Relationships between four measures of genetic distance and breeding behavior in spring wheat

We estimated the genetic distances among 10 spring wheat genotypes based on pedigree data, morphological traits and AFLP markers, used individually and combined with morphological traits, to find the best predictors of general- and specific-combining abilities among parental genotypes. Ten wheat parents were crossed in a diallel form, disregarding reciprocal hybrids, totaling 45 combinations. The F(1) hybrids, F(2) populations and parents were evaluated in the field in 2007. The experimental plots consisted of 20 plants for F(1) hybrids and 40 plants for parental and F(2) populations. All methods (pedigree data, AFLP markers and morphological traits, used individually and combined) were found to be useful for the assessment of genetic diversity. The significant coefficient correlations ranged from low (0.45) to moderate (0.67) between the distance measures and hybrid performance. There was significant agreement between the distance measures based on AFLP markers vs morphological traits + AFLP markers (r = 0.47) and between pedigree data vs morphological traits + AFLP markers (r = 0.43). The pedigree distance was positively associated with traits 100-kernel weight and grain yield per plant in F(1) (correlations of 0.67 and 0.62, respectively) and F(2) (correlations of 0.62 and 0.59, respectively) generations. These correlation values indicate that the genetic distance, based on pedigree data, could replace diallel crosses for the selection of parents with higher combining ability and with moderate reliability.     

Hybrid performance in taro (<Emphasis Type="Italic">Colocasia esculenta</Emphasis>) in relation to genetic dissimilarity of parents

Taro (Colocasia esculenta) breeding, as other root crop breeding, is based on the production and evaluation of large numbers of hybrids. The selection of parents is based on their phenotypic value in the absence of information concerning general combining ability (GCA), specific combining ability (SCA), or genetic distances between varieties. By combining data from heritability trials and from genetic diversity studies conducted with AFLP and SSR markers, we aimed at studying the relationship between hybrid vigour and genetic dissimilarity between parents. The traits studied included number of suckers, corm weight, corm dimensions, and dry matter content. Correlation coefficients between hybrid gain and dissimilarity values were calculated. The prediction of hybrid performance based on the mid-parent value was compared to the prediction based on a modified expression that takes into account the genetic relationships between parents. Correlations were all but one positive but not statistically significant for all traits, with the exception of the number of suckers, when using SSR markers for dissimilarity calculations. Accordingly, the genetic dissimilarities in the prediction of hybrid performances did not increase the correlation between predicted and observed hybrid vigour values. However, large differences were observed among the residual means from the regression between predicted and observed values when using AFLP or SSR markers, mainly due to the much higher polymorphism revealed by the latter. Models need to be further adapted to the type of molecular marker used, since their ability to reveal different rates of polymorphism will have a direct incidence on the calculation of genetic dissimilarities between genotypes. Nevertheless, since SSR markers are more polymorphic and more informative than AFLP markers, they should be preferentially used for these studies. Low genetic dissimilarity of parents yielded weak heterosis effects and future studies need to be conducted by using a broader genetic base. This is the first study assessing the relationship of hybrid vigour with the genetic distances between parents, conducted on a tropical root crop.     

玉米杂种与亲本穗分化期功能叶基因差异表达与杂种优势

为探讨玉米杂种优势的分子机理,以10个玉米自交系及其组配的38个杂交种为材料,利用cDNA-AFLP技术,分析杂种与亲本在玉米雌穗小穗分化期功能叶片的基因差异表达类型与主要农艺性状的杂种表现及杂种优势的关系。研究表明：（1）杂种的基因相对于其双亲,存在质和量的表达差异,其中质的差异表达类型包括：单亲沉默表达,双亲沉默表达,亲本显性表达和杂种特异表达等类型。（2）在雌穗小穗分化期,同一差异表达类型中不同杂交组合间差异很大;从总体平均看,杂种特异表达类型占25.22%,亲本显性表达类型占21.46%,双亲沉默表达类型占8.27%,单亲沉默表达类型占33.49%。（3）单亲沉默表达与株高的杂种表现呈显著正相关;双亲沉默表达与穗粗的杂种优势呈显著负相关,显性表达与行粒数和单株粒重的杂种优势呈显著负相关,其余表达类型与所有农艺性状杂种表现及杂种优势均不相关,并对结果进行了讨论。     

