Parental Inbred Lines Research Articles

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.

The interaction between abiotic and biotic soil factors drive heterosis expression in maize.

Heterosis or hybrid vigor refers to the superior phenotypes of hybrids relative to their parental inbred lines. Recently, soil microbes were identified as an environmental driver of maize heterosis. While manipulation of the soil microbial community consistently altered heterosis, the direction of the effect appeared to be dependent on the microbiome composition, environment, or both. Abiotic factors are well-known modifiers of heterosis expression, however, how the interactive effects between the soil microbial community and abiotic factors contribute to heterosis are poorly understood. To disentangle the proposed mechanisms by which microbes influence heterosis, we characterize the variation in heterosis expression when maize was grown in soil inocula derived from active maize farms or prairies. While we did not observe consistent differences in heterosis among plants grown in these inocula, our observations reaffirm that microbial effects on heterosis are likely specific to the local microbial community. The introduction of a nutrient amendment resulted in greater heterosis expression in the presence of an agricultural inoculum but not a prairie inoculum. We also observed an effect of soil inocula and nutrient treatment on the composition of bacterial and fungal communities in the root endosphere. In addition, the interaction between soil and nutrient treatment significantly affected bacterial community composition, whereas fungal community composition was only marginally affected by this interaction. These results further suggest that the soil microbial community plays a role in maize heterosis expression but that the abiotic environment is likely a larger driver.

Association Mapping of Seed Coat Color Characteristics for Near-Isogenic Lines of Colored Waxy Maize Using Simple Sequence Repeat Markers.

Waxy maize is mainly cultivated in South Korea for the production of food and snacks, and colored maize with increased anthocyanin content is used in the production of functional foods and medicinal products. Association mapping analysis (AMA) is supported as the preferred method for identifying genetic markers associated with complex traits. Our study aimed to identify molecular markers associated with two anthocyanin content and six seed coat color traits in near-isogenic lines (NILs) of colored waxy maize assessed through AMA. We performed AMA for 285 SSR loci and two anthocyanin content and six seed coat color traits in 10 NILs of colored waxy maize. In the analysis of population structure and cluster formation, the two parental lines (HW3, HW9) of "Mibaek 2ho" variety waxy maize and the 10 NILs were clearly divided into two groups, with each group containing one of the two parental inbred lines. In the AMA, 62 SSR markers were associated with two seed anthocyanin content and six seed coat color traits in the 10 NILs. All the anthocyanin content and seed coat color traits were associated with SSR markers, ranging from 2 to 12 SSR markers per characteristic. The 12 SSR markers were together associated with both of the two anthocyanin content (kuromanin and peonidin) traits. Our current results demonstrate the effectiveness of SSR analysis for the examination of genetic diversity, relationships, and population structure and AMA in 10 NILs of colored waxy maize and the two parental lines of the "Mibaek 2ho" variety waxy maize.

Mapping parental DMRs predictive of local and distal methylome remodeling in epigenetic F1 hybrids.

F1 hybrids derived from a cross between two inbred parental lines often display widespread changes in DNA methylation and gene expression patterns relative to their parents. An emerging challenge is to understand how parental epigenomic differences contribute to these events. Here, we generated a large mapping panel of F1 epigenetic hybrids, whose parents are isogenic but variable in their DNA methylation patterns. Using a combination of multi-omic profiling and epigenetic mapping strategies we show that differentially methylated regions in parental pericentromeres act as major reorganizers of hybrid methylomes and transcriptomes, even in the absence of genetic variation. These parental differentially methylated regions are associated with hybrid methylation remodeling events at thousands of target regions throughout the genome, both locally (in cis) and distally (in trans). Many of these distally-induced methylation changes lead to nonadditive expression of nearby genes and associate with phenotypic heterosis. Our study highlights the pleiotropic potential of parental pericentromeres in the functional remodeling of hybrid genomes and phenotypes.

A higher-yield hybrid rice is achieved by assimilating a dominant heterotic gene in inbred parental lines.

