The present study was designed to estimate the effects of the mutant su1 on the genetic regulation of fitness-related traits when introgressed into field maize backgrounds. Estimated genetic effects of agronomic traits in Su1 v. su1 plants were monitored in two separate mean generation designs. The first involved unrelated inbred lines EP42 and A631, while two Corn Belt inbred lines, A619 and A632, were used for the second design. Parents, F1s, F2s and backcrosses were crossed to the su1 inbred P39 as the donor of su1 and the 12 crosses were successively self-pollinated for 5 years. For each cross, Su1 and su1 kernels were evaluated separately in a growth chamber under controlled environmental conditions following a randomized complete block design. In addition, the genotypes were evaluated in field trials in 10 × 10 triple lattice designs during 2010 and 2011 at Pontevedra in north-western Spain; and in 2010 at Algiers, located in the sub-humid North of Algeria. The performance of su1 plants was lower when compared to the Su1 plants for all traits evaluated in both designs and across environments. The estimates of genetic effects of Su1 v. su1 plants were strongly affected by genotype and environment. The results suggest that, depending on specific sweet × field maize interaction, seedling vigour and, particularly, chlorophyll content (CCM) were the most critical traits in determining su1 viability. However, the complexity of the genetic regulation of emergence and the great heterogeneity of environmental conditions in the field evaluation prevent the estimation of the genetic regulation on sugary1 fitness.