Level Of Heterosis Research Articles

Heterosis for Biomass-Related Traits in Interspecific Triploid Hybrids of Willow (Salix spp.)

Species hybridization is key for the improvement of shrub willow (Salix spp.) bioenergy crops because hybrids often display heterosis for yield. The development of high-yielding genotypes requires numerous broad attempts at hybridization followed by field evaluation and selection for stable performance. Selection of improved shrub willow varieties for use as a bioenergy crop involves evaluation of full-sib progeny in family-based selection trials. Improving the accuracy of evaluation through the use of components of yield would greatly improve the efficiency of selection. Heterosis for biomass yield in intra- and interspecific F1 and F2 shrub willow crosses, made between Salix sections and ploidy, was examined by utilizing a suite of morphological, physiological, and chemical composition traits collected over the course of 12 weeks in the greenhouse and over 3 years in the field. Triploid families generated from diploid S. viminalis and tetraploid S. miyabeana displayed the greatest levels of heterosis for harvestable biomass and biomass-related growth traits in the greenhouse and in the field. While intraspecific S. purpurea diploids exhibited low levels of heterosis for these traits, interspecific diploids produced moderate levels of heterosis in greenhouse experiments. Differences between greenhouse and field trial results can largely be explained by pest damage, which negatively impacted interspecific diploids. Heterosis for the traits that form the basis for biomass yield, including stem growth, foliar, and physiological traits, was quantified, and family-level differences are discussed.

Underground heterosis for yield improvement in melon.

Heterosis, the superiority of hybrids over their parents, is a major genetic force associated with plant fitness and crop yield enhancement. We investigated root-mediated yield heterosis in melons (Cucumis melo) by characterizing a common variety grafted onto 190 hybrid rootstocks, resulting from crossing 20 diverse inbreds in a diallel-mating scheme. Hybrid rootstocks improved yield by more than 40% compared with their parents, and the best hybrid yield outperformed the reference commercial variety by 65% under both optimal and minimal irrigation treatments. To characterize the genetics of underground heterosis we conducted whole genome re-sequencing of the 20 founder lines, and showed that parental genetic distance was no predictor for the level of heterosis. Through inference of the 190 hybrid genotypes from their parental genomes, followed by genome-wide association analysis, we mapped multiple quantitative trait loci for root-mediated yield. Yield enhancement of the four best-performing hybrid rootstocks was validated in multiple experiments with four different scion varieties. Our grafting approach is complementary to the common roots genetic approach that focuses mainly on variation in root system architecture, and is a step towards discovery of candidate genes involved in root function and yield enhancement.

Gene Action Studies in Cowpea Inbreds and Hybrids with Varying Levels of Heterosis

Background: Cowpea is an important pulse crop grown worldwide that fits well in a variety of cropping systems. Improvement in yield and related characters along with reduced duration are desirable traits in this crop. The study of heterosis reveals the type of gene action involved which enables the plant breeder to adopt suitable breeding methodology for its improvement. Methods: The present investigation was carried out with 10 parent partial diallel design to analyse the gene action and estimate of heterosis with respect to nine yield related traits in cowpea.Result: Highly significant variances observed for all the traits indicated that hybrids and parents were different from each other for the traits under study and that variability in the breeding materials was attributed to additive and non-additive gene effects. Perusal of the data revealed significant positive heterosis for all yield related traits and significant negative heterosis for days to 50% flowering indicating earliness. Among the twenty five crosses studied, VS9 x VS43, VS24 x VS45 and VS44 x VS47 had significant heterosis for maximum number of characters. Both gca and sca variances were significant for all the characters indicating both additive and non-additive gene actions controlling the various traits. The additive variance was much higher than dominance variance for the characters days to 50% flowering, pod length, pod breadth, pod weight, pods per plant and cluster, pod yield per plant, seeds per plant and length of harvest period suggesting the preponderance of additive gene action.

