

Self‐incompatibility is one of the most effective approaches to utilizing heterosis in oilseed rape around the world. To evaluate the heterosis of double low self‐incompatibility, the possibility of combining seed yield and oil content, and the genetic effects of parents on their hybrid progenies, a 2‐year field trial using a 3 × 22 NC II mating design was conducted during the 1999‐2001 growing seasons in Wuhan, China. Significant differences in seed yield per plant and seed oil content were observed among the F1 hybrids and between F1 progenies and their parents. However, the heterosis for seed yield per plant was much greater than that for seed oil content. Mid‐parent heterosis and high‐parent heterosis of seed yield per plant ranged from 5.50 to 64.11% and from –2.81 to 46.02%, while those of seed oil content ranged from –1.55 to 7.44% and –3.61 to 6.55%, respectively. Non‐additive genetic effects were a major mechanism that accounted for the yield heterosis in addition to additive effects. In contrast, seed oil content heterosis was mainly dependent on an additive genetic effect. General combining ability (GCA) determined the stability of hybrid cultivars. In hybrid breeding, parental materials might be selected by the sum of GCAs and variances of special combining abilities (SCAs) of female and male parents for traits affected by both additive and non‐additive effects, and by the sum of GCAs of two parents for traits controlled mainly by additive effects. Primary branches and their siliques were the most important yield traits.     

Combining ability of non‐adapted sources for male‐fertility restoration in Pampa CMS of hybrid rye*

Hybrid rye breeding and seed production relies on the cytoplasmic male sterility‐inducing Pampa (P)‐Cytoplasm. High levels of restoration were recently found in non‐adapted rye accessions from Argentina (Pico Gentario, Pastoreo Massaux) and Iran (IRAN IX). To analyse their relative superiority, five seed‐parent lines in P cytoplasm were crossed with five inbred lines of these sources and four adapted restorer lines. The 45 F1 hybrids were tested for male‐fertility restoration in three locations. Significant (P = 0.01) general and specific combining ability (GCA and SCA respectively) for male‐fertility restoration were found. The non‐adapted restorer lines were able to restore all seed‐parent lines similarly, resulting in hybrids with 55‐90% pollen shedding (mean 78%) compared with 2‐74% pollen shedding (mean 44%) when adapted restorer lines were used. Significant (P = 0.05) SCA effects were detected in 11 of 45 combinations, nine of them were crosses with adapted pollinator lines. Non‐adapted restorer lines showed a high phenotypic stability of male‐fertility restoration across locations. Introgression of these exotic sources into the adapted restorer gene pool by repeated backcrossing should result in environmentally stable male fertility in Pampa‐based rye hybrids.     

Hybrid performance and AFLP- based genetic similarity in faba bean

Successful prediction of heterosis and performance of F₁-hybrids from the genetic similarity of their parents based on molecular markers has been reported in several crops and can be very helpful in hybrid breeding. The relationship between genetic similarities based on amplified fragment length polymorphism (AFLP) of 18 European faba bean lines and their hybrid performance and heterosis was investigated. Parental lines, 62 F₁-hybrids and their F₂-progenies were evaluated in field trials in four environments in Germany for seed yield, 1,000-seed weight and plant height. Results clearly demonstrated a stable superiority of the hybrids over their inbred parents and elite check cultivars, and showed a marked and varying amount of heterosis. Parental seed yield and F₂-hybrid yield were promising as predictors for F₁-hybrids. AFLP analysis of the 18 inbred lines using 26 EcoRI/MseI primer combinations resulted in 1202 polymorphic fragments. Cluster analysis based on genetic similarity estimates unambiguously identified pedigree-related inbred lines. No clear separation of the 18 inbred lines into subgroups was detected. Correlation coefficients between genetic similarity estimates and either heterosis or F₁-hybrid performance were small and not useful. Also correlations between specific genetic similarity and specific combining ability were too small for all traits to be of predictive value. Results showed that AFLP-based genetic similarities are not useful to predict the performance of hybrids or heterosis within the elite European faba bean gene pool.     