The exploitation of heterosis to integrate parental advantages is one of the fastest and most efficient ways of rice breeding. The genomic architecture of heterosis suggests that the grain yield is strongly correlated with the accumulation of numerous rare superior alleles with positive dominance. However, the improvements in yield of hybrid rice have shown a slowdown or even plateaued due to the limited availability of complementary superior alleles. In this study, we achieved a considerable increase in grain yield of restorer lines by inducing an alternative splicing event in a heterosis gene OsMADS1 through CRISPR-Cas9, which accounted for approximately 34.1%-47.5% of yield advantage over their corresponding inbred rice cultivars. To achieve a higher yield in hybrid rice, we crossed the gene-edited restorer parents harbouring OsMADS1GW3p6 with the sterile lines to develop new rice hybrids. In two-line hybrid rice Guang-liang-you 676 (GLY676), the yield of modified hybrids carrying the homozygous heterosis gene OsMADS1GW3p6 significantly exceeded that of the original hybrids with heterozygous OsMADS1. Similarly, the gene-modified F1 hybrids with heterozygous OsMADS1GW3p6 increased grain yield by over 3.4% compared to the three-line hybrid rice Quan-you-si-miao (QYSM) with the homozygous genotype of OsMADS1. Our study highlighted the great potential in increasing the grain yield of hybrid rice by pyramiding a single heterosis gene via CRISPR-Cas9. Furthermore, these results demonstrated that the incomplete dominance of heterosis genes played a major role in yield-related heterosis and provided a promising strategy for breeding higher-yielding rice varieties above what is currently achievable.

Agronomic performance and phenotypic variability of the F2 population derived from various types of okra varieties

Abstract Okra is a functional vegetable with high nutrient content and medicinal value potential. Evaluating genetic material from various genetic sources is a standard procedure in plant breeding programs. A field study was carried out to evaluate the agronomic traits of F2 populations derived from various types of varieties and assess the phenotypic variability of the traits. The research was conducted at the Research Station of the Faculty of Agriculture, Andalas University, from January to May 2021. The materials used are seeds from self-pollinated of 16 F1 populations with various varieties, i.e., hybrid, composite, introduced and local varieties. Data was collected based on an individual observation, and the data were then analyzed using descriptive statistics. Results showed that the entire population of the F2 derived from both hybrid or composite varieties, introduced or local varieties, has diverse agronomic traits, indicating their potential to be developed as parental inbred lines. All agronomic traits evaluated showed wide variability, indicating a high possibility to obtain plants with valuable and desirable traits. The exception was found for the optimum picking time; however, the optimum picking time 7, 8 or 9 DAA is sufficient to obtain fruit with higher fruit weight and fruit size.

Genetic mapping reveals new loci and alleles for flowering time and plant height using the double round-robin population of barley.

Flowering time and plant height are two critical determinants of yield potential in barley (Hordeum vulgare). Despite their role in plant physiological regulation, a complete overview of the genetic complexity of flowering time and plant height regulation in barley is still lacking. Using a double round-robin population originated from the crossings of 23 diverse parental inbred lines, we aimed to determine the variance components in the regulation of flowering time and plant height in barley as well as to identify new genetic variants by single and multi-population QTL analyses and allele mining. Despite similar genotypic variance, we observed higher environmental variance components for plant height than flowering time. Furthermore, we detected new QTLs for flowering time and plant height. Finally, we identified a new functional allelic variant of the main regulatory gene Ppd-H1. Our results show that the genetic architecture of flowering time and plant height might be more complex than reported earlier and that a number of undetected, small effect, or low-frequency genetic variants underlie the control of these two traits.

A SLAF-based high-density genetic map construction and genetic architecture of thermotolerant traits in maize (Zea mays L.).

The leaf scorching trait at flowering is a crucial thermosensitive phenotype in maize under high temperature stress (HS), yet the genetic basis of this trait remains poorly understood. In this study, we genotyped a 254 RIL-F2:8 population, derived from the leaf scorch-free parental inbred line Abe2 and the leaf scorching maternal inbred line B73, using the specific-locus amplified fragment sequencing (SLAF-seq) method. A total of 10,112 polymorphic SLAF markers were developed, and a high-density genetic map with a total length of 1,475.88 cM was constructed. The average sequencing depth of the parents was 55.23X, and that of the progeny was 12.53X. Then, we identified a total of 16 QTLs associated with thermotolerant traits at flowering, of which four QTLs of leaf scorching damage (LS) were distributed on chromosomes 1 (qLS1), 2 (qLS2.1, qLS2.2) and 3 (qLS3), which could explain 19.73% of phenotypic variation. Combining one qLS1 locus with QTL-seq results led to the identification of 6 candidate genes. Expression experiments and sequence variation indicated that Zm00001d033328, encoding N-acetyl-gamma-glutamyl-phosphate reductase, was the most likely candidate gene controlling thermotolerant traits at flowering. In summary, the high-density genetic map and genetic basis of thermotolerant traits lay a critical foundation for mapping other complex traits and identifying the genes associated with thermotolerant traits in maize.