Potential of rutabaga (Brassica napus var. napobrassica) gene pool for use in the breeding of hybrid spring Brassica napus canola

AbstractThe use of rutabaga for increasing the level of heterosis in spring canola was investigated. For this, test hybrids were produced by crossing four inbred populations, derived from F2 and BC1 of two rutabaga × spring canola crosses, to their spring canola parent, and were tested in field‐plots for agronomic and seed quality traits. Average mid‐parent heterosis (MPH) in these test hybrid populations was about 5%‐15% for yield. Compared to the F2‐derived population, the BC1‐derived population exhibited 1.8‐times greater MPH for yield. No correlation was found between inbred and test hybrid for yield; however, a positive correlation of genetic diversity of the inbred lines was found with MPH (r = .58) and hybrid yield (r = .36) suggesting that non‐additive effect of the genes may play an important role for high yield in hybrids. About 2% negative MPH was found for days to flowering, while almost no heterosis was found for seed oil and protein contents. Thus, our study demonstrates the potential of the rutabaga gene pool for use in hybrid canola breeding.

Combining ability, gene action and heterosis analyses of maize lines that were developed for maize streak virus resistance and acidic soil tolerance

Aluminium toxicity in acidic soils (Al) and the maize streak virus disease (MSV) cause significant losses in maize productivity. These constraints can occur simultaneously in sub-Saharan Africa but there are no maize hybrids that combine resistance for both stresses. Therefore, the objectives of the study were to determine combining ability, gene action and heterosis for MSV and Al tolerance in maize. Ninety-nine experimental hybrids were generated from a 10 × 10 factorial mating design. The experimental maize hybrids, and 21 commercial hybrids were evaluated for MSV resistance under artificial infestation in Zimbabwe, and for grain yield and agronomic performance across eight environments in South Africa and Zimbabwe. Ninety-seven experimental hybrids and five standard control hybrids were evaluated for Al tolerance in a laboratory in South Africa. There were significant (p < 0.05) differences among hybrids for agronomic traits, grain yield, and MSV and Al toxicity tolerance. Only general combining ability effects were significant (p < 0.05) for grain yield and grain moisture content, while specific combining ability effects were significant (p < 0.05) for number of ears and ear prolificacy. Both GCA and SCA effects were significant for the Al toxicity tolerance related traits, indicating that Al tolerance was governed by both additive and non-additive gene action. Although hybrids displayed highly significant variation for MSV resistance, the GCA and SCA mean squares were not significant and only accounted for 59% of the hybrid sum of squares, suggesting that MSV resistance was partly under qualitative inheritance. The F1 hybrids displayed MSV severity scores similar to those of their MSV resistant parents, suggesting that probably simple dominance gene effects were involved. The hybrids also displayed significantly high levels of heterosis for both Al and MSV resistance, indicating that hybridisation would be effective in generating improved varieties. At least 60% of the hybrids were resistant to Al toxicity and more than 87% were MSV resistant, indicating that there is potential to develop varieties with resistance to both stresses.

Marker-trait association for fertility restoration using Rf8 gene in T. timopheevii based male sterile cytoplasm of wheat

Hybrid wheat research has garnered interest after a gap of few decades. Heterosis levels and effective ABR system has been continuous focus of research. Effective restoration of fertility, its genetic control however remains an unresolved issue. Among 9 reported fertility restorer genes for Triticum timopheevii cytoplasm, Rf8 has been mapped on chromosome 2DS. Two F 2 populations were used to study the efficacy and robustness of markers linked with Rf8. Data was recorded on extent of fertility restoration and three linked markers namely Xwmc503, Xwmc296 and Xwmc112 were used for this study. Among these, Xwmc503 present at 3.3 cM away from Rf8 showed significant association with fertility restoration in both the crosses. In contrast, marker Xwmc296 linked at 5.8 cM did not reveal significant association in any population. However, the third marker Xwmc112 did not get amplified in any of the populations. Xwmc503 marker can potentially be useful for selecting restorers with Rf8 gene which further could be used for transferring this very gene into potentially elite genotypes to enrich hybrid male parental pool.

