Showing papers on "Heterosis published in 2001"

Overdominant Epistatic Loci Are the Primary Genetic Basis of Inbreeding Depression and Heterosis in Rice. I. Biomass and Grain Yield

Abstract: To understand the genetic basis of inbreeding depression and heterosis in rice, main-effect and epistatic QTL associated with inbreeding depression and heterosis for grain yield and biomass in five related rice mapping populations were investigated using a complete RFLP linkage map of 182 markers, replicated phenotyping experiments, and the mixed model approach. The mapping populations included 254 F 10 recombinant inbred lines derived from a cross between Lemont (japonica) and Teqing (indica) and two BC and two testcross hybrid populations derived from crosses between the RILs and their parents plus two testers (Zhong 413 and IR64). For both BY and GY, there was significant inbreeding depression detected in the RI population and a high level of heterosis in each of the BC and testcross hybrid populations. The mean performance of the BC or testcross hybrids was largely determined by their heterosis measurements. The hybrid breakdown (part of inbreeding depression) values of individual RILs were negatively associated with the heterosis measurements of their BC or testcross hybrids, indicating the partial genetic overlap of genes causing hybrid breakdown and heterosis in rice. A large number of epistatic QTL pairs and a few main-effect QTL were identified, which were responsible for >65% of the phenotypic variation of BY and GY in each of the populations with the former explaining a much greater portion of the variation. Two conclusions concerning the loci associated with inbreeding depression and heterosis in rice were reached from our results. First, most QTL associated with inbreeding depression and heterosis in rice appeared to be involved in epistasis. Second, most (~90%) QTL contributing to heterosis appeared to be overdominant. These observations tend to implicate epistasis and overdominance, rather than dominance, as the major genetic basis of heterosis in rice. The implications of our results in rice evolution and improvement are discussed.

High genetic load in the Pacific oyster Crassostrea gigas.

Abstract: The causes of inbreeding depression and the converse phenomenon of heterosis or hybrid vigor remain poorly understood despite their scientific and agricultural importance. In bivalve molluscs, related phenomena, marker-associated heterosis and distortion of marker segregation ratios, have been widely reported over the past 25 years. A large load of deleterious recessive mutations could explain both phenomena, according to the dominance hypothesis of heterosis. Using inbred lines derived from a natural population of Pacific oysters and classical crossbreeding experiments, we compare the segregation ratios of microsatellite DNA markers at 6 hr and 2-3 months postfertilization in F(2) or F(3) hybrid families. We find evidence for strong and widespread selection against identical-by-descent marker homozygotes. The marker segregation data, when fit to models of selection against linked deleterious recessive mutations and extrapolated to the whole genome, suggest that the wild founders of inbred lines carried a minimum of 8-14 highly deleterious recessive mutations. This evidence for a high genetic load strongly supports the dominance theory of heterosis and inbreeding depression and establishes the oyster as an animal model for understanding the genetic and physiological causes of these economically important phenomena.

Overdominant Epistatic Loci Are the Primary Genetic Basis of Inbreeding Depression and Heterosis in Rice. II. Grain Yield Components

Abstract: The genetic basis underlying inbreeding depression and heterosis for three grain yield components of rice was investigated in five interrelated mapping populations using a complete RFLP linkage map, replicated phenotyping, and the mixed model approach The populations included 254 F(10) recombinant inbred lines (RILs) derived from a cross between Lemont (japonica) and Teqing (indica), two backcross (BC) and two testcross populations derived from crosses between the RILs and the parents plus two testers (Zhong413 and IR64) For the yield components, the RILs showed significant inbreeding depression and hybrid breakdown, and the BC and testcross populations showed high levels of heterosis The average performance of the BC or testcross hybrids was largely determined by heterosis The inbreeding depression values of individual RILs were negatively associated with the heterosis measurements of the BC or testcross hybrids We identified many epistatic QTL pairs and a few main-effect QTL responsible for >65% of the phenotypic variation of the yield components in each of the populations Most epistasis occurred between complementary loci, suggesting that grain yield components were associated more with multilocus genotypes than with specific alleles at individual loci Overdominance was also an important property of most loci associated with heterosis, particularly for panicles per plant and grains per panicle Two independent groups of genes appeared to affect grain weight: one showing primarily nonadditive gene action explained 621% of the heterotic variation of the trait, and the other exhibiting only additive gene action accounted for 281% of the total trait variation of the F(1) mean values We found no evidence suggesting that pseudo-overdominance from the repulsive linkage of completely or partially dominant QTL for yield components resulted in the overdominant QTL for grain yield Pronounced overdominance resulting from epistasis expressed by multilocus genotypes appeared to explain the long-standing dilemma of how inbreeding depression could arise from overdominant genes