Genetic distance and heterosis in Indian mustard: developmental isozymes as indicators of genetic relationships

The use of isozymes as indicators of genetic diversity and as markers for the selection of agronomic traits has been proposed in different crop species. The present investigation was conducted to study the use of isozyme-derived genetic distance between parents in predicting the F₁ heterosis in Indian mustard. In addition, the interaction of isozyme-based diversity with quantitative trait and pedigree-based diversity measures, and its role in predicting hybrid heterosis has also been examined. Sixteen Indian mustard lines and their 48 crosses (12 × 4, line x tester crossing) were evaluated over two environments for isozyme and quantitative morphological characters. The results from this study suggest that the heterotic response to isozymic changes is more responsive in crosses derived from morphologically and pedigree-wise related parents in comparison to crosses derived from unrelated parents. It was possible to improve heterosis predictions by partitioning the isozyme-based genetic distance into general genetic distance and specific genetic distance and correlating the latter with the specific combining ability of morphological traits. The possible reasons for these observations are discussed.     

Heterosis for horticultural traits in Broccoli

Over the last three decades, broccoli (Brassica oleracea L., Italica Group) hybrids made by crossing two inbred lines replaced open-pollinated populations to become the predominant type of cultivar. The change to hybrids evolved with little or no understanding of heterosis or hybrid vigor in this crop. Therefore, the purpose of the present study was to determine levels of heterosis expressed by a set of hybrids derived by crossing relatively elite, modern inbreds (n = 9). An additional objective was to determine if PCR-based marker derived genetic similarities among the parents can be useful to predict heterosis in this crop. Thirty-six hybrids derived from a diallel mating design involving nine parents were evaluated for five horticultural characters including the head characteristics of head weight, head stem diameter, and maturity (e.g., days from transplant to harvest), and the plant vigor characteristics of plant height, and plant width in four environments. A total of 409 polymorphic markers were generated by 24 AFLP, 23 SRAP and 17 SSR primer combinations. Euclidean distances between parents were determined based on phenotypic traits. About half of the hybrids exhibited highparent heterosis for head weight (1–30 g) and stem diameter (0.2–3.5 cm) when averaged across environments. Almost all hybrids showed highparent heterosis for plant height (1–10 cm) and width (2–13 cm). Unlike other traits, there was negative heterosis for maturity, indicating that heterosis for this character in hybrids is expressed as earliness. Genetic similarity estimates among the nine parental lines ranged from 0.43 to 0.71 and were significantly and negatively correlated with highparent heterosis for all traits except for stem diameter and days from transplant to harvest. Euclidean distances were not correlated with heterosis. With modern broccoli inbreds, less heterosis was observed for head characteristics than for traits that measured plant vigor. In addition, genetic similarity based on molecular markers was more highly correlated with plant vigor characteristics than head traits. Unlike with molecular marker-based estimates of genetic similarity, euclidean distance determined using phenotypic trait data was not predictive of heterosis. In conclusion, this study has documented heterosis in Brassica oleracea L., and the ability to predict heterosis in this crop using molecular marker-based estimates of genetic similarity among parents used in producing the hybrid. The contents of this publication do not necessarily reflect the views or policies of the USDA, nor does the mention of trade names, commercial products, or organizations imply endorsement by the US Government. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked as advertisement solely to indicate this fact.     

Genetic diversity analysis in sorghum germplasm as estimated by AFLP, SSR and morpho-agronomical markers

A comparison of the different methods of the estimation of genetic diversity is important to evaluate their utility as a tool in germplasm conservation and plant breeding. Amplified fragment length polymorphism (AFLP), microsatellites or SSR and morphological traits markers were used to evaluate 45 sorghum germplasm for genetic diversity assessment and discrimination power. The mean polymorphism information content (PIC) values were 0.65 (AFLPs) and 0.46 (SSRs). The average pairwise genetic distance estimates were 0.57 (morphological traits), 0.62 (AFLPs) and 0.60 (SSRs) markers data sets. The Shannon diversity index was higher for morphological traits (0.678) than AFLP (0.487) and SSR (0.539). The correlation coefficients obtained by the Mantel matrix correspondence test, which was used to compare the cophenetic matrices for the different markers, showed that estimated values of genetic relationship given for AFLP and SSR markers, as well as for morphological and SSR markers were significantly related (p <0.001). However, morphological and AFLP data showed non-significant correlation (p >0.05). Both data sets from AFLP and SSR allowed all accessions to be uniquely identified; two accessions could not be distinguished by the morphological data. In summary, AFLP and SSR markers proved to be efficient tools in assessing the genetic variability among sorghum genotypes. The patterns of variation appeared to be consistent for the three marker systems, and they can be used for designing breeding programmes, conservation of germplasm and management of sorghum genetic resources.     