应用遣传距离预测爆裂玉米杂种优势

根据80个爆裂玉米自交系数量性状的表现估算了它们之间的遗传距离及它们之间随机组配的67个杂交组合F_1代小区产量、爆粒率和膨胀倍数的杂种优势。相关和回归分析表明,F_1代产量的成分照优势与其双亲之间的遗传距离呈显著的二次曲线关系,而F_1代品质特性爆粒率和膨胀倍数的对照优势与其双亲之间的遗传距离无确定性关系。因此,可以根据亲本间数量性状的综合遗传差异——遗传距离预测爆裂玉米杂种一代产量优势。     

Genetic distance and its association with heterosis in peas

Summary The relationship between the genetic distance of parents and both the heterosis of F₁ hybrids and the variance of F₅ lines was investigated in 72 crosses of pea (Pisum sativum L.). The genetic distance between each pair of parents was estimated, using isozyme (GDi), morphological (GDm) or quantitative (GDq) markers and finally a combination of isozyme and morphological markers (GDi+m). GDm was poorly correlated with the other measures of genetic distance, which in turn were strongly correlated with each other. Genetic distance was moderately correlated with the level of heterosis for yield over midparent in the F₁ generation, with the highest correlation obtained from GDi+m. GD was not significantly correlated with heterosis for yield over the better or best parent but it was significantly correlated with all three measures of heterosis for pods per plant and hundred seed weight. There was no correlation between genetic distance and the level of heterosis for yield and total dry matter in the F₂ generation, but GDi, GDi+m and GDq were predictive for the level of inbreeding depression in grain yield and total dry matter. When parents were high in genetic distance, crosses produced highly transgressive segregants for basal branches per plant, hundred seed weight, harvest index and onset of flowering. Genetic distance between parents was thus a useful measure for predicting a portion of hybrid performance and also of the variance of derived inbred lines. It was concluded that when choosing parents for a cross, consideration should be given to their genetic distance as well as their overall adaptation and their yield. There is considerable potential for optimising choice of parental combinations in the development of improved pea cultivars.     

Retrotransposon-related genetic distance and hybrid performance in sunflower (Helianthus annuus L.)

Heterosis is a main force leading the development of the hybrid seed industry in sunflower. The purpose of this study is to evaluate if heterosis effects for morphological traits among sunflower hybrids can be related to differences in the repetitive component of the genome of parental lines. The assumption is that, at least for certain traits, heterosis results from mutations in the cis-regulatory elements of genes, largely related to retrotransposon insertions and/or removals. Our experimental approach consists of a correlation study between hybrid performance and retrotransposon-related genetic distances between inbreds. Six sunflower inbred lines of different origin were crossed in a half diallel fashion; comparing parental lines and hybrids, mid parent heterosis of F₁ hybrids was evaluated for six traits. We estimated the parental genetic distances between the six inbreds on data gathered by the inter-retrotransposon-amplified-polymorphism (IRAP) protocol. Different retrotransposons previously isolated in sunflower were targeted by 11 primer pairs designed on conserved LTR domains. As a control, genetic distances were also calculated using 86 genic SNPs. We analysed the correlation between the mid-parent heterosis for each of the six traits analysed and the genetic distance (calculated on data obtained by SNP or IRAP analyses) between the parental lines. Differences between parents showed to be largely related to variations in the retrotransposon component of the genome. Retrotransposon-related genetic distance between parents resulted to be larger than that related to genic SNPs, and significantly correlated to seed yield and, at a lesser extent, to plant height and stem diameter in hybrids. The hypothesis that variations in the repetitive component of the genome, especially LTR-retrotransposons, affect the displaying of heterosis is discussed.     

细胞质雄性不育海岛棉与陆地棉三交种的杂种优势表现

 以海岛棉和陆地棉不育系及其恢复系为杂交亲本,配制了10个海岛棉与陆地棉种间三交种（简称海陆三交种）和4个单交种。经两年田间试验表明,海陆三交种相对于海海单交种产量极显著提高,与海陆单交种无显著差异,但比陆陆单交种显著减产;纤维品质接近于海陆单交种,显著高于陆陆单交种;制种产量虽然不及陆陆单交种,但比海海单交种显著增产。选育海陆三交种应注重选择早熟的海岛棉不育系,高衣分的陆地棉临时保持系,大铃的陆地棉恢复系,且叶型和株型相对一致的亲本配制组合。     

基于SSR标记的不同组群杂交中籼稻亲本配组优势分析

本研究利用48个SSR标记将12个不育系(保持系)、8个恢复系划分为4个组群,并利用NCⅡ设计共配制96个组合,研究不同组群亲本配组的杂种优势表现。研究结果表明,不育系和恢复系分别被分为3和2个组群,共产生6种配组模式,两系主栽不育系×扬稻6号类群恢复系(G2×G3)、三系保持系×三系恢复系(G4×G1)、扬稻6号类群不育系×三系恢复系(G3×G1)三类配组模式杂种优势明显。进一步研究显示遗传距离与杂种优势之间相关不显著。生育期是三系恢复系与两系主栽不育系配组(G2×G1)杂种低产的限制因子。扬稻6号类群不育系×三系恢复系(G3×G1)是一种新的杂种优势模式,因此,筛选、培育与扬稻6号属于同一类群的新型不育系,可进一步拓宽现有三系恢复系的利用范围,提高籼型杂种优势利用水平。     