Genetic diversity among maize (Zea mays L.) inbred lines adapted to Japanese climates.

Understanding the genetic diversity of inbred lines is vital for development of superior F1 varieties. The present study aimed to analyze Japanese maize parental inbred lines and determine their genetic diversity for future breeding. Genetic analyses were conducted using multiple methods. Principal component analysis (PCA), phylogenetic trees, and Bayesian clustering reflected borders between heterotic groups according to the derivation of each inbred line. A self-pollinated line derived from a classic F1 variety and another line from an open-pollinated population from the same derivation were classified as separate components by PCA and Bayesian clustering. The result suggests that open pollination could be essential in modern breeding. Of those classified as dent or flint based on their derivation, some had a combination of all components or clusters. Therefore, the classification of inbred lines should be based on their derivation and DNA markers. The findings will be valuable for breeding and genetic studies in Japan. Additionally, these techniques may be used to obtain a more significant number of SNPs and related phenotypic data.

Exploration of Diallel Method for Assessing Heterosis and Combining Ability in Maize (Zea mays L.)

During the Kharif season of 2018 and Rabi season of 2018-19, an experimental study was conducted. The selection of seven maize genotypes was based on quantitative traits, growth duration, suitability for the Kharif season, and yield. These genotypes were then crossed in a half diallel mating design, resulting in the production of 21 single-cross hybrids. The cultivation of these hybrids, along with the seven parental inbred lines, totaling 28 genotypes, followed a randomized block design. Each plot had dimensions of 23.10m by 1.0m and maintained a plant density of 240 plants per plot. To assess the quantitative traits, observations were recorded from five randomly selected plants per plot. The analysis of variance indicated significant genetic variability among the genotypes, particularly in traits such as days to 50% germination, silking, maturity, plant height, number of leaves per plant, biological yield, cob ear weight, number of rows per cob, and number of seeds per cob. This variability was attributed to both additive and non-additive genetic components, as evident from significant variances due to general combining ability (GCA) and specific combining ability (SCA). The GCA/SCA ratio was less than unity for most traits. For most traits, parental lines P1, P2, and P4 exhibited high GCA effects. Additionally, F1 hybrids P4x P3, P3x P1, P5x P3, and P7 x P5 were found to be desirable in terms of yield and related traits. In terms of yield, seven crosses (P1 x P6, P2 x P7, P2x P5, P1 x P2, P3x P4, P5 x P7, and P3 x P5) outperformed the check hybrid, demonstrating their potential for future breeding programs aimed at enhancing maize yield.

Diallel analysis of maize inbred lines for estimating superiority and combining ability

The phenomenon of heterosis has provided the most important genetic tools for crop yield improvement. Identification of specific parental combinations capable of producing the highest level of heterotic effects in F1 has immense value for commercial exploitation of heterosis. The objective of this study was to assess the combining ability variances and superiority in twenty one combinations developed by crossing seven maize (Zea mays L.) inbred lines in half diallel fashion design. The resulting 21 hybrids, along with two check hybrids, were evaluated in Randomised Complete Block Design, in three locations during 2022 season in Egypt. The results showed that both additive and non-additive gene actions were important in controlling all the measured traits. The General Combining Ability (GCA) variance was found to be greater than Specific Combining Ability (SCA) variance, indicating predominance of additive and additive by additive gene effects in the inheritance for all studied traits. Cross P2×P3 significantly out yielded the best check (SC. 168) for the grain yield trait. The parental inbred lines, P1, P2 and P3, possessed significant desirable (GCA) effects for the grain yield trait. The cross combinations (P1×P5),(P2×P7), (P3×P7),(P4×P5),(P4×P6) and (P6×P7) showed significant positive sca effects for grain yield. Cross P2×P3 (10.32**) obtained superiority (%) relative to the check hybrid SC.168 for grain yield. On the other hand, five crosses viz. (P1×P3), (P1×P5), (P2×P3), (P2×P5) and (P3×P5) expressed positive superiority (%) over the check hybrid SC.3444 for same trait. Thus, these crosses could be recommended to be released as commercial hybrids by Maize Research Programme after further evaluation and testing in multi-locations in Egypt.

Prediction of additive, epistatic, and dominance effects using models accounting for incomplete inbreeding in parental lines of hybrid rye and sugar beet.

