Relationship between heterosis and genetic divergence in 'Tongil'-type rice

Improving grain yield and quality of ‘Tongil’‐type rice (indica/japonica) continues to be a major breeding objective in Korea. In this study, genetic divergence among 13‘Tongil’‐type rice cultivars was evaluated and the relationship between genetic distance and hybrid performance in all possible nonreciprocal crosses between them assessed. The 78 F₁ hybrids together with the 13 parents were evaluated for eight traits of agronomic importance, including yield, in a replicated field trial. The 13 parents were examined for DNA polymorphism using 71 micro‐satellite or simple sequence repeats and 46 random decamer oligonucleotide primers. A total of 319 polymorphic variants were generated and, based on the polymorphism data, genetic distances (GDs) ranged from 0.021 to 0.437. Cluster analysis based on GDs revealed associations among cultivars which was in agreement with the pedigree data. Heterosis was observed in hybrids for most of the traits, and yield exhibited the highest heterosis among the eight traits examined. The correlation values of GDs with F₁ performance were mostly nonsignificant, except for yield, culm length and spikelets per panicle. The correlations of GDs with midparent and better‐parent heterosis were not significant enough to be of predictive value. These results indicate that GDs based on the microsatellite and random amplified polymorphic DNA (RAPD) markers may not be useful for predicting heterotic combinations in ‘Tongil’‐type rice and support the idea that the level of correlation between hybrid performance and genetic divergence is dependent on the germplasm used.     

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.     

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.     

Inheritance in Solanum aethiopicum,the scarlet eggplant

Summary Analyses of F₁ and F₂ hybrid progenies from crosses between the ancestral species Solanum anguivi and cultivars of its domesticated derivative S. aethiopicum, have proved the mode of inheritance of prickles, stellate hairs and some other morphological characters and suggested the mode for several more. Most wild-type traits were dominant: many recessive domesticated traits involved imperfect morphogenesis suggesting loss of genetic control. F₁ hybrids between cultivars show marked heterosis and are recommended for crop production.     

陆地棉主要农艺与纤维品质性状的双列杂交分 析简

 本文利用加性-显性与环境互作的遗传模型（ADE模型）,分析8个陆地棉亲本及其F1在不同环境下的农艺和纤维品质性状,在估算遗传方差分量、遗传效应的基础上,分析各类性状间的遗传相关性,并预测F1和F2的杂种优势,为棉花杂种优势利用和新品种选育提供了较有价值的信息。研究表明,农艺与纤维品质性状的遗传主要受加性、显性和加性与环境互作效应控制。遗传相关分析表明,皮棉产量与纤维品质性状的显性相关系数值较大,利用杂种优势在早期世代可以得到协同改良,纤维品质性状间易实现协同改良。杂种优势分析表明,F₁和F₂的皮棉产量均具有显著的超亲优势,纤维品质性状的杂种优势不明显。     

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.     

黄淮地区大豆重要亲本间产量的杂种优势、配合力及其遗传基础

2003-2005年以选自黄淮地区及美国的8个大豆重要亲本品种(系)及其组配的28个双列杂交组合为材料, 分析大豆亲本间的产量杂种优势及其配合力, 探讨高优势组合的遗传基础, 包括杂种优势与亲本系数、SSR标记遗传距离的相关。结果表明: (1)黄淮地区大豆亲本间存在产量超亲优势, 平均20.39%, 组合间差异甚大, 变幅–5.34%~76.88%, 优选出豫豆22×晋豆27、淮豆4号×晋豆27、诱变30×蒙90-24, 超亲优势分别为76.88%、29.90%和34.42%, 超标率均在25.00%以上, 晋豆27和诱变30为优秀亲本材料。单株荚数及单株粒数的优势和产量优势相对一致;(2) 大豆亲本间产量杂种优势既与双亲一般配合力之和及特殊配合力有关, 又不完全相关。高优势高产组合的亲本产量配合力特点为亲本之一具有较高的一般配合力, 或双亲具有较高的一般配合力之和, 兼有较高的特殊配合力。单株荚数和单株粒数的情况和产量一致;(3) 按亲本系数聚类和按SSR标记遗传相似系数聚类揭示的8个亲本间的遗传关系相对一致, 均分为两组, 一组包含6个黄淮中、南部品种(系), 另一组包含1个山西和1个美国品种。要获得高优势高产组合, 亲本间必须具有一定的遗传距离, 但遗传距离大并不一定都高产高优势, 还有其他因素决定杂种优势。     