Genetic diversity of oilseed Brassica napus inbred lines based on sequence‐related amplified polymorphism and its relation to hybrid performance

Abstract: Significant heterosis for seed yield in oilseed rape has created interest in the development of hybrid cultivars. The DNA-based marker protocol. sequence-related amplified polymorphism (SRAP) was used to determine genetic diversity among oilseed rape maintainer and restorer lines. This measure was used in an attempt to establish an association between genetic distance and heterosis in hybrids for various agronomic traits. A total of 118 polymorphic loci were generated by 18 SRAP primer combinations. Based on the polymorphism generated by the markers, calculated similarity index values ranged from 0.46 to 0.97. Cluster analysis grouped 10 maintainer and 12 restorer lines into three groups, with the exception of two maintainer lines, PM5 and PM9, which fell outside these groups. The grouping of the lines was largely in agreement with the available pedigree data on their origin and agronomic performance. Analysis of variance among inbred lines and their resulting F 1 hybrids over two locations revealed significant differences for plant height, days to maturity and seed yield, but not for oil content. Substantial mid-parent heterosis was observed only for seed yield, and ranged from 26% to 169%. All hybrids surpassed their respective inbred lines for this trait, except for a single cross combination of related lines. In general, crosses of lines located in different clusters yielded more than those from the same clusters. Regression analysis revealed a statistically significant relationship between the genetic distance of the parents and seed yield in their hybrid, and their derived mid-parent and high-parent heterosis, The correlation coefficient between genetic distance and yield (0.64) indicated a moderately strong relationship, so it is possible that some of the SRAP markers might be linked to quantitative trait loci for seed yield.

EVALUATION OF d2, A MICROSATELLITE MEASURE OF INBREEDING AND OUTBREEDING, IN WOLVES WITH A KNOWN PEDIGREE

Abstract: We have evaluated a microsatellite measure proposed as an indicator of inbreeding and outbreeding using a captive wolf population with known inbreeding levels and founder sources. The measure, which is based on the difference in the repeat number for microsatellite alleles within an individual, was not more predictive of the known inbreeding coefficient than microsatellite heterozygosity (it was actually less predictive). We also found no support that the measure was predictive of the level of outbreeding. However, we could not determine if the measure was predictive of very low levels of inbreeding due to matings between remote relatives. Overall, it appears that the usefulness of this measure to identify individuals on the inbred-outbred continuum beyond that of heterozygosity and identify biologically important associations with fitness-related traits may be limited. We suggest that the measure be examined theoretically to determine when (and how much) the predictive value of the measure is different from that of heterozygosity for inbreeding or outbreeding levels in a variety of different scenarios.

Heterotic groups based on yield-specific combining ability data and phylogenetic relationship determined by RAPD markers for 28 tropical maize open pollinated varieties.

Abstract: Twenty eight maize open pollinated varieties (OPVs) were crossed in a diallel scheme and the 378 F1's were evaluated in 10 environments in Brazil. Based on yield-specific combining ability data (SCA), these varieties were classified in four heterotic groups. The consistence of the proposed heterotic groups was confirmed comparing intra- and inter-group F1 values and midparent heterosis. Superior OPVs combinations for use as a source of inbreds in hybrid breeding programs were determined. RAPD markers were used to genotype these varieties. A UPGMA dendogram, based on marker data from 50 primers and 178 polymorphic bands, was obtained. Phylogeny obtained with RAPD markers agreed with known pedigree data. Dent germplasm tended to group separately from flint germplasm. Multidimensional Scaling Analysis on marker data and morphological data showed a higher degree of genetic divergence among the dent germplasm than among the flint germplasm used in this study. Correlation between RAPD marker estimated genetic distance and SCA for yield was low and positive (r = 0.16**).