Genomic models for prediction of additive and non-additive effects within and across different heterotic groups are lacking for breeding of hybrid crops. In this study, genomic prediction models accounting for incomplete inbreeding in parental lines from two different heterotic groups were developed and evaluated. The models can be used for prediction of general combining ability (GCA) of parental lines from each heterotic group as well as specific combining ability (SCA) of all realized and potential crosses. Here, GCA was estimated as the sum of additive genetic effects and within-group epistasis due to high degree of inbreeding in parental lines. SCA was estimated as the sum of across-group epistasis and dominance effects. Three models were compared. In model 1, it was assumed that each hybrid was produced from two completely inbred parental lines. Model 1 was extended to include three-way hybrids from parental lines with arbitrary levels of inbreeding: In model 2, parents of the three-way hybrids could have any levels of inbreeding, while the grandparents of the maternal parent were assumed completely inbred. In model 3, all parental components could have any levels of inbreeding. Data from commercial breeding programs for hybrid rye and sugar beet was used to evaluate the models. The traits grain yield and root yield were analyzed for rye and sugar beet, respectively. Additive genetic variances were larger than epistatic and dominance variances. The models' predictive abilities for total genetic value, for GCA of each parental line and for SCA were evaluated based on different cross-validation strategies. Predictive abilities were highest for total genetic values and lowest for SCA. Predictive abilities for SCA and for GCA of maternal lines were higher for model 2 and model 3 than for model 1. The implementation of the genomic prediction models in hybrid breeding programs can potentially lead to increased genetic gain in two different ways: I) by facilitating the selection of crossing parents with high GCA within heterotic groups and II) by prediction of SCA of all realized and potential combinations of parental lines to produce hybrids with high total genetic values.

Performance of some Three-Way Cross Hybrids and Their Parents of Maize in the Middle Region of Iraq

There is increasingly demand of maize as a staple food in poultry industry in Iraq, where the average production of yield 4.5 tons, which is still faint as compared to neighbor countries. 30 of Three-Way Cross Hybrids of Maize along with five parental inbred lines were evaluated in four replications during the 2017 fall season at the research station of Agriculture College/Al-Jadrya, Baghdad to evaluate their performances and estimate the heterosis for grain yield (GY), and related traits. Most of the studied three-way cross hybrids out-yielded their parental inbred lines for the studied traits. TW8 and TW10 were identified as the excellent hybrids with average yield 219 and 214 gm/plant respectively with positive heterosis reached 72 and 62% respectively.

Transgenerational epigenetic inheritance and immunity in chickens that vary in Marek's disease resistance

Marek's disease virus (MDV), a naturally oncogenic, highly contagious alpha herpesvirus, induces a T cell lymphoma in chickens that causes severe economic loss. Marek's disease (MD) outcome in an individual is attributed to genetic and environmental factors. Further investigation of the host-virus interaction mechanisms that impact MD resistance is needed to achieve greater MD control. This study analyzed genome-wide DNA methylation patterns in 2 highly inbred parental lines 63 and 72 and 5 recombinant congenic strains (RCS) C, L, M, N, and X strains from those parents. Lines 63 and 72, are MD resistant and susceptible, respectively, whereas the RCS have different combinations of 87.5% Line 63 and 12.5% Line 72. Our DNA methylation cluster showed a strong association with MD incidence. Differentially methylated regions (DMRs) between the parental lines and the 5 RCS were captured. MD-resistant and MD-susceptible markers of DNA methylation were identified as transgenerational epigenetic inheritable. In addition, the growth of v-src DNA tumors and antibody response against sheep red blood cells differed among the 2 parental lines and the RCS. Overall, our results provide very solid evidence that DNA methylation patterns are transgenerational epigenetic inheritance (TEI) in chickens and also play a vital role in MD tumorigenesis and other immune responses; the specific methylated regions may be important modulators of general immunity.

Comparison of genomic-enabled cross selection criteria for the improvement of inbred line breeding populations.