Combining ability for yield,protein and oil of peanut lines from South American centers of diversity

Summary Ten peanut (Arachis hypogaea L.) lines, two from each of five centers of diversity in South America, and the F₂ generation of all possible crosses among them were used to characterize the variation for yield, fruit and seed traits and protein and oil content and to determine the breeding potential of the parents. Two of the parental lines belong to subspecies hypogaea and the other eight to subspecies fastigiata.Several crosses gave heterotic responses for yield. The parents of the crosses with significant heterosis generally came from different centers of diversity.Variation among both general and specific combining abilities was significant for all traits with the exception of the SCA estimate for protein percent. The component of variation for GCA was larger than the SCA component for all traits.A Spanish line and a Valencia-like intermediate line from the Guarani region had the highest GCA effects for fruit yield, seed yield and meat content and transmitted consistently their characteristics to their F₂ progeny. Some lines showed significant but small maternal effects for oil, protein and oil + protein percent. Differences between reciprocal crosses were significant for fruit length, fruit weight and oil + protein percent.A significant portion of the variation among crosses was explained by differences among parental lines within centers of diversity. This supports the fact that centers are founded because of the diversity of the peanuts grown there.The performance of parental lines per se was useful in predicting the performance of the lines in hybrid combination for all traits except fruit yield.Paper number 6141 of the Journal Series of the North Carolina Agricultural Research Service (USA). This work was partially supported by CSRS Research Agreement 701-15-51.     

Estimates of additive and dominance effects for Fusarium head blight resistance of winter triticale

The most effective strategy to control Fusarium head blight (FHB), a devastating disease of small‐grain cereals, is breeding resistant cultivars. This resistance study of F₁ crosses, F₂ and backcross generations of triticale estimates heterosis, general and specific combining ability (GCA, SCA), additive and dominance effects and compares parents with segregating generations. The genetic material consisted of 10 parents with their 45 F₁ crosses and of six parents with their 15 F₂ progeny and backcrosses to each parent. Genotypes were grown in various environments and artificially inoculated with an aggressive isolate of F. culmorum. FHB was assessed, by visual rating, as the mean of four to five individual ratings of disease development. Heterosis for FHB was of little importance. The correlation between the FHB rating of F₁ crosses and their mid‐parent performance was close. GCA was the predominant source of variation, although the significance of the SCA variance also implied non‐additive allelic interaction. The preponderance of additive gene effects is encouraging for increasing resistance by a recurrent selection programme. The relationship between the GCA effect of a parent and its per se performance was close, which gives the possibility of predicting FHB resistance in F₁ crosses. Additive effects were predominant in the F₂ progeny and also in the backcrosses. Transgressive segregants could not be detected. Searching for them should be postponed to the F₃ or later generations.     

Heterosis and heritability in crosses among Asian and Ethiopian parents of hot pepper genotypes

Hot pepper is the most important worldwide grown and consumed spice and vegetable crop. Though hybrid breeding has been proposed for genetic improvement in the crop, but there is lack of information on heterosis in crosses among crop genotypes in Ethiopia. Twelve genotypes (nine Asian and three Ethiopian parents) of hot pepper were crossed in 2003 cropping season in a half-diallel fashion to fit Griffing’s fixed effect model analysis. An open field experiment was conducted in 2004/2005 to investigate heterosis for fourteen traits in 66 F₁ hybrids grown together with their 12 selfed parents. Highly significant genotypic differences were observed for all the traits except for leaf area. Variance component due to specific combining ability (dominance) were larger than that due to general combining ability (additive) for each of the studied traits with few exceptions. Broad sense heritability (H _b²) for fruit traits were more than 60% and with wide gap from narrow sense heritability (h _n²) for most of the important traits like number of fruit per plant (H _b² = 88.3% and h _n² = 46.0%), days to maturity (H _b² = 87.2% and h _n² = 23.1%) and dry fruit yield per plant (H _b² = 72.6% and h _n² = 14.6%). Maximum heterosis over mid-parent and better-parent, and economic superiority of hybrid over standard check were recorded, respectively for dry fruit yield per plant (163.8, 161.8 and 92.1%), number of fruits per plant (104.4, 79.6 and 136.4%) and days to maturity (−29.8, −31.5 and −23.6%). These observations suggested a possibility of utilizing dominance genetic potentiality available in diverse genotypes of the crop by heterosis breeding for improving hot pepper to the extent of better economic return compared to the current commercial cultivar under production in the country. Low narrow sense versus very high broad sense heritability for days to maturity and dry fruit yield per plant could be a sign for achievability of earliness and high fruit yield using heterosis in hot pepper. The maximum heterobeltiosis were recorded either from F₁s obtained from Ethiopian and Asian crosses or from within Asian crosses, suggesting the possibility of maximizing heterosis by considering genetically diverse parental genotypes. The manifestation of highest heterosis in hybrids from among Asian lines indicated existence of genetic diversity among Asian genotypes and the potentiality for improvement of hot pepper using genotypes from different regions of the world along with elite inbred lines from local cultivars.     

