Genotype by Environment Interaction Effect and Fresh Root Yield Stability of Cassava Genotypes under Contrasting Nitrogen Regimes

Abstract Nitrogen (N) is an important nutrient element needed by cassava for optimum yield and it is a vital component of nucleotides (nucleic acids), enzymes, amino acids (proteins), chlorophyll molecules and hormones, among other essential compounds required for growth and development of cassava. Nitrogen stress is a major cassava production constraint, the study aimed to examine genotype by environment interaction (GEI) effects and fresh root yield stability of 203 diverse cassava clones to identify genotypes with stable performance under low and optimum nitrogen regime across environments using AMMI and GGE biplot analysis. Experiments were conducted using augmented block design with three replications for two years in three locations in Nigeria, under low and optimum N condition. There were significant differences (p<0.001) in the genotype’s mean performances as well as significant differences (p<0.001) in the environments mean performances for all the traits measured in both nitrogen regimes. The AMMI analysis of variance showed significant effects (p<0.001) for genotypes, environments and the interactions for fresh root yield in both nitrogen regimes. The biplot analysis showed that for fresh root yield in the optimum nitrogen regime, the principal component axis 1 explained 61.88% of the total variation while the principal component axis 2 explained 19.66%, which accounted for 81.54% of the G+GE (Genotype plus and Genotype by Environment) variation. For the G+GE for fresh root yield in the low nitrogen regime, axis 1 (50.40%) and axis 2 (21.24) together accounted for a total of 71.64% of the variation. Ten genotypes were identified as the best genotypes under the optimum nitrogen regime, while eleven genotypes were the best genotypes under the low nitrogen regime. Three genotypes under optimum nitrogen regimes were high-yielding but were unstable in their fresh root yield performance across the environments and can be recommended as specifically adapted to the environments they performed best. Three other genotypes were high-yielding genotypes under low nitrogen but were highly unstable in their fresh root yield mean performance across the environments. The environments Otobi_YR1, Igbariam_YR2, and Umudike_YR1 were identified as most discriminatory amongst the test environments. The environments Umudike_YR2 and Igbariam_YR1 were identified as most representative of the test environments and can represent a mega-environment.