High Level Of Heterosis Research Articles

Heritability and Variability of Productivity Traits in Spring Soft Wheat Hybrids of the First to Fourth Generations

Abstract A higher varietal specificity in the manifestation of traits in parental varieties was noted compared to hybrids. Two component traits of ear productivity in a series of generations were analyzed against the background of various factors, shifts in their average values and their impact on yield were predicted and determined. The phenotypic dominance index (hp) in the first generation was determined by the number of grains per ear and the weight of 1000 grains, combinations with a high level of heterosis were identified. Under the conditions of the Apsheron region, the effects of interaction between genotype and environment were determined in nine varieties of spring soft wheat and seven hybrid populations F1…F4 formed with their participation. A reliable effect of environmental conditions on all the studied traits was established. The contribution of the “year” factor to the number of grains per ear in varieties and hybrids was 10.9 and 13.9%, respectively; to the weight of 1000 grains – 5.8 and 19.5%; to the yield – 47.3 and 41.1%. The genetic component made a significant contribution to the weight of 1000 grains in varieties and hybrids (81.5 and 58.8%), as well as to the number of grains in varieties (38.4%).

Advances in lentil production through heterosis: Evaluating generations and breeding systems.

Heterosis is defined as increased performance of the F1 hybrid relative to its parents. In the current study, a cohort of populations and parents were created to evaluate and understand heterosis across generations (i.e., F1 to F3) in lentil, a self-pollinated annual diploid (2n = 2× = 14) crop species. Lentil plants were evaluated for heterotic traits in terms of plant height, biomass fresh weight, seed number, yield per plant and 100 grain weight. A total of 47 selected lentil genotypes were cross hybridized to generate 72 F1 hybrids. The F1 hybrids from the top five crosses exhibited between 31%–62% heterosis for seed number with reference to the better parent. The five best performing heterotic crosses were selected with a negative control for evaluation at the subsequent F2 generation and only the tails of the distribution taken forward to be assessed in the F3 generation as a sub selection. Overall, heterosis decreases across the subsequent generations for all traits studied. However, some individual genotypes were identified at the F2 and sub-selected F3 generations with higher levels of heterosis than the best F1 mean value (hybrid mimics). The phenotypic data for the selected F2 and sub selected F3 hybrids were analysed, and the study suggested that 100 grain weight was the biggest driver of yield followed by seed number. A genetic diversity analysis of all the F1 parents failed to correlate genetic distance and divergence among parents with heterotic F1’s. Therefore, genetic distance was not a key factor to determine heterosis in lentil. The study highlights the challenges associated with different breeding systems for heterosis (i.e., F1 hybrid-based breeding systems and/or via hybrid mimics) but demonstrates the potential significant gains that could be achieved in lentil productivity.

The formation of hybrid fish derived from hybridization of Megalobrama amblycephala (♀) × Siniperca chuatsi (♂)

Crossbreeding has been conducted in many fish species. However, crosses between distant relatives that may result in higher levels of heterosis are hard to conduct due to reproductive isolation. In this study, diploid hybrids (BM) of blunt snout bream (Megalobrama amblycephala, BSB, ♀, order Cypriniformes, 2n = 48) × mandarin fish (order Siniperca chuatsi, MD, ♂, Perciformes, 2n = 48) were successfully produced. BM possessed 48 chromosomes from BSB. The body colour of BM (silver grey with many black spots) was different from that of BSB (silvery white) and MD (yellow with black stripes). The body shape of BM (small head with a slender body) was different from that of BSB (small head with a high back) and MD (body larger and flatter). We confirmed successful hybridization with microsatellite DNA markers and analysed the 5S rDNA patterns among the parental and hybrid lines. BM inherited its 5S rDNA entirely from the female parent (BSB). This study will provide a foundation for fish crossbreeding, and the successful hybrids in this study will potentially be an excellent commercial variety.

Identifying quantitative trait loci for the general combining ability of yield-relevant traits in maize.