Genetic Diversity for RFLPs in European Maize Inbreds

Restriction fragment length polymorphisms (RFLPs) have been proposed for predicting the yield potential of different types of cross. Their has been evaluated in 15 flint and 12 dent inbreds from the European maize (Zea mays L.) germplasm as well as in 68 F₁ crosses (21 flint × flint, 14 dent × dent, and 33 flint × dent) produced between them. The materials were evaluated for F₁ performance and midparent heterosis of grain yield, dry matter content (DMC) and plant height in two environments in Germany. Genetic distances (GDs) between parental lines, calculated from RFLP data of 194 clone-enzyme combinations, showed greater means for flint × dent (0.67) than dent × dent (0.62) and flint × flint (0.55) crosses. Cluster analysis based on GDs resulted in a clear separation of flint and dent lines and agreed well with pedigree information. For the complete set of 64 crosses analyzed (excluding 4 crosses between closely related lines) correlations of GD with F₁ performance and heterosis were significant for all traits except F₁ performance of DMC. When separate calculations were performed for individual subjets of crosses, correlations of GD with Fl performance and heterosis were significantly positive (0.48 ≤ r ≤ 0.80) for all traits in the flint × flint crosses, but not significant for the subsets of flint × dent and dent × dent crosses. Our results confirm those of previous investigations in that the predictive value of RFLP data is restricted to crosses between lines from the same heterotic group, and cannot be applied to crosses between lines from genetically divergent heterotic groups.     

光子陆地棉种质资源主要性状的遗传评价

以102份光子陆地棉材料为母本,分别与遗传标准系TM-1杂交,获得102个F₁群体。采用随机区组设计,设置3个重复,对光子陆地棉材料主要性状进行遗传评价。结果表明,调查的11个性状表型差异均较大,材料间产量性状(株高、果枝数、铃数、铃重、衣分和子指)差异大于纤维品质性状(纤维长度、纤维强度、马克隆值、整齐度和伸长率),特别是衣分、铃数等性状差异更明显; 除果枝数、马克隆值、伸长率以外,光子亲本群体其他性状的平均值都小于F₁群体。而亲本群体所有性状的变异系数均大于F₁,不同光子材料的杂种优势有很大差别,中亲优势和超亲优势也有很大的差别,有些种质某些性状的中亲、超亲优势为负值,其后代性状表现劣势; 纤维品质性状的中亲、超亲优势与毛子程度均呈负相关,而产量性状的中亲、超亲优势与毛子程度均呈正相关,说明可利用光子材料杂种优势改良纤维品质,而其后代产量性状的杂种优势利用受到限制; SSR分子标记遗传相似系数与各个性状的中亲、超亲优势的相关都不显著,说明在光子材料的育种中,杂种优势是不能通过亲本之间的遗传背景相似程度来预测的。     

Prospects for hybrid breeding in winter triticale: II. Relationship between parental genetic distance and specific combining ability

Significant relative midparent heterosis (MPH%) for grain yield in triticale (×Triticosecale Wittm.) has generated interest in the development of hybrid cultivars. The objectives of this study were to (i) examine the association between parental genetic distance (GD) and specific combining ability (SCA), (ii) investigate the existence of genetically distant heterotic groups in elite germplasm, and (iii) draw conclusions for future hybrid breeding in winter triticale. Genetic distance between 61 lines was estimated, based on 93 polymorphic simple sequence repeat (SSR) marker loci and 10 AFLP (amplified fragment length polymorphism) primer‐enzyme combinations (PEC). Agronomic data of 206 F₁ crosses and their 61 parental lines grown in six German environments were published recently in a companion study. Correlations were made between SCA for grain yield, number of spikes/m², 1000‐kernel weight and number of kernels per spike with GD estimates of the 56 female and five male parents (testers). Principal co‐ordinate analyses (PCoA) based on SSR data revealed no distinct subgroups in the germplasm. Correlations between GD and SCA were low for all traits (|r| ≤ 0.31), which hampers the prediction of SCA from molecular data. A multi‐stage procedure is recommended for future hybrid breeding in triticale by applying a pragmatic approach for the grouping of germplasm following the early history of hybrid breeding of maize.     