Genetic Analysis of Seedling Growth under Cold Temperature Stress in Grain Sorghum

Abstract: Planting of grain sorghum [Sorghum bicolor (L.) Moench] earlier in the season should contribute to a longer growing season and more effective utilization of late spring and early summer rainfall, but early planting is hindered by poor seedling vigor under cold temperature conditions. Sources of cold tolerance have been identified, but little is known about the inheritance of this trait. This study was conducted to determine combining ability for seedling growth characteristics under cold temperature conditions in genetically diverse sorghum lines using a Design-II mating scheme. Parental lines and hybrids were evaluated under early and normal planting conditions in the field. The traits measured included emergence, emergence index, leaf number, vigor, and dry weight. Significant differences were observed among entries. Among hybrids, these differences were primarily due to effects of general combining ability. These results indicate that general combining ability is more important than specific combining ability in breeding for seedling vigor in sorghum. Heterosis had favorable effects on all seedling traits measured.

Heterotic Relationships among Nine Temperate and Subtropical Maize Populations

Abstract: The introgression of exotic germplasm could increase the heterosis among maize (Zea mays L.) populations. Our objective was to assess heterotic relationships among BSSS (R) (Reid' germplasm) and BS 26 (Lancaster' germplasm) from the temperate USA; the southern African cultivars Salisbury White, Southern Cross, and Natal Potchefstroom Pearl Elite Selection (NPP ES); and the subtropical CIMMYT Populations 34, 42, 44, and 47. The nine cultivars and their diallel crosses were evaluated at five Mexico, Zimbabwe, and U.S. locations. Populations 34, 42, 44, and 47 and NPP ES demonstrated the highest per se grain yield with Population 44 ranking first (8.42 Mg ha -1 ). Low to moderate levels of high parent heterosis was observed for their crosses; nonetheless, they occurred frequently as parents of superior crosses at Mexico where Population 42 x Population 47 ranked first (8.42 Mg ha -1 ). BSSS (R) demonstrated the best general combining ability with variety heterosis effects averaging 1.34 Mg ha -1 . Diversity among varieties was determined on the basis of dominance-associated gene effects. When the diversity was resolved by principle coordinate analysis, BSSS (R) was separated from BS 26, and Salisbury White from Southern Cross along different dimensional axes, suggesting that the two pairs are sources of different genes for heterosis. The highest yielding cross (9.28 Mg ha -1 ) and best heterotic combination involved Population 44 and BSSS (R). BSSS (R), NPP ES, and Populations 44 and 42 performed well outside their target ecologic zones, indicating their potential benefit to breeding programs in new geographic areas.

Heterosis, combining ability and genetics for vitamin C, total soluble solids and yield in tomato ( Lycopersicon esculentum ) at 1700 m altitude

Abstract: A study was conducted on a 15 x 15 diallel set of tomato excluding reciprocals to find out the extent of heterosis, combining ability and nature of gene action for yield with two important quality traits: ascorbic acid (vitamin C) and total soluble solids (TSS). Significant differences among genotypes were obtained for all three traits. Positive high significant heterosis was found for yield (41.97, 157.84 and 28.94%), for ascorbic acid (16.68, 54.57 and 161.33%) and for TSS (25.97, 11.93 and 19.02) over the top, the better parent and the commercial control respectively. The magnitude of variance due to general as well as specific combining ability were highly significant indicating the importance of both additive and non-additive gene action. However degree of dominance (o -2 g/o -2 s) revealed the prevalence of a non-additive gene effect. Cross combinations Arka Vikas × Sel-12 (13.19), KS-10 x Pant T-3 (1.66) and EC 818703 x EC 13042 (0.88) were best specific combiners for ascorbic acid, total soluble solids and yield/plant. Predominance of non-additive gene action plays a greater role in the inheritance of ascorbic acid and total soluble solids in tomato under hill conditions.

Use of DNA Markers in Prediction of Hybrid Performance and Heterosis for a Three-Line Hybrid System in Rice

Abstract: Two Cytoplasmic Male Sterile lines were crossed with fourteen restorer lines of rice widely grown in the western regions of Maharashtra, India, to produce 28 F1 hybrids which were evaluated for eight agronomically important traits, contributing to yield potential, in replicated field trials. The hybrid performance was recorded along with heterosis and heterobeltiosis. All the rice lines under investigation were subjected to marker-based variability analysis. An attempt was made to correlate genetic distance based on specific markers for each trait individually, as well as average genetic distance based on all specific markers, with hybrid performance and heterosis, by regression analysis. Specific markers could cluster the parental lines in different groups and showed significant correlation with hybrid performance. The data also supports the proposition that epistasis is the basis of heterosis. The analysis, however, revealed a lack of significant predictive values for field application.

