Effects of exogenous MeJA on the growth, physiology, and biochemistry of Viola philippica

In this study, we investigated the effects of different methyl jasmonate (MeJA) concentrations on the growth, physiology, and biochemistry of Viola philippica. We used V. philippica as the experimental materials and sprayed its leaves on the underside with five different MeJA concentrations (0, 1.25, 2.5, 5, and 10 mmol·L⁻¹) to quantitatively study their effects on the number of Tetranychus mites, growth index, antioxidase activities, and soluble sugar and chlorophyll content. Compared with the non-sprayed MeJA (CK), exogenous MeJA could reduce the Tetranychus mite infection rate of the leaves of V. philippica. All growth indexes in the plants increased, as well as the activities of catalase, peroxidase, superoxide dismutase, and lipoxygenase, and the chlorophyll and soluble sugar content, while the malondialdehyde content decreased. When the MeJA concentration was 10 mmol·L⁻¹, the mite damage index was the lowest and the anti-overfull effect was the best, while at the MeJA concentration of 2.5 mmol·L⁻¹, all growth indexes reached the maximum. These results showed that exogenous MeJA could improve the resistance of V. philippica to the mite by affected the activities of various enzymes and corresponding physiological indexes, which was beneficial to its growth and development.