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Developing high-yield maize hybrids is critical for sustaining maize production, especially in the face of rapid climate changes and the growing global population. Exploring the genetic diversity and combining ability in parental inbreds is needed for developing such high-yielding hybrids. Consequently, this study aimed at evaluating parental genetic diversity employing simple sequence repeats (SSR) markers, estimating effects of general (GCA) and specific (SCA) combining abilities for grain yield and yield contributing characters, identifying high yielding hybrids, and evaluating the association of SCA effects and performance of hybrids with genetic distance. Half-diallel mating scheme was utilized to develop 21 F1 hybrids from seven diverse maize inbred lines. The F1 hybrids along with check hybrid (SC-10), were investigated in a field trial over two growing seasons under arid conditions. The assessed F1 hybrids displayed significant genetic variations across all recorded traits. The inbreds P1 and P3 were detected as effective combiners to develop early maturing hybrids. Additionally, P3 and P4 were recognized as better combiners for improving grain yield and yield attributed characters. The hybrids P1 × P5 and P4 × P7 displayed significant SCA effects coupled with favorable agronomic performance. These hybrids are recommended for further evaluation and release as variety for arid environments to increase total maize production and contribute to food security. The alleles per locus differed between 2 and 5, with average of 3.5 alleles/locus. The polymorphic information content (PIC) altered between 0.21 to 0.74, with a mean of 0.56. Unweighted neighbor-joining tree grouped the inbred lines into three clusters, providing a valuable tool to decrease the crosses needed to be assessed in the trial field. Parental genetic distance varied from 0.63 to 0.90, averaging 0.79. The relationship between genetic diversity assessed through SSR markers and SCA effects was insignificant for all considered traits. Otherwise, SCA demonstrated a significant correlation with hybrid performance, suggesting that SCA serves as a reliable predictor for hybrid performance. The assessed maize inbred lines and developed hybrids revealed substantial genetic variability, offering valuable resources for enhancing maize productivity under arid conditions. The identified promising inbred lines (P1, P3, and P4) might be regarded as effective combiners for developing early-maturing genotypes and excellent combiners for enhancing yield attributes. Notably, the developed hybrids P1 × P5 and P4 × P7 possessed significant SCA alongside superior yield traits. SCA demonstrated a significant correlation with hybrid performance, suggesting its potential as a reliable predictor for the performance of developed hybrids. [ABSTRACT FROM AUTHOR]

Accurate identification of agricultural pests is a major component of integrated pest management. The seedcorn maggot, Delia platura (Meigen) (Diptera: Anthomyiidae), is a cosmopolitan polyphagous pest species that may be found in high numbers in numerous crops. Two morphologically identical genetic lines of D. platura (H and N) with distinct distributions were recently identified. To date, no study has investigated the reproductive compatibility of the two lines and thus the possibility that they may actually be two unique biological entities. A previous study described the reproductive traits of the two lines and suggested that H‐line females are highly selective toward the male with which they mate, pointing to a possible pre‐mating isolation mechanism between the lines. Using laboratory‐reared colonies originating from the Montérégie region in Québec, Canada, this study investigates the reproductive compatibility of the two D. platura lines. We found that only one of 30 H‐line females was inseminated by an N‐line male, further suggesting mate choice as a pre‐mating isolation mechanism between the lines. However, N‐line females were readily inseminated by H‐line males, suggesting a lack of pre‐mating isolation in this type of cross. The eggs laid by N‐line females mated with H‐line males had a lower hatching rate than the ones laid by females of intraline crosses, suggesting either post‐mating pre‐zygotic or post‐zygotic partial isolation. However, the larvae that did hatch had a comparable developmental success to those from intraline crosses in terms of survival and developmental time from larval hatching to adult emergence, pupal mass, and adult sex ratio, suggesting a lack of post‐zygotic isolation for these life stages. Considering the different biological traits of the two lines, we suggest the use of the 'biotype' terminology to designate the two biological entities and discuss their implications for integrated pest management. [ABSTRACT FROM AUTHOR]

Genomic selection and doubled haploids hold significant potential to enhance genetic gains and shorten breeding cycles across various crops. Here, we utilized stochastic simulations to investigate the best strategies for optimize a sweet corn breeding program. We assessed the effects of incorporating varying proportions of old and new parents into the crossing block (3:1, 1:1, 1:3, and 0:1 ratio, representing different degrees of parental substitution), as well as the implementation of genomic selection in two distinct pipelines: one calibrated using the phenotypes of testcross parents (GSTC scenario) and another using F1 individuals (GSF1). Additionally, we examined scenarios with doubled haploids, both with (DH) and without (DHGS) genomic selection. Across 20 years of simulated breeding, we evaluated scenarios considering traits with varying heritabilities, the presence or absence of genotype-by-environment effects, and two program sizes (50 vs 200 crosses per generation). We also assessed parameters such as parental genetic mean, average genetic variance, hybrid mean, and implementation costs for each scenario. Results indicated that within a conventional selection program, a 1:3 parental substitution ratio (replacing 75% of parents each generation with new lines) yielded the highest performance. Furthermore, the GSTC model outperformed the GSF1 model in enhancing genetic gain. The DHGS model emerged as the most effective, reducing cycle time from 5 to 4 years and enhancing hybrid gains despite increased costs. In conclusion, our findings strongly advocate for the integration of genomic selection and doubled haploids into sweet corn breeding programs, offering accelerated genetic gains and efficiency improvements. [ABSTRACT FROM AUTHOR]

