Genetic diversity among early provitamin A quality protein maize inbred lines and the performance of derived hybrids under contrasting nitrogen environments

Open Access JournalInformation on population structure and genetic diversity of germplasm in a breeding programme is useful because it enhances judicious utilisation of genetic resources to achieve breeding objectives. Seventy early maturing provitamin A (PVA) quality protein maize (QPM) inbreds developed by the IITA- maize improvement programme were genotyped using 8171 DArTseq markers. Furthermore, 96 hybrids derived from 24 selected inbreds plus four checks were evaluated under low-N and optimal environments in Nigeria during 2016 and 2017. Genotypic and phenotypic data of inbreds and hybrids respectively, were analysed to (i) assess the level of genetic dissimilarities and population structure of the inbreds, and (ii) investigate the grain yield performance of derived hybrids under low-N, optimal and across environments

Genetic analysis of grain yield and agronomic traits of early provitamin A quality protein maize inbred lines in contrasting environments

Open Access Article; Published online: 17 Oct 2019Early-maturing provitamin A (PVA) quality protein maize (QPM) hybrids with combined drought and low soil nitrogen (low-N) tolerance are needed to address malnutrition and food security problems in sub-Saharan Africa (SSA). The current study's objectives were to (i) examine combining ability of selected early maturing PVA-QPM inbreds for grain yield and other agronomic traits under drought, low-N, optimal environments and across environments, (ii) determine gene action conditioning PVA accumulation under optimal environments, (iii) classify inbreds into heterotic groups and identify testers and (iv) assess yield and stability of hybrids across environments. Ninety-six hybrids generated from 24 inbred lines using the North Carolina Design II together with four commercial hybrid controls were evaluated under drought, low-N and optimal environments in Nigeria in 2016 and 2017. Fifty-four selected hybrids were assayed for PVA carotenoid and tryptophan content. Additive genetic effects were greater than non-additive effects for grain yield and most agronomic traits under each and across environments. The gene action conditioning accumulation of PVA carotenoids under optimal growing conditions followed a pattern similar to that of grain yield and other yield-related traits. The inbred lines were categorized into four heterotic groups consistent with the pedigree records and with TZEIORQ 29 identified as the best male and female tester for heterotic group IV. No tester was found for the other groups. Hybrid TZEIORQ 24 × TZEIORQ 41 was the highest yielding and most stable across environments and should be further tested for consistent performance for commercialization in SSA

Genetic diversity, population structure and inter-trait relationships of combined heat and drought tolerant early-maturing maize inbred lines from west and central Africa

Open Access Journal; Published online: 04 Sept 2020Adequate 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

Phenotypic characterization and validation of provitamin A functional genes in early maturing provitamin A-quality protein maize (Zea mays) inbred lines

Open Access Article; Published online: 20 Dec 2019The number of drought and low‐N tolerant hybrids with elevated levels of provitamin A (PVA) in sub‐Saharan Africa could increase when PVA genes are optimized and validated for developed drought and low‐N tolerant inbred lines. This study aimed to (a) determine the levels of drought and low‐N tolerance, and PVA concentrations in early maturing PVA‐quality protein maize (QPM) inbred lines, and (b) identify lines harbouring the crtRB1 and LcyE genes as sources of favourable alleles of PVA. Seventy early maturing PVA‐QPM inbreds were evaluated under drought, low‐N and optimal environments in Nigeria for two years. The inbreds were assayed for PVA levels and the presence of PVA genes using allele‐specific PCR markers. Moderate range of PVA contents was observed for the inbreds. Nonetheless, TZEIORQ 55 combined high PVA concentration with drought and low‐N tolerance. The crtRB1‐3′TE primer and the KASP SNP (snpZM0015) consistently identified nine inbreds including TZEIORQ 55 harbouring the favourable alleles of the crtRB1 gene. These inbreds could serve as donor parents of the favourable crtRB1‐3′TE allele for PVA breeding in maize

Gains in grain yield of extra-early maize during three breeding periods under drought and rain-fed conditions

