Eustressors to Improve Plant Secondary Metabolites Production: Insect Frass and Physical Factors as Examples Applied in Agriculture and Horticulture

The effect of stressors on plants has been studied for years and currently, they are initiated to be studied based on the hormesis phenomenon because of the possibility of finding improvement (eustressors) in the growth and development of different crops. Eustressors can be classified as chemical, biological (also called “elicitors”), or physical, and the controlled elicitation of crops may result in higher production of secondary metabolites, an increase in fruit yield, and tolerance to environmental stresses. Among the different types of biological eustressors, currently those originating from residues from insect rearing called “frass” has become an interesting possibility to be evaluated as an elicitor in plant production. Moreover, eustressors of a physical nature have been of recent interest due to the easiness of their application and control. In this category, accessible elicitors such as UV light, electric field, and sound have been considered. In this chapter, the fundaments of hormesis and the study of frass and physical eustressors are described in plants. Some elicitation arrangements and setups from laboratory to greenhouse scale and the development effects in different crops of interest such as chili pepper, bean, broccoli, and medicinal plants are discussed. The possibility to scale up the application of these elicitors in a controlled and safe manner will open up opportunities to produce crops with better quality, while at the same time, decreasing the negative impact on the environment.