Title : 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, β-myrcene, (Z)-3-hexen-1-yl acetate, 1-hexyl acetate, (Z)-ocimene, linalool, benzyl acetate, methyl salicylate, indole, methyl anthranilate, geranyl acetate, β-caryophyllene, (E)-β-farnesene and (Z)-3-hexenal, (Z)- 3-hexen-1-ol, (Z)-3-hexen-1-yl acetate, (Z)-ocimene, linalool, indole, methyl anthranilate, geranyl acetate, β-caryophyllene and (E)-β-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 3 m 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.
Take Away Notes:
• Protecting crops against insect pest using environmental-friendly practices is a growing concern in Europe. This concern led the European commission to re-evaluate and limit the use of pesticides on all crops, banning a number of existing pesticides that were found to be inefficient, redundant or too harmful for the environment or the end-user. Although insecticides are invaluable tools that have no equivalent in flexibility of use and efficacy, a number of problems have arisen in the past due to their repeated and unfocussed use, selecting insect strains resistant to entire families of insecticide molecules, and contaminating and targeting beneficial insects, wild games and sometimes ending up as in acceptable residue levels in the food offered to the consumer.