Heterosis In Hybrids Research Articles

Сравнително проучване на морфологичните качества и люпимостта на яйцата от чисти линии и кръстоски от общоползвателно и яйценосно направление

During the recent decades, the scientific community turned its attention towards the dual purpose lines and crosses that might offer a suitable solution for two problems in poultry breeding - the use of male chickens for meat and the use of female chickens for rearing in alternative types of systems for egg production. Hence, a study with four groups of birds: a dual purpose cross „Salmon“, a dual purpose purebred line „BB“, a laying line „L“ and a laying hybrid line „ISA-Brown“ was conducted. The aim was to compare the morphological traits, as well as the fertility and the hatchability of the eggs, obtained from „ISA-Brown“, compared to the dual purpose „Salmon“ reared at IAS-Kostinbrod, and the local dual purpose and laying lines involved in its creation. As a result of the conducted research, we can conclude that the selection for high performance, larger eggs and the presence of heterosis in hybrids has to some extent a positive influence on most of the morphological traits determining the quality of the eggs produced. In addition, negative consequences for their hatchability, embryo survival and some morphological parameters such as increased width of the egg and increased diameter of the yolk were also observed. On the other hand, in the stock hybrids, compared to the purebred lines and the dual purpose crosses, this can also be considered as a sign of deterioration of the nutritional quality of the eggs.

The formation of nicotine heterosis is mainly achieved by enhancing the nicotine transport capacity in hybrids

Nicotine exhibits obvious heterosis, which can be used to create Nicotiana tabacum L. (tobacco) varieties with varying nicotine content. However, the reasons for the formation of nicotine heterosis and its relationship to nicotine transport and accumulation remain unknown. This study conducted a comprehensive analysis of six tobacco hybrids with varying heterosis levels and their parent materials from various aspects, such as phenotype, physiology, and transcriptomics. The results showed that the direct path coefficient of transport heterosis to nicotine heterosis was highest in hybrids, at 0.98, and a highly significant positive correlation between the two. The plant height, thick stalk circumference, large flow of tissue fluid in the stalk, and high nicotine concentration of tobacco were the underlying factors that led to the strong nicotine transport capacity of hybrids. The formation of nicotine transport heterosis in hybrids was mainly influenced by non-additive gene effects (accounting for 89.93%), with over-dominant effects playing a dominant role (accounting for 58.79%). Among non-additive expression DEGs, nicotine transporter related multi antimicrobial extrusion protein, drug/metabolite transporter, ABC family transporter, and glutathione S-transferase were significantly upregulated in hybrid strains. The RT-qPCR results indicated that these genes related nicotine transport also exhibited heterosis at the expression level. Our results revealed that the formation of nicotine heterosis is mainly achieved by enhancing the nicotine transport capacity in hybrids. The results are not only beneficial for promoting the theoretical study of nicotine heterosis in tobacco and the breeding and utilization of hybrids, but are also of great significance for guiding nicotine production and promoting its multipurpose utilization.

Molecular mechanisms of heterosis under drought stress in maize hybrids Zhengdan7137 and Zhengdan7153.

Maize is one of the most successful crops in utilizing heterosis which significantly improves maize stresses resistance and yield. Drought is a destructive abiotic stress that significantly reduces crop yield, particularly in maize. Drought stress and re-watering frequently occur during the growth and development of maize; however, the molecular mechanisms of heterosis under drought stress and re-watering have rarely been systematically investigated. Zhengdan7137 and Zhengdan7153 are two maize hybrid varieties with robust heterosis, and separately belongs to the SS×NSS and Reid×Tangsipingtou heterotic groups. 54 transcriptomes of these two hybrids and their parental inbred lines were analyzed under well-watering (WW), water-deficit (WD), and re-watering (RW) conditions using RNA-Seq. In this study, we identified 3,411 conserved drought response genes (CDRGs) and 3,133 conserved re-watering response genes (CRRGs) between Zhengdan7137 and Zhengdan7153. When comparing CDRGs and CRRGs to overdominance and underdominance genes, we identified 303 and 252 conservative drought response overdominance genes (DODGs) and underdominance genes (DUDGs), respectively, and 165 and 267 conservative re-watering response overdominance genes (RODGs) and underdominance genes (RUDGs), respectively. DODGs are involved in stress response-related processes, such as L-phenylalanine metabolism, carbohydrate metabolism, and heat response, whereas DUDGs are associated with glucose metabolism, pentose-phosphate shunt, and starch metabolism. RODGs and RUDGs contribute to the recovery of hybrids from drought stress by upregulating cell propagation and photosynthesis processes, and repressing stress response processes, respectively. It indicated overdominant and underdominant genes conservatively contributed to hybrid heterosis under drought stress. These results deepen our understanding of the molecular mechanisms of drought resistance, uncover conservative molecular mechanisms of heterosis under drought stress and re-watering, and provide potential targets for improving drought resistance in maize.