Open Access Article; Published online: 30 Aug 2018Drought is a key maize (Zea mays L.) production constraint in sub-Saharan Africa. Fourteen, fifteen, and twenty-five extra-early maturing maize cultivars, with varying Striga resistance and drought and low soil N tolerance, were developed from 1995 to 2000 (Period 1), 2001 to 2006 (Period 2), and 2007 to 2012 (Period 3), respectively. The objectives of this study were to examine yield gains in the cultivars and to investigate inter-trait relationships and yield stability under six drought and 17 rainfed conditions in West Africa from 2013 to 2016. Annual rate of yield increase across cultivars was 0.034 (3.28%) and 0.068 Mg ha−1 (2.25%), whereas yield gains per period were 0.17 and 0.38 Mg ha−1 under drought and rainfed environments, respectively. Yield gains under drought and rainfed environments were related to prolonged flowering period, increased plant and ear heights, improved stalk lodging, and ear and plant aspects, whereas delayed leaf senescence and increased number of ears per plant accompanied yield improvement under drought only. Ear aspect and number of ears per plant were primary contributors to yield and could be used as selection criteria for yield enhancement under drought and rainfed conditions. High-yielding and stable cultivars across all environments based on additive main effects and multiplicative interaction (AMMI) biplot included ‘2004 TZEE-Y Pop STR C4’ and ‘TZEE-W Pop STR BC2 C0’ of Period 2 and ‘2009 TZEE-W STR’, ‘TZEE-Y STR 106’, ‘TZEE-W STR 107’, and ‘TZEE-W DT C0 STR C5’ of Period 3. These cultivars could be commercialized to improve food self-sufficiency in sub-Saharan Africa

Genetic diversity of provitamin-A cassava (Manihot esculenta Crantz) in Sierra Leone

Open Access Article; Published online: 04 Mar 2020Understanding the genetic diversity among accessions and germplasm is an important requirement for crop development as it allows for the selection of diverse parental combinations for enhancing genetic gain in varietal selection, advancement and release. The study aimed to characterize 183 provitamin A cassava (Manihot esculenta Crantz) accessions and five Sierra Leonean varieties using morphological traits, total carotenoid content and SNP markers to develop a collection for conservation and further use in the cassava breeding program. Both morphological parameters and 5634 SNP markers were used to assess the diversity among the provitamin-A cassava accessions and varieties. Significant differences were observed among the accessions for most of the traits measured. The first five PCs together accounted for 70.44% of the total phenotypic variation based on yield and yield components among the 183 provitamin-A cassava accessions and five Sierra Leonean varieties. The present study showed that provitamin-A cassava accessions in Sierra Leone have moderate to high diversity based on morphological and molecular assessment studies. The similarity index among the 187 and 185 cassava accessions grouped them into 6 and 9 distinct clusters based on morphological and molecular analyses, respectively. A significant positive, but low correlation (r = 0.104; p\0.034), was observed between the two dendrograms. The results obtained will serve as a guide and basis of germplasm management and improvement for total carotenoid content, yield and African cassava mosaic disease resistance in Sierra Leone

Genetic analysis of gain yield of IITA and CIMMYT earlymaturing maize inbreds under Strigainfested and lowsoil nitrogen environments

Accepted paper, posted 17 November, 2014Breeding maize (Zea mays L.) hybrids resistant to Striga and tolerant to low soil nitrogen (low-N) will reduce grain yield losses due to stresses in West Africa (WA). Studies were conducted to determine if selection for Striga resistance and/or drought tolerance in early-maturing maize populations improved low-N tolerance in hybrids derived from selected inbreds from International Institute of Tropical Agriculture (IITA) and International Centre for Maize and Wheat Improvement (CIMMYT) under Striga-infested, low-N and optimum environments in Nigeria. One hundred and fifty hybrids developed from crosses involving 30 lines using North Carolina Design II plus six checks were evaluated at two locations each under low-N, artificial Striga infestation, and optimum environments for 2 yr. Lines with combined resistance or tolerance to Striga as well as low-N were identified. Striga-resistant– as well as low-N–tolerant hybrids with outstanding performance under both stress environments could be obtained through the accumulation of favorable alleles for resistance or tolerance in both parental lines. Although selection for Striga resistance and/or drought tolerance resulted in improved performance of genotypes under low-N, it is important to test genotypes under low-N to identify those with outstanding performance under the target stress. ENT 11 × TZEI 4 and TZEI 65 × ENT 11 were identified as the most stable and high-yielding hybrids

