Detection of Diseases and Volatile Discrimination of Plants: An Electronic Nose and Self-Organizing Maps Approach

Plant Diseases And Vocs

The first studies on the emission of VOCs from plants were conducted in the Soviet Union in the 1920s and 1930s and since then VOCs from many plant speices have been investigated (Kesselmeier & Staudt, 2004). Generally, in order to effectively combat invasion by microbial pathogens, attacks by herbivorous insects or even mechanical damage, plants require a broad range of defense mechanisms (Choudhary, Johr & Prakash, 2008). Hence, they have evolved various strategies to defend themselves against herbivores and pathogens; one of which is to emit specific and exclusive VOCs to battle the potential attackers. Although some of these strategies are constitutive and present at all times, others are induced only in response to herbivore feeding or pathogen infection (Frost, et al., 2008). These defenses are often categorized in two groups: a) direct defense in which they emit toxic or repel VOCs that reduce herbivores and b) indirect defense where volatiles attract parasitoids that increase herbivore mortality (Fernandes et al., 2010; Butrym & Hartman, 1998). In view of both direct and indirect defenses, plant VOCs play significant roles in plant–herbivore and plant–pathogen exchanges and are promising targets for improved crop protection (Kant et al., 2009). The composition of VOCs emitted by plants depends on the mode of damage such as single wounding, continuous wounding, herbivore feeding, and egg deposition (Maffei, 2010). Biologically, VOCs are produced by a wide range of physiological processes in many different parts of the plant tissues and are themselves also extremely diverse and usually include alkanes, alkenes, alcohols, aldehydes, eters, esters and carboxylic acids (Peñuelas, 2004).