Assessment of Heterosis in Inter-varietal Hybrids of Mangalore Melon (Cucumismelo var. acidulus) for Yield and Quality Traits

Mangalore melon is one of the distinct class of Cucurbitaceae family widely grown in southern part of India. Despite of having many nutritional values, there is scope for systematic hybridization study to improve the many qualitative and quantitative traits. An investigation was undertaken to develop inter-varietal hybrids and their evaluation to assess the extent of heterosis in newly developed hybrids between selected genotypes of Mangalore melon during kharif, 2019 and 2020 at College of Horticulture, Sirsi, Karnataka, India. A total of 16 intervarietal hybrids were developed by crossing 15 parental lines. Hybrids were developed using hand emasculation and hand pollination technique and the developed hybrids were evaluated using RCBD design with two replications. The results showed significant positive heterosis over mid parent and better parent for all the hybrids. The hybrids Soubhagya×RNMS-1 exhibited highest and significant heterosis over both mid parent (88.05%) and better parent (72.69%) followed by MS-19×MS-5 over mid parent (73.09%) and better parent (61.10%). From this study, it was concluded that hybrid Soubhagya X RNMS-1 was superior over their parents for most of the traits with the total yield of 8.44 kg plant-1. These best performing hybrids are need to be studied for their stability and commercial exploitation, resistance of pest and diseases, keeping quality of hybrids (storability) and experimentation on hybrid seed production technologies as well as storability of seeds should be done.

Performance of Provitamin a Maize Hybrids for Yield and Desirable Agronomic Traits

To find improved F1 hybrids for breeding procedures, the heterosis of maize hybrids must be determined. Therefore, to identify prospective hybrids for use in future provitamin A maize breeding systems, this study was carried out to evaluate the amount of standard heterosis for grain yield and related attributes. Fifteen provitamin A maize inbred lines were crossed through the diallel-II design. The resulting Eight four F1 hybrids along with four standard checks (BHQPY545, BH549, BH546, and BH547) were evaluated using RCBD (20 entries) and Alpha-Lattice Design (68 entries) with two replications during 2022/2023 main cropping season at Bako National Maize Research Center. Analysis of variance revealed significant variations for most of the traits indicating the existence of genetic variability. The Standard heterosis assessment noticed significant positive and negative heterosis for the majority of the traits investigated. Cross combinations over BHQPY 545, such as L10 × L3, L10 × L6, and L13×L12, demonstrated the largest proportion of traditional heterosis for grain yield (more than 25% yield advantage). Because BH546 and BH547 are normal maize with grain production potential, the majority of crossings yielded negative and significant results over commercial checks. The highest found heterosis for grain yield and associated factors indicated that maize genotypes' heterotic potential may be beneficial to boost yield. The findings of this study could be valuable for researchers looking to develop high-yielding provitamin A maize hybrids. As a result, possible hybrids might be recommended for commercial usage once the results have been verified by repeating the research over time and across places, as well as incorporating quality attributes analysis data.