Maize is the most important staple crop worldwide. Many of its agronomic traits present with a high level of heterosis. Combining ability was proposed to exploit the rule of heterosis, and general combining ability (GCA) is a crucial measure of parental performance. In this study, a recombinant inbred line population was used to construct testcross populations by crossing with four testers based on North Carolina design II. Six yield-relevant traits were investigated as phenotypic data. GCA effects were estimated for three scenarios based on the heterotic group and the number of tester lines. These estimates were then used to identify quantitative trait loci (QTL) and dissect genetic basis of GCA. A higher heritability of GCA was obtained for each trait. Thus, testing in early generation of breeding may effectively select candidate lines with relatively superior GCA performance. The GCA QTL detected in each scenario was slightly different according to the linkage mapping. Most of the GCA-relevant loci were simultaneously detected in all three datasets. Therefore, the genetic basis of GCA was nearly constant although discrepant inbred lines were appointed as testers. In addition, favorable alleles corresponding to GCA could be pyramided via marker-assisted selection and made available for maize hybrid breeding.

Inheritance and variability of productivity traits in hybrids of spring soft wheat of the first to fourth generations

The effects of genotype-environment interaction of nine spring soft wheat varieties and seven hybrid populations F1 - F4 formed using these varieties were determined under the conditions of the Kirov region. The significant influence of environmental conditions on all studied traits was established. The contribution of the “year” factor to the number of grains per head in varieties and hybrids was 10.9 and 13.9%, respectively; to the mass of 1000 grains – 5.8 and 19.5%; to the yield – 47.3 and 41.1%. The genetic component made a significant contribution to the mass of 1000 grains in varieties and hybrids (81.5 and 58.8%), as well as to the number of grains in varieties (38.4%). There was a higher varietal specificity in the manifestation of traits in parental varieties compared to the hybrids. The analysis was done for two component traits of head productivity in a series of generations against the background of the action of various lim-factors, the shifts in their average values and the influence on yield were predicted and determined. The indicator of phenotypic domination (hp) in the first generation was determined according to the number of grains per head (hp = -5.00...+ 7.82) and 1000 grains mass (hp = + 0.23...+ 12.00), the combinations with a high level of heterosis were picked out (Baganskaya 95 x Novosibirskaya 44 and Baganskaya 95 x Aktjube 3). The calculation of the breeding differential and the effectiveness of the selections in contrasting environmental conditions of the second (2016) and third (2017) hybrid generations was carried out. Under the conditions of 2018, the yield of the initial populations varied within 219.0...789.6 g/m2, while the figures for the selected progenies were 317.0...647.6 g/m2. The average yield increase of the progenies that had been selected in the dry year was 56.8 g/m2 in relation to the initial populations (11.1%); the increase of the progenies, selected in the conditions of excess moisture was 10.8 g/m2 (3.0%). The correlation analysis revealed the average positive relationship between the first-generation hp indicator and the selection differential in subsequent generations according to the «1000 grains mass» (r = 0.18...0.63) and «number of grains per head» (r = 0.35...0.37) traits. The correlation was weak between the level of heterosis and the selection reaction (r = -0.12…0.27). The selection of genotypes with a high level of selection differential according to the number of grains per head was more effective than the selection according to the mass of 1000 grains. The correlation coefficient between the degree of phenotypic dominance of traits in the first generation and average values of traits in the F2-F4 generations varied within r = 0.35...0.68 (significant values at 5% level r = 0.75).

Genetic variability, character association and genetic divergence in groundnut (Arachis hypogaea L.) accessions

Present investigation was conducted in 31 groundnut accessions to assess genetic divergence, characters association involving 13 quantitative characters and path coefficients in order to identify superior accessions exhibiting higher genetic diversity. Number of pods/plant, secondary branches, kernel width, and pod yield displayed a higher level of coefficient of variation both at phenotypic and genotypic level. Genetic advance with higher heritability indicated preponderance of additive variance for pod length, pod yield, and number of pods/plant. Number of secondary branches, kernel width, pod length, and number of pods/plant revealed significant positive correlation with pod yield. Path coefficient analysis revealed exertion of high positive direct effects on pod yield through pod length, kernel width and number of pods/plant. Cluster analysis exhibited substantial diversity among 31 accessions forming 13 clusters. Two clusters [X (two accessions) and XII (one accession)] showed the largest distance, which suggests hybridization between these accessions to achieve high level of heterosis for further exploitation. Five accessions viz., TAG-24, TG-69, ICGV-02005, TG-73 and TG-80 were identified as the most divergent for future use.