Spodoptera frugiperda, also known as fall armyworm (FAW), is an invasive crop pest that can feed on a variety of host plants, posing a serious threat to food security. There are two sympatric strains of FAW that are morphologically identical but described with different food preferences: the "rice strain" (SfR) and the "corn strain" (SfC). A few genetic loci exist to identify these two strains. Mitochondrial and Z‐chromosome‐linked haplotypes are the most used, but the biggest part of the genome displays little polymorphism between strains that could explain their adaptation to different plants. We have previously observed consistent transcription differences between the strains in both laboratory and natural populations. Therefore, we wonder if there are effects from host‐strain‐associated loci, maternally or paternally inherited, on FAW performance that could explain the divergence between the two FAW strains. To test this hypothesis, we first produced two F1 hybrid generations (SfR ♀ × SfC ♂, SfC ♀ × SfR ♂). These reciprocal hybrids should be heterozygous for all chromosomes except for the maternally inherited mitochondrial and sexual W chromosomes. To evaluate whether plant preference is determined by these genetic loci, we cultivated the two hybrids and the two parental strains in triplicate on an artificial diet and recorded several phenotypic traits such as weight over time, survival rate, emerging rate, developmental time, and sex ratio. Then, the same performance experiment was carried out on corn plants. Surprisingly, on the artificial diet, the two hybrid genotypes were both more performant than the two parental strains in terms of survival rate, pupal emerging rate, and developmental time, whereas they were intermediate to the inbred parental strains in pupal weight. On the corn plant diet, both hybrid genotypes outperformed the two parental strains in larval weight. Although these asymmetrical results revealed that mitochondrial or sex‐linked haplotypes alone cannot explain the performance differences, they suggested a heterosis effect in FAW. A reduction of the female number for the CR genotype and the decreased F1 offspring reproduction in both hybrids suggested the possibility of Haldane's rule, which might be explained by the dominance model. [ABSTRACT FROM AUTHOR]

Flowering time (FT) is a key maize domestication trait, variation in which allows maize to grow in a wide range of latitudes. Although previous studies have investigated the genetic control of FT-related traits per se, few studies of FT hybrid performance have been published. We characterized the genomic architecture associated with hybrid performance for FT in a hybrid panel by testcrossing Chang 7–2 with 328 Ye478 × Qi319 recombinant inbred lines (RILs). We identified 11 quantitative trait loci (QTL) for hybrid performance in FT-related traits, including a major QTL qFH10 that controls hybrid performance and heterosis in a summer maize-growing region. However, this locus acts in regulating FT traits per se only in a spring maize-growing region. We validated ZmCCT10 as a candidate gene for qFH10 and found that differences between hybrids and their parental lines in DNA methylation in the differentially methylated region (DMR, –700 to –1520) of the ZmCCT10 promoter affected gene expression pattern and thereby FT in the summer maize-growing region.

Genomic prediction (GP) in plant breeding has the potential to predict and identify the best-performing hybrids based on the genotypes of their parental lines. In a GP experiment, 34 elite inbred lines were selected to make 285 single-cross hybrids in a partial-diallel cross design. These lines represented a mini-core collection of Chinese maize germplasm and comprised 18 inbred lines from the Stiff Stalk heterotic group and 16 inbred lines from the Non-Stiff Stalk heterotic group. The parents were genotyped by sequencing and the 285 hybrids were phenotyped for nine yield and yield-related traits at two locations in the summer sowing area (SUS) and three locations in the spring sowing area (SPS) in the main maizeproducing regions of China. Multiple GP models were employed to assess the accuracy of trait prediction in the hybrids. By ten-fold cross-validation, the prediction accuracies of yield performance of the hybrids estimated by the genomic best linear unbiased prediction (GBLUP) model in SUS and SPS were 0.51 and 0.46, respectively. The prediction accuracies of the remaining yield-related traits estimated with GBLUP ranged from 0.49 to 0.86 and from 0.53 to 0.89 in SUS and SPS, respectively. When additive, dominance, epistasis effects, genotype-by-environment interaction, and multi-trait effects were incorporated into the prediction model, the prediction accuracy of hybrid yield performance was improved. The ratio of training to testing population and size of training population optimal for yield prediction were determined. Multiple prediction models can improve prediction accuracy in hybrid breeding. [ABSTRACT FROM AUTHOR]

Fall armyworm (FAW, Spodoptera frugiperda) emerged as a major lepidopteran pest destroying maize in sub‐Saharan Africa. A diallel mating design was used to generate 210 experimental hybrids from 21 lines. Experimental hybrids and four checks were evaluated in two locations. Commercial checks suffered higher foliar and ear damage compared to the top 15 hybrids. Mean squares associated with the genotypic variation were higher than genotype‐by‐environment interactions for foliar and ear damage traits. Heritabilities were moderate to high. Significant correlations were observed between grain yield (GY) with ear rot (−0.54) and ear damage (−0.45). Positive and significant GCA effects were observed for GY in seven parental lines, which were developed from multiple insect resistance breeding programmes. CKSBL10153 has the highest GCA value for GY and shows significant GCA effects for foliar and ear damage traits. These lines were identified as the ideal combiners for GY and FAW resistance and are therefore recommended for utilization as testers in the development of FAW‐resistant three‐way cross‐hybrid maize with correlated response for increased GY. GCA and marker‐based prediction correlations of GY were 0.79 and 0.96, respectively. Both GCA effects and marker‐based models were effective in predicting hybrid performance for FAW resistance. [ABSTRACT FROM AUTHOR]

In temperate world-wide regions, maize kernels are often infected with the fumonisin-producing fungus Fusarium verticillioides which poses food and feed threats to animals and humans. As maize breeding has been revealed as one of the main tools with which to reduce kernel contamination with fumonisins, a pedigree selection program for increased resistance to Fusarium ear rot (FER), a trait highly correlated with kernel fumonisin content, was initiated in 2014 with the aim of obtaining inbred lines (named EPFUM) with resistance to kernel contamination with fumonisins and adapted to our environmental conditions. The new released EPFUM inbreds, their parental inbreds, hybrids involving crosses of one or two EPFUM inbreds, as well as commercial hybrids were evaluated in the current study. The objectives were (i) to assess if inbreds released by that breeding program were significantly more resistant than their parental inbreds and (ii) to examine if hybrids derived from EPFUM inbreds could be competitive based on grain yield and resistance to FER and fumonisin contamination. Second-cycle inbreds obtained through this pedigree selection program did not significantly improve the levels of resistance to fumonisin contamination of their parental inbreds; however, most EPFUM hybrids showed significantly better resistance to FER and fumonisin contamination than commercial hybrids did. Although European flint materials seem to be the most promising reservoirs of alleles with favorable additive and/or dominance effects for resistance to kernel contamination with fumonisins, marketable new Reid × Lancaster hybrids have been detected as they combine high resistance and yields comparable to those exhibited by commercial hybrids. Moreover, the white kernel hybrid EPFUM-4 × EP116 exploits the genetic variability within the European flint germplasm and can be an alternative to dent hybrid cultivation because white flint grain can lead to higher market prices. [ABSTRACT FROM AUTHOR]