Схема селекции и уровень гетерозиса гибридов сорго сахарного

Creation and introduction of new hybrids of sugar sorghum adaptive to arid conditions allow stabilizing and increasing the productivity of forage mass over the years, which is of current importance. The aim of the research was to clarify the scheme and methods of selection of the initial material, assess the level of true heterosis, quantitative traits of green mass yield and plant height in the best obtained hybrids of sugar sorghum. The research was carried out according to the methods of laboratory and field experiments. The scheme of the breeding process included nurseries of source material and breeding nurseries, as well as creation of self-pollinated and sterile lines, hybridization, assessment of samples for CMS, combining ability, and testing new hybrids by saturating crosses and topcross. According to this scheme, sterile lines ‘A-63’, ‘Knyazhna’, ‘Zersta 38A’ were created. By methods of multiple and individual selection with subsequent inbreeding from hybrid populations, fertile paternal forms ‘Stavropolskoe 36’, ‘Galia’ and ‘Larets’ were created. Also, obtained on their basis hybrids ‘Silosnoe 88’ (standard), ‘Alga’, ‘Kalaus’, ‘Yarik’ served as the object of research. On average for 2016–2019, the most significant plant height under the conditions of the “North-Caucasus Federal Agrarian Research Center” was found in late-ripening combinations ‘Yarik’ (301.4 cm) and ‘Kalaus’ (289.0 cm). The level of true heterosis of this trait was 41.7 % and 31.6 %, respectively. In the studied hybrids, the pollination period of the parental forms coincides, the heterosis of the thickness of the stems is observed. The significant leafiness of the plants is also found to be in the late-ripening forms (15.7–16.0 %). The maximum yield of green mass was obtained from hybrids ‘Yarik’ (102.0 t/ha) and ‘Kalaus’ (86.7 t/ha). The level of true heterosis of the studied trait in these combinations was 67.9 t/ha and 47.0 t/ha, respectively, or 66.5 % and 54.2 %. The combination of other genetic plasmas provided a lower level of true heterosis. The late-ripening hybrids ‘Yarik’ and ‘Kalaus’ have significantly higher sugar content in the juice of the stems (12.89–14.03 %) compared with the mid-ripening ‘Silosnoe 88’ (8.9 %) and the medium-late ‘Alga’ (11.14 %).

НОВЫЙ СОРГО-СУДАНКОВЫЙ ГИБРИД ГВАРДЕЕЦ

Arid conditions in Central Ciscaucasia caused a shortage of green fodder for animal husbandry. In the current circumstances, new sorghum-sudan hybrids creation and introduction into production are of great importance. The aim of the research is twofold: to assess green mass, hay and grain productivity and quality; to determine the main biomorphological characteristics and level of heterosis of the new sorghum-sudan hybrid ‘Gvardeets’. The experiments were carried out in competitive and environmental testing. In the Novgorod Oblast, the new hybrid provided 43.0 t/ha of green mass; the same indicator in the Altai FASC comprised 42.1 t/ha exceeding standard hybrid ‘Navigator’ by 2.6 and 0.9 t/ha, respectively. The data were obtained in a competitive test by methods of field and laboratory experiments, as well as environmental testing in various regions of Russia. On average for 2015–2020, in the conditions of the Stavropol Territory, the new hybrid provided 53.87 t/ha of green and 11.55 t/ha of dry matter exceeding standard hybrid ‘Navigator’ by 5.03 and 1.26 t/ha or 10.3 and 12.2%, respectively. ‘Gvardeets’ is a mid-ripening hybrid. The first mowing can be carried out in the booting phase or at the end of June/first half of July, the second one – in the second half of August. Furthermore, in moderately warm and humid summers, it is possible to obtain the third mowing in late September/early October. The new hybrid ‘Gvardeets’ has a high rate of initial plants growth on the 30th day of vegetation (80 cm), as well as a high content of leaves in the green mass (34.7 %). The content of protein in dry matter is 11.8 %, fat – 1.9 %, fiber – 30.9%, ash – 6.3 %. One kilogram of new combination feed contains 0.67 feed units, 70 g of digestible protein, 31.9 g of sugar, 81.2 mg of carotene. The provision of one feed unit with digestible protein is 123 g. There is 8.59 MJ/kg of exchange energy, which is better than that of the standard hybrid ‘Navigator’. The stems of ‘Gvardeets’ plants have a juicy core; plants are resistant to drought, lodging, pests and diseases. The parental forms of the hybrid (‘Zersta 90C’ x ‘Sputnitsa’) are distinguished by a high combinational ability and provide a level of true heterosis of the yield of green mass in the amount of 20.81 t/ha (62.9%). The new sorghum-sudan hybrid ‘Gvardeets’ has been included in the State Register of Breeding Achievements of the Russian Federation since 2021 in the North Caucasus, Lower Volga, Central Black Earth and West Siberian regions.