Why SR52 is such a great maize hybrid? I. Heterosis and generation mean analysis

SR52 is the first single cross maize hybrid to be commercialised in the world and forms the basis of maize breeding in Zimbabwe and Eastern and Southern Africa region. Although SR52 is such an exceptional hybrid, the genetic basis of its outstanding yield and heterosis has never been explained. Therefore genetic components of yield and associated traits in SR52 were studied using a generation mean analysis. Parents (P1 and P2), F1 and segregating F2 and backcross generations (BCP1 and BCP2) were evaluated. The experiment was laid out as a randomised complete block design with two replications across two sites in South Africa, during the 2012/2013 season. The study confirms high levels of heterosis exceeding 300 % for grain yield potential and revealed a significant lack of fit of the additive–dominance model for yield and most secondary traits. Consequently, the role of epistasis was investigated by partitioning it into additive × additive , additive × dominance and dominance × dominance gene effects. The full model confirmed presence of epistasis of highly significant (P ≤ 0.01) additive × additive nature for grain yield though negligible in magnitude (<10 %). Both dominance and additive gene effects were highly significant for yield and associated traits. However, dominance gene action contributed over 80 % to grain yield potential. Additive and additive × additive gene effects played a significant but minor role for grain yield potential (less than 20 %). We therefore concluded that dominance gene action is the basis for exceptional heterosis displayed by SR52.

Exploitation of wild annual Cicer species for widening the gene pool of chickpea cultivars

AbstractIntrogression of unadapted genes from the wild Cicer species could contribute to the widening of genetic base of important traits such as yield, yield attributes and resistance to major biotic and abiotic stresses. An attempt was made successfully to intercross two wild annual Cicer species with three cultivated chickpea cultivars. Four interspecific cross‐combinations were made, and their true hybridity was ascertained through morphological and molecular markers. These cross‐combinations were also studied for some important quantitative traits under real field conditions. The range, mean and coefficient of variation of agro‐morphological traits were assessed in the parental lines, their F1 and F2 generations to determine the extent of variability generated in cultivated chickpea varieties. A high level of heterosis was recorded for number of pods/plant and seed yield/plant in F1 generation. Three cross‐combinations of ‘Pusa 1103’ × ILWC 46, ‘Pusa 256’ × ILWC 46 and ‘Pusa 256’ × ILWC 239 exhibited substantially higher variability for important yield‐related traits. The present research findings indicate that these wild annual Cicer species can be easily exploited to broaden the genetic base of cultivated gene pool for improving seed yield as well as adaptation.

Seed and Seedling Vigour in Tropical Maize Inbred Lines

Abstract Seed and seedling vigour is an aspect of seed quality which affects field establishment and performance. Low maize yields have been reported to be affected by several factors in which poor quality seed with low seed and seedling vigour. Information is scarce on seed and seedling vigour in maize inbred lines developed for tropical environments. Fifteen genotypes of tropical maize (Zea mays L.) inbred lines were evaluated to determine the level of differences in seed and seedling vigour traits, and extent of relationships among traits and their heritability. A substantial amount of genetic variability was found, which suggested that most of the traits under study could be improved through selection and utilized in breeding programs. Positive and significant interrelationship among seed germination and seedling traits and a positive correlation between seed germination and seed vigour and field emergence showed that these could be given due consideration in crop improvement for seed and seedling vigour. High genotypic coefficient of variation, heritability and genetic advance were obtained for seed germination, seed emergence, shoot length and seedling vigour index I and II, revealing the possibility of improvement in these characters through direct selection. The principal component analysis (PCA) identified seed emergence, shoot length, seedling vigour index I and II and tetrazolium vigour as characters that contributed greatly to variation in seed vigour in the maize inbred lines. Cluster analysis partitioned the genotypes into two groups, with group I consisting of seven genotypes and group II comprised the other eight genotypes, which suggested that hybridization between the two groups could lead to high level of heterosis. Genotype V5 had superior seedling vigour traits compared to other genotypes. Seedling emergence, shoot length, seedling vigour index I, seedling vigour index II and tetrazolium vigour are effective characters for good seedling vigour traits in maize inbred lines investigated.