Relationship between phenotypic and genetic diversity of parental genotypes and the frequency of transgression effects in barley (Hordeum vulgare L.)

The aim of the study was to evaluate the relationship between genetic and phenotypic distances of parents and the genetic potential of crosses as measured by the frequency of transgressive segregants in homozygous populations. Material for the study involved 17 barley cross‐combinations. In each cross, the parental genotypes, F₂ hybrids and doubled haploid (DH) lines were analysed. Yield and yield‐related traits were observed in the experiments. Phenotypic (univariate and multivariate) and genetic distances (GD) were investigated between pairs of parental genotypes. Genetic distance was evaluated by using random amplified polymorphic DNA markers. In F₂ generations, the genetic coefficient of variability (GCV) was evaluated. Within all the cross‐combinations studied, each DH line was compared with both parents to distinguish the positive and negative transgressive lines. In addition, the coefficient of gene distribution (r) along parental genomes was evaluated. Relationships between frequency of transgression and both phenotypic and GDs, GCV and r, were assessed by regression analysis. It was found that for all the traits studied the frequency of transgressive lines depended mainly on gene distribution (r). Genetic distance between parents appeared to be significant for the occurrence of transgression effects in plant height, ear length, grain weight per ear and grain yield per plot. Regression analysis has shown that phenotypic differences between parental genotypes were also important for the frequency of transgressive lines. A weak relationship was found between the variation of F₂ hybrids and the occurrence of transgressive lines. The results indicate that occurrence of transgressive segregants in a homozygous population should be considered as a phenomenon dependent simultaneously on several factors characterizing parental genotypes. Among them, the most important are: gene distribution, phenotypic diversity and GD.     

Genetic effects and genetic values of fiber properties in F2 and F3 hybrids between germplasm lines and high yield cultivars

Utilization of cotton (Gossypium hirsutum L.) germplasm for genetic improvement of fiber properties requires determination of genetic effects in the germplasm lines. A study was designed to analyze genetic populations derived from multiple crosses between nine germplasm lines as male parents and five cultivars and elite breeding lines as female parents to determine genetic values of fiber properties. Parents and F₂ populations were planted at 2 field sites in 2010 and 2011 with 4 and 3 replicates, respectively, and parents and F₃ populations were planted at 2 field sites in 2011 with 3 replicates. Lint yield and seven fiber properties were analyzed by an additive and dominant model with genotype by environment interaction effects. Significant additive and dominant effects were identified for both lint yield and fiber properties. Germplasm lines JC60, JC65, JC186, and SP205 were good general combiners for micronaire, elongation, strength, 50 % span length, short fiber content, and fineness. Six to fifteen crosses were detected with favorable heterozygous dominant effects for lint yield and diverse fiber traits, which suggest useful heterosis of these hybrids. Favorable additive correlations were identified between fiber properties such as micronaire versus 50 % span length (?0.57), micronaire versus fineness (0.82), strength versus 50 % span length (0.54), strength versus short fiber content (?0.69), and 50 % span length versus short fiber content (?0.78) while unfavorable additive correlations were not identified among fiber properties. These results indicated potential of simultaneous genetic improvement for these multiple properties in breeding populations derived from these germplasm lines.     