To exploit the novel genetic diversity residing in tropical sorghum germplasm, an expansive backcross nested-association mapping (BC-NAM) resource was developed in which novel genetic diversity was introgressed into elite inbreds. A major limitation of exploiting this type of genetic resource in hybrid improvement programs is the required evaluation in hybrid combination of the vast number of BC-NAM populations and lines. To address this, the utility of genomic information was evaluated to predict the hybrid performance of BC-NAM populations. Two agronomically elite BC-NAM populations were chosen for evaluation in which elite inbred RTx436 was the recurrent parent. Each BC1F3 line was evaluated in hybrid combination with an elite tester in two locations with phenotypes of grain yield, plant height, and days to anthesis collected on all test cross hybrids. Lines from both populations were found to outperform their recurrent parent. Efforts to utilize genetic distance based on genotyping-by-sequence (GBS) as a predictive tool for hybrid performance was ineffective. However, utilizing genomic prediction models using additive and dominance GBLUP kernels to screen germplasm appeared to be an effective method to eliminate inferior-performing lines that will not be useful in a hybrid breeding program. [ABSTRACT FROM AUTHOR]

Objective: To study the heterosis and agronomic performance of raspberry (Rubus idaeus) F1 families derived from open-pollinated parents, and to investigate the heterotic relationships between yield and its components. Design/methodology/approach: A total of thirty-five genotypes, including eight open-pollinated raspberry cultivars, their 28 F1 families and one check, were evaluated for vegetative and fruit traits. The trial was carried out under a randomized block design and under open field conditions. Results: Mid-parent heterosis (MH) ranged from -94.83 to 311.67 %, whereas the better parent heterosis (BPH) values varied from -94.26 to 235.00%. We observed that the heterosis values for yield had a strong and positive correlation (r=0.89) with the heterosis values for number of fruits per plant. Limitations on study/implications: Heterosis and performance of F1 families in raspberry would depend on the pedigree of parents as their relativeness is a key factor to exploit the heterosis in plants. Findings/conclusions: High values of heterosis were found in some raspberry crosses. Progeny derived from parents MU1 and TD865 showed considerable mid-parent heterosis (MH) and good performance for fruit size-related traits, soluble solids content and yield, evidencing that both parents may be utilized as donor parents in raspberry breeding program. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) breeders in the West and Central Africa have developed and commercialized extra-early and early-maturing maize hybrids, which combine high yield potentials with tolerance/resistance to drought, low soil-N and Striga infestation. Hybrids of both maturity groups have not been investigated for tolerance to high plant density and N application and are new to the farmers; thus, the urgent need to recommend appropriate agronomic practices for these hybrids. We investigated the responses of four hybrids, belonging to the extra-early and early-maturity groups, to three plant densities and three N rates in five locations of different agroecologies. The early-maturing hybrids consistently out-yielded the extra-early maturing hybrids in all the five agroecologies. The hybrids showed no response to N-fertilizer application above 90 kg ha−1. All interactions involving N had no significant effect on grain yield and other measured agronomic traits except in few cases. The extra-early and early-maturing hybrids had similar response to plant density; their grain yield decreased as density increased. Contrarily, flowering was delayed and expression of some other agronomic traits such as plant and ear aspects were negatively impacted by increased density. Optimal yield for hybrids of both maturity groups was obtained at approximately 90 kg N ha−1 and 66,666 plants ha−1. Most of the measured traits indicated high repeatability estimates across the N levels, densities and environments. Evidently, the hybrids were intolerant of elevated density. It therefore, becomes necessary to improve maize germplasms for high plant density tolerance in the region.

Genome-wide prediction is a promising approach to boost selection gain in hybrid breeding. Our main objective was to evaluate the potential and limits of genome-wide prediction to identify superior hybrid combinations adapted to Northwest China. A total of 490 hybrids derived from crosses among 119 inbred lines from the Shaan A and Shaan B heterotic pattern were used for genome-wide prediction of ten agronomic traits. We tested eight different statistical prediction models considering additive (A) effects and in addition evaluated the impact of dominance (D) and epistasis (E) on the prediction ability. Employing five-fold cross validation, we show that the average prediction ability ranged from 0.386 to 0.794 across traits and models. Six parametric methods, i.e. ridge regression, LASSO, Elastic Net, Bayes B, Bayes C and reproducing kernel Hilbert space (RKHS) approach, displayed a very similar prediction ability for each trait and two non-parametric methods (random forest and support vector machine) had a higher prediction performance for the trait rind penetrometer resistance of the third internode above ground (RPR_TIAG). The models of A + D RKHS and A + D + E RKHS were slightly better for predicting traits with a relatively high non-additive variance. Integrating trait-specific markers into the A + D RKHS model improved the prediction ability of grain yield by 3%, from 0.528 to 0.558. Of all 6328 potential hybrids, selection of the top 44 hybrids would lead to a 6% increase in grain yield compared with Zhengdan 958, a commercially successful hybrid variety. In conclusion, our results substantiate the value of genome-wide prediction for hybrid breeding and suggest dozens of promising single crosses for developing high-yielding hybrids for Northwest China.

