Volatile organic compounds released by maize following herbivory or insect extract application and communication between plants

To protect themselves from herbivory, plants have evolved an arsenal of physical and chemical defences and release a variety of volatile organic compounds (VOCs). By releasing these VOCs, a signalling plant can both reduce herbivory, sometimes by more than 90%, and also warn neighbouring plants about an attack. The aim of this study was to assess the influence of herbivory and insect extract application on VOC release by damaged/treated and nearby undamaged/untreated maize plants. We confirmed that European corn borer (Ostrinia nubilalis) larvae attack or larvae extract application induced maize VOC release. Greater amounts of (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, -myrcene, (Z)-3-hexen-1-yl acetate, 1-hexyl acetate, (Z)-ocimene, linalool, benzyl acetate, methyl salicylate, indole, methyl anthranilate, geranyl acetate, -caryophyllene, (E)--farnesene and (Z)-3-hexenal, (Z)-3-hexen-1-ol, (Z)-3-hexen-1-yl acetate, (Z)-ocimene, linalool, indole, methyl anthranilate, geranyl acetate, -caryophyllene and (E)--farnesene were released as a result of biotic stress after insect attack or insect extract application. The amounts of each VOC released were qualitatively and quantitatively distinct and dependent on time after biotic stress exposure. However, for all biotic stresses, significantly lower VOC induction was measured when leaves were damaged/treated for three days, as compared to seven days. Our work also demonstrated that undamaged/untreated neighbouring plants also release significant amounts of VOCs. This suggests that VOC emission by a damaged/treated plant stimulates VOC induction in nearby undamaged/untreated plants. However, the concentrations of all VOCs released by neighbouring undamaged/untreated maize plants were lower than those from damaged/treated plants and were negatively correlated with distance from a damaged/treated plant. Still, significant VOC induction occurred in undamaged/untreated plants even at 3m distance from a damaged/infected plant. Our work suggests that maize plant protective defence responses (VOC emission) can be induced via application of European corn borer extracts.