Romanian Maize (Zea mays) Inbred Lines as a Source of Genetic Diversity in SE Europe, and Their Potential in Future Breeding Efforts

Maize has always been under constant human selection ever since it had been domesticated. Intensive breeding programs that resulted in the massive use of hybrids nowadays have started in the 60s. That brought significant yield increases but reduced the genetic diversity at the same time. Consequently, breeders and researchers alike turned their attention to national germplasm collections established decades ago in many countries, as they may hold allelic variations that could prove useful for future improvements. These collections are mainly composed of inbred lines originating from well-adapted local open pollinated varieties. However, there is an overall lack of data in the literature about the genetic diversity of maize in SE Europe, and its potential for future breeding efforts. There are no data, whatsoever, on the nutritional quality of the grain, primarily dictated by the zein proteins. We therefore sought to use the Romanian maize germplasm as an entry point in understanding the molecular make-up of maize in this part of Europe. By using 80 SSR markers, evenly spread throughout the genome, on 82 inbred lines from various parts of the country, we were able to decipher population structure and the existing relationships between those and the eight international standards used, including the reference sequenced genome B73. Corroborating molecular data with a standardized morphological, physiological, and biochemical characterization of all 90 inbred lines, this is the first comprehensive such study on the existing SE European maize germplasm. The inbred lines we present here are an important addition to the ever-shrinking gene pool that the breeding programs are faced-with, because of the allelic richness they hold. They may serve as parental lines in crosses that will lead to new hybrids, characterized by a high level of heterosis, nationwide and beyond, due to their existing relationship with the international germplasm.

Broadening the genetic base of lentil cultivars through inter‐sub‐specific and interspecific crosses of Lens taxa

AbstractWild Lens taxa are invaluable sources of useful traits for broadening genetic base of cultivated lentil. Nine inter‐sub‐specific and interspecific crosses were made successfully between cultivated (Lens culinaris ssp. culinaris) and wild lentils (L. culinaris ssp. orientalis, odemensis, lamottei and ervoides). The effect of species groups, day length and temperature on crossability in lentils was evident under normal winter sowing in New Delhi and in summer Himalayan nursery at Sangla in Himachal Pradesh, India, although pollen fertility assessed in all the cross‐combinations showed no significant variation. True hybridity of nine inter‐sub‐specific and interspecific crosses was confirmed through morphological and molecular (ISSR) markers, in which three of 120 primers could confirm the hybridity of all the crosses. All cross‐combinations were also studied for important quantitative traits related to yield. The range, mean and coefficient of variation were estimated in parental lines, F1 and F2 generations to determine the extent of variability generated in cultivated lentils through the introgression of genes from wild L. taxa. A high level of heterosis was observed in F1 crosses for important traits studied. Substantially higher variations for seed yield and its attributing traits were exhibited in F2 generations indicating transgressive segregation. The results of the present investigation revealed that wild L. taxa can be successfully exploited for lentil improvement programmes, and the variations generated could be easily utilized for broadening the genetic base of cultivated lentil gene pool for improving the yield as well as wider adaptation.

