Chlorophyll Content, Hill Reaction and PEPcase Activity in Relation to Hybrid Vigour in Pearl Millet during Early Seedling Growth

Three hybrids of Pennisetum americanum L. Leeke were analyzed for growth and photosynthetic components during early growth and compared with their respective parents. Growth in terms of shoot length, fresh weight and dry weight along with the chlorophylls, and Hill activity revealed better parental and/or mid parental heterosis in all the hybrids over their respective parents. However, PEPcase activity displayed heterosis only in BJ-104. In other two hybrids no heterosis over the parents could be observed indicating thereby that the activity of this enzyme may not be rate limiting in parental lines.
Nevertheless, it appears that in pearl millet hybrids improved photosynthetic apparatus as observed in chlorophyll contents and Hill reaction may be one of the early expressions of hybrid vigour.     

Relationship between phenotypic and genetic diversity of parental genotypes and the specific combining ability and heterosis effects in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

The purpose of the study was to evaluate the relationship between the genetic distances (GD) and phenotypic distances (PD) of parents and the specific combining ability (SCA) and heterosis effects. The experiment comprised 18 parental genotypes of wheat (Triticum aestivum L.) and 76 F₂ hybrids, obtained after crossing in a line × tester scheme. Parents and hybrids were examined in a field experiment conducted in a block design with three replications. SCA as well as mid-parent heterosis effects were estimated for selected morphological and technological traits. PDs and GDs were investigated between pairs of parental genotypes. GD between parental genotypes was evaluated by using randomly amplified polymorphic DNA markers. Heterosis was observed in all hybrids, and protein content exhibited the highest heterosis among the seven examined traits. The relationship between PD and GD as well as the SCA and mid-parent heterosis effects were evaluated using correlation coefficient. The correlation between PD, SCA and heterosis were low and not significant for the examined traits, whereas the correlation between SCA, heterosis and GDs were significant for protein content and rheological properties. The results indicate that GDs between parents can be used to predict performance of hybrids for selected technological traits.     

爆裂玉米距离分析与杂种优势

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，又估算了由其中49个自交系间随机组配的67个杂交组合F1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，F1代产量的对照优势与其双亲间的遗传距离呈显著的二次曲线关系，而F1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     

过氧化物酶杂合性与玉米F1产量性状相关性分析

探讨过氧化物酶的同工酶在产量杂种优势预测中的作用,在利用玉米F1代杂种优势群的基础上,选用安徽科技学院玉米研究所选育的6个高产组合,分析了玉米F1代杂交种过氧化物酶的同工酶杂合性与产量性状的相关性。产量杂种优势与亲本数目具有一定的相关性,同时,产量性状与过氧化物酶的同工酶杂合性具有一定的关系,但并非杂合性越高产量杂种优势越强;利用过氧化物酶的同工酶杂合性可以作为预测产量杂种优势表现的一个参考指标。     

IAA分解代谢相关酶（IAAO、POD）的研究进展

吲哚乙酸IAA参与植物体内诸多生理活动,其分解代谢相关酶吲哚乙酸氧化酶（IAAO）、过氧化物酶（POD）在IAA代谢过程中起着关键作用,二者通过调控植物体内IAA的水平来调控复杂的植物生长,该文综合总结了IAAO和POD近年来研究的相关进展,尤其是结合生物化学和分子生物学方面阐述了这两种酶在IAA代谢中的作用及其相关性。     

稀土元素对小麦芽鞘生长及内源吲哚乙酸含量的影响

本文研究了稀土元素对小麦芽鞘生长,吲哚乙酸氧化酶活性,过氧化物酶同工酶,内源吲哚乙酸水平的影响.结果表明:100ppm—1000ppm的硝酸稀土可促进小麦芽鞘的生长,尤以1000ppm浓度明显.这种生长的促进伴随着吲哚乙酸氧化酶活性的增加,过氧化物酶同工酶带数目的增多及内源吲哚乙酸水平的下降.稀土元素也可加强外源吲哚乙酸对小麦芽鞘生长的促进,抵消外源脱落酸对芽鞘生长的抑制.     

