The type of gene action conferring combined resistance to maize streak virus (MSV) and maize stripe virus (MStV) was investigated in a Quality Protein Maize (QPM) population, ART/98/SW6-OB. Full-sib and half-sib progenies generated using North Carolina Design I mating scheme were evaluated in 2015 and 2016 in two locations endemic to the viral diseases in Nigeria. Serological study was also conducted on the progenies to validate the disease scores on the field. Significant mean square of

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... es was observed for MSV severity, MStV incidence and severity, plant height and days to flowering, while mean square of environment by females in males' interaction was significant for grain yield and MSV incidence. Estimates of additive variances were larger than dominance variance for grain yield and MSV severity with moderate to high narrow-sense heritability estimates. This indicates that there is adequate genetic variability for improving grain yield and resistance to MSV in the maize population. The mean titre values of MSV and MStV for the progenies were significantly higher than the healthy control. MSV and MStV incidence were negatively correlated to days to 50% silking. Titre values were negatively correlated with grain yield but positively correlated with MSV and MStV incidence. Recurrent selection method that capitalizes on both additive and dominance variances would be effective in improving the population for grain yield and resistance to MSV and MStV diseases.