Early-maturing Maize Inbred Lines Research Articles

Combining Abilities and Heterotic Patterns among Early Maturing Maize Inbred Lines under Optimal and Striga-Infested Environments.

Information on the general combining ability of inbred lines and the specific combining ability of hybrid combinations is crucial for successful hybrid development. The objectives of this study were to (i) determine the combining ability of thirty selected early maturing maize inbred lines under Striga-infested and optimal environments, (ii) classify the inbred lines into heterotic groups using the general combining ability effects of multiple traits (HGCAMT) and the single nucleotide polymorphism genetic distance (SNP- GD) methods, and (iii) assess the effectiveness of the heterotic grouping methods. One hundred and fifty single-cross hybrids were generated from the thirty inbred lines using the North Carolina Design II mating method. The hybrids and six local check varieties were tested across optimal and Striga-infested environments in Ghana and Nigeria in 2016 and 2017. The inheritance of grain yield was controlled by the non-additive gene action under both environments and the additive gene action across the two research environments. The non-additive gene action modulated the inheritance of measured traits under Striga-infested environments, except for the Striga damage syndrome rating at 8 weeks after planting. Maternal effects were observed for most traits in each environment and across environments. The inbred lines TZEI 127 and TZEI 40 exhibited significant and positive GCA male and female effects for grain yield under each environment and across the two research environments, indicating the presence of favorable alleles for yield improvements. The SNP-GD heterotic grouping method was identified as the most adequate in grouping the thirty inbred lines.

Combining Ability and Heterotic Patterns of Tropical Early-Maturing Maize Inbred Lines under Individual and Combined Heat and Drought Environments.

Information on combining ability and heterotic patterns of multiple stress-tolerant inbred lines are fundamental prerequisites for devising appropriate breeding strategies for the development of climate-resilient maize hybrids. In the present study, we evaluated 150 single cross hybrids derived from the North Carolina Design II (NCD II) along with six commercial checks under terminal drought stress (TDS), heat stress (HS), and combined drought and heat stress (CHDS)conditions. The objectives of the study were to: (i) determine the combining ability of the inbred lines and identify the best testers across the stresses; (ii) classify the inbred lines into heterotic groups (HGs) based on the general combining ability of multiple traits (HGCAMT) and sequencing-based diversity array technology (DArTseq) and (iii) assess the performance and stability of the lines in hybrid combinations. The inbred lines showed significantly (p < 0.01 and p < 0.05) positive and negative general combining ability (GCA) and specific combining ability (SCA) effects for grain yield (GY) and most other measured traits. The inbred line TZEI 135 displayed relatively larger positive GCA effects for GY when mated either as male or female and was identified as the best tester. TZEI 135 × TZEI 182 was identified as the best single-cross tester across environments. Results of the assessment of the relative importance of GCA and SCA effects revealed the predominance of additive gene action over the non-additive. Six HGs of inbreds were identified using the HGCAMT and three, based on the DArTseq marker genetic distance method, were the most efficient. The best hybrids in this study significantly out-yielded the best checks by 21, 46, and 70% under CHDS, HS, and TDS, respectively. These hybrids should be extensively tested in on-farm trials for possible commercialization in sub-Saharan Africa.

Line X Tester Analysis of Early Maturing Maize Inbred Lines for Yield And Secondary Traits

Line X Tester Analysis of Early Maturing Maize Inbred Lines for Yield And Secondary Traits

Mapping QTL for flowering time-related traits under three plant densities in maize

Flowering time is an indicator of adaptation in maize and a key trait for selection in breeding. The genetic basis of flowering time in maize, especially in response to plant density, remains unclear. The objective of this study was to identify maize quantitative trait loci (QTL) associated with flowering time-related traits that are stably expressed under several plant densities and show additive effects that vary with plant density. Three hundred recombinant inbred lines (RIL) derived from a cross between Ye 478 and Qi 319, together with their parents, were planted at three plant densities (90,000, 120,000, and 150,000 plants ha−1) in four environments. The five traits investigated were days to tasseling (DTT), days to silking (DTS), days to pollen shed (DTP), interval between anthesis and silking (ASI), and interval between tasseling and anthesis (TAI). A high-resolution bin map was used for QTL mapping. In the RIL population, the DTT, DTS, and DTP values increased with plant density, whereas the ASI and TAI values showed negligible response to plant density. A total of 72 QTL were identified for flowering time-related traits, including 15 stably expressed across environments. Maize flowering time under different densities seems to be regulated by complex pathways rather than by several major genes or an independent pathway. The effects of some stable QTL, especially qDTT8-1 and qDTT10-4, varied with plant density. Fine mapping and cloning of these QTL will shed light on the mechanism of flowering time and assist in breeding early-maturing maize inbred lines and hybrids.