Heterosis contributes a big proportion to hybrid performance in maize, especially for grain yield. It is attractive to explore the underlying genetic architecture of hybrid performance and heterosis. Considering its complexity, different from former mapping method, we developed a series of linear mixed models incorporating multiple polygenic covariance structures to quantify the contribution of each genetic component (additive, dominance, additive-by-additive, additive-by-dominance, and dominance-by-dominance) to hybrid performance and midparent heterosis variation and to identify significant additive and non-additive (dominance and epistatic) quantitative trait loci (QTL). Here, we developed a North Carolina II population by crossing 339 recombinant inbred lines with two elite lines (Chang7-2 and Mo17), resulting in two populations of hybrids signed as Chang7-2 × recombinant inbred lines and Mo17 × recombinant inbred lines, respectively. The results of a path analysis showed that kernel number per row and hundred grain weight contributed the most to the variation of grain yield. The heritability of midparent heterosis for 10 investigated traits ranged from 0.27 to 0.81. For the 10 traits, 21 main (additive and dominance) QTL for hybrid performance and 17 dominance QTL for midparent heterosis were identified in the pooled hybrid populations with two overlapping QTL. Several of the identified QTL showed pleiotropic effects. Significant epistatic QTL were also identified and were shown to play an important role in ear height variation. Genomic selection was used to assess the influence of QTL on prediction accuracy and to explore the strategy of heterosis utilization in maize breeding. Results showed that treating significant single nucleotide polymorphisms as fixed effects in the linear mixed model could improve the prediction accuracy under prediction schemes 2 and 3. In conclusion, the different analyses all substantiated the different genetic architecture of hybrid performance and midparent heterosis in maize. Dominance contributes the highest proportion to heterosis, especially for grain yield, however, epistasis contributes the highest proportion to hybrid performance of grain yield.

Heterosis contributes a big proportion to hybrid performance in maize, especially for grain yield. It is attractive to explore the underlying genetic architecture of hybrid performance and heterosis. Considering its complexity, different from former mapping method, we developed a series of linear mixed models incorporating multiple polygenic covariance structures to quantify the contribution of each genetic component (additive, dominance, additive-by-additive, additive-by-dominance, and dominance-by-dominance) to hybrid performance and midparent heterosis variation and to identify significant additive and non-additive (dominance and epistatic) quantitative trait loci (QTL). Here, we developed a North Carolina II population by crossing 339 recombinant inbred lines with two elite lines (Chang7-2 and Mo17), resulting in two populations of hybrids signed as Chang7-2 × recombinant inbred lines and Mo17 × recombinant inbred lines, respectively. The results of a path analysis showed that kernel number per row and hundred grain weight contributed the most to the variation of grain yield. The heritability of midparent heterosis for 10 investigated traits ranged from 0.27 to 0.81. For the 10 traits, 21 main (additive and dominance) QTL for hybrid performance and 17 dominance QTL for midparent heterosis were identified in the pooled hybrid populations with two overlapping QTL. Several of the identified QTL showed pleiotropic effects. Significant epistatic QTL were also identified and were shown to play an important role in ear height variation. Genomic selection was used to assess the influence of QTL on prediction accuracy and to explore the strategy of heterosis utilization in maize breeding. Results showed that treating significant single nucleotide polymorphisms as fixed effects in the linear mixed model could improve the prediction accuracy under prediction schemes 2 and 3. In conclusion, the different analyses all substantiated the different genetic architecture of hybrid performance and midparent heterosis in maize. Dominance contributes the highest proportion to heterosis, especially for grain yield, however, epistasis contributes the highest proportion to hybrid performance of grain yield. [ABSTRACT FROM AUTHOR]

Abstract Background Small RNA (sRNA) sequences are known to have a broad impact on gene regulation by various mechanisms. Their performance for the prediction of hybrid traits has not yet been analyzed. Our objective was to analyze the relation of parental sRNA expression with the performance of their hybrids, to develop a sRNA-based prediction approach, and to compare it to more common SNP and mRNA transcript based predictions using a factorial mating scheme of a maize hybrid breeding program. Results Correlation of genomic differences and messenger RNA (mRNA) or sRNA expression differences between parental lines with hybrid performance of their hybrids revealed that sRNAs showed an inverse relationship in contrast to the other two data types. We associated differences for SNPs, mRNA and sRNA expression between parental inbred lines with the performance of their hybrid combinations and developed two prediction approaches using distance measures based on associated markers. Cross-validations revealed parental differences in sRNA expression to be strong predictors for hybrid performance for grain yield in maize, comparable to genomic and mRNA data. The integration of both positively and negatively associated markers in the prediction approaches enhanced the prediction accurary. The associated sRNAs belong predominantly to the canonical size classes of 22- and 24-nt that show specific genomic mapping characteristics. Conclusion Expression profiles of sRNA are a promising alternative to SNPs or mRNA expression profiles for hybrid prediction, especially for plant species without reference genome or transcriptome information. The characteristics of the sRNAs we identified suggest that association studies based on breeding populations facilitate the identification of sRNAs involved in hybrid performance.