Genomic and transcriptomic analysis to investigate the growth heterosis mechanisms of pearl oysters (Pinctada fucata martensii)

Pinctada fucata martensii, a bivalve mollusk highly valued for seawater pearl production, exhibits growth traits crucial for pearl yield and quality. Although hybridization promotes growth, the mechanisms underlying growth heterosis in pearl oysters remain unclear. This study utilized two inbred populations (PB and PY) and one hybrid population (F) constructed from pearl oysters. Comparative analysis of growth traits, along with whole-genome sequencing (WGS) and RNA sequencing (RNA-seq), revealed that hybrid F showed superior growth traits. Compared with the parents, hybrid F exhibited significant heterosis for shell height (10.422%), shell length (11.361%), shell width (11.411%), and total weight (36.254%). Analysis of population genetic structure indicated increased heterozygosity in hybrid F through hybridization. Expression pattern analysis revealed that approximately 93.79% of the DEGs displayed dominant expression, with approximately 6.21% exhibited overdominant, indicating pivotal roles of dominant genes in heterosis development. There were more paternal dominant genes than maternal genes, suggesting that paternal genetic information significantly impacts heterosis in hybrid F. Furthermore, selective sweep and expression pattern analyses revealed that immune defense, metabolism, and regulatory processes are correlated with hybrid phenotypic growth traits in pearl oysters. In conclusion, this study explored the molecular mechanisms that influence the hybrid growth advantage of pearl oysters, with the aim of providing valuable insights and ideas for breeding research in aquaculture.

Manifestation of the Effect of Growth Heterosis in Intraspecific Hybrids of Soft Wheat

The presented article presents the results of the study of height inheritance in hybrid combinations of the first generation (F1) of bread wheat. The research was conducted in the 2019-2020 growing season at the Apsheron District Experimental Farm under irrigation conditions. In 32 combinations of hybrids of the first generation (F1), obtained as a result of reciprocal crossing of 9 local varieties («Mirbashir-128», «Azeri», «Gobustan», «Fatima», «Gyrmyzy gul-1», «Murov-2», «Askeran», «Matin» and «Onur»). Studied the height of plants in comparison with parental forms and determined the degree of true heterosis and dominance. In the studied hybrid combinations, a variety from high dominance to depression was found in the transmission of heredity. When analyzing hybrids of bread wheat of the first generation (F1) according to the inheritance of plant height, high dominance was determined in 19 combinations (59.4%), depression — in 8 combinations (25.0%), intermediate heredity - in 5 combinations (15.6% ). Positive heterosis was revealed in 19 combinations (59.4%), negative heterosis - in 13 combinations (40.6%). As a result of the research, it is possible to initially conclude that it is possible to obtain low-growing hybrids by involving in the hybridization a variety of the same height.

Transcriptome analysis reveals the key role of overdominant expression of photosynthetic and respiration-related genes in the formation of tobacco(Nicotiana tabacum L.) biomass heterosis

BackgroundLeaves are the nutritional and economic organs of tobacco, and their biomass directly affects tobacco yield and the economic benefits of farmers. In the early stage, our research found that tobacco hybrids have more leaves and larger leaf areas, but the performance and formation reasons of biomass heterosis are not yet clear.ResultsThis study selected 5 parents with significant differences in tobacco biomass and paired them with hybrid varieties. It was found that tobacco hybrid varieties have a common biomass heterosis, and 45 days after transplantation is the key period for the formation of tobacco biomass heterosis; By analyzing the biomass heterosis of hybrids, Va116×GDH94 and its parents were selected for transcriptome analysis. 76.69% of the differentially expressed genes between Va116×GDH94 and its parents showed overdominant expression pattern, and these overdominant expression genes were significantly enriched in the biological processes of photosynthesis and TCA cycle; During the process of photosynthesis, the overdominant up-regulation of genes such as Lhc, Psa, and rbcl promotes the progress of photosynthesis, thereby increasing the accumulation of tobacco biomass; During the respiratory process, genes such as MDH, ACO, and OGDH are overedominantly down-regulated, inhibiting the TCA cycle and reducing substrate consumption in hybrid offspring; The photosynthetic characteristics of the hybrid and its parents were measured, and the net photosynthetic capacity of the hybrid was significantly higher than that of the parents.ConclusionThese results indicate that the overdominant expression effect of differentially expressed genes in Va116×GDH94 and its parents plays a crucial role in the formation of tobacco biomass heterosis. The overdominant expression of genes related to photosynthesis and respiration enhances the photosynthetic ability of Va116×GDH94, reduces respiratory consumption, promotes the increase of biomass, and exhibits obvious heterosis.