Genetic Diversity and Inter-Trait Relationships among Maize Inbreds Containing Genes from Zea diploperennis and Hybrid Performance under Contrasting Environments

Accurate estimation of genetic variability present in tropical maize inbreds with varying reactions to Strigahermonthica infestation is essential for efficient and sustainable utilization to ensure increased genetic gain in a breeding program. Thirty-six early maturing maize inbred lines and 156 single cross hybrids were evaluated under Striga-infested and non-infested conditions in Nigeria during the 2014 and 2015 cropping seasons. Under Striga infestation, grain yield ranged from 1134 kg ha−1 for TZEI 26 × TZEI 5 to 5362 kg ha−1 for TZdEI 173 × TZdEI 280. The average yield reduction of the hybrids under Striga infestation was 44% relative to the performance under non-infested environments. Using 4440 high-quality DArT markers, clustering and population structure analyses separated the inbred lines into three distinct groups based on the genetic distance indicating high level of genetic variability among the lines. The base index of the International Institute of Tropical Agriculture (IITA) identified 50% of the inbred lines as Striga resistant. The genetic diversity study provided an opportunity for selecting divergent parents for tagging candidate genes and quantitative trait loci for marker-assisted introgression of Striga resistance genes into early maturing tropical maize breeding populations. The most reliable secondary trait for indirect selection for grain yield under Striga infestation was the ear aspect.

Genetic Diversity, Population Structure and Inter-Trait Relationships of Combined Heat and Drought Tolerant Early-Maturing Maize Inbred Lines from West and Central Africa

Adequate knowledge and understanding of the genetic diversity and inter-trait relationships among elite maize inbred lines are crucial for determining breeding strategies and predicting hybrid performance. The objectives of this study were to investigate the genetic diversity of 162 early maturing white and yellow tropical maize inbred lines, and to determine the population structure, heterotic groups and inter-trait relationships among the lines. Using 9684 DArT single nucleotide polymorphism (SNP) markers, a gene diversity (GD) of 0.30 was recorded for the inbred lines with polymorphic information content (PIC) ranging from 0.08 to 0.38. The genetic relatedness among the inbred lines evaluated revealed six different groups based on the history of selection, colour of endosperm and pedigree. The genotype-by-trait (GT) biplot analysis identified inbred 1 (TZEI 935) as outstanding in terms of combined heat and drought (HD) tolerance with the base index analysis identifying 15 superior inbreds in the HD environment. A wide range of genetic variability was observed among the inbred lines, indicating that they are an invaluable resource for breeding for HD tolerance in maize breeding programmes, especially in West and Central Africa.

Efficiencies of Heterotic Grouping Methods for Classifying Early Maturing Maize Inbred Lines

The success of a hybrid breeding program is dependent on available heterotic patterns for exploitation of grain-yield heterosis. The efficiency of the assignment of germplasm lines into heterotic groups is a prerequisite for obtaining useful heterotic patterns among germplasm lines. A total of 256 maize hybrids, comprising 244 top crosses, six diallel cross hybrids, and six checks, were grown under Striga infestation, drought, and optimal conditions, from 2015 to 2017. The study determined the combining abilities of the parental inbreds, classified the inbreds into heterotic groups, and compared the efficiencies of the following four grouping methods for classifying the inbreds: specific combining ability (SCA) effect of grain yield; general combining ability (GCA) effects of multiple traits (HGCAMT); SCA and GCA (HSGCA) for yield; and single nucleotide polymorphism-based genetic distance (SNP-based genetic distance (GD)). Significant GCA and/or SCA mean squares were revealed for most measured traits in all test environments. Sums of squares (SS) due to GCA were higher than SCA SS for measured traits in all test environments. The HSGCA, SCA, and SNP-based GD methods identified four heterotic groups, whereas the HGCAMT identified three groups, in all environments. The additive gene effect was preponderant in the inheritance of most measured traits. The efficiencies of the grouping methods varied with the test environments. The HSGCA and SCA methods were the most efficient for grouping in all test conditions. For practical breeding purposes, the HGCAMT and HSGCA methods were recommended under Striga infestation and drought, respectively. The heterotic patterns, which were revealed in this study, were effective for planning hybridization schemes for developing high-yielding, Striga-tolerant/resistant, and drought-tolerant maize hybrids for stressful environments.