全生育期耐盐恢复系在正常灌溉条件下性状表现及耐盐杂交稻的选育

利用前期以明恢86为轮回亲本与全球水稻分子育种计划的4个供体亲本(Gayabyeo、沈农265、早籼14和Y134)杂交构建的高代回交导入群体,在浙江省三门县沿海滩涂采用0.5%盐浓度的海水全生育期灌溉,筛选出150个耐盐恢复系群体,考察了耐盐恢复系在正常灌溉条件下的性状分离及与两个三系不育系测交种的优势表现。结果表明,耐盐恢复系在正常灌溉条件下的产量及其相关性状出现明显的分离,性状分离的类型及特点因选择群体和性状本身不同而异,从中选育出30个单株产量和耐盐性显著好于轮回亲本明恢86的株系,这些株系大多表现穗长缩短,株高和千粒重下降,但单株有效穗和结实率显著增加,导致产量的显著提高。4个组合的耐盐恢复系群体与两个三系不育系(II-32A和川345A)测交种的性状分离明显,与明恢86和两个三系不育系的测交种相比,多数测交种表现穗长缩短,株高降低,单株有效穗数相仿,但与II-32A测交的杂种千粒重显著增加,杂种表现趋势与耐盐恢复系本身不完全相同。分别鉴定出22个和23个耐盐恢复系,其与两个不育系测交的杂种产量显著高于明恢86与相应不育系的测交种,表现出较强的杂种优势,其中比生产对照种汕优10号显著或极显著增产的测交组合分别有7个(II-32A为母本)和4个(川345A为母本)。研究表明,利用优良恢复系的回交导入后代在大田盐胁迫条件下筛选耐盐单株,结合耐盐后代在正常灌溉条件下产量及相关性状的鉴定筛选,可以有效地改良恢复系的耐盐性,并选育出耐盐性提高的强优势组合。     

西南骨干玉米自交系主要农艺性状和产量正反交杂优效应分析

为了比较玉米自交系主要农艺性状和产量的正反交杂优效应,以9份西南地区骨干玉米自交系组配的72份单交种为材料,采用随机区组试验,对自交系及其正反交杂种F1代主要农艺性状和产量进行比较研究。结果表明,正反交效应对不同玉米自交系杂种F1代主要农艺性状和产量的影响不同;T检测表明,大多数玉米自交系正反交杂种F1代主要农艺性状和产量差异不显著。玉米自交系海9-21、5003、478正反交杂种F1代在穗粗、百粒重、单穗粒重、穗下茎节强度及穗位高等性状上差异显著或极显著。由此得出,不同自交系正反交杂种F1代在主要农艺性状和产量上具有不同的杂种优势,其中穗位高/株高具有负向杂种优势。由于玉米穗位高/株高具有负向杂种优势,即杂种F1代穗位高/株高值较自交系有所降低,因此在自交系选育时,不宜对亲本材料过分追求低的穗位高/株高。     

Conversion of the RAPD OPC021150 marker of the Rfo restorer gene into a SCAR marker for rapid selection of oilseed rape

The Rfo fertility restorer gene for the Ogura cytoplasmic male sterility (CMS) applied for oilseed rape hybrid seed production can be monitored with the use of the RAPD OPC02₁₁₅₀ marker while molecular breeding. The aim of this work was to convert the RAPD marker into a more suitable SCAR marker. Total DNA was isolated from a doubled haploid line derived from the line BO20 (INRA, France). A fragment of 1150‐bp linked to the Rfo gene was PCR amplified with the use of the RAPD OPC02 primer, cloned and sequenced. A pair of primers was designed and PCR amplification was performed to develop a SCAR marker for the Rfo gene. The new marker was applied for analysis of 220 oilseed rape lines comprising doubled haploid and inbred restorer lines, restored hybrids as well as F₁ and F₂ recombinant generations involving restorer lines. Simultaneously, the RAPD OPC02 marker was used and it revealed that the markers are equivalent to each other. However, the developed new SCAR marker has made the analysis more practical, rapid and efficient.     

