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Genetic Variation and Genotype x Environment Interaction for Yield and Other Agronomic Traits in Cassava in Nigeria

^a National Root Crops Res. Inst. (NRCRI), Umudike, PMB 7006, Umuahia, Abia State, Nigeria
^b Int. Inst. for Tropical Agric. (IITA), Oyo Rd., PMB 5320, Ibadan, Oyo State, Nigeria

^* Corresponding author (cegesi{at}yahoo.com)

Received for publication October 19, 2006. The identification of superior genotypes and mega-environments on the basis of multiple traits is a key objective of multi-environment trials in cassava (Manihot esculenta Crantz). The objective of this study was to examine the genetic variation and genotype x environment interaction (GEI) effects for fresh root yield, six other agronomic traits, and severity ratings for cassava mosaic disease (CMD) and cassava green mite (CGM) in 40 genotypes of cassava. Experiments were conducted using a randomized complete-block design with four replications for 2 yr in three representative agro-ecological zones in Nigeria. Site regression (SREG) analysis revealed that GEI was a major source of fresh root yield variation and the different testing sites discriminated among the genotypes. Genotypes TMS 98/0581, TMS 97/4763, TMS 98/0002, TMS 99/3073, and M98/0068 were highest yielding at Otobi and Umudike, whereas TMS 98/0510, TMS 97/4779, and TMS 92B/00068 yielded the most at Ishiagu. TMS 98/2226, TMS 92/0325, and M98/0028 had the poorest performance across all locations. Genotypes with the highest yield showed the lowest CMD scores, whereas very tall (well above 2 m) plants had low harvest index on the basis of multiple trait analysis. We identified optimally adapted genotypes for commercial cassava production in different areas in Nigeria.

Abbreviations: CGM, cassava green mite severity • CMD, cassava mosaic disease severity • E, environment main effect • G, genotype main effect • GEI, genotype x environment interaction • GGE, genotype plus genotype x environment interaction • GL, genotype x location interaction • GT, genotype x trait interaction • GY, genotype x year • GYL, genotype x year x location interaction • L, location main effect • MET, multi-environment trials • PC, principal component • SREG, site regression • Y, year main effect • YL, year x location interaction