Genetic Gains of Grain Yield among the Maize Cultivars Released over a Century from the National Breeding Program of Zimbabwe

Abstract

Monitoring genetic gain is required in crop improvement programs in order to assess the effectiveness of breeding initiatives. The periodic measurement of genetic gain will quantify the efficiency of new technologies incorporated into the program. Here, a total of 24 cultivars (20 released from Zimbabwe’s National Breeding program (ZNBP) plus 4 released by the largest and oldest private seed company in Zimbabwe, Seed Co) over the period of 1900–2016, were evaluated across 10 locations in Zimbabwe. The testing locations represented agro-ecologies where maize is optimally grown and where maize production is under threat from climate change-induced abiotic stresses, particularly drought and heat stress, in Zimbabwe. The 24 cultivars were laid out across all the locations using the alpha (0.1) lattice design replicated two times with six incomplete blocks nested in each of the replicates. The genetic gains were estimated at 61 kg ha−1 yr−1, 25 kg ha−1 yr−1, 6 kg ha−1 yr−1, and 2 kg ha−1 yr−1 under optimal, random drought stress, heat stress, and managed drought stress conditions, respectively. The results were comparable with those from other studies where newly released cultivars yielded more than old cultivars. Overall, the results demonstrated that over a century, the ZNBP has been making significant progress in yield increments in its maize genotypes.