Abstract
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 unguiculata
Highlights
The existence of appreciable genotype-by-environment interaction (GxE) presupposes that genotypes would not be consistent across ecologies and as such, a genotype is rarely expected to be the best in all environments as often, best yielders appear in different environments and thereby necessitating groping of genotypes based on adaptation to specific environments (Gauch and Zobel, 1997; Yan et al, 2000; Samonte et al, 2005; Egesi et al, 2007)
This study examined grain production of Cowpea genotypes in locations representing contrasting production environments in the Ogun State and scrutinized the plant and environmental factors implicated in the variability
The treatment accounted for 61.30% of the total sum of squares comprising the largest contribution of 28.70% by the environment while the interaction and genotype fractions captured 20.20% and 12.40% respectively
Summary
Appreciable grain production by cowpea cultivars, with minimal and erratic rainfalls a strong indicator of acceptability by farmers, when such is coupled with concomitant good grain quality. The implication is serious loss in grain yield especially when cultivated variety is not adapted to such stress. A number of reports (Aremu et al, 2007; Ezeaku et al, 2012; Simion et al, 2018) have indicated the possibility of having stable cowpea genotype for cultivation in fairly related ecologies. Some of the stable varieties are more or less average yielders by virtue of having near zero PC1 and often placed around the mean yield line of the G×E biplots (Krisnawati and Adie, 2018; Simion et al, 2018). The existence of appreciable genotype-by-environment interaction (GxE) presupposes that genotypes would not be consistent across ecologies and as such, a genotype is rarely expected to be the best in all environments as often, best yielders appear in different environments and thereby necessitating groping of genotypes based on adaptation to specific environments (Gauch and Zobel, 1997; Yan et al, 2000; Samonte et al, 2005; Egesi et al, 2007)
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