Hybrid performance and heterosis in strawberry (Fragaria × ananassa Duchesne), regarding acidity,soluble solids and dry matter content in fruits

A top‐cross‐mating design among 29 S₄ inbred lines and tester (cultivar ‘Dukat’) was carried out to study their breeding value in terms of general combining ability (GCA). The objectives of this study were to evaluate the acidity, soluble solids and dry matter contents in fruits of progeny F₁ in comparison with S₄ inbred lines as well as the cultivars (S₀); identify strawberry genotypes with high value of GCA for use in cultivar development; and determine mid‐parent heterosis regarding S₄ inbred lines and cultivated strawberry. The 2‐year observations showed statistically significant differences between tested genotypes in terms of the studied traits. The highest breeding value based on GCA was estimated for Chandler 123‐5 for soluble solids and dry matter content, and Kent 7‐6 for acidity. Estimated mid‐parent heterosis had positive and negative values. The highest heterosis in terms of extract and dry matter content (26.71% and 17.50%, respectively) occurred in the offspring Chandler 123‐5 × ‘Dukat’, but as regards acidity in hybrid Chandler 123‐22 with cv. ‘Dukat’. The study of genetic divergence by dendrograms may help to identify parents suitable for obtaining hybrids with higher heterosis effects.     

Inheritance and potentials of a mutated dwarfing gene ndf1 in Brassica napus

A dwarf mutant ‘NDF‐1′, approximately 70 cm high, was derived from a 200‐cm high doubled haploid (DH) line ‘3529’ (Brassica napus), seeds of which were jointly treated with chemical inducers and bombardment of fast neutron. The leaves of the ‘NDF‐1’ mutant were wrinkled and thicker compared with the wild‐type control. The mutant had much lower values than its original parents for all agronomic traits, except for its seed weight. A genetic analysis revealed that dwarfism is under the control of a major gene (designated as ndf1) with a mainly additive effect and non‐significant dominance effect. Because of the high level of resistance to lodging, breeding programmes for double low dwarf oilseed rape and heterosis utilization were initiated. Some new dwarf strains with improved agronomic performance were developed. The hybrid of the cross between the tall parent and the dwarf line showed increased harvest index and significantly higher seed yield than the tall parent or the control variety ‘Zhongyou 821’ and presented an estimated heterosis vigour rate as high as 12.5–25.8%. The dwarf trait will be a promising marker for a simple, economic and efficient way to control the purity of F₁ hybrid varieties in hybrid production of B. napus.     

Are ordinal rating scales better than percent ratings? a statistical and “psychological” view

Cytoplasmic male sterility (CMS) is considered an efficient genetic tool in pearl millet hybrid breeding. Of the several CMS sources available in pearl millet, A₁ is the only CMS widely exploited to produce commercial hybrids in India. To explore the possibility of using alternate CMS sources, we studied the cytoplasmic effects of different CMS sources on agronomic characters in pearl millet. Five CMS (A) lines representing A₁, A₂, A₃, A₄ and A₅ cytoplasms, their respective maintainer (B) lines and eight restorer (R) lines were used to generate 40 A × R and B × R experimental crosses. The experimental material was evaluated at two different locations in India. Analysis of combining ability and heterosis revealed that A₄ and A₅ cytoplasms had desirable effects for earliness. The A₅ CMS was found to be particularly promising, as compared to other CMS sources for improving grain yield. The study also indicated that the cytoplasmic effects on general combining ability (GCA) for various agronomic characters were largely non-significant. However, cytoplasmic effects on specific combining ability and heterosis were found to be modulated by cytoplasmic-nuclear interactions and influenced by the environmental conditions. The study also demonstrated the advantage of utilizing diverse male-sterile and restorer combinations in maximizing the productivity as well as for genetic and cytoplasmic diversification of hybrids in pearl millet.     

Indica-Japonica differentiation of paddy rice and its relationship with heterosis

The Indica‐Japonica differentiation of three photoperiod‐sensitive and/or thermosensitive genetic male‐sterile rice (PGMS or TGMS, respectively) lines and 47 male parental lines from seven ecotypes were studied for their restriction fragment length polymorphism marker data to determine which ecotype crosses with the three PGMS and/or TGMS lines could lead to higher yield potential, and to estimate the relationship between the Indica‐Japonica differentiation of parents and heterosis in grain yield and its components. The results indicated that hybrids derived from ‘N422s’ and the early‐middle ripening Indica varieties from southern China, and hybrids between ‘Pei'ai64s’ and three Japonica ecotypes, including North‐eastern Japonica varieties, restoring lines of Japonica hybrid rice and north China Japonica varieties, showed the highest grain yields. There was less variation of yield among the F1s between ‘108s’ and the seven ecotypes than among the other F₁s. Highly significant positive correlations between heterosis of the F₁ yield and genetic distance of the parents were detected, although the correlation between F₁ yield performance and genetic distance did not reach a significant level. Considerable variation of correlation between heterosis and genetic distance was also detected in the Indica × Indica crosses and Indica × Japonica crosses. There was much higher correlation (r = 0.63) between the F₁ yield performance and the genetic distance of parents in the Indica × Indica crosses than in the others. It is proposed that a genetic distance of 0.4‐0.8 between the two parents of hybrid rice might be appropriate not only for F₁ performance, but also for heterosis.