Features of heterosis manifestation in interlinear hybrids of sweet pepper in unheated film greenhouses

The dynamics of changes in an important economic trait of sweet pepper “average fruit weight” and the manifestation of heterosis have been studied on the example of 10 hybrids and their parental lines with multiple harvests in an unheated film greenhouse. It was found that the average weight, regardless of its value, was maximum and relatively stable during the first 5 harvests, which corresponds to the return of an early yield in the first month of fruiting. At the last collection, there was a decrease in the average weight of the fruit by 1.3-2.5 times. It has been established that a decrease in fruit weight with late harvests in hybrids occurs at a later date and is less pronounced than in parental lines, which indicates their higher adaptive ability. With an early harvest in 3 combinations, the level of true heterosis was 5.4-19.7%, a hypothetical heterosis at the level of 5.4-24.4% was found in 7 hybrids. At an early harvest and a late harvest in 50% of sweet pepper hybrids, the value of heterosis varied, but had the same character; in 50% of hybrids, a change in the sign of heterosis to the opposite was noted.2 hybrid combinations with a more stable average fruit weight were identified with multiple harvests - (Bs1xF46Kt22706) and (San1xF46Kt2181) with varying traits within 77-99 g and 81-123 g. the effect in 80% of large-fruited (17.6-27.3%) and medium-fruited hybrids (8.5-49.3%) was noted after the early harvest on July 21.The maximum effect of heterosis does not correspond to the maximum value of fruit weight in the experiment and is associated with a more pronounced reaction of the parental lines compared to hybrids to extreme temperatures during the period of fruit formation.

Assessment of economic traits’ inheritance of winter rye at intraspecific hybridization

Intraspecific hybridization in winter rye selection (Secale cereale L. ssp. cereale) is a source of intrapopulation genotypic variability with the possibility of using the effect of interpopulation heterosis. The inheritance of the crop yield, the regeneration degree after overwintering and the weight of 1000 grains in reciprocal and back winter rye F1intervarietal hybrids was established. Different types of inheritance prevailed in reciprocal and back crossings. The regeneration inheritance and the weight of 1000 grains had a specificity. Traits’ overdominance prevailed in reciprocal crossings (45% of hybrids). The yield of reciprocal hybrids was inherited mainly according to the overdominance type (68% of the hybrids), the weight of 1000 grains - according to the intermediate type (50%), regeneration - according to the overdominance type and transitionally - equally (36% each). Intermediate traits’ inheritance prevailed in back crossings (62% of hybrids). The rarest type of traits’ inheritance was complete dominance of the best parent (2 hybrids). 4 F1hybrids with the greatest overdominance in yield, regeneration, weight of 1000 grains were allocated. The degree of true and competitive heterosis of reciprocal F1hybrids in terms of yield was determined. The level of true heterosis of F1hybrids in terms of yield varied within 6-123%. Economically significant competitive heterosis in terms of yield was established in 7 F1hybrids.