Specific changes in total and mitochondrial proteomes are associated with higher levels of heterosis in maize hybrids

The phenomenon of hybrid vigor (heterosis) has long been harnessed by plant breeders to improve world food production. However, the changes that are essential for heterotic responses and the mechanisms responsible for heterosis remain undefined. Large increases in biomass and yield in high-heterosis hybrids suggest that alterations in bioenergetic processes may contribute to heterosis. Progeny from crosses between various inbred lines vary in the extent of vigor observed. Field-grown maize F₁ hybrids that consistently exhibited either low or high heterosis across a variety of environments were examined for changes in proteins that may be correlated with increased plant vigor and yield. Unpollinated ears at the time of flowering (ear shoots) were selected for the studies because they are metabolically active, rich in mitochondria, and the sizes of the ears are diagnostic of yield heterosis. Total protein and mitochondrial proteomes were compared among low- and higher-heterosis hybrids. Two-dimensional difference gel electrophoresis was used to identify allelic and/or isoform differences linked to heterosis. Identification of differentially regulated spots by mass spectrometry revealed proteins involved in stress responses as well as primary carbon and protein metabolism. Many of these proteins were identified in multiple spots, but analysis of their abundances by label-free mass spectrometry suggested that most of the expression differences were due to isoform variation rather than overall protein amount. Thus, our proteomics studies suggest that expression of specific alleles and/or post-translational modification of specific proteins correlate with higher levels of heterosis.

Breeding for male fertility restoration incorporating Basmati rice quality

Basmati is the most highly valued rice commodity in the world agricultural trade market. Pusa Basmati 1, released in India, combines both high yield and ideal Basmati quality. In Pakistan, semi-tall Pak 385 and Pak 386 are reported to be better yielding than Basmati 370. Results at IARI have demonstrated the possibility of developing hybrids with Basmati grain quality and a high level of heterosis. Such Basmati hybrids would raise yields further.

Combining ability and heterosis effect in hexaploid wheat group

The main goal of hybrid wheat breeding is the identification of parents with high specific combining ability for grain yield and other agronomic traits. This kind of data facilitate the development of hybrid combinations with high level of heterosis in first filial generation (F1 generation). The use of species from the hexaploid wheat group (e.g. Triticum spelta L. Triticum compactum HOST...) is representing an opportunity for the increase of heterosis level in the germplasm of common wheat (Triticum aestivum L.). The study of combining ability and heterosis effect in hexaploid wheat group was carried out using crosses between thirteen inbred lines of common wheat (6 lines x 7 testers) and inter-species crosses (T. aestivum L. ? T. spelta L., T. aestivum L. ? T. compactum HOST, T. aestivum L. ? T. sphaerococcum PERCIV., T. aestivum L. ? T. macha DEKAPR. et MENABDE, T. aestivum L. ? T. petropavlovskyi UDACZ. et MIGUSCH, T. aestivum L. ? T. vavilovii (THUM.) JAKUBZ.). The 42 common wheat F1 hybrids were tested during two seasons (2010/11 and 2011/12) on the Selection center Ptuj. The experiment was carried out in a randomized block design with four replications. The 43 interspecies F1 hybrids were tested on the same location in the season 2011/12 and the experiment was designed as an randomized block with three replications. The results were analyzed using statistical package AGROBASE generation II and STATGRAPHICS Centurion XVI. The analysis of variance was significant for both, GCA and SCA variances (P &lt; 0,01). Generally, SCA variances were lower than GCA variances. We could state, that the improvement of heterosis level in the common wheat germplasm through the use of relatives with the same genome (genome BAD) is possible. As an example we can point out the interspecies F1 hybrid between common wheat variety Garcia and an accession of the Triticum sphaerococcum PERCIV. species (accession number 01C0201227).

