Ovary abscisic acid concentration does not induce kernel abortion in field-grown maize subjected to drought

This study investigated the effects of drought of different duration and severity on ovary abscisic acid (ABA) concentration and yield components in field-grown maize (Zea mays L. cv. Loft). The study was conducted in a field lysimeter of the Royal Veterinary and Agricultural University (KVL) in Hojbakkegaard (55 degrees C40'N; 12 degrees C18'E; 28 masl), Denmark in 1997. Irrigation was withheld at four different dates to induce drought of different duration and severity at the reproductive stage of the plants. Plots were re-watered shortly after silking and kept at field capacity for the remainder of the season. Soil water status, plant height, and early morning leaf water potential were monitored during the treatment. Ovary ABA concentration was determined at four dates before and after fertilization. Final grain yield, total DM, harvest index (HI), mean kernel weight, kernel weight distribution, and kernel number per cob were determined at maturity. Plant height was significantly (P < 0.05) reduced by 40 and 25%, respectively, in the two most severe drought treatments. In the two shorter drought treatments no effect of drought stress on plant height or biomass was observed. Leaf water potential decreased slowly as a function of relative available soil water content and resulted in -0.4 MPa at the end of the longest and -0.12 MPa at the end of the shortest stress period. Under fully watered conditions, plot yields averaged 1400 g m(-2) for total dry matter (DM) and 700 g m(-2) for grain yield, with a HI of about 0.5. Initiation of a drying cycle close to flowering did not change yields. Long drying cycles resulted in significant (P < 0.05) yield reductions up to 70% of the fully watered controls. Kernel number per cob was reduced up to 60% under long drought conditions and not affected under short-term drought. Drought imposed about two weeks prior to fertilization resulted in 30% reduction in kernel number per cob, but this effect was balanced by an increase of 25% in mean kernel weight. Long and severe drought increased ovary ABA concentration prior to fertilization, whereas short-term drought did not. At fertilization no increase of ovary ABA as compared to fully watered controls was found in any treatment. It is concluded that drought induced grain yield losses in field grown maize cannot be attributed to kernel size reduction or kernel abortion due to ovary ABA concentrations as reported by some authors for studies on maize and wheat under controlled conditions, as ovary ABA concentrations peaked before zygote formation and endosperm development.