Herbicides can exert a phytotoxic effect on maize (Zea mays L.) plants. High maize cross-breeds tolerance to herbicides can be obtained by proper selection of parent material. Based on the knowledge of phenotypic signs of damage, it is possible to discard the parents that are the most susceptible to herbicides. The aim of the study wasto compare the response of maize cross-breeds Dumka and Rywal, their parental forms, and lines to bromoxynil – the herbicide belonging to PSII photosynthesis inhibitor group. Herbicide was used at the recommended (400 g ha-1) and double (800 g ha-1) rates. Bromoxynil phytotoxicity was reflected in changes in plant morphological traits,growth inhibition, and green matter reduction of the female parent of cross-breed Dumka and its component S64423- 2. This indication was confirmed in the study of photosynthesis parameters –chlorophyll content and chlorophyll fluorescence in leaves. The cross-breed Rywal and their male parent proved to be tolerant to the bromoxynil.