Seed development-related genes contribute to high yield heterosis in integrated utilization of elite autotetraploid and neo-tetraploid rice.

Autotetraploid rice holds high resistance to abiotic stress and substantial promise for yield increase, but it could not be commercially used because of low fertility. Thus, our team developed neo-tetraploid rice with high fertility and hybrid vigor when crossed with indica autotetraploid rice. Despite these advances, the molecular mechanisms underlying this heterosis remain poorly understood. An elite indica autotetraploid rice line (HD11) was used to cross with neo-tetraploid rice, and 34 hybrids were obtained to evaluate agronomic traits related to yield. WE-CLSM, RNA-seq, and CRISPR/Cas9 were employed to observe endosperm structure and identify candidate genes from two represent hybrids. These hybrids showed high seed setting and an approximately 55% increase in 1000-grain weight, some of which achieved grain yields comparable to those of the diploid rice variety. The endosperm observations indicated that the starch grains in the hybrids were more compact than those in paternal lines. A total of 119 seed heterosis related genes (SHRGs) with different expressions were identified, which might contribute to high 1000-grain weight heterosis in neo-tetraploid hybrids. Among them, 12 genes had been found to regulate grain weight formation, including OsFl3, ONAC023, OsNAC024, ONAC025, ONAC026, RAG2, FLO4, FLO11, OsISA1, OsNF-YB1, NF-YC12, and OsYUC9. Haplotype analyses of these 12 genes revealed the various effects on grain weight among different haplotypes. The hybrids could polymerize more dominant haplotypes of above grain weight regulators than any homozygous cultivar. Moreover, two SHRGs (OsFl3 and SHRG2) mutants displayed a significant reduction in 1000-grain weight and an increase in grain chalkiness, indicating that OsFl3 and SHRG2 positively regulate grain weight. Our research has identified a valuable indica autotetraploid germplasm for generating strong yield heterosis in combination with neo-tetraploid lines and gaining molecular insights into the regulatory processes of heterosis in tetraploid rice.

Heterosis for Resistance to Insect Herbivores in a 3-Line Hybrid Rice System.

Three-line hybrid rice is produced by crossing male sterile (A line) rice with a fertility-restorer (R line). Fertile lines (B lines) are also required to maintain A line seed for breeding programs. We used a range of hybrids and their parental lines to assess the frequency and nature of heterosis for resistance to the whitebacked planthopper (Sogatella furcifera), brown planthopper (Nilaparvata lugens) and yellow stemborer (Scirpophaga incertulas). Heterosis is defined as trait improvement above the average of the parental lines as a result of outbreeding. Based on the results from a greenhouse study that challenged hybrids and their parental lines with each herbivore species, we found that susceptibility to planthoppers was associated with one of the eight A lines tested, but resistance was improved by crossing with a relatively resistant restorer. Higher frequencies of heterosis for susceptibility in comparisons between hybrids and their B lines suggest that susceptibility was not related to the cytoplasmic genomes of the associated sterile A lines. Furthermore, because none of the parental lines possessed currently effective resistance genes, improved resistance against planthoppers was probably due to quantitative resistance. In a related field trial, hybrids had generally higher yields than their fertile parents and often produced larger grain; however, they were often more susceptible to stemborers, leaffolders (Cnaphalocrocis medinalis) and other caterpillars (Rivula atimeta). This was largely a consequence of hybrid heterosis for plant biomass and was strongly affected by crop duration. We make a series of recommendations to improve hybrid breeding to reduce the risks of herbivore damage.

High-quality genome assembly enables prediction of allele-specific gene expression in hybrid poplar.