A crucial step in inbred plant breeding is the choice of mating design to derive high-performing inbred varieties while also maintaining a competitive breeding population to secure sufficient genetic gain in future generations. In practice, the mating design usually relies on crosses involving the best parental inbred lines to ensure high mean progeny performance. This excludes crosses involving lower performing but more complementary parents in terms of favorable alleles. We predicted the ability of crosses to produce putative outstanding progenies (high mean and high variance progeny distribution) using genomic prediction models. This study compared the benefits and drawbacks of seven genomic cross selection criteria (CSC) in terms of genetic gain for one trait and genetic diversity in the next generation. Six CSC were already published and we propose an improved CSC that can estimate the proportion of progeny above a threshold defined for the whole mating plan. We simulated mating designs optimized using different CSC. The 835 elite parents came from a real breeding program and were evaluated between 2000 and 2016. We applied constraints on parental contributions and genetic similarities between selected parents according to usual breeder practices. Our results showed that CSC based on progeny variance estimation increased the genetic value of superior progenies by up to 5% in the next generation compared to CSC based on the progeny mean estimation (i.e. parental genetic values) alone. It also increased the genetic gain (up to 4%) and/or maintained more genetic diversity at QTLs (up to 4% more genic variance when the marker effects were perfectly estimated).

Biochemical Characterization of Parental Inbred Lines and Hybrids of Maize (Zea mays L.) under Different Irrigation Conditions

Maize (Zea mays L.) is a significant crop with extensive agricultural and economic importance worldwide. With increasing concerns over water scarcity and climate change, understanding the responses of maize plants under water stress conditions is crucial to develop drought-tolerant cultivar (s). In present investigation, alteration in different biochemical parameters, including chlorophyll content, malondialdehyde (MDA) levels, hydrogen peroxide (H2O2) content, peroxidase, glutathione reductase (GR), and catalase activities, among 12 parental inbred lines along with 66 hybrids and two checks under irrigated and partial irrigated conditions were examined. Under irrigated conditions, the chlorophyll content was highest in the parental inbred line IL8, intimately followed by IL6, while IL5 exhibited the lowest content. MDA levels were significantly higher in the parental line IL8 and hybrid IL1 × IL6, whereas IL5 and IL3 × IL11 exhibited the lowest levels. H2O2 content was found to be highest in the parental line IL5 and hybrid IL8 × IL12, whereas IL4 and IL2 × IL5 displaying the lowest levels. Peroxidase activity was highest in IL7 and hybrid IL1 × IL7, whilst IL6 and IL4 × IL7 showed the lowest activity. Glutathione reductase activity was found highest in IL1 and IL9 × IL12, whereas IL6 and hybrid IL1 × IL3 exhibited the lowest activity. Catalase activity was highest in IL8 and IL2 × IL10, while IL4 and IL2 × IL6 displayed the lowest activity under irrigated conditions. Under partial irrigated conditions, almost similar trends were documented for the most of parameters, with slight variations in the expression levels. Notably, the drought-tolerant genotypes demonstrated higher chlorophyll content, peroxidase, glutathione reductase, and catalase activities, while drought-sensitive genotypes unveiled elevated MDA levels and H2O2 content. Phylogenetic analysis revealed five major clusters, indicating significant variability in different biochemical profiles among the genotypes. The heat map analysis supported the identification of distinct expression patterns of biochemical parameters, contributing to our understanding of the genotypic responses to varying irrigation conditions. These findings provide valuable insights for maize breeding programmes aimed to breed drought-tolerant cultivar (s) with enhanced antioxidant defences and stress tolerance.

Sunflower Hybrids and Inbred Lines Adopt Different Physiological Strategies and Proteome Responses to Cope with Water Deficit.

Sunflower is a hybrid crop that is considered moderately drought-tolerant and adapted to new cropping systems required for the agro-ecological transition. Here, we studied the impact of hybridity status (hybrids vs. inbred lines) on the responses to drought at the molecular and eco-physiological level exploiting publicly available datasets. Eco-physiological traits and leaf proteomes were measured in eight inbred lines and their sixteen hybrids grown in the high-throughput phenotyping platform Phenotoul-Heliaphen. Hybrids and parental lines showed different growth strategies: hybrids grew faster in the absence of water constraint and arrested their growth more abruptly than inbred lines when subjected to water deficit. We identified 471 differentially accumulated proteins, of which 256 were regulated by drought. The amplitude of up- and downregulations was greater in hybrids than in inbred lines. Our results show that hybrids respond more strongly to water deficit at the molecular and eco-physiological levels. Because of presence/absence polymorphism, hybrids potentially contain more genes than their parental inbred lines. We propose that detrimental homozygous mutations and the lower number of genes in inbred lines lead to a constitutive defense mechanism that may explain the lower growth of inbred lines under well-watered conditions and their lower reactivity to water deficit.