玉米不同基因型气孔特征和叶温差的研究

为了探讨玉米不同基因型和杂种优势在气孔及蒸腾上的特征，对3个高产杂交种(农大108、农大103和中原单32)及其所有亲本进行了气孔形态、气孔频率和叶温差的观察与测量。结果表明，3个玉米杂交种在气孔特征及叶温上都表现出显著的杂种优势，其中农大108和农大103的杂交种气孔长度都表现正向超亲，杂种优势率分别为10．55％和9．30％，但气孔频率为负向超亲(杂种优势率分别为39．25％和20．43％)；中原单32的杂交种在气孔长度和气孔频率都表现正向超亲，杂种优势率分别为9．47％和16．48％；但从3个杂交种组合均值看，气孔长度为正向超亲，气孔频率为负向超亲。3个玉米杂交种的叶温差都表现正向超亲。相关分析表明，气孔长度与气孔频率呈显著负相关(r=-0．6460^*)；气孔长度与叶温差呈正相关，而气孔频率与叶温差呈负相关，但都不显著。     

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。     

A comparative physiologico-genetical study of activities of some enzymes in a heterotic single cross hybrid of maize (Zea mays L.)

Summary In field trials conducted over three growth seasons I studied the differences in activities of the enzymes: polyphenoloxidase, ascorbateoxidase and peroxidase, with a heterotic single-cross hybrid of maize and its pollen-sterile analogue. Additional observations were made for differences between the single-cross hybrids and their parental lines. The samples (staminate spikelets) were taken at random just before and after tasselling. Significant differences could be established concerning the object set. Comparison of the self-pollinating line of maize with the pollen-sterile analogue revealed the down ward trend in peroxidase (P) activity with the pollen-sterile line; the upward trend in polyphenoloxidase (PPO) activity and the downward trend in ascorbateoxidase (A) activity were observed with the pollen-sterile line before tasselling. After tasselling, activity of PPO showed a downward and that of A an upward trend. The single-crospollen-sterile hybrid revealed, compared to the parental lines, an upward trend in its PPO and A activities before tasselling and a downward trend in the same enzymes after tasselling; while activity of P in this single-cross, pollen-sterile hybrid indicated the downward trend in general. Compared with the parental forms, the pollen-fertile hybrid of maize showed a trend towards lower activities of the studied enzymes for all seasons and periods under observation. Comparing results in the single-cross hybrids there was an indication of higher activities of PPO and A in the pollen-sterile analogue; whereas the same analogue revealed a lower activity of P before tasselling and higher value after tasselling.     

Heterotic patterns in rapeseed (Brassica napus L.): II. Crosses between European winter and Chinese semi-winter lines

Chinese semi-winter rapeseed is genetically diverse from European winter rapeseed. Our objectives were (1) to evaluate the potential of semi-winter rapeseed for winter rapeseed hybrid breeding, (2) to assess the relative importance of general combining ability (GCA) vs. specific combining ability (SCA) among combinations between Chinese semi-winter and European winter rapeseed, and (3) to compare the strategies to predict heterosis based on parental genetic distance (GD) estimated from AFLP marker data and GCA for hybrid performance. Four winter male sterile lines from Germany as testers were crossed with 14 Chinese semi-winter rapeseed lines to develop 56 hybrids, which were evaluated together with their parents and commercial hybrids for seed yield, oil content and protein content under three environments in Germany. The Chinese parental lines were not adapted to local environmental conditions as demonstrated by lacking winter hardiness and poor seed yields per se . However, the hybrids between the Chinese parents and the adapted winter rapeseed lines exhibited high heterosis for seed yield. About 20% of the hybrids were significantly superior to the respective hybrid control under three environments. Additive gene effects mainly contributed to hybrid performance since the variance components of GCA were higher as compared with SCA. The correlation between parental GD and hybrid performance was found to be low whereas the correlation between GCA and hybrid performance was high and significant, with correlation coefficients of 0.95 for seed yield, 0.87 for oil content, and 0.91 for protein content, indicating that GCA can predict hybrid performance. These results demonstrate that Chinese semi-winter rapeseed germplasm has a great potential to increase seed yield in winter rapeseed hybrid breeding programmes in Europe.     

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.     

Heterosis and Genetic Variances and their Implications for Breeding Improved Varieties of Spring Beans (Vicia faba L.)*

Handcrosses were made in a factorial manner with 24 Vicia faba inbred lines m three sets, each between four male and four female parents. The resulting 48 hybrids, their parental inbreds and three commercial varieties were grown in performance trials during the years 1985—87 with three replications at one location. Yield and yield components were recorded on single plant basis. The average superiority of the hybrids above the control varieties was 26 % in plant yield. The best crosses outyielded the controls by more than 50 %. However, a few inbred lines also reached, the yield level of the controls. The average heterosis was significant for all characters except for maturity date. In plant yield the average heterosis was 75%, ranging between 34% and 148% in the various cross combinations. The highest average heterosis of 110 % was observed in yield at the lateral stems. In all characters the best inbreds were superior to the lower hybrids and in some characters even equal to the average of the hybrids. A strong positive relationship was found for all characters between hybrid performance and mid-parent value and between the per se performance of the inbreds and their general combining ability. Genotypic differences between the hybrids as well as between the inbreds were highly significant. Most of the variability between the hybrids in all characters were attributed to general combining, ability with only little evidence for specific combining ability. In the discussion the results are evaluated according to the choice of the breeding category of the partial allogamous faba bean species.     