Hybrid indoor and outdoor localisation system has generated substantial interest from researchers due to its potential use in many fields. Many research papers on hybrid localisation were focused on localisation accuracy and computation time instead of the process for seamless switching during the subject's indoor-outdoor movement. Seamless and stable switching can improve the usability and practicality of a system in an ever-changing scenario. This paper presents a hybrid localisation system that can adapt to the changes in the environment. Two hybrid systems – Enhanced Fusion Hybrid (EFH) and Enhanced Unified Hybrid (EUH), and novel signal selection and switching algorithms suitable for dynamic environment where signal fluctuations and transient condition frequently occur, i.e. the Clean Radio Signal Label (CRSL) classification algorithm and the Adaptive Signal Thresholding (AST) algorithm are proposed. From the experimental results of EFH and EUH methods, the GPS and Wi-Fi combination produces the best results as compared to the combinations of GPS and GSM or GSM and Wi-Fi. The accuracy of estimates was improved to 2.0 m to 5.0 m. Further work shown that an accuracy of 2.0 m or less could be achieved with an increase in Wi-Fi nodes from three to four for the system. [ABSTRACT FROM AUTHOR]

Maize plant height related traits including plant height, ear height, and internode number are tightly linked with biomass, planting density, and grain yield in the field. Previous studies have focused on understanding the genetic basis of plant architecture traits per se, but the genetic basis of combining ability remains poorly understood. In this study, 328 recombinant inbred lines were inter-group crossed with two testers to produce 656 hybrids using the North Carolina II mating design. Both of the parental lines and hybrids were evaluated in two summer maize-growing regions of China in 2015 and 2016. QTL mapping highlighted that 7 out of 16 QTL detected for RILs per se could be simultaneously detected for general combining ability (GCA) effects, suggesting that GCA effects and the traits were genetically controlled by different sets of loci. Among the 35 QTL identified for hybrid performance, 57.1% and 28.5% QTL overlapped with additive/GCA and non-additive/SCA effects, suggesting that the small percentage of hybrid variance due to SCA effects in our design. Two QTL hotspots, located on chromosomes 5 and 10 and including the qPH5-1 and qPH10 loci, were validated for plant height related traits by Ye478 derivatives. Notably, the qPH5-1 locus could simultaneously affect the RILs per se and GCA effects while the qPH10, a major QTL (PVE > 10%) with pleiotropic effects, only affected the GCA effects. These results provide evidence that more attention should be focused on loci that influence combining ability directly in maize hybrid breeding.

Abstract The capacity for inter-specific hybridisation to yield improvements in animal production has long been realised in the aquaculture sector. However, the extension of hybridisation to improve production of giant clams (Tridacninae) has received little research attention. Aquaculture production of giant clams is directed primarily at aquarium markets, and hybridisation offers an opportunity to diversify available products. Here we report on the successful inter-specific hybridisation of Tridacna maxima and T. noae , and assess hybrid performance during hatchery culture. Both maternal and paternal hybrid crosses of T. maxima / T. noae yielded competent larvae. Fertilisation success was significantly lower (40.7 ± 3.2%) for the T. maxima♀ / T. noae♂ cross compared to the T. noae ♀ / T. maxima ♂ cross (89.3 ± 1.8%; χ2 = 154.03, P < 0.01). Despite the disproportionate fertilisation success, the two hybrids had similar survival curves (survival = 2.03 × days -2.08, r2 = 0.67, P = 0.13) for the first 30 days of culture. Antero-posterior shell growth (APM) was superior in the T. maxima ♀/ T. noae♂ hybrid (APM = 10(2.158+0.019× days)) when compared to the T. noae♀ / T. maxima♂ hybrid (APM = 10(2.169+0.016× days)) over the same time frame (r2 = 0.92, P < 0.001). Both survival and growth of the hybrids exceeded that reported in the literature for pure-strain hatchery culture of giant clam species. This suggests capacity for hybridisation to contribute to giant clam aquaculture production. The application of hybridisation to supply aquarium markets and necessary considerations for manipulating stock genetics are discussed in view of these results. Highlights • First report of hybridization of Tridacna spp. • Successful hybridisation of Tridacna maxima and Tridacna noae. • Hybrid survival and growth exceeded pure-strain performance of other giant clam species. • Capacity for hybridisation to contribute to giant clam aquaculture production. • Potential for hybridisation to contribute to aquarium markets is discussed. [ABSTRACT FROM AUTHOR]

Maize plant height related traits including plant height, ear height, and internode number are tightly linked with biomass, planting density, and grain yield in the field. Previous studies have focused on understanding the genetic basis of plant architecture traits per se , but the genetic basis of combining ability remains poorly understood. In this study, 328 recombinant inbred lines were inter-group crossed with two testers to produce 656 hybrids using the North Carolina II mating design. Both of the parental lines and hybrids were evaluated in two summer maize-growing regions of China in 2015 and 2016. QTL mapping highlighted that 7 out of 16 QTL detected for RILs per se could be simultaneously detected for general combining ability (GCA) effects, suggesting that GCA effects and the traits were genetically controlled by different sets of loci. Among the 35 QTL identified for hybrid performance, 57.1% and 28.5% QTL overlapped with additive/GCA and non-additive/SCA effects, suggesting that the small percentage of hybrid variance due to SCA effects in our design. Two QTL hotspots, located on chromosomes 5 and 10 and including the qPH5-1 and qPH10 loci, were validated for plant height related traits by Ye478 derivatives. Notably, the qPH5-1 locus could simultaneously affect the RILs per se and GCA effects while the qPH10 , a major QTL (PVE > 10%) with pleiotropic effects, only affected the GCA effects. These results provide evidence that more attention should be focused on loci that influence combining ability directly in maize hybrid breeding. [ABSTRACT FROM AUTHOR]

Background: Small RNA (sRNA) sequences are known to have a broad impact on gene regulation by various mechanisms. Their performance for the prediction of hybrid traits has not yet been analyzed. Our objective was to analyze the relation of parental sRNA expression with the performance of their hybrids, to develop a sRNA-based prediction approach, and to compare it to more common SNP and mRNA transcript based predictions using a factorial mating scheme of a maize hybrid breeding program. Results: Correlation of genomic differences and messenger RNA (mRNA) or sRNA expression differences between parental lines with hybrid performance of their hybrids revealed that sRNAs showed an inverse relationship in contrast to the other two data types. We associated differences for SNPs, mRNA and sRNA expression between parental inbred lines with the performance of their hybrid combinations and developed two prediction approaches using distance measures based on associated markers. Cross-validations revealed parental differences in sRNA expression to be strong predictors for hybrid performance for grain yield in maize, comparable to genomic and mRNA data. The integration of both positively and negatively associated markers in the prediction approaches enhanced the prediction accurary. The associated sRNAs belong predominantly to the canonical size classes of 22- and 24-nt that show specific genomic mapping characteristics. Conclusion: Expression profiles of sRNA are a promising alternative to SNPs or mRNA expression profiles for hybrid prediction, especially for plant species without reference genome or transcriptome information. The characteristics of the sRNAs we identified suggest that association studies based on breeding populations facilitate the identification of sRNAs involved in hybrid performance. [ABSTRACT FROM AUTHOR]

