ABSCISIC-ACID CONCENTRATION IN MAIZE LEAVES - GENETIC-CONTROL AND RESPONSE TO DIVERGENT SELECTION IN 2 POPULATIONS

The genetic control of abscisic acid (ABA) concentration in the leaf a nd the direct and correlated responses to divergent selection for this trait were investigated in maize (Zea mays L.) populations obtained f rom the single crosses Os420 x IABO78 and Mo17 x B88 grown under droug ht conditions. Generation means analysis indicated that. the genetic v ariability in Os420 x IABO78 was mainly due to additive and dominance effects while in Mo17 x B88 significant digenic interactions were also detected. Broad sense heritability was 0.41 in Os420 x IABO78 and 0.3 7 in Mo17 x B88. Leaf ABA concentrations al anthesis in the F-3 progen ies selected for high ABA (H-ABA-F-3) and for low ABA (L-ABA-F-3) were 491 and 350 ng ABA g(-1) dry wt in Os420 x IABO78 and 345 and 305 ng ABA g(-1) dry wt in Mo17 x B88, respectively. In Os420 x IABO78, the H -ABA-F-3 showed later flowering, larger ear leaf, higher drought susce ptibility, and lower grain yield than L-ABA-F-3 (2.67 vs. 3.64 Mg ha(- 1)). In Mo17 x B88, the H-ABA-F-3 were characterized by larger ear lea f, higher drought susceptibility, and higher yield than L-ABA-F-3 (4.2 6 vs. 3.37 Mg ha(-1)). In Mo17 x B88, after a second cycle of selectio n, the difference between the H-ABA-F-4, and L-ABA-F-4 was 112 ng ABA g(-1) dry wt. The H-ABA-F-4 were also characterized by later flowering , shorter plants, higher drought susceptibility, and lower grain yield than L-ABA-F-4 (1.91 vs. 2.18 Mg ha(-1)). The contrasting results obs erved for yield difference between the two selected groups in the F-3 and F-4 generations could be related to the different dynamics of the drought episodes which occurred in the two years of evaluation. Althou gh our results indicate the feasibility of selecting for leaf ABA conc entration in field-grown maize, it seems unlikely that this trait can be adopted as a general selection criterion to improve maize yield und er drought.