Genetic analysis of drought-adaptive traits at seedling stage in early-maturing maize inbred lines and field performance under stress conditions

Maize hybrids that are tolerant to drought at the seedling stage are needed to boost productivity in the rainforest agro-ecology of West Africa. Genetics of tolerance of maize seedling to drought stress is not well understood and is poorly documented. The objectives of this study were to screen early-maturing maize lines for seedling drought tolerance, determine the inheritance and the combining ability of selected inbred lines, and evaluate the performance of seedling drought-tolerant hybrids under field conditions. Forty-nine early maize lines were screened for drought tolerance at the seedling stage. Ten drought-tolerant and two susceptible inbred lines were selected and used in diallel crosses to generate 66 hybrids. The twelve inbred lines and their hybrids were evaluated under induced drought at seedling stage in the screen house and under marginal growing conditions on the field for two seasons. Data collected were subjected to analysis of variance using the DIALLEL-SAS program. Mean squares for both GCA and SCA were significant for most traits in all research environments, indicating that additive and non-additive gene actions are controlling seedling traits under stress conditions. However, for most traits, SCA was preponderant over GCA in all environments, indicating overdominating effect of non-additive gene action. Which in turn implied that the best improvement method for the traits is hybridization. Inbred TZEI 7 had the best GCA effect for seedling traits under screenhouse conditions and for grain yield and other agronomic traits under drought conditions in the field. Hybrids TZEI 357 × TZEI 411 and TZEI 380 × TZEI 410 showed superior SCA effects under screen house conditions. In conclusion, the study established wide genetic variability for drought tolerance at seedling stage among tropical early-maturing maize germplasm however, the non-additive gene action was more important for most seedling traits.

English

English

Genetic analysis of early-maturing maize (Zea Mays L.) inbred lines under stress and nonstress conditions

ABSTRACTEarly-maturing maize (Zea Mays L.) germplasm developed from diverse sources has the potential for use in developing maize hybrids suitable for increasing maize production in the dry ecologies of eastern Africa. A diallel study was conducted to estimate general combining ability (GCA) of 12 early-maturing maize inbred lines, identify potential single-cross hybrids for use as parents, assess genetic diversity among the inbred lines, and relate genetic distance to specific combining ability (SCA) and hybrid performance. Sixty-six F1 diallel hybrids were evaluated under optimal and drought stress conditions at four locations in Kenya and Uganda. The parental inbred lines were genotyped using 94 single nucleotide polymorphism (SNP) markers. Additive gene action was more important than nonadditive gene action for inheritance of grain yield (GY) under optimal conditions. However, nonadditive gene effects were more important in the inheritance of GY under drought and across all environments. Inbred lines CKL0722, VL058014, and CZL0724 were among the best with positive GCA effects for GY across both optimal and drought stress conditions. The correlation between SCA and both genetic distance and F1 GY was significant under both drought stress and across all environments. Inbred lines with desirable GCA effects for GY and other agronomic traits and hybrids with good performance under both optimal and drought stress conditions are potential parents for development of various types of high-yielding, stress-tolerant, and early-maturing hybrids.

Path Coefficient Analysis of Early Maturing Maize (Zea Mays) Inbred Lines in Central Rift Valley of Ethiopia

This work was executed to work out direct and indirect effects of yield related traits on grain yield by path coefficient analysis in early maturing maize inbred lines. Hence, fifteen inbred lines were crossed in a diallel mating system. Two standard checks along with one candidate variety and hybrids were evaluated in Alpha Lattice Design with two replications at Melkassa Research Center. Path-coefficient analysis indicated that most traits; exerted positive direct effects on grain yield both at genotypic and phenotypic levels on grain yield. This suggests that grain yield could simultaneously be improved by selecting for these traits. In general, this study identified inbred lines and hybrid associations that had desirable expression of important traits. This will be useful for the selection of high yielding and early maturing hybrids for the location.