Analysis of phenotypic stability in 25 cowpea genotypes across six environments

Twenty-five cowpea (Vigna unguiculata L) genotypes were evaluated across six contrasting environments for phenotypic yield stability. Combined analysis of variance revealed significant differences among the genotypes and the main effects. A1B×D, BC×M, L1B×M, A1B×M, and BA×I were the best performing and stable genotypes. The non-parametric analysis showed that genotype IT93K-503-1 had the highest yield and BC×D had the lowest yield. Shukla stability analysis revealed Beledi A and Dan lla as the most stable across test environments and genotypes A1B×D, BC×M and BA×I were good performers. The coefficient of variability graphical approach showed that genotypes BC×I, A1B×M, A1B×D, Dan lla, TA×M, Mouride, L1B×I, BC×M and L1B×D were high yielding. This implies they would do well across the testing sites. However, genotype IT93K-503-1 should be promoted for cultivation in drought-prone environments

Genetic variances and heritabilities of early yellow maize population following cycles of improvement for Striga resistance and drought tolerance

Drought and Striga are principal constraints to maize production in sub-Saharan Africa. An early yellow maize population, TZE-Y Pop DT STR that had undergone five cycles of selection for resistance to Striga, followed by three cycles of improvement for drought tolerance was investigated for yield gains, changes in genetic variances and interrelationships among traits under drought-stress and optimum environments. Two hundred and forty S1 lines comprising 60 each from the base population and subsequent populations from three selection-cycles improved for grain yield and drought tolerance, were assessed under drought and optimal environments in Nigeria, 2010 – 2012. Genetic improvements in grain yield of 423 and 518 kg ha-1 cycle-1 were achieved under drought-stress and optimum environments. Predicted improvements in selection for yield were 348 and 377 kg ha-1 cycle-1 under drought-stress and optimum environments, respectively. The highest yield observed in C3 was accompanied by reduced days to silking, anthesis-silking interval, improved plant aspect, ear aspect, and increased plant height and ears per plant across research environments as well as improved stay green characteristic under drought. The level of genetic variability for yield and some few other traits were maintained under drought and optimal environments in the population. Presence of residual genetic variability for yield and other assayed traits in C3 indicated that progress could be made from future selection in the population depending on the ability of breeders to identify outstanding genotypes and precision level of experimentation. Substantial improvement has been made in yield and drought tolerance in C3 of population

Genome-wide association study reveals genetic architecture and candidate genes for yield and related traits under terminal drought, combined heat and drought in tropical maize germplasm

Open Access Journal; Published online: 15 Feb 2022Maize (Zea mays L.) production is constrained by drought and heat stresses. The combination of these two stresses is likely to be more detrimental. To breed for maize cultivars tolerant of these stresses, 162 tropical maize inbred lines were evaluated under combined heat and drought (CHD) and terminal drought (TD) conditions. The mixed linear model was employed for the genome-wide association study using 7834 SNP markers and several phenotypic data including, days to 50% anthesis (AD) and silking (SD), husk cover (HUSKC), and grain yield (GY). In total, 66, 27, and 24 SNPs were associated with the traits evaluated under CHD, TD, and their combined effects, respectively. Of these, four single nucleotide polymorphism (SNP) markers (SNP_161703060 on Chr01, SNP_196800695 on Chr02, SNP_195454836 on Chr05, and SNP_51772182 on Chr07) had pleiotropic effects on both AD and SD under CHD conditions. Four SNPs (SNP_138825271 (Chr03), SNP_244895453 (Chr04), SNP_168561609 (Chr05), and SNP_62970998 (Chr06)) were associated with AD, SD, and HUSKC under TD. Twelve candidate genes containing phytohormone cis-acting regulating elements were implicated in the regulation of plant responses to multiple stress conditions including heat and drought. The SNPs and candidate genes identified in the study will provide invaluable information for breeding climate smart maize varieties under tropical conditions following validation of the SNP markers