Two Seed Treatments with Methyl Jasmonate Differentially Alter the Emission of Volatile Organic Compounds in Broccoli Plants.

Jasmonic acid (JA) is a key regulator of plant development and plant defence. Seed priming with JA and methyl jasmonate (MeJA) has been proposed as an ecologically-sound and cost-effective method to improve crop protection. While several studies have shown their efficacy in boosting production of non-volatile defensive compounds, the effects of seed treatments on volatile organic compounds (VOCs) are largely unknown. Using broccoli and Plutella xylostella as a model system, we tested how two pre-sowing MeJA treatments (0.1 and 0.01 mM MeJA) impact constitutive and herbivore-induced VOC emissions, net photosynthesis (A) and stomatal conductance (Gs). The results showed that at 0.1 mM MeJA, the treatment significantly increased the emissions of (Z)-3-hexen-1-ol and (Z)-3-hexenyl acetate. In contrast, the emission of (E, E)-α-farnesene was significantly reduced in MeJA-seed treated plants, compared to untreated plants. At 0.01 mM MeJA, no effect of the MeJA treatment on the whole blend was observed, although there was an effect of MeJA on (E, E)-α-farnesene, which decreased. However, at this concentration plants were primed for a greater VOC response upon herbivore damage. Although A and Gs tended to increase in plants grown from seeds treated with 0.1 mM MeJA, no significant changes were observed for either of the concentrations. The treatment did not significantly affect leaf consumption or oviposition, even though more eggs were laid on the MeJA treated plants compared to the control, at the concentration of 0.1 mM MeJA. Together, the results showed that MeJA can alter the VOC emissions, and suggest that, 0.01 mM MeJA can prime herbivore-induced VOCs, without promoting oviposition of the pest.