Parental Selection of Hybrid Breeding Based On Maternal and Paternal Inheritance of Traits in Rapeseed (Brassica napus L.)

Parental selection is crucial for hybrid breeding, but the methods available for such a selection are not very effective. In this study, a 6×6 incomplete diallel cross was designed using 12 rapeseed germplasms, and a total of 36 hybrids together with their parental lines were planted in 4 environments. Four yield-related traits and seed oil content (OC) were evaluated. Genetic distance (GD) was estimated with 359 simple sequence repeats (SSRs) markers. Heterosis levels, general combining ability (GCA) and specific combining ability (SCA) were evaluated. GD was found to have a significant correlation with better-parent heterosis (BPH) of thousand seed weight (TSW), SCA of seeds per silique (SS), TSW, and seed yield per plant (SY), while SCA showed a statistically significant correlation with heterosis levels of all traits at 1% significance level. Statistically significant correlations were also observed between GCA of maternal or paternal parents and heterosis levels of different traits except for SS. Interestingly, maternal (TSW, SS, and OC) and paternal (siliques per plant (SP) and SY) inheritance of traits was detected using contribution ratio of maternal and paternal GCA variance as well as correlations between GCA and heterosis levels. Phenotype and heterosis levels of all the traits except TSW of hybrids were significantly correlated with the average performance of parents. The correlations between SS and SP, SP and OC, and SY and OC were statistically significant in hybrids but not in parents. Potential applications of parental selection in hybrid breeding were discussed.     

Dominance Is the Major Genetic Basis of Heterosis in Rice as Revealed by Qtl Analysis Using Molecular Markers

A set of 194 F(7) lines derived from a subspecific rice cross showing strong F(1) heterosis was backcrossed to the two parents. The materials (388 BC(1)F(7) lines, 194 F(8) lines, two parents, F(1)) were phenotyped for 12 quantitative traits. A total of 37 significant QTLs (LOD >/= 2.0) was detected through 141 RFLP markers in the BC(1)F(7) populations. Twenty-seven (73%) quantitative trait loci (QTLs) were detected in only one of the BC(1)F(7) populations. In 82% of these cases, the heterozygotes were superior to the respective homozygotes. The remaining 10 (27%) QTLs were detected in both BC(1)F(7) populations, and the heterozygote had a phenotype falling between those of the two homozygotes and in no instances were the heterozygotes found to be superior to both homozygotes. These results suggest that dominance complementation is the major genetic basis of heterosis in rice. This conclusion was strengthened by the finding that there was no correlation between most traits and overall genome heterozygosity and that there were some recombinant inbred lines in the F(8) population having phenotypic values superior to the F(1) for all of the traits evaluated--a result not expected if overdominance was a major contributor to heterosis. Digenic epistasis was not evident.     

Assessing wheat (Triticum aestivum L.) genetic diversity using quality traits, amplified fragment length polymorphisms, simple sequence repeats and proteome analysis

The genetic diversity among 10 Iranian bread wheat (Triticum aestivum) genotypes was analysed using 12 quality traits, 320 amplified fragment length polymorphisms (AFLP) polymorphic fragments, 491 simple sequence repeats (SSR) alleles and 294 proteome markers. The results revealed that the genotypes differed for quality traits, AFLP, SSR and proteome markers. The average genetic diversity based on quality traits (0.684 with a range of 0.266–0.997) was higher than AFLP (0.502 with a range of 0.328–0.717), SSR (0.503 with a range of 0.409–0.595) and proteome (0.464 with a range of 0.264–0.870) markers. Although there were apparent similarities between the groupings of particular genotypes, the overall correspondence between the distance matrices appeared to be rather low. In this study, the cluster analysis based on AFLP data showed the closest agreement with genotypes’ regions of origin or pedigree information. In addition to the genetic diversity assessment, specific proteins with known function were detected uniquely for the studied genotypes. Our results suggest that the classification based on quality traits and genotypic markers of these wheat genotypes will be useful for wheat breeders to plan crosses for positive traits.     