Additive and Over‐dominant Effects Resulting from Epistatic Loci Are the Primary Genetic Basis of Heterosis in Rice

A set of 148 F9 recombinant inbred lines (RILs) was developed from the cross of an indica cultivar 93-11 and japonica cultivar DT713, showing strong F1 heterosis. Subsequently, two backcross F1 (BCF1) populations were constructed by backcrossing these 148 RILs to two parents, 93-11 and DT713. These three related populations (281BCF1 lines, 148 RILs) were phenotyped for six yield-related traits in two locations. Significant inbreeding depression was detected in the population of RILS and a high level of heterosis was observed in the two BCF1 populations. A total of 42 main-effect quantitative trait loci (M-QTLs) and 109 epistatic effect QTL pairs (E-QTLs) were detected in the three related populations using the mixed model approach. By comparing the genetic effects of these QTLs detected in the RILs, BCF1 performance and mid-parental heterosis (HMP), we found that, in both BCF1 populations, the QTLs detected could be classified into two predominant types: additive and over-dominant loci, which indicated that the additive and over-dominant effect were more important than complete or partially dominance for M-QTLs and E-QTLs. Further, we found that the E-QTLs detected collectively explained a larger portion of the total phenotypic variation than the M-QTLs in both RILs and BCF1 populations. All of these results suggest that additive and over-dominance resulting from epistatic loci might be the primary genetic basis of heterosis in rice.

Genome‐wide association analysis reveals cryptic alleles as an important factor in heterosis for fatness in chicken F2 population

Genome-wide association studies have become possible in the chicken because of the recent availability of the complete genome sequence, a polymorphism map and high-density single nucleotide polymorphism (SNP) genotyping platforms. We used these tools to study the genetic basis of a very high level of heterosis that was previously observed for fatness in two F(2) populations established by crossing one outbred broiler (meat-type) sire with dams from two unrelated, highly inbred, light-bodied lines (Fayoumi and Leghorn). In each F(2) population, selective genotyping was carried out using phenotypically extreme males for abdominal fat percentage (AF) and about 3000 SNPs. Single-point association analysis of about 500 informative SNPs per cross showed significant association (P < 0.01) of 15 and 24 markers with AF in the Broiler x Fayoumi and Broiler x Leghorn crosses respectively. These SNPs were on 10 chromosomes (GGA1, 2, 3, 4, 7, 8, 10, 12, 15 and 27). Interestingly, of the 39 SNPs that were significantly associated with AF, there were about twice as many homozygous genotypes associated with higher AF that traced back to the inbred lines alleles, although the broiler line had on average higher AF. These SNPs are considered to be associated with QTL with cryptic alleles. This study reveals cryptic alleles as an important factor in heterosis for fatness observed in two chicken F(2) populations, and suggests epistasis as the common underlying mechanism for heterosis and cryptic allele expression. The results of this study also demonstrate the power of high marker-density SNP association studies in discovering QTL that were not detected by previous microsatellite-based genotyping studies.

Genetic diversity of ash gourd [ Benincasa hispida (Thunb.) Cogn.] inbred lines based on RAPD and ISSR markers and their hybrid performance

Ten inbred lines of ash gourd [ Benincasa hispida (Thunb.) Cogn.] were crossed to produce 45 F 1 hybrids (without reciprocal) which were evaluated along with the parents for 20 growth- and yield-related traits, in a replicated field trial. High level of heterosis was observed among the hybrids for most of the traits examined, including yield. These inbred lines were analysed by using 42 RAPD primers those produced 282 DNA marker bands. A total of 130 RAPD markers were obtained with a mean of 3.1 per primer, which in combination discriminated all the inbreds from each other. Pair-wise genetic distance measurements ranged from 0.07 to 0.31, suggesting a wide genetic diversity for these inbreds. These inberds were also analysed with five ISSR primers of which four were informative. Twenty-six ISSR marker bands were generated of which 11 were polymorphic with an average of 2.80 per primers. The percentage of polymorphic bands produced were higher in ISSR markers (>80%) than generated through RAPD markers (46%). Although the results indicated significant positive correlations of genetic distance with hybrid performance and heterosis, the RAPD based genetic distance measures and use of limited ISSR markers in this present study could not effectively predict hybrid performance in this crop. The genetic variation among ash gourd inbred lines examined, herein, defined a marker array (combined ISSR and RAPD) for the development of a standard reference for further genetic analyses, and the selection of potential parents for predicting hybrid performance and heterosis.

