GENETIC AND ENVIRONMENTAL-EFFECTS ON ALBSCISIC ACID ACCUMULATION IN LEAVES OF FIELD-GROWN MAIZE

This study analyzes the components of phenotypic variation for abscisi c acid (ABA) content in maize (Zea mays L.) leaves and the correlation s with drought sensitivity index (DSI) and silk delay (SD), involved i n the reaction to water deficit. Eight early- and seven medium-maturit y inbreds were examined in field trials: in 1990 with low irrigation v olume and in 1991 with low and high irrigation volumes. ABA concentrat ion and DSI were investigated at growth stages (S) corresponding to st em elongation (S3), appearance of the first husks (S4), and mid-end of silking (S5). The ABA concentration was significantly higher in condi tions of water deficit and in the later growth stage. The genetic comp onent for ABA concentration attained higher relative values than those shown by DSI in the same growth stages and by SD; moreover, it increa sed from growth stage 3 to stage 5. The genotype x year and genotype x irrigation volume interactions were smaller for ABA concentration tha n for DSI and SD. The broad sense heritability on a plant basis, estim ated in drought conditions, for ABA concentration ranged from 21.4 to 55.1% according to maturity group and growth stage. A wide variation w as observed among lines for ABA concentration: the medium-maturity gro up showed a three-fold range (from 219 to 605 ng ABA g(-1) dry weight) . No clear relationships between ABA concentration, DSI and SD were fo und. These results indicate the feasibility of a selection for ABA con centration within segregating populations derived from crosses between the inbred lines herein tested.