STRESS AND USE OF HERBICIDES IN FIELD CROPS

When herbicides are combined under natural conditions or applied in stress conditions (drought, for instance), the efficiency of their action may decrease which results in considerable yield losses. The reason thereto is that another herbicide or stressor can trigger the adaptation mechanism in weed plants, and they survive, resulting in weed infestation. In particular, it applies to such herbicides as acetyl-CoA-carboxylase inhibitors or socalled graminicides, which are effective only for grass weeds control. The efficiency of this groups of herbicides is heavily dependent on the environment and often decreases when combined with herbicides, efficient against dicotyledon weeds. It turns out that this occurs due to the fact their final phytotoxicity is not determined at the level of the site of action (herbicide target) but depends on the stage of herbicide-induced pathogenesis - processes, occurring due to the interaction between the herbicide and its site of action. The stress response of the weeds may make its contribution into herbicide-induced pathogenesis. Plants are known to respond to the action of various abiotic stressors in the form of non-specific stress response and depending on the intensity and duration of the stressor's action, a plant either adapts or dies. At present there are sufficient data, demonstrating that programmed cell death (PCD) is involved in the herbicide-induced pathogenesis. Reactive oxygen species (ROS) induce PCD in specific classes of herbicides. The participation of ROS and PCD in herbicide-induced pathogenesis allows for targeted effects on the phytotoxic action of herbicides, for instance, via combined application of herbicides with possible PCD inducers and prooxidants. The confirmation of the role of nonspecific response in the development of phytotoxic action of herbicides is found in the phenomena of cross adaptation (activation of antioxidant defense) and cross-synergism (activation of oxidative stress) under the application of herbicides. Based on our own research and literature data, the importance of cross-adaptation and cross-synergism in applying herbicides in drought conditions and to determine the nature of the interaction in herbicide complexes is discussed. In particular, the review discusses the reduction of phytotoxicity of the ACCase herbicides due to the phenomenon of cross-adaptation in drought conditions and in combination with herbicides, which are acetolactate synthase inhibitors. The results of investigations were presented about the reduction of antagonism in the mixtures of herbicides, which are ACCase and ALS inhibitors, because of the use of substances with prooxidant properties, as well as the inhibitor of the antioxidant enzyme superoxide dismutase. On the other hand, we analyzed the possibility of increasing the phytotoxic effect of herbicides, ACCase inhibitors, in combination with herbicides with prooxidant properties - inhibitors of electron transport in Photosystem 2 (FS 2) chloroplasts and protoporphyrinogen oxidase (PROTOX) inhibitors. It became the foundation for the elaboration of efficient herbicide compositions for wheat and onion fields. While combining herbicides, the issue of synergism is becoming relevant due to the problem of the spread of target-site resistance, since, to prevent this type of resistance, it is necessary to combine herbicides with different mechanisms of phytotoxicity. The presented data demonstrate that the increased activity of antioxidant defense systems, which is the result of a long process of evolutionary adaptation of weeds to the action of abiotic stressors, is an element of non-target-site-based resistance to herbicides. Possible ways to prevent the negative impact of non-specific stress response on the efficiency of herbicides, as well as the prospects of the chemical method of weeds control are discussed.

Automated summary

Combining herbicides under natural or stress conditions may lead to decreased efficiency and activation of adaptation mechanisms in weed plants, causing weed infestation. The final phytotoxicity of herbicides depends on the interaction between the herbicide and its site of action, with stress response potentially contributing to herbicide-induced pathogenesis.