Inheritance of threshability in synthetic hexaploid (Triticum turgidum×T. tauschii) by T. aestivum crosses

Triticum tauschii provides breeders with a valuable source of resistance and tolerance genes. Elucidation of the inheritance of traits in this species that hinder its use in breeding programmes is therefore of interest to wheat breeders. Inheritance of threshability was investigated in the crosses of four non-free-threshing (NFT) synthetic hexaploids (Triticum turgidum×T. tauschii) and two free-threshing (FT) T. aestivum cultivars during four crop seasons over 3 years at E1 Batan and Ciudad Obregon, Mexico. The parents, their F₁ Hybrids and individual F₂ plant-derived F₃ progenies of the crosses revealed that ‘Altar 84’/T. tauschii (219), ‘Chen’/T. tauschii (205), ‘Chen’/T. tauschii (224), and ‘Duergand’/T. tauschii (214) have independently segregating loci with two dominant alleles controlling threshability. Intercrosses among the synthetics, except ‘Altar 84’/T. tauschii (219), showed the genes to be allelic to each other. The cross between the FT cultivars showed no segregation in the F₃ generation, indicating common recessive genes. Based on these findings, population sizes of the synthetic-derived breeding materials should be increased to improve the chances of selecting FT desirable plants in the programme.     

Relationship between genetic divergence and hybrid performance in japonica rice grown in a cold water-irrigated field

The present study was carried out to evaluate genetic divergence among eleven japonica rice cultivars and to assess the relationship between genetic distance and hybrid performance in partial non-reciprocal crosses among them. The 44 F1 hybrids along with the eleven parents were evaluated for five cold tolerance-related traits; discoloration at seedling stage, days to heading, culm length, fertility, and spikelets per panicle in a cold water screening nursery (17 ^°C). The eleven parents were examined for DNA polymorphism using amplified fragment length polymorphisms(AFLPs). A total of 855 polymorphic variants were generated and based on the polymorphism data, genetic distances (GDs) ranged from 0.023 to0.524. Very little heterosis was observed in hybrids for most of the traits,whereas heterosis was high for fertility. The correlation values of GDs with F1 performance were mostly non-significant except for discoloration and fertility. The correlations of GDs with mid-parent and better-parent heterosis were not significant and proved to be of no predictive value. Our results indicate that GDs based on AFLP markers are not useful for predicting heterosis for cold tolerance in japonica hybrids. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Heterosis in Primary Hexaploid Triticale with Heterozygous Wheat or Rye Genome*)

Twelve primary hexaploid triticale (X Triticosecale Wittmack), synthesized from, three lines of tetraploid wheat (Triticum durum L., T. turgidum L.) and four inbred lines of rye (Secale cereale L.), were used to produce 18 crosses with homozygous wheat and heterozygous rye genome and 12 crosses with heterozygous wheat and homozygous rye genome. Parents and crosses of triticale, wheat, and rye were tested for two years (rye for one year only) in two-replicate block designs with 1 m²-plots. Data were assessed for plant height, grain yield and for yield-related traits. Performance of triticale crosses was considerably lower than that of the wheat and rye crosses. The amount of heterosis varied greatly between years. Positive and mainly significant heterosis was revealed in triticale generations F₁ and F₂. The average values were closer to those in wheat than to those in rye. For most characters a high level of heterosis was retained in tnucalt1 generation F₂. Heterozygosity of the wheat and rye genome both contributed to heterosis in triticale. However, gene action of the rye genome strongly depended on the homozygous wheat background: one wheat line almost completely suppressed and another greatly stimulated the heterotic effect of the rye genome. In the later case, the amount of heterosis was related to that in rye per se. Information from hybrid rye breeding may therefore be used when establishing gene pools for hybrid breeding in triticale.     

Comparisons of genetic and morphological distance with heterosis between Medicago sativa subsp. sativa and subsp. falcata

Biomass yield heterosis has been shown to exist between Medicago sativasubsp. sativa and Medica gosativa subsp. falcata. The objective of this study was to gain a better understanding of what morphological and genetic factors were most highly correlated with total biomass yield heterosis. We calculated genetic distances among nine sativa and five falcate genotypes based on amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) DNA markers. Genetic distance did not correlate with specific combining ability (SCA) or mid-parent heterosis. In contrast, a morphological distance matrix based on seventeen agronomic and forage quality traits was significantly correlated with heterosis; the agronomic traits of maturity, midseason regrowth, and autumn regrowth showed strong association with heterosis. Heterosis was also correlated with subspecies. We suggest that in many cases progeny heterosis can be accounted for by the interaction of genes controlling morphologically divergent traits between the parents. In other cases, progeny heterosis could also be due to divergence between the parents at particular genetic loci that do not control field-level phenotypic differences. Genetic distanceper se between parental genotypes, based on neutral molecular markers, however, does not reflect the potential of individual genotypes to produce heterosis in their progeny. This revised version was published online in August 2006 with corrections to the Cover Date.