Poplar (Populus) is a well-established model system for tree genomics and molecular breeding, and hybrid poplar is widely used in forest plantations. However, distinguishing its diploid homologous chromosomes is difficult, complicating advanced functional studies on specific alleles. In this study, we applied a trio-binning design and PacBio high-fidelity long-read sequencing to obtain haplotype-phased telomere-to-telomere genome assemblies for the 2 parents of the well-studied F1 hybrid "84K" (Populus alba × Populus tremula var. glandulosa). Almost all chromosomes, including the telomeres and centromeres, were completely assembled for each haplotype subgenome apart from 2 small gaps on one chromosome. By incorporating information from these haplotype assemblies and extensive RNA-seq data, we analyzed gene expression patterns between the 2 subgenomes and alleles. Transcription bias at the subgenome level was not uncovered, but extensive-expression differences were detected between alleles. We developed machine-learning (ML) models to predict allele-specific expression (ASE) with high accuracy and identified underlying genome features most highly influencing ASE. One of our models with 15 predictor variables achieved 77% accuracy on the training set and 74% accuracy on the testing set. ML models identified gene body CHG methylation, sequence divergence, and transposon occupancy both upstream and downstream of alleles as important factors for ASE. Our haplotype-phased genome assemblies and ML strategy highlight an avenue for functional studies in Populus and provide additional tools for studying ASE and heterosis in hybrids.

Imprinting but not cytonuclear interactions determines seed size heterosis in Arabidopsis hybrids.

The parent-of-origin effect on seeds can result from imprinting (unequal expression of paternal and maternal alleles) or combinational effects between cytoplasmic and nuclear genomes, but their relative contributions remain unknown. To discern these confounding factors, we produced cytoplasmic-nuclear substitution (CNS) lines using recurrent backcrossing in Arabidopsis (Arabidopsis thaliana) ecotypes Col-0 and C24. These CNS lines differed only in the nuclear genome (imprinting) or cytoplasm. The CNS reciprocal hybrids with the same cytoplasm displayed ∼20% seed size difference, whereas the seed size was similar between the reciprocal hybrids with fixed imprinting. Transcriptome analyses in the endosperm of CNS hybrids using laser-capture microdissection identified 104 maternally expressed genes (MEGs) and 90 paternally expressed genes (PEGs). These imprinted genes were involved in pectin catabolism and cell wall modification in the endosperm. Homeodomain Glabrous9 (HDG9), an epiallele and one of 11 cross-specific imprinted genes, affected seed size. In the embryo, there were a handful of imprinted genes in the CNS hybrids but only 1 was expressed at higher levels than in the endosperm. AT4G13495 was found to encode a long-noncoding RNA (lncRNA), but no obvious seed phenotype was observed in lncRNA knockout lines. Nuclear RNA Polymerase D1 (NRPD1), encoding the largest subunit of RNA Pol IV, was involved in the biogenesis of small interfering RNAs. Seed size and embryos were larger in the cross using nrpd1 as the maternal parent than in the reciprocal cross, supporting a role of the maternal NRPD1 allele in seed development. Although limited ecotypes were tested, these results suggest that imprinting and the maternal NRPD1-mediated small RNA pathway play roles in seed size heterosis in plant hybrids.

Adaptation and plasticity of yield in hybrid and inbred sorghum

AbstractLocal adaptation and genotype by environment (G×E) interactions affect the expression of phenotypes in crop species. An investigation on the interplay between adaptation and G×E on sorghum heterosis phenotypes is lacking. To address this question, a set of 112 diverse grain sorghum hybrids and their 22 inbred parents of local and exotic origins, representing the primary female and male heterotic groups, were tested in five contrasting sorghum‐growing environments across 2 years in Queensland, Australia. Plant height, days to flowering, seed yield, grain weight, and grain number were measured and used in the estimation of heterosis. Midparent heterosis for yield ranged from –25% to 217% and was highly influenced by grain number. In contrast to observations in maize, the magnitude of heterosis for yield was not associated with site mean. Striking differences were observed in heterosis in hybrids from locally developed inbred parents compared with hybrids that were developed from exotic inbred parents developed in other countries. Heterosis in the latter combination was higher on average across all the test environments for the majority of traits. We hypothesize maladaptive phenotypic plasticity in the exotic parents contributed to the observed differences in heterosis estimates. These data confirm that heterosis estimates in sorghum must be obtained and interpreted in relevant genetic and environmental contexts. Breeders in developing countries with low sorghum hybrid seed uptake will find these insights useful when selecting hybrids for broader adaptation, improving efficiency of their breeding programs.