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.     

Differential gene expression between wheat hybrids and their parental inbreds in seedling leaves

Differential display of mRNA was used to analyze the differences of gene expression in seedling leaves between heterotic hybrid/nonheterotic hybrid and their parental inbreds in order to study the molecular basis of heterosis in wheat. The results indicated that patterns of gene expression in hybrids differ significantly from their parents. Both quantitative and qualitative differences were observed. The quantitative differences include gene over-expression, gene under-expression in hybrid and dominant expression of highly-expressed parental genes in hybrids. The qualitative differences include silencing in hybrids of genes expressed either in male or female parent, and silencing in hybrids of genes expressed in both parents. Expression in hybrid of genes only expressed either in male or female parent was also observed. It was also found that some genes expressed at high level in heterotic hybrid were underexpressed or expressed at low level in nonheterotic hybrid. One differentially expressed cDNA fragment 4B was cloned and sequenced after being confirmed through Northern blot analysis. Homology search in GenBank proved that the cDNA fragment is a new sequence. The selection of primers for differential RNA display in wheat and the relationship between wheat heterosis and alteration of gene expression in hybrids as compared to their parental inbreds were also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heterosis,molecular diversity,combining ability and their interrelationships in short duration maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) across the environments

Five inbred lines, 10 single cross maize (Zea mays L.) hybrids and two standard cultivars as check were used to study the combining abilities and heterosis under three environmental conditions. Random amplified polymorphic DNAs (RAPDs) markers were used to study the genetic diversity (GD) and further to analyze relationship of RAPDs based GD with combining ability and heterosis in short duration maize. Spearman’s rank correlation coefficients and linear regressions were analyzed to identify the most important factor determining heterosis and per se performance of the hybrids. Variances due to general combining ability (GCA), specific combining ability (SCA) and their interactions with environment were found to be significant. Twenty random primers generated 179 RAPD fragments. Of these, 102 RAPD fragments were polymorphic. GD was determined using Jaccard’s similarity coefficient, and a dendogram was constructed by UPGMA cluster analysis. The RAPDs based GD exhibited non-significant negative or positive association, non-significant linear regression along with very low coefficient of determination (R ²) with SCA, high and mid parent heterosis (HP and MP) and per se performance of the hybrids. Significant positive correlations and regressions along with high coefficients of determination were recorded for SCA with HP, MP and per se performance of the hybrids. The HP and MP also established significant positive association and linear regression along with high coefficient of determination with per se performance of hybrids whereas the parental mean did not establish any significant correlations with the GD, HPH, MPH and grain yield of F₁s. The present investigation, therefore, did not find any role of RAPDs based GD in determining hybrid heterosis and hybrid performance in short duration sub-tropical maize. The SCA, however, has emerged as the most important factor in determination of heterosis as well as per se performance of the hybrids in short duration maize.     

基于产量相关性状SSR分子标记的大豆杂种优势群划分

利用杂种优势可显著提高大豆单产,但亲本的创制及杂交组合的配制缺乏有效的理论指导,导致杂交种组配工作存在盲目性,强优势大豆杂交种的产出周期较长。针对上述问题,以中国东北部和国外的43份亲本为材料,利用经过筛选的14个大豆产量性状相关SSR分子标记进行遗传多样性分析和杂种优势类群划分。结果发现,所用SSR标记共扩增出31个等位变异位点,平均每个标记检测到2.2143个等位变异位点,变幅为2.0000~4.0000;主效基因频率为0.4419~0.9302,平均为0.6817;基因遗传多样性指数为0.1298~0.6101,平均为0.4043;多态性信息含量为0.1214~0.5272,平均为0.3280。根据遗传距离将43份亲本材料划分为2个类群;25个杂交种的35份亲本材料分属于2个类群;且27个杂交种的39份亲本材料为国内和国外材料之间配制的杂交组合,反映出中国东北与国外材料之间存在较强的杂种优势。对本研究所用的杂交种亲本间遗传距离分析发现,遗传距离在0.4~0.6时杂种优势利用效率较高。上述结果为优异亲本的选育方向和强优势杂交种亲本的合理组配提供参考。     