Molecular diversity and its relationship with hybrid performance and heterosis in ash gourd [Benincasa hispida (Thunb.) Cogn.

SummaryAsh gourd or wax gourd [Benincasa hispida (Thunb.) Cogn.], belonging to the family Cucurbitaceae, is an underexploited vegetable in spite of having considerable economic and medicinal importance. Very little information is available on the genetic diversity and exploitation of heterosis in this crop. In the present study, nine inbred lines of ash gourd were crossed to produce all (72) possible F1 hybrids, including reciprocals, which were evaluated along with the nine parents for 13 growth- and yield-related traits and 14 quality traits, in a replicated field trial. A high level of heterosis was observed among the hybrids for most of the traits examined, including iron and zinc content. Significant reciprocal differences in heterosis were observed. The inbred lines were analysed using 130 RAPD primers, of which 26 were informative and amplified 163 DNA marker bands. A total of 47 polymorphic bands were obtained with a mean of 1.8 per primer which, in combination, discriminated all the inbreds from each other. Pair-wise genetic distance measurements ranged from 0.056 to 0.179, suggesting a narrow genetic base for the inbreds. Although the results indicated significant positive correlations of genetic distance with hybrid performance and heterosis, the magnitudes of the correlations were not high enough to be of predictive value.

QTL-Based Analysis of Heterosis for Grain Shape Traits and Seedling Characteristics in an indica-japonica Hybrid in Rice (Oryza saliva L.)

A set of BC1F1, i.e., indica/japonica//japonica and indica/japonica//indica, were produced to specifically compare the effect of heterozygotes and homozygotes at each QTL locus in an indica-japonica hybrid in rice. Grain shape traits and seedling characteristics were measured, in BC1F1 and BC1F2, respectively. Five QTLs were detected for grain width on chromosome 1, 2, 5 and 7. Two QTLs were detected for the 1000-grain weight on chromosomes 4 and 5. Three QTLs were detected for the grain thickness on chromosomes 2 and 5. Four QTLs were detected for the seedling weight on chromosomes 5, 6 and 12, in addition to three QTLs for other seedling traits, length of first leaf, seedling height and chlorophyll content, on chromosomes 1, 3 and 6, respectively. In the comparison of marker genotypes of AA, Aa and aa, QTLs were detected either between AA and Aa or between Aa and aa, and there was no case in which Aa was superior to AA and aa. In both analyses, each positive effect was contributed from either one of the parents. So far as the present data concern, it was able to conclude that the high level of heterosis in the current indica-japonica hybrids was manifested by a cumulative partial dominant effect of the heterozygotes at many loci and not by overdominance. Then, the set of QTL data for positive effects are considered to be systematically utilized in breeding of parental lines by using molecular markers.

Exploiting Heterosis in Pearl Millet for Population Breeding in Arid Environments

In the desert region of Rajasthan, India, farmers mainly grow pearl millet [Pennisetum glaucum (L.) R. Br.] landraces. The adoption of modern cultivars is generally low because of their poor adaptation to extreme drought stress. The objective of this study was to evaluate the performance of six elite breeding populations and three landraces and to determine the heterotic pattern among the 36 diallel crosses of those populations. Field experiments were conducted in eight environments in India. Mean grain yields (GYs) in the three environments with favorable growing conditions were double to threefold those in the three arid environments. The elite populations generally showed higher GY than the landraces; stover yield (SY) was similar in both population types. The landraces flowered earlier, had a higher tillering potential, and smaller seeds. Mean level of midparent heterosis was generally low, ranging from 0.85% for time to flowering (TF) to 6.57% for SY. For GY, expression of heterosis for individual population crosses was between −14 and +30% under drought stress, and between −9 and +17% in the favorable environments. For SY, mean heterosis was always positive and higher than for GY. The elite × landrace population crosses with high mean GY and high levels of heterosis under drought stress could be beneficial to widen the germplasm base and to combine the high yield potential of elite materials with the good adaptation of the landraces.