Doubled Haploid Broccoli (Brassica olearacea var. italica) Plants from Anther Culture.

Broccoli (Brassica olearecea var. italica) is a cole crop grown for its floral heads and stalks. It is rich in bioactive chemicals good for human health. Broccoli has been consumed as a vegetable since Roman times, but its production and consumption have increased significantly over the past few decades. Breeders try to develop new broccoli varieties with high yield, improved quality, and resistance to biotic and abiotic stresses. Almost all new broccoli varieties are F1 hybrids. Development of inbred broccoli lines that can be used as parents in hybrid production is a time-consuming and difficult process. Haploidization techniques can be utilized as a valuable support in broccoli breeding programs to speed up the production of genetically pure genotypes. Haploid plants of broccoli can be produced from immature male gametophytes via anther and microspore cultures with similar success rates. The most important parameters affecting the success of haploidization in broccoli are the genetic background (genotype) and the developmental stage of the microspores. Broccoli genotypes differ in their responses to androgenesis induction. The highest androgenesis response could be induced from microspores in late uninucleate and early binucleate stages. Recovery of diploid broccoli plants from haploids is possible via spontaneous and induced doubling. Doubled haploid (DH) broccoli lines are considered to be fully homozygous. Therefore, the production of DH lines is an alternative way to obtain pure inbred lines that can be utilized as parents in the development of new F1 hybrid varieties showing high levels of heterosis, high-quality heads, and uniform harvestable crop. We are using an anther culture-based haploid plant production system to develop DH broccoli lines in our broccoli breeding program. DH broccoli lines are produced from different genetic backgrounds within a year and handed to broccoli breeders.

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

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

Heterotic implications for yield and quality traits in rice (Oryza sativa L.)

Forty two rice first filial crosses were generated during rabi 2018-19 period utilizing seven lines and six testers adopting line x tester crossing fashion to get a hold of yield superiority hybrids with blast tolerance. The heterotic components were investigated for yield and quality traits on test hybrids. The results signified the greater heterotic vigour for yield and its component traits while the quality traits particularly length breadth ratio, length elongation ratio breadth elongation ratio and amylase content adjudged to express lower level of heterosis. Thirty five crosses exhibited significantly positive value for relative heterosis while twenty four hybrids showed positive and significant heterobeltiosis. The cross involving White Ponni (128.73 to 157.16), IR 20 (102.85 to 133.32) and CO 50 (95.80 to 125.49) as female parent witnessed to perform extremely superior for yield among the lines deployed. Considering yield and its component traits, the crosses viz., White ponnix Thuyamalli, Whiteponnix Chandaikar, ADT 38 x ADT39, IR 20 xThuyamalli, IR 20 x ADT 39, ACK14072 xSivappumalli, CR 1009 sub 1 x ADT 39, ADT 38 xThuyamalli can be consistently exploited for evolution of great performing rice varieties.

A New Theory Producing Heterosis of Crops

In this paper, the theory of heterosis controlled by core traits (genes) was put forward. Growth period traits and stem type traits were two core traits of heterosis in crops. However, due to the low yield of early-maturing parents, although the relative advantage was high, the absolute yield level of heterosis in the F1 generation was not necessarily high. Because seed production requires that the difference between two parents’ growth periods should not be very big, it also limited the potential of using gene interaction of growth periods to improve heterosis. In addition, the genes that control the growth period also included the genes that control each growth stage, so that the genes that control the growth period were not many, but not very few, because there were more genes that disperse and weaken the action intensity of major genes and increasing heterosis of the F1 generation was difficult. The genes controlling different stem types were all single. When the maturity of two parents is the same or similar, the combinations with different stem types got the maximum heterosis of grain yield, and the F1 absolute yield level is also the highest. Therefore, in heterosis utilization breeding, the differences of stem types should be mainly used and differences of growth periods should be properly used. Mechanism and root producing heterosis of crops were that strong interaction of major genes among different types of the most important quality traits (ecological traits) lead to great improvement in the vitality of all quantitative traits. Growing period and Stem type were two nucleus traits producing heterosis of crops. Therefore this theory was called as core trait theory producing heterosis of crops.

