ABSTRACT
Onion (Allium cepa) is one of the oldest vegetables that is widely cultivated worldwide. It is ranked second after tomato. The onion bulb and skin contain various bioactive compounds, such as organosulfur compounds, thiosulfinates, phenolic acids, flavonoids (quercetin and kaempferol), anthocyanins and ascorbic acid. In addition, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, ferric reducing antioxidant power (FRAP), radical scavenging activity and hydroxyl radicle ( –•OH) radical scavenging activity also have been detected in onion bulbs or leaves. These antioxidants play a crucial role in the suppression of oxidative stress, which may be used against various diseases. Allium cepa has been considered a potent antimicrobial agent against infectious diseases where many bacteria, fungi and viruses were found to be susceptible to different solvent extracts of A. cepa. Thus, it is important to know the adverse impacts caused by the environment through the production of onions. Stress due to biotic and abiotic factors is among the major constraints in exploiting the yield potential of the onion crop. Therefore, there is increasing momentum in studying the effects of biotic and abiotic stresses on immune-boosting food crops like onion and also in developing rescue strategies that will help policymakers to suggest better guidelines for food security. In the following sections of this chapter, we will review the abiotic and biotic stressors on onion plants and mitigation strategies.