Genetic distances revealed by morphological characters,isozymes, proteins and RAPD markers and their relationships with hybrid performance in oilseed rape (<Emphasis Type="Italic">Brassica napus</Emphasis> L.)

Genetic distances (GDs) based on morphological characters, isozymes and storage proteins, and random amplified polymorphic DNAs (RAPD) were used to predict the performance and heterosis of crosses in oilseed rape (Brassica napus L.). Six male-sterile lines carrying the widely used Shaan2A cytoplasm were crossed with five restorer lines to produce 30 F₁ hybrids. These 30 hybrids and their parents were evaluated for seven agronomically important traits and their mid-parent heterosis (MPH) at Yangling, Shaanxi province in Northwest China for 2 years. Genetic similarity among the parents based on 34 isozyme and seven protein markers was higher than that based on 136 RAPDs and/or 48 morphological markers. No significant correlation was detected among these three sets of data. Associations between the different estimates of GDs and F₁ performance for some agronomic traits were significant, but not for seed yield. In order to enhance the predicting efficiency, we selected 114 significant markers and 43 favoring markers following statistical comparison of the mean values of the yield components between the heterozygous group (where the marker is present only in one parent of each hybrid) and the homozygous group (where the marker is either present or absent in both parents of each hybrid) of the 30 hybrids. Parental GD based on total polymorphic markers (GD_total, indicating general heterozygosity), significant markers (GD_sign, indicating specific heterozygosity) and favoring markers (GD_favor, indicating favoring-marker heterozygosity) were calculated. The correlation between GD_favor or GD_sign and hybrid performance was higher than the correlation between GD_total and hybrid performance. GD_sign and GD_favor significantly correlated with plant height, seeds per silique and seed yield, but not with the MPH of the other six agronomic traits with the exception of plant height. The information obtained in this study on the genetic diversity of the parental lines does not appear to be reliable for predicting F₁ yield and heterosis.     

板栗与锥栗杂交F1代叶片表型变异及杂种优势研究

为探索栗属杂交F₁代幼林期叶片性状遗传变异规律及杂种优势,以板栗、锥栗种内和种间9个杂交组合235个杂交单株及其亲本为研究材料,利用巢式方差分析、Pearson相关性分析及主成分分析等统计学方法对其14个叶表型及光合生理性状进行分析。结果表明:①栗属杂交F₁代叶表型及光合生理性状存在丰富的遗传多样性,14个性状平均变异系数范围为4.40%~27.76%;②性状组合间表型分化系数VST均值为32.32%,组合内变异是主要的变异来源;③性状中亲优势率为-27.16%~90.53%,且不同组合性状杂种优势存在差异;④Pearson相关性分析结果显示14个性状中分别有46对和13对相关性达到极显著(P<0.01)和显著水平(P<0.05),其中叶长、叶宽等5个叶表型性状及叶绿素a、叶绿素b等4个光合生理指标相互间影响较大;⑤利用主成分分析法筛选出“魁栗×YLZ 15号”和“魁栗×YLZ 1号”两个优良杂交组合,其子代叶片具有叶面积大、干物质含量及光合有关色素含量高的特点,可为进一步筛选优良杂交子代提供主要素材。     

Molecular marker heterozygosity and hybrid performance in indica and japonica rice

An essential assumption underlying markerbased prediction of hybrid performance is a strong linear correlation between molecular marker heterozygosity and hybrid performance or heterosis. This study was intended to investigate the extent of the correlations between molecular marker heterozygosity and hybrid performance in crosses involving two sets of rice materials, 9 indica and 11 japonica varieties. These materials represent a broad spectrum of the cultivated rice gene pool including landraces, primitive cultivars, historically important cultivars, modern elite cultivars and parents of superior hybrids. Varieties within each set were intermated in all possible nonreciprocal pairs resulting in 36 crosses in the indica set and 55 in the japonica set. The F₁s and their parents, 111 entries in total, were examined for performance of seven traits in a replicated field trial. The parents were surveyed for polymorphisms using 96 RFLP and ten SSR markers selected at regular intervals from a published molecular marker linkage map. Molecular marker genotypes of the F₁ hybrids were deduced from the parental genotypes. The analysis showed that, with very few exceptions, correlations in the indica dataset were higher than in that of their japonica counterparts. Among the seven traits analyzed, plant height showed the highest correlation between heterozygosity and hybrid performance and heteorsis in both indica and japonica datasets. Correlations were low to intermediate between hybrid performance and heterozygosity (both general and specific) in yield and yield component traits in both indica and japonica sets, and also low to intermediate between specific heterozygosity and heterosis in the indica set, whereas very little correlation was detected between heterosis and heterozygosity (either general or specific) in the japonica set. In comparison to the results from our previous studies, we concluded that the relationship between molecular marker heterozygosity and heterosis is variable, depending on the genetic materials used in the study, the diversity of rice germplasms and the complexity of the genetic basis of heterosis.     

