Estimation of Variance Components, Heritability and Genetic Advance of Nitrogen Use Efficiency (NUE) and Yield Traits in Cassava (Manihot esculenta Cranz)

Abstract

This study evaluated 265 diverse cassava genotypes under low and optimum nitrogen conditions using an augmented block design at the National Root Crops Research Institute, Umudike, during the 20202021 cropping season. The objective was to estimate variance components, heritability, and genetic gain for nitrogen use efficiency (NUE) and yield-related traits. The findings showed that environmental variance contributed more to the phenotypic variance of most traits than genetic variance, except for leaf nitrogen content, where genotypic variance accounted for 65.45%. Under low nitrogen conditions, two traits exhibited low genotypic coefficient of variation (GCV), four had intermediate GCV, and six had high GCV. Similarly, under optimum nitrogen, three traits had low GCV, three had intermediate GCV, and six had high GCV. Phenotypic coefficient of variation (PCV) was consistently higher than GCV across all traits. Broad-sense heritability (H2b) was low for six traits under low nitrogen, with the rest showing intermediate or medium heritability. Under optimum nitrogen, eight traits had low heritability, three had moderate heritability, and only leaf nitrogen content exhibited high heritability. Genetic advance as a percentage of mean (GAM) was highest for starch content, indicating strong additive gene effects, especially under both nitrogen regimes (373.69% and 96.77% GAM for low and optimum nitrogen, respectively). The study suggests that direct selection could effectively improve cassava yield traits, particularly starch content, due to the presence of significant additive genetic effects.