Understanding the genetic control of agronomic traits is important in designing crop improvement programs. Study was conducted to analyse the genetic control of root length under water stress. A full diallel cross of four spring wheat lines, along with their F₁ progenies was evaluated under –0.82 MPa water stress in a hydroponic culture. Analysis of variance showed highly significant (P < 0.01) difference among the parental lines and their F₁ progenies. Genotypes Santa Elena, Colotana 296–52 and Pato showed comparable longer roots whereas Tincurrin grew significantly (P < 0.05) shorter roots. Genotypes with long roots were found to have more dominant genes than those with shorter roots. Both general and specific combining abilities were highly significant (P < 0.01) indicating the importance of additive and dominant gene effects in the control of root length under water stress. Genotype Santa Elena was found to be the best general combiner whereas the specific cross Santa Elena × Pato was the best hybrid. Moderate narrow-sense heritability (38%) was observed indicating the possibility of improving root length under water stress. The highly significant specific combining ability value (dominant genetic control) suggests that genotypes with more dominant genes should be selected as parents for hybridisation and the hybrid wheat approach might be helpful in improving water stress resistance.