Selection for drought tolerance increases maize yields across a range of nitrogen levels

It is not known whether selection for improved tolerance to a specific abio tic stress leads to correlated changes in performance under other stresses. Drought and N deficiency are important constraints to production in the tr opics. We examined the effect of selection for drought tolerance on perform ance of tropical maize (Zea mays L.) under a range of N levels. Original an d advanced selections of four populations, improved for tolerance to midsea son drought for two to eight recurrent selection cycles each, were evaluate d in two experiments under severe N stress, one experiment under medium N s tress, and two well-fertilized experiments. Nitrogen accumulated in the abo veground biomass at maturity averaged 52 63, 105, 151, and 163 kg N ha(-1) in the five experiments, and grain yields of 3.0, 2.9, 5.2, 6.0, and 6.5 Mg ha(-1) were obtained. Selection for tolerance to midseason drought stress increased grain yields by an average of 86 kg ha(-1) yr(-1) with nonsignifi cantly larger gains under severe N stress (100 kg ha(-1) yr(-1)). Drought-t olerant selections had increased biomass and N accumulation at maturity, th e changes being largest under severe N stress. Additionally, drought-tolera nt selection cycles were associated with delayed leaf senescence and an inc reased or unchanged N harvest index, indicating that leaf N was used more e fficiently for grain production. Selection for tolerance to midseason droug ht stress appears to increase grain yield across a range of N stress levels and may lead to morphological and physiological changes that are of partic ular advantage under N stress.