The ability to predict the agronomic performance of single-crosses with high precision is essential for selecting superior candidates for hybrid breeding. With recent technological advances, thousands of new parent lines, and, consequently, millions of new hybrid combinations are possible in each breeding cycle, yet only a few hundred can be produced and phenotyped in multi-environment yield trials. Well established prediction approaches such as best linear unbiased prediction (BLUP) using pedigree data and whole-genome prediction using genomic data are limited in capturing epistasis and interactions occurring within and among downstream biological strata such as transcriptome and metabolome. Because mRNA and small RNA (sRNA) sequences are involved in transcriptional, translational and post-translational processes, we expect them to provide information influencing several biological strata. However, using sRNA data of parent lines to predict hybrid performance has not yet been addressed. Here, we gathered genomic, transcriptomic (mRNA and sRNA) and metabolomic data of parent lines to evaluate the ability of the data to predict the performance of untested hybrids for important agronomic traits in grain maize. We found a considerable interaction for predictive ability between predictor and trait, with mRNA data being a superior predictor for grain yield and genomic data for grain dry matter content, while sRNA performed relatively poorly for both traits. Combining mRNA and genomic data as predictors resulted in high predictive abilities across both traits and combining other predictors improved prediction over that of the individual predictors alone. We conclude that downstream "omics" can complement genomics for hybrid prediction, and, thereby, contribute to more efficient selection of hybrid candidates. [ABSTRACT FROM AUTHOR]

Genomics-based prediction of hybrid performance promises to boost selection gain. The main goal of our study was to investigate the relevance of additive, dominance, and epistatic effects for determining hybrid seed yield in a biparental rapeseed population. We re-analyzed 60,000 SNP array and seed yield data points from an immortalized F2 population comprised of 318 hybrids and 180 parental lines by performing genome-wide QTL mapping and predictions in combination with five-fold cross-validation. Moreover, an additional set of 37 hybrids were genotyped and phenotyped in an independent environment. The decomposition of the phenotypic variance components and the cross-validated results of the QTL mapping and genome-wide predictions revealed that the hybrid performance in rapeseed was driven by a mix of additive, dominance, and epistatic effects. Interestingly, the genome-wide prediction accuracy in the additional 37 hybrids remained high when modeling exclusively additive effects but was severely reduced when dominance or epistatic effects were also included. This loss in accuracy was most likely caused by more pronounced interactions of environments with dominance and epistatic effects than with additive effects. Consequently, the development of robust hybrid prediction models, including dominance and epistatic effects, required much deeper phenotyping in multi-environmental trials.

Heterosis has been extensively exploited for yield gain in maize ( Zea mays L.). Here we conducted a comparative metabolomics-based analysis of young roots from in vitro germinating seedlings and from leaves of field-grown plants in a panel of inbred lines from the Dent and Flint heterotic patterns as well as selected F1 hybrids. We found that metabolite levels in hybrids were more robust than in inbred lines. Using state-of-the-art modeling techniques, the most robust metabolites from roots and leaves explained up to 37 and 44% of the variance in the biomass from plants grown in two distinct field trials. In addition, a correlation-based analysis highlighted the trade-off between defense-related metabolites and hybrid performance. Therefore, our findings demonstrated the potential of metabolic profiles from young maize roots grown under tightly controlled conditions to predict hybrid performance in multiple field trials, thus bridging the greenhouse-field gap. [ABSTRACT FROM AUTHOR]

Sorghum ( Sorghum bicolor L. Moench) is regarded a drought-tolerant alternative to maize as a bioenergy and fodder crop, but its early-stage chilling sensitivity is obstructing a successful implementation in temperate areas. While several studies have identified quantitative trait loci ( QTL) underlying chilling tolerance-related traits in sorghum lines, little is known about the inheritance of these traits in F1 hybrids. We have conducted a comprehensive approach to analyse heterosis, combining ability and the relation between line per se and hybrid performance for emergence and early shoot and root development comprising both field trials and controlled environment experiments including chilling tests. To our best knowledge, this is the first study analysing heterosis for sorghum root parameters under chilling. Our results show that most traits are heterotic and that the mid-parent values are rather poor predictors of hybrid performance. Hybrid breeding programmes should focus on efficient GCA tests and the establishment of genetically diverse pools to maximise heterosis rather than on a too strict selection among lines based on their per se performance. The medium-to-high heritabilities estimated for seedling emergence and juvenile biomass suggest that a robust breeding progress for these complex traits is feasible. [ABSTRACT FROM AUTHOR]

Predicting hybrid performance from the parental generation could largely enhance the efficiency of hybrid breeding programmes. To determine the relationship of parental distances estimated from phenotypic traits and SSR markers with F1 performance, average heterosis and heterobeltiosis in 44 indigenous and exotic genotypes of Indian mustard [Brassica juncea (L.) Czern. and Coss.], were studied. Jaccard’s genetic distances (JD) and Manhattan genetic distances (MD) were taken as criteria to classify the genotypic pairs into four diversity groups, viz. high, intermediate high, intermediate low and low. Seventy crosses representing the four diversity groups each for JD and MD were evaluated. Placement of higher number of significantly better hybrids was in extreme diversity groups created using JD, while, it was higher in intermediate diversity groups generated through MD. Low regression values were observed between JD among genotypic pairs and mean performance (R2 = 0.02), average heterosis (R2 = 0.046) and heterobeltiosis (R2 = 0.15). Similarly, low regression values were observed between MD among genotypic pairs and mean performance (R2 = 0.033), average heterosis (R2 = 0.046) and heterobeltiosis (R2 = 0.009). The slope of linear regression curve, placement of hybrids on the plot and low regression values in all the cases revealed that there is no significant association between genetic distance and hybrid performance. Therefore, desirable genetic diversity, in form of heterotic pools, needs to be identified from indigenous and exotic germplasm for expression of heterosis.

