Effects of exogenous application of methyl jasmonate on foliar volatile emission in citrus

Methyl jasmonate (MeJA) is a well-known activator of chemical defenses in plants.  We tested the ability of MeJA to elicit changes in the aroma profile of the growing shoots of citrus trees.  Young foliage is the prime target of the Asian citrus psyllid (ACP), vector of the causal agent that causes the devastating citrus disease known as huanglongbing or citrus greening.  Various concentrations of MeJA dissolved in a 0.1% aqueous detergent solution were sprayed on the foliage of potted sweet orange (Citrus sinesis cv Ridge Pineapple) trees in a greenhouse.  Purge and trap headspace collections were made on growing terminal shoots using Porapak Q as a sorbent, with collections conducted for four hours during mid-day on three consecutive days.  The samples were eluted with hexane and analyzed by GC-MS.  At the highest concentration of MeJA tested (10 mM), alterations were observed in headspace composition relative to that of untreated control trees.  The number of sesquiterpenes present increased, nitrogeneous compounds such as indole were observed, and more E-β-ocimene was emitted than limonene, a reversal from the situation observed in control trees.  These compounds have been observed in other plant species treated with MeJA or attacked by herbivores.  Ongoing studies will determine an optimal dosage for MeJA for eliciting changes in foliar aroma and the behavioral responses of ACP and its natural enemies to foliar aromas altered by MeJA application will be measured.