Heterotic grouping of tropical early-maturing maize inbred lines based on combining ability in Striga-infested and Striga-free environments and the use of SSR markers for genotyping

Identification of heterotic groups among inbreds is crucial to the success of a maize (Zea mays L.) hybrid breeding program. The objectives of this study were to determine the combining ability of 28 early maturing inbreds, classify them into heterotic groups, identify suitable testers under Striga-infested and Striga free environments and to assess the efficiency of three heterotic grouping methods. Three hundred and seventy-eight hybrids derived from diallel crosses of 28 early inbreds along with two checks were evaluated in Striga-infested and Striga-free environments for 2 years at two locations in Nigeria. Twenty-seven of the 28 inbreds were genotyped with 46 polymorphic simple sequence repeats (SSR) markers previously mapped on the 10 maize chromosomes. Analysis of variance revealed highly significant (P<0.01) general combining ability (GCA) and specific combining ability (SCA) mean squares for most traits under test conditions. Based on the SCA effects and heterotic group's specific and general combining ability (HSGCA) for grain yield, four and five heterotic groups were identified under Striga-infested and Striga-free environments, respectively. Two inbreds could not be classified into any of the four groups under Striga-infestation. The SSR markers revealed a wide genetic variability among the inbred lines as the genetic distance ranged between 0.21 and 0.68. Four heterotic groups were identified based on genetic distance (GD) derived from the SSR analysis. Correlation analyses showed that grouping using GD was more consistent with grouping based on SCA under Striga-free than under Striga-infested environments. The HSGCA method was the most effective in classifying early maturing maize inbreds under Striga-infested and Striga free environments. A total of 4 and 8 inbred testers were identified under Striga-infested and Striga-free environments, respectively. These inbred testers are invaluable resources for tropical maize breeding programs.

Identification of early-maturing maize inbred lines based on multiple traits under drought and low N environments for hybrid development and population improvement

Badu-Apraku, B. and Akinwale, R. O. 2011. Identification of early-maturing maize inbred lines based on multiple traits under drought and low N environments for hybrid development and population improvement. Can. J. Plant Sci. 91: 931–942. Drought and low nitrogen stresses are major limiting factors to maize (Zea mays L.) production and productivity in West and Central Africa. Studies were conducted from 2007 to 2009 at three locations in Nigeria under induced drought stress and low nitrogen conditions. The objective was to identify superior inbred lines for use as parents for hybrid production and for introgression into maize breeding populations. The inbreds TZEI 17, TZEI 13, TZEI 23, TZEI 2, TZEI 3, TZEI 22, TZEI 7, TZEI 11, and TZEI 8 were identified as the most promising parents under drought stress. Under low N, TZEI 7, TZEI 11, TZEI 2, TZEI 4, TZEI 10, TZEI 8, and TZEI 22 were selected. TZEI 11, TZEI 2, TZEI 8, and TZEI 22 had combined tolerance to drought stress and low N and could be used as germplasm sources for introgression of tolerance genes as well as for the development of drought and/or low-N-tolerant hybrids. Under drought stress, TZEI 17, TZEI 3, TZEI 23, and TZEI 13 were the closest to the ideal genotype, while TZEI 7, TZEI 2, and TZEI 11 were the closest under low-N conditions.

Inheritance of Resistance to Leaf Freckles and Wilt Caused byClavibacter michiganensesubsp.nebraskensein Early Maturing Maize Inbred Lines

The inheritance of resistance to leaf freckles and wilt was studied in two greenhouse and two field trials of a set of diallel crosses between 10 early maturing maize inbred lines. Inheritance of resistance in six F 2 populations derived from resistant X susceptible and intermediate X susceptible crosses was also studied in the greenhouse and field. General combining ability was much more important than specific combining ability for disease resistance. General combining ability effects were generally consistent between trials, whereas specific combining ability effects were not (...)