Salicylic Acid-induced Resistance of Rosa chinensis Against Spodoptera exigua and Its Chemical Mechanism

To determine the exogenous salicylic acid(SA)-induced resistance of Rosa chinensis against Spodoptera exigua, and to explore the chemical mechanism in the resistance, dual-choice bioassays were used to study ovipositional behaviours of S. exigua, and GC−MS was used to determine the changes in SA−induced volatile organic compounds(VOCs) released by S. exigua. The chemicals with their activities to S. exigua were also researched. The ovipositing amounts of S. exigua on the SA−treated R. chinensis decreased significantly(P< 0.05) as a result of the treatment of the plants by SA solution at concentration of 1.0 mmol/l. The total egg numbers decreased by 35.4%, 38.9%, and 47.5% after the treatment for 6 d, 9 d, and 12 d with SA when comparing to the controls, respectively. Furthermore, the VOCs of the control and SA−treated R. chinensis were collected with the method of dynamic headspace absorption(DHSA) and the VOCs solutions were sprayed on the 2 same bouquets of healthy R. chinensis twigs without any treats. The results showed that the amounts of eggs on the twigs sprayed with the mixture of volatiles from SA−treated roses were significantly less than the control roses(P< 0.05). The inhibiting index were 23.9%, 25.4%, and 36.2% after the treatment for 6 d, 9 d, and 12 d , respectively. The GC−MS results demonstrated that the obvious changes in VOCs from R. chinensis were induced by SA treatment. Several chemicals including 2−ethylhexanoic acid, tetradecanol, methyl palmitate, and hexadecyl acetate are not produced naturally by healthy R. chinensis plants, and these chemicals could be produced by R. chinensis only when the plants were induced by SA. Additionally, the induction of SA to the 4 chemicals clearly exhibited temporal effect, and the relations of dosage effects of these chemicals to repel oviposition of S. exigua were recorded clearly in the experiments. The results demonstrated that induced resistance in R. chinensis plant against S. exigua occurs as a consequence of the induction of R. chinensis by SA and the changes in VOCs are responsible for the resistance.