Water‐use efficiency of maize may be increased by the plant growth regulator paclobutrazol

Abstract Contradictory results of the paclobutrazol (PAC) effect on maize plants were obtained under semiarid compared to well‐watered conditions with grain yield improvements versus depressions, respectively. In addition, maize cultivars differed in their reactions to similar PAC dosages. Thus, in the present study PAC was applied in the appropriate dosage at growth stage V5 to six maize cultivars ( Zea may s L. cvs. Amanova, Severeen, Hubble, Galactus, Fabregas, Pioneer 3906) grown in a container experiment under well‐watered conditions. PAC caused significant decreases in plant height, increases in culm diameter and reduced transpiration rates in comparison with the untreated control plants. At anthesis, start and duration of pollen production, start of silking and anthesis‐silking interval (ASI) were mostly unaffected by PAC application. Senescence of PAC‐treated plants was delayed by one week. Apart from cultivar Galactus, PAC treatment caused significant grain yield reductions between 9% and 20%, which were solely based on decreases in kernel number because higher single kernel weights were obtained. In all cultivars, reductions in straw yield of 28% to 49% were achieved with PAC application, which were responsible for significant improvements of the harvest index by 8%–36%. PAC‐treated plants showed reduced water consumption (11%–21%), resulting in significantly improved WUE grain during the critical period of kernel setting of the cultivars Amanova, Severeen, Galactus and Fabregas. The results indicate that PAC treatment of maize plants bears several advantages such as reduced water demand and improved water‐use efficiency (WUE), higher mechanical strength of the stalk and an enhanced harvest index. Possible grain yield decreases per plant under well‐watered conditions could be counteracted by moderate increases in plant density, yet concurrently this might diminish some of the beneficial PAC effects.