GENETIC PURITY AND DIVERSITY ASSESSMENT OF PARENTAL CORN INBRED LINES USING SSR MARKERS FOR PHILIPPINE HYBRID BREEDING

Accurate data and relevant insights on parental corn inbred lines' and hybrids’ genetic purity and diversity are essential for hybrid development and seed production. Here, the genetic purity and diversity of 19 parental yellow corn inbred lines were assessed using SSR markers. A total of 91 SSR markers were utilized, of which 61 were highly polymorphic and had high polymorphism information content value (PIC = 0.379). Genetic purity and diversity parameters were calculated from the generated SSR marker data. Observed pairwise genetic distances ranging from 0.257 to 0.808 implied high genetic dissimilarities among the accessions. Cluster analysis separated the parental lines into three distinct subclusters, which can potentially be a basis for generating heterotic groupings among the parental lines. Eight (8) out of the 19 parental lines showed considerable residual heterozygosity of ≤10%. Inbred line CML 431 displayed complete homozygosity across all 61 SSR markers. Inbred lines that have residual heterozygosity of >15% need purification through further breeding and selection. Out of the resultant F1 hybrids analyzed, only four (4) showed genetic impurity of ≤10%. It may be attributed to the intrinsic genetic impurity of parental line CML 452 (21.67%). In contrast, hybrids generated from two genetically pure parents (e.g., CML 431 and CML 575) showed low to no off-types. Overall, genetic purity and diversity determination of promising parental lines can be valuable for future yellow corn breeding programs in the Philippines.

Predicting zinc‐enhanced maize hybrid performance under stress conditions

AbstractThe low yield potential of most biofortified maize is a barrier to its full adoption and reduces its potential to curb various macro‐ and micronutrient deficiencies highly prevalent in low‐income regions of the world, such as sub‐Saharan Africa (SSA). By crossing biofortified inbred lines with different nutritional attributes such as zinc (Zn), provitamin A and protein quality, breeders are attempting to develop agronomically superior and stable multi‐nutrient maize of different genetic backgrounds. A key question, however, is the relationship between the biofortified inbred lines per se and hybrid performance under stress and non‐stress conditions. In this study, inbred line per se and testcross performance were evaluated for grain yield and secondary traits of Zn‐enhanced normal, provitamin A and quality protein maize (QPM) hybrids and estimated heterosis under combined heat and drought (HMDS) and well‐watered (WW) conditions. Responses of all secondary traits, except for the number of days to mid‐anthesis, significantly differed for HMDS and WW conditions. The contribution of heterosis to grain yield was highly significant under both management levels, although higher mid and high‐parent heterosis was observed under WW than HMDS conditions. However, the findings suggest that inbred line performance was the best determinant of hybrid performance under HMDS. Strong correlations were observed between grain yield and secondary traits for both parents and hybrids, and between secondary traits of inbred lines and hybrids under both management levels, indicating that hybrid performance can be predicted based on intrinsic inbred line performance. Phenotypic correlation between grain yield of inbred lines and hybrids was higher under HMDS than WW conditions. This study demonstrated that under HMDS conditions, performance of Zn‐enhanced hybrids could be predicted based on the performance of their corresponding inbred lines. However, the parental inbred lines should be systematically selected for desirable secondary traits correlated with HMDS tolerance during inbred line development.

Assessment of the Degree of Relatedness of Some Inbred Lines Created at ARDS Turda

Knowledge of relatedness among maize elite breeding genotypes is useful in planning crosses for hybrid and inbred line improvement and assigning them into heterotic groups. This study investigated phenotypic and genetic similarities or diversities between 7 flint inbred lines (of common origin) adapted to the early maize growing regions created at ARDS Turda-Romania. They were studied for per se traits and in two crossing systems: a diallel crossing system, resulting in 21 hybrids and a cyclic system using four testers, thus resulting in 28 maize hybrids. Both parental inbred lines and hybrids were evaluated for several traits over three years. The level of relatedness/diversity was determined by various methods, grouped into: phenotypic methods and genetic methods. Similarities were identified between certain lines and a degree of differentiation between others. The analysis of the hybrid combinations from the diallel crossings between the seven sister lines highlighted the TD236 inbred line as the only one that differs genetically from the other. Following the analysis of the data obtained in the cyclic system, some inbred lines can be sources of favorable traits: TD236 and TD233 for yield, ear weight, grain/ear weight; TD233 and TD234 for the number of kernels/row, TD237 for plant breaking resistance.