Identification of QTLs for salt tolerance at germination and seedling stage of Sorghum bicolor L. Moench

Upland cotton (Gossypium hirsutum L.) hybrids display commercially useful levels of heterosis for lint yield. Cotton lint yield is primarily a multiplicative product of boll number and lint per boll, both of which can be further dissected into sub-components. Relationships among the yield components are complex where they further interact with the environment. To identify different yield components of hybrid cotton lint yield and their relationship with environment, three cotton varieties, DP51, STV474 and LA887 and, their respective hybrids were evaluated for lint yield components across five environments. Heterosis was observed for lint yield as well as yield components. The relationship between heterosis and mean environmental yield was negative for two hybrid combinations, whereas one hybrid showed increased heterosis from low to high yielding environments. Boll number was the major yield component contributing to lint yield. However, yield components contributing to the change in heterosis from low to high yielding environments were different for the three hybrids. The change in lint yield heterosis across environments was correlated with lint per boll and lint per seed for DP51 × STV474 and LA887 × DP51. Whereas, bolls number and boll retention were the main yield components contributing to higher lint yield heterosis of STV474 × LA887 in low yielding environments. Results also reveal effects of parental entries on lint yield as well as relationship of heterosis and environment.     

Prediction of heterosis for grain yield in rice using 'key' informative EST-SSR markers

This study was undertaken to assess the comparative potential of 25 Expressed Sequence Tag derived simple sequence repeats (EST-SSRs) and 25 genomic SSRs in the prediction of grain yield heterosis using a set of nine cytoplasmic male sterile (CMS) lines and 32 restorer lines of rice. EST-SSRs and genomic SSRs exhibited an average Polymorphism Information Content value of 0.37 and 0.45, respectively. The coefficient of marker polymorphism among parental lines with respect to a set of hypervariable EST and genomic SSRs was correlated with standard heterosis for grain yield of six public bred rice hybrids. EST-SSRs gave a better correlation (r = 0.75) as compared with genomic SSRs (r = 0.09). When 10 'key' informative EST-SSR markers which showed a higher positive correlation with grain yield heterosis were validated in a new set of 14 experimental hybrids, the markers exhibited a higher correlation (r = 0.79), indicating the predictive value of these EST-SSRs. We recommend these 10 'key' informative EST-SSR markers for analysis of genetic diversity of parental lines and prediction of heterosis in hybrid rice breeding programmes.     

Heterosis in rice over environments

Summary Ten CMS (A) lines and their maintainers (B) and seven restorers (R) were used to make 70 crosses (A/R) and 70 reciprocals (R/B) following line x tester design. The 140 crosses and 17 parents (10 B + 7 R lines) were evaluated in six environments created by three nitrogen fertility levels (0, 60, 120 kg N/ha) and two seasons wet (WS) and dry (DS). Hybrids (both A/R and R/B) were superior to their parents in yield. Hybrids flowered earlier and were taller than the parents. Substantial heterosis, heterobeltiosis and standard heterosis were observed in different environments. Extent of heterosis was higher in WS (stress environment) than in DS (favorable environment). Twenty four hybrids outyielded the standard check (IR46) significantly. Most of them were derived from crosses with parental lines: IR54752A/B, IR58057A/B, IR46 and IR54. For days to flowering, the overall mean heterosis, heterobeltiosis and standard heterosis were all negative values. Heterosis for plant height did not change the plant type of hybrids from semi-dwarf to tall because the parents possessed same dwarfing gene. With proper choice of parents hybrids possessing higher yield potential, early maturity and semi-dwarf plant type can be developed for the tropics.     

Self-compatibility and heterosis in white clover (Trifolium repens L.)

Inbred lines of white clover (Trifolium repens L.) have been produced utilising the rare self-fertility (Sf) allele. Twenty-two lines of four distinct groups have been maintained through five generations of selfing by single seed descent. Fourteen lines were used in crosses to produce F¹s. Both parents and hybrids were analysed for a range of morphological characters. Positive heterosis for dry matter production was observed in half the hybrids. No other trait showed significant heterosis. The degree of heterosis appears to be related to the extent of variation in morphological characters between the parental lines, some combinations of lines yielding heterotic hybrids in all cases, others in none. The majority of the F¹ hybrids are superior in terms of dry matter production to eight control varieties. This revised version was published online in July 2006 with corrections to the Cover Date.