Phenotypic plasticity, the ability of an individual to alter its phenotype in response to changes in the environment, has been proposed as a target for breeding crop varieties with high environmental fitness. Here, we used phenotypic and genotypic data from multiple maize (Zea mays L.) populations to mathematically model phenotypic plasticity in response to the environment (PPRE) in inbred and hybrid lines. PPRE can be simply described by a linear model in which the two main parameters, intercept a and slope b, reflect two classes of genes responsive to endogenous (class A) and exogenous (class B) signals that coordinate plant development. Together, class A and class B genes contribute to the phenotypic plasticity of an individual in response to the environment. We also made connections between phenotypic plasticity and hybrid performance or general combining ability (GCA) of yield using 30 F 1 hybrid populations generated by crossing the same maternal line with 30 paternal lines from different maize heterotic groups. We show that the parameters a and b from two given parental lines must be concordant to reach an ideal GCA of F 1 yield. We hypothesize that coordinated regulation of the two classes of genes in the F 1 hybrid genome is the basis for high GCA. Based on this theory, we built a series of predictive models to evaluate GCA in silico between parental lines of different heterotic groups., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Crossability relationships between six species of the Mediterranean, North American and Asian firs was tested using Abies alba and A. nordmanniana as female parents and A. alba, A. numidica, A. procera, A. grandis, and A. holophylla as pollen parents. An overwhelming majority of the crosses attempted was found to be compatible. In particular, it is true of the A. alba cross with A. numidica and those of A. nordmanniana with A. alba, A. numidica, A. procera, and A. holophylla. The crossing A. nordmanniana × A. grandis was the only exception producing empty seeds. Cytological study revealed the gametophytic incompatibility to be responsible for reproductive isolation of these species. At seedling level, all the interspecific crosses of A. nordmanniana surpassed in height growth self-pollinated control. The cross A. alba × A. numidica was comparable in this respect with control variants from open and self-pollination. Except for height growth, some characteristics of needle stomata are provided for individual crosses. The crosses A. nordmanniana with A. procera and A. holophylla represent unique interspecific combinations whose existence has not been reported yet. Based on needle stomata characteristics, the potential for increased resistance and drought tolerance of the hybrids with A. numidica involved as parental species is discussed. [ABSTRACT FROM AUTHOR]

Predicting single-cross performance is of special interest in hybrid breeding of triticale. We used molecular and phenotypic data of factorial triticale crosses and compared several approaches to predict their single-cross performance. Twenty-three inbred lines and their 76 incomplete factorial crosses were field evaluated for grain yield, plant height, and heading time at five locations in Central Europe. In addition, the parental lines were genotyped with 52 SSR markers. Plant height and heading time were predicted with high accuracy based on mid-parent performance. In contrast, prediction of hybrid performance based on mid-parent value was not accurate for grain yield. Using general combining ability effects led to an enhanced prediction accuracy of hybrid grain yield performance. This accuracy could be slightly improved using best linear unbiased prediction approaches. The prediction accuracy was considerably high even if the number of tested hybrids was small. Consequently, best linear unbiased prediction of hybrid performance is a promising tool for hybrid triticale breeding programs. [ABSTRACT FROM AUTHOR]

Overview and scope of the presentation: Efficient exploitation of heterosis is central for successful hybrid breeding in sunflower. Here we discussed important genetic hypotheses of the phenomenon of heterosis including dominance, overdominance, and epistasis. Moreover, we presented different approaches suggested for prediction of hybrid performance. Outline of recent major discoveries: Several experimental designs have been proposed to study the causes of heterosis. Among them, QTL analyses based on triple test cross in combination with the immortalized F2 design or the use of triple test cross designs based on near-isogenic lines are of particular interest. Several approaches have been used to predict hybrid performance using phenotypic, genomic, transcriptomic, and metabolomic data. Prediction accuracies have been studied using experimental data of maize, which clearly points towards the large potential for knowledge-based hybrid breeding. Perceived significant gaps in research, current debates, and perspectives for future directions of research: Experimental design and quantitative genetic theory is ready to be applied in sunflower to study the genetic basis of heterosis. Furthermore, we speculate that genomic selection possesses great potential to revolutionize hybrid prediction in sunflower. [ABSTRACT FROM AUTHOR]

Two Pinus patula hybrids, P. greggii × P. patula and P. patula × P. tecunumanii, were planted across a number of sites in southern Africa. The growth and survival for each species/taxon was assessed at either 5 or 8 years of age at each site and compared to the respective parental species. Pinus greggii, as a pure species, has greater drought tolerance and is better adapted to harsher sites than P. patula. At 8 years the P. greggii × P. patula hybrid had similar survival and was more productive than P. patula at the two sites where it was tested. Furthermore, the performance of the hybrid was better than pure species on the site with average poorer growth suggesting that this hybrid could be planted on poorer, more marginal sites not well suited to P. patula. Pinus tecunumanii is a productive species with good tolerance to the pitch canker fungus (PCF). Previous work has shown that the P. patula × P. tecunumanii hybrid is more tolerant to PCF after field inoculations. The latter hybrid was assessed at 5 years on three sites and compared to both parent species. The hybrid had similar survival and was more productive than both parent species. Large variation in performance between individual P. patula × P. tecunumanii families suggests that comprehensive testing and selection should be conducted in tandem with any operational deployment of this hybrid. [ABSTRACT FROM AUTHOR]

