Divergent selection for osmotic adjustment results in improved drought tolerance in maize (Zea mays L.) in both early growth and flowering phases

The value of the capacity for osmotic adjustment (OA) as a trait, which can contribute effectively to yield maintenance under drought, has not yet been established for maize (Zea mays L.) using cultivars of similar genetic background. Here we report results obtained using crops of two S4 populations derived from a cross between inbred lines exhibiting the highest and lowest capacities for osmotic adjustment in a screening applied to 20 inbred lines. The mean values of OA for the two S4 populations were 0.47 MPa for the high OA population (HOA) and 0.06 MPa for the low (LOA). Crops of these populations were grown under a rain-out shelter and subjected to 30-day droughts either before or during flowering. In both experiments, exposure to drought evoked a significant (p < 0.05) decrease in osmotic potential measured at full turgor in the HOA population, no change was found in the LOA population. This induced response became evident in plants of the HOA population in measurements effected 16-18 days after suspension of irrigation. Irrespective of the timing of drought, the HOA crops extracted significantly more water from deeper in the soil profile during the stress period, exhibited higher leaf area duration and attained Greater grain yields and, in the crop droughted at flowering, greater harvest index than the LOA crops. The components of yield and their determinants (i.e., floret number per ear, grain set, grain number and weight per grain) exhibited differential responses with timing of the drought and in response to level of OA. Under irrigation, there were no differences between populations in either experiment in terms of yield and its components, or in harvest index, leaf area duration, or soil water extraction. We conclude that OA can contribute to drought tolerance in maize crops exposed to water deficit both before and during flowering, and that the trait carries no yield penalty under irrigation. (c) 2005 Elsevier B.V. All fights reserved.