Eustressors: Chemical and physical stress factors used to enhance vegetables production

Worldwide plants are exposed to different biotic and abiotic stress factors limiting yield, growth, quality and performance. Agricultural and horticultural practices for food production aim at plant cultivation at minimized stress using different production systems either under protected or open field conditions. However, it is also possible to stress plants to enhance horticultural production. The theory of stress indicates a dose/response relationship between the strength and length of the stress factor (stressor) and the plant response. Plant responses to cope stress are triggered after recognition of a range of biological, chemical, and physical stressors. Slight doses of stressors might cause positive effects on plant performance (positive stress or eustress), whereas on the contrary, high doses provoke negative effects (negative stress or distress). Managed as eustress dose and lenght, an eustressor might stimulates the plant response in such a way that plant production and quality are improved. A myriad of literature has reported beneficial effects for the applications of biological (biostimulants/elicitors) and non-biological chemical eustressors in horticulture. However, physical eustressors have not been exhaustively studied in this sense. The present review aims at presenting the current status of the concepts, case studies and applications of eustressors in horticulture. Moreover, the review focuses on the necessity of exploring physical eustressors as stress factors that modulate and increase the quality of horticultural commodities.