The performance of microgametophytes is affected by inbreeding depression and hybrid vigor in the sporophytic generation

Abstract: Inbreeding reduces the level of heterozygosity, thereby exposing deleterious recessives to selection and simultaneously reducing the number of loci expressing heterosis (overdominance). In contrast, hybridization increases the level of heterozygosity, thereby masking deleterious recessives and simultaneously increasing the number of loci expressing heterosis. Most studies of inbreeding depression/hybrid vigor have focused on sporophytic performance such as survivorship, vegetative growth rates, fruit and seed production and (rarely) pollen production. Because the genetic mechanisms that underlie inbreeding depression/hybrid vigor are relevant only to the diploid stage of the life cycle, most studies have tacitly assumed that they have no effects on pollen performance (pollen germination, pollen tube growth rate, ability to achieve fertilization under conditions of pollen competition). However, we reasoned that because pollen is dependent upon the sporophyte for the resources necessary to develop, germinate and initiate tube growth, the level of heterozygosity (vigor) in the pollen-producing parent can affect pollen performance by affecting the ability of the sporophyte to provision its pollen. In a series of studies conducted under field conditions over 7 years, we experimentally varied the level of heterozygosity in wild gourd (Cucurbita pepo) plants (four levels of inbreeding, f = 0.75, 0.50, 0.25, 0 and a zucchini × wild gourd F1). We found that sporophytic vigor (e.g., flower and fruit production) increased with the level of heterozygosity and that the level of heterozygosity of the sporophyte affects the in vitro and in vivo performance of the microgametophytes it produces. These findings are analogous to the ”maternal environmental effects” frequently observed in seeds.

Heterosis in maize investigated using connected RIL populations

Abstract: Understanding the genetic basis of heterosis in a given species is a major issue for both evolutionary research and applied purposes. In order to map QTLs involved in heterosis in maize and to estimate their effect, we evaluated the hybrids between three connected RIL populations and the three initial parental inbreds, yielding a total of 1278 hybrids. A specific data analysis approach using multilocus models was developed using MCQTL software. Thirteen regions with significant effect on variation were detected for grain yield and 11 for grain moisture at harvest. These two traits display different genetic effects: only few significant dominance effects could be detected for moisture, whereas all yield QTLs displayed such effects. Furthermore, most yield QTLs displayed apparent overdominance effects.

Heterosis in crop mutant crosses and production of high yielding lines using doubled haploid systems

Abstract: Heterosis appearing in crosses between mutants derived from the same parent variety and crosses of mutants with parent varieties has been observed by many authors for many plant species including such important crops as barley, faba bean, maize, pea, pearl millet, rice, sunflower, sesame, sweet clover, triticale and wheat. Mutant heterosis was reported for crosses of spontaneous mutants, mutants obtained after treatment with various mutagens and recently also for somaclonal variants. The heterotic effects are usually related to an increase in some yield components. There is a lack of correlation between mutation of a particular plant character and appearance of heterotic effect. The yielding performance of a mutant was not correlated with its potential to give yield heterosis in crosses with another mutant, often also a very poor one, or with the parent variety. Poor yielding barley mutants from the collection of semi-dwarf forms of the Department of Genetics, Silesian University gave heterosis in crosses with other mutants or parent varieties for such characters as tillering, grain number and weight per plant. In addition to mutants with deleterious mutations of such characters as chlorophyll synthesis or fasciated stem there were also lines mutated for earliness, semi-dwarfness, low glucoside or high protein and lysine content which gave significant heterosis in crosses. One possible explanation of the phenomenon of mutant heterosis is related to the frequency of mutations induced by chemical and physical mutagens. The appearance and the level of heterotic effect of mutated genes will depend on their interaction with other mutated genes or with genes from the parental genotype. High specific combining ability of mutants giving heterotic effect makes hybrid seed production, based on crosses with defined sources of cytoplasmic or genetic male sterility, unfeasible or even impossible. Doubled haploids provide a unique system to attempt the ‘fixing’ of hybrid performance in homozygous lines and to avoid the step of hybrid seed production. The assumption on the ‘fixability’ of hybrid yield in homozygous lines based on reports that large additive genetic variance is responsible for yield heterosis in wheat or barley was proven also for mutant crosses.