Estimation of Hetrosis in F1 Hybrids of Bread Wheat Genotypes

The experiment was conducted for estimation of the heterosis in F1 hybrids in wheat genotypes. The research was conducted at the experimental field of Seed Production Development Centre, Sindh Agriculture University Tandojam during Rabi growing season 2019-20. The experiment was laid-out in randomized complete block design (RCBD) using three replications. The performance of parents and their hybrids, and heterotic effects were measured in various aspects like earliness characters (days taken to 75% heading, days taken to 75% maturity), morphological and yield traits like plant height, tillers plant-1, yield plant-1, and a physiology related trait; relative water content. The study consisted of six varieties and their six F1 hybrids. The parents used were TD-1, Benazir-2013, TJ-83, Hamal, Imdad-2005, Kiran-95 and their crosses were as TD-1 × Hamal, TD-1 × Benazir-2013, Benazir-2013 × TD-1, TJ-83 × Benazir-2013, TJ-83 × Imdad, Kiran-95 ×Benazir-2013. Results revealed that all the parents and hybrids were highly significant for all the parameters studied at P<0.01 level. The F1 hybrids Benazir-2013 × TD-1, TD-1 × Benazir-2013, TD-1 × Hamal and Kiran -95 × Benazir-2013 had showed better response in mid parent heterosis and heterobeltiosis for most of the traits except plant height. On the basis of current findings, it could be concluded that these cross combinations may be used in bread wheat for yield improvement

BREEDING AND GENETIC FEATURES OF SOYBEAN VARIETIES BASED ON THE MANIFESTATION OF TRAITS IN F1 HYBRIDS IN TOPCROSSES

Further increase in gross soybean production requires the introduction of new varieties with an optimal combination of elements of the crop structure. Hybridization in soybeans is the main effective method of creating new varieties. Increasing the efficiency of hybridization in obtaining heterotic offspring is possible when using parental forms with high combinational ability in crosses. In the study, a two-tester analysis of topcrosses of soybean varieties differing in economically valuable traits was used. Based on the results of the combinational ability assessment, the value of soybean varieties was determined by the elements of the yield structure. Heterotic combinations in first-generation hybrids were identified, from which it is more likely to select highly productive forms in later hybrid populations F2-F4. The high effects of ZKZ and SCZ on plant height in varieties Medea, Kyivska 97, Sawyer 2-95 and KiVin tester; on the height of lower bean attachment in varieties Sawyer 2-95, Ustia, Kharkivska skoroglya and KiVin tester; on the number of productive nodes - in varieties Kyivska 97 and Goverla tester; by the number of beans per plant - in varieties Sawyer 2-95, Kyivska 97 and tester Goverla; by the number of seeds per plant - in varieties Medea, Kyivska 97 and tester KiVin; by the weight of 1000 seeds - in varieties Sawyer 2-95, Kyivska 97 and tester Goverla; by the weight of grain per plant - in varieties Sawyer 2-95, Kyivska 97 and tester Goverla. It was found that additive effects of genes were predominant in the genetic control of plant height and lower bean attachment, elements of yield structure and grain weight per plant, but there is a smaller influence of non-additive effects. The manifestation of true heterosis (dominance in 100% of cases) in hybrids (F1) was found in crosses with both testers for the number of productive nodes, number of beans and seeds per plant, and grain weight per plant.

