effect of brassinosteroids on the morphology, development and yield of field-grown maize

The response of two field-grown inbred lines of maize (Zea mays L.) and their F1 hybrid to the application of 10⁻⁸-10⁻¹⁴ M solutions of 24-epibrassinolide or synthetic androstane analogue of castasterone in V3/4 and V6/7 developmental stages was followed during the vegetative and early reproductive phases of plant development. Brassinosteroids (BRs) significantly affected (either positively or negatively, depending on the genotype and the developmental stage they were applied) the height of plants during the early weeks after their application, but not the final plant height nor the number of leaves. Spraying of plants with BRs in V3/4 developmental stage usually also increased the length of the 7th to 10th leaf, whereas the application in V6/7 developmental stage had the opposite effect. The beginning of the reproductive phase of plant development and the course of flowering was strongly influenced by the application of BRs. Treatment of plants in V3/4 stage delayed and treatment of plants in V6/7 stage advanced the dates of anthesis and silking, regardless of the type of BR used, its concentration or plant genotype. The influence of BRs on the development of the secondary ear was the least pronounced in the F1 hybrid; in both inbred lines it strongly depended on the concentrations of BRs used. Various yield parameters were also affected by treatment of plants with BRs, but this effect depended on the developmental stage during which the application of BRs occured, the plant genotype, the type of BR and its concentration.