Genetic analysis in recombinant inbred lines of early dent forage maize. I: QTL mapping for yield, earliness, starch and crude protein contents from per se value and top cross experiments

Abstract: Quantitative trait loci (QTL) affecting forage maize agronomic traits were analyzed in a set of 131 recombinant inbred lines (RIL) descended from the cross between the early dent lines F288 and F271 together with 108 SSR markers. Traits studied were yield, plant height, ear height, earliness as silking date and dry matter content, starch content, soluble carbohydrate content, crude protein content and a yield adjusted crude protein content. Field evaluation was performed among the RIL population studied per se (3 years, 3 locations in year 1, 2 locations for the other two years, 3 replicates per location), and after top crossing with the early flint line F286 (2 years, 3 locations per year, 3 replicates per location). Root traits were also investigated in lines (1 year, 1 location). Heterosis was considered as the difference between hybrid (RIL x F286) value and average value of the parents (RIL and F286 per se). The genotype effects were highly significant and always greater than genotype x environment interactions. Highly transgressive lines were observed for yield, lint not for earliness. Moreover, genetic variation for crude protein content was low. Putative QTL were identified through composite interval mapping, and are given for LOD values higher than 2.0. Additive x additive epistatic effects were investigated. Six QTL for top cross yield, and three for RIL per se yield were observed, but only one was common to RIL per se and top cross. A QTL for yield heterosis was observed in a location where no QTL for yield was found. In top cross, only one QTL for starch content, and one for soluble carbohydrate content, were found. Two QTL for silking date were observed in RIL per se and top cross, and four QTL were observed for silking date heterosis, but none was common between RIL per se, top cross or heterosis. Four and respectively three QTL were observed in top cross and RIL per se for dry matter content at harvest, two of which were common between RIL per se and top cross. Numerous QTL related to crude protein content were found, but with little additive effects. In the only experiment where it was investigated, numerous QTL with high LOD values were evidenced for root morphology traits related to lodging susceptibility.

Heterosis in two closely related species of earthworm (Eisenia fetida and E. andrei).

Abstract: The importance of heterosis, and in particular allozyme-associated heterosis, in natural populations remains unclear. Much of the scepticism that surrounds allozyme-associated heterosis comes from inconsistent and unreliable detection of the relationship. Thus, evaluating the genetic mechanisms that may cause allozyme-associated heterosis in natural populations has proven difficult. The most prevalent hypotheses that have been put forward to explain the genetic basis of heterosis are the general dominance and the local overdominance hypotheses. A factorial crossing design was used to survey eight polymorphic allozyme loci in the parent and offspring generations of two species of earthworms in order to evaluate possible mechanisms of allozyme-associated heterosis for growth rate. Significant heritable variation for growth rate was detected only within a single cross. Allozyme-associated heterosis for growth rate was detected only within this cross. This relationship did not persist after the effects of interfamily variation were removed. These results indicate that simple heritability of a fitness-related trait may be necessary for predictive power and repeatability of allozyme-associated heterosis, and that the allozyme-associated heterosis detected in this study was the result of general dominant genetic effects.

Heterosis for yield and other agronomic traits of winter triticale F1 and F2 hybrids

Abstract: Triticale is generally treated as a self-pollinating crop and line breeding is practised. Hybrid breeding has been discussed for some time, but there is little information for winter triticale. This study investigated heterosis for eight agronomic traits in F 1 and F 2 hybrids grown together with their parents as drilled plots in three environments. On average, grain yield heterosis was 12.5 dt/ha (a relative 10.5%) compared with the mid-parent value for F 1 hybrids, and 6.2 dt/ha (5.0%) for F 2 hybrids and with a wide range of 4.4-17.1 dt/ha for F 1 hybrids. A positive contribution to the heterosis of yield was made by kernels/spike and 100-kernel weight, whereas spikes/m 2 showed negative heterosis. Hybrid plants in F 1 and F 2 were taller than mid-parents (8.3 cm and 5.3 cm, respectively), with a tendency to earlier heading. The negative heterosis for falling number in F 1 and F 2 hybrids could be a problem for commercial production of triticale hybrids. By selecting parents for combining ability and the identification of heterotic patterns, grain yield heterosis of 20% appears feasible.

Genetic effects and heterosis of flowering and fruit characteristics of tropical pumpkin

Abstract: Tropical pumpkin is an important vegetable in many lowland tropics. Estimation of genetic effects for a fixed set of genotypes may yield information on the presence of different types of gene action for important traits. Six landraces and one diallel set of their progeny were evaluated for time from planting to female anthesis and fruit characteristics. Variety effects and heterosis mean squares were significant for the days to female anthesis, the weight of the first mature fruit, the mean fruit weight and soluble solids, indicating the presence of both additive and non-additive gene actions. Only variety effects were significant for the days to the first mature fruit. These characters could be improved by recurrent selection. Selection for heterosis would be effective except for the days to the first fruit to mature.