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.     

Genetic diversity among Japanese indigenous common buckwheat (Fagopyrum esculentum) cultivars as determined from amplified fragment length polymorphism and simple sequence repeat markers and quantitative agronomic traits.

We assessed the genetic diversity in Japanese indigenous common buckwheat (Fagopyrum esculentum) cultivars using amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers and investigated the relationships between the genetic diversity and agronomic traits. The average expected intracultivar hetero zygosity was 0.303 for AFLP and 0.819 for SSR. The differentiations among agroecotypes, among cultivars within an agroecotype, and among cultivars were small (0.002, 0.024, and 0.026 for SSR and 0.013, 0.013, and 0.026 for AFLP, respectively) but statistically significant from zero except for the SSR differentiation among agroecotypes. In principal coordinates analysis, cultivars within the same agroecotype tended to cluster, indicating that agroecotypes well reflected the genetic relationships among cultivars. In AFLP, the differentiation among the agroecotypes was more distinct than in SSR, and genetic distance showed a moderate correlation with the difference in quantitative traits, indicating that AFLP can resolve the relationships among cultivars with better resolution than SSR. By contrast, SSR may be more sensitive to demographic changes. Four of the five SSR markers showed a significant positive correlation (Kendall's tau = 0.382-0.607) between allelic richness and variation in flowering timing, indicating that cumulative bottleneck events have occurred during the population history, with a decline in the variation of photosensitivity of flowering.     

Gene expression analyses in maize inbreds and hybrids with varying levels of heterosis

Background  

Heterosis is the superior performance of F₁ hybrid progeny relative to the parental phenotypes. Maize exhibits heterosis for a wide range of traits, however the magnitude of heterosis is highly variable depending on the choice of parents and the trait(s) measured. We have used expression profiling to determine whether the level, or types, of non-additive gene expression vary in maize hybrids with different levels of genetic diversity or heterosis.     

Heterosis Is Prevalent for Multiple Traits in Diverse Maize Germplasm

Background

Heterosis describes the superior phenotypes observed in hybrids relative to their inbred parents. Maize is a model system for studying heterosis due to the high levels of yield heterosis and commercial use of hybrids.

Methods

The inbred lines from an association mapping panel were crossed to a common inbred line, B73, to generate nearly 300 hybrid genotypes. Heterosis was evaluated for seventeen phenotypic traits in multiple environments. The majority of hybrids exhibit better-parent heterosis in most of the hybrids measured. Correlations between the levels of heterosis for different traits were generally weak, suggesting that the genetic basis of heterosis is trait-dependent.

Conclusions

The ability to predict heterosis levels using inbred phenotype or genetic distance between the parents varied for the different traits. For some traits it is possible to explain a significant proportion of the heterosis variation using linear modeling while other traits are more difficult to predict.     

Molecular identification of new varieties of<Emphasis Type="Italic">Nierembergia linariaefolia</Emphasis> (Graham), a native Argentinean ornamental plant

Six Nierembergia linariaefolia clones were selected for ornamental traits during a native germplasm development program. For fingerprinting diagnosis, 13 anchored inter-simple sequence repeat (ISSR) primers and 6 amplified fragment length polymorphism (AFLP) primer-enzyme combinations were used. Both markers revealed high levels of polymorphism, enabling genetic discrimination of the accessions analyzed by using 443 informative ISSRs and 541 AFLP markers. Both molecular techniques are suitable for monitoring genetic diversity in Nierembergia linariaefolia and, under our experimental conditions, they showed correlation coefficients of 0.629 for similarity matrices and of 0.649 in the cophenetic matrices. These results suggest that ISSRs are a good choice for DNA analysis in N. linariaefolia when simple manipulation and a low budget are required.     

