LC-ESI-MS quantification of the endogenous phytohormones JA and SA in sweet potato leaves. The healthy third leaf of a sweet potato plant without treatment was used as a control (cK). The JA and SA levels were quantified at 0.25, 0.5 and 6 h after the third leaf was damaged by: (A) MW; or (B) HA (second instar larvae of Spodoptera littoralis). The level of JA and SA was expressed as ng JA/SA per g FW. (* represents P < 0.05; ** represents P < 0.01; *** represents P < 0.001; ‘ns’ non-significant represents P > 0.05). Values are the means (±SE) of three replicates (n = 6).