Combining ability of standardized indices for multi-trait selection in tobacco

ABSTRACT Several traits must be simultaneously considered in selection of tobacco cultivars for meeting the requirements of farmers, manufacturers and consumers. Breeders should have an understanding of associations between economically-important traits in order to devise the best strategy to have response to selection for all them. Utilization of selection indices has been shown to be one of the most efficient strategy for selecting for correlated characters. In tobacco, no reports can be found within the academic literature for multiple trait selection. In this study we demonstrate the efficiency of the Sum of the Standardized Variables Index (SSV) for multi-trait selection in tobacco. The method was evaluated using a collection of thirteen inbred lines and hybrids derived using a diallel scheme. The hybrids, parental lines, and checks were evaluated in two field locations. The traits assessed were yield (YLD), general quality index (GQI), leaf stem to lamina ratio, percent total alkaloids, and percent total sugars. We considered weights according to the economic importance of each trait: 0.4 for YLD, 0.3 for GQI and 0.1 for the remaining characters. The SSV index proved to be efficient and easy to interpret, and could be used to generate genetic gain for almost all characters in the desired direction. General combining ability (GCA) explained the larger part of the variation of the index in the diallel analysis. The mean heterosis estimate was 2.02%. Some hybrid combinations exhibited heterosis levels greater than 10%, indicating that increased attention might need to be given to commercialization of F1 hybrids.

Genetic Diversity of Pineapple (Ananas comosus) Germplasm in Malaysia Using Simple Sequence Repeat (SSR) Markers.

Assessments of genetic diversity have been claimed to be significantly efficient in utilising and managing resources of genetic for breeding programme. In this study, variations in genetic were observed in 65 pineapple accessions gathered from germplasm available at Malaysian Agriculture Research and Development Institute (MARDI) located in Pontian, Johor via 15 markers of simple sequence repeat (SSR). The results showed that 59 alleles appeared to range from 2.0 to 6.0 alleles with a mean of 3.9 alleles per locus, thus displaying polymorphism for all samples at a moderate level. Furthermore, the values of polymorphic information content (PIC) had been found to range between 0.104 (TsuAC035) and 0.697 (Acom_9.9), thus averaging at the value of 0.433. In addition, the expected and the observed heterozygosity of each locus seemed to vary within the ranges of 0.033 to 0.712, and from 0.033 to 0.885, along with the average values of 0.437 and 0.511, respectively. The population structure analysis via method of delta K (ΔK), along with mean of L (K) method, revealed that individuals from the germplasm could be divided into two major clusters based on genetics (K = 2), namely Group 1 and Group 2. As such, five accessions (Yankee, SRK Chalok, SCK Giant India, SC KEW5 India and SC1 Thailand) were clustered in Group 1, while the rest were clustered in Group 2. These outcomes were also supported by the dendrogram, which had been generated through the technique of unweighted pair group with arithmetic mean (UPGMA). These analyses appear to be helpful amongst breeders to maintain and to manage their collections of germplasm. Besides, the data gathered in this study can be useful for breeders to exploit the area of genetic diversity in estimating the level of heterosis.

