G×E Interaction Effects on Yield and Yield Components of Landraces and Improved Cassava Genotypes in the Savanna Regions of Nigeria

Genetic enhancement of cassava aimed at increasing production and productivity through the provision of broad-based improved germplasm is a major goal for Cassava breeders. At IITA, Nigeria, eighteen varieties comprising twelve landraces and six broad-based and improved varieties were evaluated at four locations in 3 years in a randomized complete block design in four replicates to determine variability among cultivars for yield components and adaptation to different environments. Results showed fresh root yield was significantly correlated (P<0.001) with number of roots, harvest index, shoot weight and number of stands harvested. AMMI analysis partitioned main effects into genotypes, environments and G×E with all the components showing highly significant effects (P<0.001). Environment had the greatest effect (70.3%), G×E interaction (19.0%) and genotype(10.7%). AMMI1 and unadjusted means selected the same winner in nine out of twelve environments (75%), but differently in three environments. The GGE biplot (E and G×E interaction) delineated environments into three mega-environments. Cultivar 4(2)1425 (moderately yielding) was the most stable and specifically adapted to Zaria. ABBEY-IFE, ATU-IWO and 2ND-AGRIC though moderately yielding were highly tolerant to CMD, suggesting a rich resource within the germplasm that could be enhanced for further genetic improvement of the crop.