Heterotic performance of hybrids is dependent upon the amount of genetic variability among parents and combining ability of alleles at the loci associated with target traits. This study was carried out to determine if (1) pedigree-based genetic distance could explain molecular levels of genetic diversity, and (2) molecular marker-based genetic distance could predict the degree of hybrid performance in barley. The average value of Random Amplified Polymorphic DNA (RAPD)-based genetic similarity for all 58 genotypes was 0.641. Twenty-two hulless barley and eight malt barley varieties showed low levels of genetic diversity with higher similarity values than the average of all or of the hulled barley variety pool. Coefficients of parentage (COPs) computed for 1,653 pairs of 58 Korean barley varieties ranged from 0 to 0.984 with a mean of 0.048. Correlation between the genealogical and RAPD-based genetic similarity matrices was 0.256 (P < 0.01). Correlation values for the related and for all (related + unrelated) genotype pairs were almost similar to each other, indicating that the unrelated genotypes share a large portion of genomes alike in state, not identical by descent. RAPD-based genetic similarity estimates among parents were poorly correlated with their hybrid performance such as 1,000-grain weight (r = 0.34), biomass yield (r = −0.12), and grain yield (r = −0.04) for 11 genotype pairs of hulled barley. However, correlations between heterozygosity at marker loci and hybrid performance for biomass and grain yield slightly increased when two F1 hybrids were excluded in the analysis due to their low yield. [ABSTRACT FROM AUTHOR]

Heterosis, or hybrid vigour, describes the superior performance of heterozygous hybrid individuals compared with their homozygous parental inbred lines. Although heterosis has been intensively used in plant breeding, the molecular and genetic mechanism underlying the phenomenon remains largely unknown. During the last years numerous laboratories initiated genomic approaches with new, often genome wide tools toward the elucidation of the molecular basis of heterosis. Various studies described differences in genome organization and gene expression of hybrids and their parental inbred lines. In maize, a considerable loss of co-linearity at many loci between different inbred lines was observed. Expression profile comparisons between inbred lines and hybrids revealed complex transcriptional networks specific for different developmental stages and tissues mainly in maize (Zea mays), rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana). Allele-specific expression data resolved the relative parental contributions and allowed figuring out the regulatory basis for expression variation in hybrids. Integrating all these complex expression data might help to get an idea about the molecular basis of heterosis. Thereby molecular processes during early seed development shortly after fertilization might be of particular importance, because the allelic interplay has to be coordinated after the unification of two diverse genomes and these processes might contribute to establish the basis for future performance of the sporophyte. Besides these fundamental interests in the molecular basis and manifestation of hybrid vigour applied aspects of the phenomenon are of high importance to support plant breeding and agriculture. Prediction methods are of special interest to identify the most promising parental lines of hybrid varieties, greatly reducing the financial effort and increasing the efficiency to develop new hybrid cultivars. Until now, most prediction approaches were based on genomic markers. The available heterosis associated expression data provide evidence to support the idea that gene regulatory networks at the level of transcription are involved in the control of hybrid vigour. If so, the transcriptome characteristics of inbred lines resulting from their individual genomic constitution should be useful as quantitative markers to predict the performance of hybrids generated by crosses of these inbred lines. Additionally, expression based prediction models promise to contribute substantially to the understanding of the genetic causes of heterosis by establishing a direct link between the transcriptome and hybrid performance. [ABSTRACT FROM AUTHOR]

The objectives of this study were to determine the crossing performance of highland maize inbred lines for grain yield, days to silk and plant height; estimate genetic distance (GD) among the inbred lines and in association with tester parents, and to investigate the relationship of GD with hybrid performance and midparent heterosis (MPH). A total of 26 inbred lines were crossed with six (population and line) testers in a factorial-mating scheme. The F1’s and the parents were evaluated at five locations in Ethiopia. Nine amplified fragment length polymorphism (AFLP) primer pairs were used to genotype all the parents. The F1’s were found to vary widely for grain yield and other traits measured. Yield superiority of more than 30% over the best hybrid check was obtained for some testcross hybrids. Midparent heterosis on average was moderate for grain yield and, plant height. And for days to silking, MPH values were mostly negative. Mean GD values determined from the inbred lines by population tester (0.680) and line tester (0.661) combinations were not significantly different. Cluster analysis separated the tester parents from the corresponding inbred lines. AFLP grouping of the inbred lines was in agreement with their pedigree records. Genetic distances derived from the inbred lines × all testers and from the population testers’ sub-group were not positively correlated with hybrid performance and MPH for most traits. In contrast, correlations of GDs involving the line testers’ sub-group with F1’s and MPH were significantly positive but with low magnitude to be of predictive value. [ABSTRACT FROM AUTHOR]

Development of hybrids is considered to be a promising avenue to enhance the yield potential of crops. We investigated (i) the amount of heterosis observed in hybrid progeny, (ii) relative importance of general (GCA) versus specific (SCA) combining ability, and (iii) the relationship between heterosis and genetic distance measures in four agronomic traits of spring bread wheat. Eight male and 14 female lines, as well as 112 hybrids produced in a factorial design were grown in replicated trials at two environments in Mexico. Principal coordinate analysis based on Rogers' distance (RD) estimates calculated from 113 SSRs revealed three different groups of parents. Mid-parent heterosis (MPH) for grain yield averaged 0.02 t ha−1 (0.5%) and varied from −15.33% to 14.13%. MPH and hybrid performance (F1P) were higher for intra-group hybrids than for inter-group hybrids, with low values observed in inter-group crosses involving two non-adapted Chinese parents. Combined analyses of variance revealed significant differences among parents and among hybrids. Estimates of GCA variances were more important than SCA variances for all traits. Tight correlations of GCA with line per se performance, and mid-parent value with F1P were observed for all traits. In contrast, correlations of MPH with RD and coefficient of parentage were not significant. It was concluded that the level of heterosis in spring wheat was too low to warrant a commercial exploitation in hybrids. SSRs proved to be a powerful tool for the identification of divergent groups in advanced wheat breeding materials. [ABSTRACT FROM AUTHOR]