Heterosis from eucalypt single and multi-cross hybrids

Hybridizing is one of the most important ways to genetically improve eucalypts; especially to tropical species. Because of the high efficiency of asexual using hybrid heterosis, the current planting eucalypt varieties in most tropical areas in the world are hybrids. It’s well known that crossing different eucalypt species in different ways can create hybrids with different characters. But, it’s unclear what kind of species matings tend to create more heterosis. Here we systematically made and tested hybrids of: pure species by pure species (single cross), pure species by hybrids (three-way cross), hybrids by hybrids (double cross). The tropical eucalypt species we used as parents include: Eucalyptus urophylla, E. grandis, E. pellita, E. tereticornis and hybrids between them. The field testing results found: the overall performance of tree volume was: single cross > three way cross > intraspecies cross > double cross. Their 4-year advantages over intraspecies cross were: 29.9%, 8.0% and -12.5%. The coefficient of variation of the 4 types were: 55.3%, 61.2%, 64.0% and 67.1%. As for the survival rate, 4-year result was: double cross (72.6%) > three way cross (71.6%) > single cross (70.8%) > intraspecies cross (54.0%). This shows that the interspecies hybrids had similar environmental adaption, and they were all significantly higher than that of intraspecies cross. The single and multi-cross hybrids had similar coefficient of variation on survival rate. Combining with the results on family and individual tree level heterosis frequency and magnitude, we found that single-cross has more heterosis on volume growth while muti-cross has more heterosis on adaption. Genetic parameter analysis showed that single-cross hybrids have both high additive and high dominant heritability. But the heritability value on different species combinations can be very different. Three way-cross hybrids had the highest additive heritability, but very low dominant heritability. The double-cross hybrids had high dominant heritability, but very low additive heritability.

Moving towards a rolling front strategy for VERACEL's advanced-generation eucalypt hybrid breeding program

The eucalyptus breeding program at VERACEL started in the mid-1990s driven by the objective of producing outstanding clones adapted to the Bahia South (Brazil) environment, and thus creating highly productive stands with high quality pulpwood. The breeding population initially comprised several introduced pure species collections (mainly E. grandis and E. urophylla) from Australian provenances and ex-Brazilian hybrids (mostly E. urophylla × E. grandis). These populations were first structured according to a typical reciprocal recurrent selection scheme to identify outstanding urograndis F1 hybrids. In the early 2000s, the program developed and tested several second-generation F1 hybrids, in addition to some progeny and clonal trials with a few introduced new species and hybrids. More recently, starting in 2016, a new set of F2 progeny and clonal hybrid trials were established from previously selected F1 parents. This second generation of hybrids was complemented with other 2-way and 3-way hybrid crosses to form an advanced generation synthetic population. To manage such breeding population, including pure species, F1 and advanced F2 hybrids, and backcross hybrids, VERACEL is restructuring its breeding program to implement a more flexible multispecies rolling front selection and mating scheme. This would allow the strategy to effectively combine all available phenotypic and pedigree information. Currently, the database, spanning three generations of breeding, includes 105 progeny and clonal trials, over 2,300 individual clones, and more than 30,000 pure and hybrid seedling progenies. We expect that the breeding and selection strategy will ensure optimum long-term progress in the additive genetic merit of selected parents, as well as exploit the hybrid heterosis and non-additive genetic effects to identify outstanding clones in the short term. Our study describes in some detail the current state-of-the-art of VERACEL’s breeding and clonal populations, and discusses key elements of this strategy. We discuss the challenges posed by the increasing relevance of good adaptations to climate change and diseases, and the complex genetics of inter-specific hybridization, especially as the program enters its 3rd generation of testing and selections.

Fine mapping and identification of CaTTG1, a candidate gene that regulates the hypocotyl anthocyanin accumulation in Capsicum annuum L.

