Genotype × environment analysis of cowpea grain production in the forest and derived savannah cultivation ecologies

Differential performance of genotypes in different cultivation environments has remained a challenge to farmers and plant breeders, the emphasis being the selection of high yielding and stable genotypes, across similar ecologies. A set of nine cowpea genotypes were  cultivated in Ago-Iwoye and Ayetoro, two locations representing high and moderate moisture zones. Plantings were done with the early and late season rains in Ago-Iwoye and mid-late season rains of Ayetoro. Statistical analysis was done to understand genotype reaction to the different environments and the plant and environment factors mediating the performance. The Additive Main Effect and Multiplicative Interaction (AMMI) model captured 61.30% of the total sum of squares (TSS). The main effects: genotype (G) environment (E) and their interaction (GxE) were significant with the largest contribution of 28.70% by the environment while the interaction and genotype fractionscaptured 20.20% and 12.40%, respectively. The percentage contribution of the main effects and GxE to total sum of squares (TSS) for traits was not consistent. The Genotype plus Genotype-by-Environment (GGE) analysis summarized 91.30% of the variation in genotype performance across environment. The cultivation environments were separated into two, with IT 95M 118 as the vertex genotype in the Ayetoro while TVU 8905 was the topmost genotype in Ago-Iwoye. The two genotypes recorded the highest grain weight per plant (GWPP) but were also the most unstable The stable genotypes IT 95M 120 and IT 86 D 716 flowered relatively late compared to others, are taller, had higher vegetative score and are low grain producers. Key words: AMMI, drought, GGE, stability, Vigna unguiculat

Assessment of heterotic patterns of tropical low-nitrogen–tolerant maize (Zea mays L.) inbred lines using testcross performance, morphological traits and SNP markers

Published online: 30 Sep 2020Breeding efforts in West and Central Africa (WCA) have focused on the development of Low‐N‐tolerant (LNT) maize inbreds and their classification into heterotic groups. This study was conducted to classify LNT maize lines into heterotic groups using testcross performance, morphological and SNP markers and to compare the consistency of groupings by the three methods. Thirty‐six LNT inbreds were crossed to two contrasting inbred testers to generate 72 testcrosses that were evaluated under low‐N conditions in Nigeria in 2014. Also, the 36 inbreds and the two testers were evaluated for per se performance under similar conditions as the testcrosses in 2014 and genotyped in 2015 using 1,123,196 SNP markers. Based on testcross performance, 33 of the 36 LNT inbreds were grouped by the two testers. Morphological characterization from per se performance and genetic relationship by SNP markers classified the inbreds into four groups that were inconsistent with their pedigree. Correlation analysis showed non‐concurrence of the three grouping methods. However, information from these groupings would assist in reducing the number of crosses to be made and evaluated

Heterotic grouping of tropical maize inbred lines and their hybrid performance under stem borer infestation and low soil nitrogen condition in west and central Africa

Published online: 03 Jan 2021Low soil nitrogen (low-N) and stem borer attack are two of the major stresses limiting maize production in West and Central Africa (WCA). Thus, there is need to intensify efforts aimed at identifying inbred lines with resistance and tolerance to these stresses for hybrid development. The objectives of the study were to determine the combining ability of maize inbred lines, classify them into heterotic groups using both conventional and marker-based approaches, compare the efficiency of the different grouping methods and evaluate the performance of the hybrids generated from the inbred lines under contrasting environments. Ten white maize inbred lines with varying levels of resistance to stem borers were selected and crossed in a diallel in 2015. The resulting 45 hybrids were evaluated together with five checks in 10 environments under low-N, artificial stem borer infestation and non-stress conditions in Nigeria. General combining ability (GCA) and specific combining ability (SCA) were highly significant (p ≤ 0.01) for most of the traits studied but GCA was predominant over SCA under each and across research conditions. Inbred line 2 combined significant positive GCA for grain yield with significant negative GCA for traits of resistance to stem borers and tolerance to low-N. Each of the grouping methods classified the inbred lines into 3 heterotic groups but SCA and heterotic groups’ specific and general combining ability had the joint highest breeding efficiency. Hybrids 1 × 4, 2 × 3, 1 × 6 and 2 × 5 were identified to be high yielding and stable across environments and can serve as candidates for further on-farm evaluations and eventual release in WCA

Assessment of genetic diversity among low-nitrogen-tolerant early generation maize inbred lines using SNP markers

Low soil nitrogen (low-N) level is responsible for yield reduction in maize (Zea mays L.) fields in sub-Saharan Africa. A clear understanding of the genetic diversity among early generation inbred lines selected from various elite low-N- tolerant populations offers an opportunity to obtain lines that could be used in parental combinations to develop high-yielding low-N-tolerant maize hybrids. A total of 115 S3 lines derived from four low-N-tolerant populations were assessed for genetic diversity using 15 670 single nucleotide polymorphism (SNP) markers. The SNP markers were highly polymorphic with polymorphic information content ranging from 0.0 to 0.38. The genetic diversity among the inbred lines ranged from 0.0 to 0.50 and thus indicated the high level of dissimilarity among the inbred lines. The neighbour-joining clustering algorithm and model-based population structure classified the 115 lines into four distinct groups that were generally consistent with the genetic backgrounds of the inbred lines. The information obtained from this study revealed genetic diversity among the inbred lines and may guide the selection of potential parents for detailed combining ability studies and eventual use in hybrid combinations. The selected inbred lines would be invaluable in the development of low-N-tolerant hybrids