African and Asian origin pearl millet populations: Genetic diversity pattern and its association with yield heterosis

AbstractPearl millet [Pennisetum glaucum(L.) R. Br.] is a staple food crop of arid and semi‐arid regions of Asia and Africa. Forty‐five pearl millet populations of Asian and African origin were assessed for genetic diversity using 29 simple sequence repeat (SSR) markers. The SSR‐based clustering and structure analyses showed that Asian origin–Asian bred (As‐As) and African origin–African bred (Af‐Af) populations were distributed across seven clusters, indicating no strong relationship among populations with their geographical origin. Most of the African origin–Asian bred (Af‐As) populations had a higher average number of alleles per locus than As‐As or Af‐Af populations, and the majority of them clustered separately from As‐As or Af‐Af populations, indicating that introgression of African origin breeding materials led to the development of new gene pools adapted to the Asian region. Fourteen populations representing seven clusters were crossed according to a diallel mating design to generate 91 population hybrids (seeds of direct and reciprocal crosses were mixed) and evaluated at three locations in 2016. All the 91 hybrids when partitioned into three groups based on genetic distance (GD) between parental combinations (low, moderate, and high), revealed no correlation between GD and panmictic midparent heterosis in any of the groups, indicating that grain yield heterosis cannot be predicted based on GD. Two population hybrids (GB 8735 × ICMP 87307 and Sudan I × Ugandi) exhibited high levels of yield heterosis over standard checks and can be further utilized using different breeding schemes to develop high‐yielding pearl millet cultivars.

Phenotypic plasticity for biomass partitioning in maize: genotype effects across a range of environments

Abstract Maize grain yield is determined by genotype (G), environment (E) and G × E interaction effects that influence the expression of traits along the crop cycle. Inbreds and hybrids may differ in their responses to fluctuations in environmental conditions, determining changes in heterosis levels across environments and consequently the target environment for their evaluation. The objectives of this work were (i) to compare traits related to grain yield, aboveground biomass production and its partitioning in two contrasting genotypic groups (inbreds and hybrids) and (ii) to analyze their performance across environments for the assessment of their phenotypic plasticity as well as environmental effects on the expression of heterosis. We built a balanced environmental index based on normalized plant grain yield (BEINPGY) from 14 contrasting environments using a 6-inbred complete diallel mating design and analyzed the response of the 12 evaluated traits to this index for each genotypic group. This approach allowed us to (i) differentiate among traits with simple linear (grain yield, total biomass, kernel numbers, the anthesis-silking interval and plant reproductive efficiency), bilinear (harvest index, individual kernel weight, prolificacy and apical ear reproductive efficiency) or no response (ear and plant growth rates around flowering as well as their relationship) in phenotypic plasticity of each group to the BEINPGY, and (ii) group traits depending upon their absolute heterosis response (i.e., heterosis plasticity) to the BEINPGY, which varied in sign (positive, null or negative) depending upon the trait. There was a clear and positive relationship between absolute heterosis plasticity and traits plasticities, which was mainly driven by hybrids. Genotypic groups differed in the association patterns of traits values per se as well as of their phenotypic plasticities, indicative of the different genetic bases that determine them. The fact that percent heterosis for grain yield and other relevant secondary traits did not vary across environments, whereas heritability is expected to decrease under stressful conditions, may contribute to guide future breeding efforts aiming to develop superior hybrids with successful performance, particularly in future challenging environmental scenarios.

Прояв і мінливість біометричних ознак у ліній–батьківських компонентів та гібридів кукурудзи за використання різних генетичних плазм при зрошенні

Прояв і мінливість біометричних ознак у ліній–батьківських компонентів та гібридів кукурудзи за використання різних генетичних плазм при зрошенні

The Pitfalls of Heterosis Coefficients.

Heterosis (hybrid vigour) is a universal phenomenon of crucial agro-economic and evolutionary importance. We show that the most common heterosis coefficients do not properly measure deviation from additivity because they include both a component accounting for “real” heterosis and a term that is not related to heterosis, since it is derived solely from parental values. Therefore, these coefficients are inadequate whenever the aim of the study is to compare heterosis levels between different traits, environments, genetic backgrounds, or developmental stages, as these factors may affect not only the level of non-additivity, but also parental values. The only relevant coefficient for such comparisons is the so-called “potence ratio”. Because most heterosis studies consider several traits/stages/environmental conditions, our observations support the use of the potence ratio, at least in non-agronomic contexts, because it is the only non-ambiguous heterosis coefficient.