Genetic diversity in colonial bentgrass (Agrostis capillaris L.) revealed by EcoRI-MseI and PstI-MseI AFLP markers.

Colonial bentgrass (Agrostis capillaris L.) is a potential source for genetic improvement of resistance to environmental stress and disease for other bentgrass species (Agrostis spp.). To conserve and study the existing genetic resources of colonial bentgrass for use in breeding, genetic diversity was investigated using amplified fragment length polymorphism (AFLP) markers. Included in this study were 22 accessions from US Department of Agriculture germplasm collected from 11 countries, in conjunction with 14 accessions from northern Spain and 3 commercial cultivars. Ten EcoRI-MseI and 6 PstI-MseI AFLP primer combinations produced 181 and 128 informative polymorphic bands, respectively. Cluster analysis of genetic similarity estimates revealed a high level of diversity in colonial bentgrass species with averages of 0.51 (EcoRI-MseI) and 0.63 (PstI-MseI). Greater genetic diversity was detected by the EcoRI-MseI AFLP primer combinations. A low but significant positive correlation (r = 0.44, p = 0.0099) between the 2 Jaccard similarity matrices was obtained by the Mantel test. Commercial cultivars of bentgrass showed a narrow genetic background. The assessment of genetic diversity among colonial bentgrass accessions suggested the potential value of the colonial bentgrass germplasm in turfgrass cultivar improvement.     

Genetic Variability in Pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) Estimated by Morphological Data and Amplified Fragment Length Polymorphism Markers

Data on genetic similarity among crop cultivars is of vital importance for the plant breeder. The objectives of this study were to group pepper (Capsicum annuum L.) genotypes into clusters according to their distances as estimated by morphological traits and amplified fragment length polymorphism (AFLP) markers and to assess the relationships between the two. Thirty-nine pepper genotypes obtained from different countries were grown in the greenhouse at University of the Free State, South Africa, during 2001 and 2002 in a randomized complete block design with three replications. A total of 20 different morphological traits were measured and six AFLP primer pairs were used to estimate pairwise genetic distances. Both datasets showed high genetic distances among the different genotypes, indicating high genetic diversity among them. The mean genetic distance among Ethiopian pungent elongated-fruit genotypes, was lower than that between them and the introduced ones. Morphological and AFLP distance estimations generally clustered together genotypes with similar fruit sizes. Significant, positive correlation was observed between morphological and AFLP diversity estimations. The narrow genetic basis among the Ethiopian pungent elongated-fruit cultivars suggests that the pepper breeding program of Ethiopia should focus on enriching its germplasm through local collection and introductions from other parts of the world.     

Relationship of Parental Genetic Distance with Heterosis and Specific Combining Ability in Sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) Based on Phenotypic and Molecular Marker Analysis

The genetic distance analysis for selection of suitable parents has been established and effectively used in many crops; however, there is dearth of conclusive report of relationship of genetic distance analysis with heterosis in sesame. In the present study, an attempt was made to estimate the associations of genetic distances using SSR (GDSSR), seed-storage protein profiling (GDSDS) and agro-morphological traits (GDMOR) with hybrid performance. Seven parents were selected from 60 exotic and Indian genotypes based on genetic distance from clustering pattern based on SSR, seed-storage protein, morphological traits and per se performance. For combining ability analysis, 7 parents and 21 crosses generated from 7 × 7 half diallel evaluated at two environments in a replicated field trial during pre-kharif season of 2013. Compared with the average parents yield (12.57 g plant^?1), eight hybrids had a significant (P < 0.01) yield advantage across environments, with averages of 26.94 and 29.99% for better-parent heterosis (BPH) and mid-parent heterosis (MPH), respectively, across environments. Highly significant positive correlation was observed between specific combining ability (SCA) and per se performance (0.97), while positive non-significant correlation of BPH with GDSSR (0.048), and non-significant negative correlations with GDMOR (? 0.01) and GDSDS (? 0.256) were observed. The linear regressions of SCA on MPH, BPH and per se performance of F₁s were significant with R² value of 0.88, 0.84 and 0.95 respectively. The present findings revealed a weak association of GDSSR with F₁’s performance; however, SCA has appeared as an important factor in the determination of heterosis and per se performance of the hybrids. The present findings also indicated that parental divergence in the intermediate group would likely produce high heterotic crosses in sesame.