Components of genetic variation in short-duration pigeonpea crosses under waterlogged conditions

Abstract: Waterlogging inflicts considerable stress and yield-loss on short-duration pigeonpea and the present study investigates the genetical control of phenotypic variation expressed in the basic generations of some elite crosses under waterlogged conditions. Comparisons of the parental and Fl families for the 22 traits representing various facets of morphological variability revealed that the additive and dominance effects were present for a large number of these traits. Better parent heterosis was present in one or more crosses for all except two traits (ILN40 and NTR40) and a maximum of five (out of six) crosses showed heterosis for plant height (PH40) and days to lenticel formation (DYL). Analyses of the PI( P2, nents of genetic variation in short-duration pigeonpea crosses under waterlogged conditionsF1( F2, F3> Bcu and Bct^ generations further indicated that the genetical control of various traits was rather complex. Epistasis was detected for S6 (out of 126) cross/trajt combinations and there was no trait for which epistasis was non-significant in all the crosses. Presence of predominantly duplicate epistasis also pointed to a transient advantage for the hybrid varieties and better prospects of extracting superior recombinant inbred lines. In general, crosses between the tolerant and susceptible lines showed more variation compared to those involving only the tolerant lines and therefore possessed better potential for further breeding. Lack of apparent association between plant vigour and tolerance to waterlogging also indicated that plant vigour does not play a direct role in determining the tolerance to waterlogging in short-duration pigeonpea.

II. Heterosis for leaf area and dry matter accumulation

Abstract: A pot experiment was conducted to investigate the heterosis for morphological characters and to examine the relationship among some characters at active tillering, flowering and dough ripe stages of 12 F, hybrids from crosses between japonica and indica rice. Heterosis for plant height, number of tillers, green leaf area and dry matter accumulation per plant was positive at all stages. The intensity of heterosis was higher at the active tillering stage for number of tillers, leaf area and dry matter accumulation per plant. A significant positive relationship was found between tiller number and leaf area per plant at active tillering and flowering stages. Significant positive relationships between leaf area and dry matter accumulation, and between tiller number and dry matter accumulation per plant were observed at all stages. A significant positive relationship was found between leaf area per plant at an early stage and dry matter accumulation per plant at a later stage, suggesting that early development of leaf area is an important factor for higher dry matter accumulation in F, hybrids. Although heterosis for percent dead leaf blade was positive at the flowering stage due to early leaf senescence in some Ft hybrids, a larger leaf area was also found in F, hybrids at this stage and leaves of Fi hybrids remained green longer compared to parent cultivars up to the dough ripe stage. : Dry matter, Fx hybrid, Heterosis, Leaf area.

Evaluation of Yield and Yield Components in Inbred Maize Lines I. Heterosis and Line x Tester Analysis of Combining Ability

Abstract: In maize, three male testers and six female lines together with their 18 F1 hybrids were evaluated to study the general and specific combining ability estimates and heterosis following line x tester approach. Analysis of variance indicated the existence of significant variation among F1 and parents for all characteristics. Average heterosis was significant for all characteristics studied and was positive, except for days to tasseling, with the average yield of hybrids being 79.8% above that of the parents. In view of the general combining ability effects of the parents, the parental lines YUZ P709 and FR 64A were identified as being the best overall parent combiners in the experiment for grain yield and yield components. Combining ability analysis showed that general combining ability (GCA) effects were significant for all attributes and specific combining ability (SCA) effects were significant for ear diameter, ear height and grain yield per unit area. With respect to ear height and grain yield per unit area, SCA effects were more pronounced when compared to GCA effects, indicating the predominance of non-additive gene action in the inheritance of these traits.

Use of Heterosis in Maize Breeding: History, Methods and Perspectives - A Review

Abstract: The hybrid vigor is one of the greatest practical contribution of genetics to the agricultural world and had its most significant expression in maize crops, being intensively explored by breeders and seed production companies. This review presents aspects of the genetic basis for heterosis, biometrical assessment, and improvement methods to obtain heterotic hybrids and reciprocal recurrent selection in maize. Contributions from Biotechnology and Molecular Genetics as tools for hybrid programs to diminish hand pollination work to obtain inbred lines and to form heterotic groups through molecular markers are also reported. Finally, the identification of QTLs to help select superior lines and confirm genetic hypotheses is presented to completely elucidate the heterosis phenomena.