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A major QTL affecting root traits and leaf ABA concentration was identified in maize (Zea mays L.) and named root-ABA1. For this QTL, back-cross-derived lines (BDLs) homozygous either for the (+) or for the (-) allele increasing or decreasing, respectively, root size and leaf ABA concentration, were developed. This study was conducted to evaluate the QTL effects in various genetic backgrounds and at different water regimes. The (+/+) and (-/-) BDLs were crossed with five or 13 inbred tester lines of different origin, thus producing two sets of test-crosses that were evaluated in Italy and China, respectively. Testing was conducted under both well-watered and water-stressed conditions. In Italy, the test-crosses derived from (+/+) BDLs, as compared with those derived from (-/-) BDLs, showed, across both water regimes, higher leaf ABA concentration (on average 384 versus 351 ng g(-1) DW) and lower root lodging (28.0 versus 52.5%), and lower grain yield under water-stressed conditions (4.88 versus 6.27 Mg ha(-1)). In China, where root lodging did not occur, the test-crosses derived from (+/+) BDLs were less productive at both water regimes (on average, 6.83 versus 7.49 Mg ha(-1)). The lower grain yield of the test-crosses derived from (+/+) BDLs was due to a lower number of ears per plant and to lower kernel weight. The results indicate that the (+) root-ABA1 allele confers not only a consistently lower susceptibility to root lodging but also a lower grain yield, especially when root lodging does not occur.

Abscisic acid (ABA) concentration can affect plant responses to drought and has been suggested as a selection criterion to improve drought tolerance. Divergent selection for high (H) and low (L) leaf ABA concentration was conducted under moderate drought conditions in the F2 of maize (Zea mays L.) single crosses Os420 × IABO78 and Mo17 × B88. Objectives of this study were to evaluate direct and correlated responses to the divergent selection. For each cross, the F2 and the H‐ and L‐populations (H‐P and L‐P) were compared. For Os420 × IABO78, the comparison was made in one location, for 2 yr, and at three irrigation volumes (corresponding to 0, 60, and 120% of crop evapotranspiration). At all irrigation volumes, H‐P exceeded L‐P for leaf ABA concentration, drought sensitivity, leaf temperature, silk delay, and lodging resistance, while it showed lower plant height and grain yield (on average, 3.61 vs. 5.14 Mg ha−1). The F2 was intermediate for most traits. Significant differences were not detected for water status traits. For Mo17 × B88, populations were compared at one irrigation volume (60% of evapotranspiration) in three environments. In all environments, H‐P was superior to L‐P for leaf ABA concentration and drought sensitivity, and it was shorter, and less productive (on average, 4.71 vs. 6.95 Mg ha−1). The F2 was intermediate for leaf ABA concentration but not for grain yield. Results indicate that selection for low leaf ABA concentration led to populations with better agronomic performance than did selection for high leaf ABA concentration.

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