Pepper (Capsicum annuum L.) is a typical self-pollinating crop with obvious heterosis in hybrids. Consequently, the use of morphological markers during the pepper seedling stage is crucial for pepper breeding. The color of hypocotyl is widely used as a phenotypic marker in crossing studies of pepper. Pepper accessions generally have purple hypocotyls, which are mainly due to the anthocyanin accumulation in seedlings, and green hypocotyls are rarely observed in pepper. Here we reported the characterization of a green hypocotyl mutant of pepper, Cha1, which was identified from a pepper ethyl methanesulfonate (EMS) mutant library. Fine mapping revealed that the causal gene, CaTTG1, belonging to the WD40 repeat family, controlled the green hypocotyl phenotype of the mutant. Virus-induced gene silencing (VIGS) confirmed that CaTTG1 regulated anthocyanin accumulation. RNA-seq data showed that expression of structural genes CaDFR, CaANS, and CaUF3GT in the anthocyanin biosynthetic pathway was significantly decreased in Cha1 compared to the wild type. Yeast two-hybrid (Y2H) experiments also confirmed that CaTTG1 activated the synthesis of anthocyanin structural genes by forming a MBW complex with CaAN1 and CaGL3. In summary, this study provided a green hypocotyl mutant of pepper, and the Kompetitive Allele Specific PCR (KASP) marker developed based on the mutation site of the underlying gene would be helpful for pepper breeding.

Identification and Functional Analysis of the Phosphatidylethanolamine-Binding Protein (PEBP) Gene Family in Liriodendron Hybrids

The plant phosphatidylethanolamine-binding protein (PEBP) gene family plays important roles in regulating flowering time and vegetative growth. Compared with its parents, Liriodendron hybrids (Liriodendron chinense (Hemsl.) Sarg. × L. tulipifera L.), have obvious heterosis in terms of higher seed germination, fast growth, bright flower colors, and long growth seasons. However, the genome-wide identification and functional analysis of PEBP genes that contribute to the heterosis of Liriodendron hybrids have not been studied. In this study, we characterized four members of expressed LhPEBP genes in Liriodendron hybrids and divided them into three subfamilies based on their phylogenetic relationships: FT-like (LhFT), TFL1-like (LhTFL1), and MFT-like (LhMFT1 and LhMFT2). A functional analysis of Arabidopsis showed that the overexpression of LhFT significantly promoted flowering, and the LhTFL1 gene induced a wide dispersion of the flowering timing. LhMFTs function differently, with LhMFT2 suppressing flowering, while LhMFT1 accelerates it and had a stronger promoting effect on the early stage of seed germination. Additionally, the seed germination of the LhMFT lines was relatively less influenced by ABA, while the transgenic LhFT and LhTFL1 lines were sensitive to both ABA and GA3. These results provide valuable insights into the functions of LhPEBP genes in flowering and seed germination.

Carbohydrate metabolism and cytology of S-type cytoplasmic male sterility in wheat.

Cytoplasmic male sterility (CMS) is an important tool for hybrid heterosis utilization. However, the underlying mechanisms still need to be discovered. An adequate supply of nutrients is necessary for anther development; pollen abortion would occur if the metabolism of carbohydrates were hampered. In order to better understand the relationship between carbohydrate metabolism disorder and pollen abortion in S-CMS wheat, the submicroscopic structure of wheat anthers was observed using light microscopy and transmission electron microscopy; chloroplast proteome changes were explored by comparative proteomic analysis; sugar measuring and enzyme assays were performed; and the expression patterns of carbohydrate metabolism-related genes were studied using quantitative real-time PCR (qRT-PCR) method. These results indicated that the anther and microspore in S-CMS wheat underwent serious structural damage, including premature tapetum degeneration, nutritional shortage, pollen wall defects, and pollen grain malformations. Furthermore, the number of chloroplasts in the anthers of S-CMS lines decreased significantly, causing abnormal carbohydrate metabolism, and disintegration of osmiophilic granules and thylakoids. Meanwhile, some proteins participating in the Calvin cycle and carbohydrate metabolism were abnormally expressed in the chloroplasts of the S-CMS lines, which might lead to chloroplast dysfunction. Additionally, several key enzymes and genes related to carbohydrate metabolism were significantly inhibited in S-CMS. Based on these results, we proposed a carbohydrate metabolism pathway for anther abortion in S-type cytoplasmic male sterility, which would encourage further exploration of the pollen abortion mechanisms for CMS wheat.