茉莉酸诱导桑枝对桑天牛卵啮小蜂的引诱作用及桑枝挥发物组分分析

【目的】探讨茉莉酸诱导的桑树Morus alba枝挥发物对桑天牛卵啮小蜂Aprostocetus prolixus趋性行为的影响,研究桑枝挥发物的动态变化规律,为揭示茉莉酸诱导桑枝产生的间接抗虫作用机理提供理论依据。【方法】本试验利用嗅觉测定仪,研究了不同浓度茉莉酸处理24,48和72 h后的桑枝对桑天牛卵啮小蜂的引诱作用,并采用气相色谱-质谱联用仪(GC/MS)对茉莉酸(1 000μmol/L)处理不同时间后的桑枝挥发物组分进行了分析。【结果】在10μmol/L茉莉酸处理后的不同时间内,桑枝对桑天牛卵啮小蜂均未表现出明显的引诱作用;当茉莉酸浓度为100μmol/L时,桑枝仅在处理48 h后对桑天牛卵啮小蜂具有显著的引诱活性;然而,经1 000μmol/L茉莉酸处理24 h和48h后,桑枝对桑天牛卵啮小蜂的引诱活性明显高于对照(24 h,P0.05;48 h,P0.01),72 h后桑枝的引诱作用消失。Spearman等级相关性分析表明,茉莉酸浓度与桑枝对桑天牛卵啮小蜂的引诱百分率显著正相关(ρ=0.791,P=0.006)。茉莉酸(1 000μmol/L)处理桑枝挥发物组分包括醇类、酯类、萜类物质、芳香族化合物和含氮化合物,其中萜类物质种类最多(13种)。随着处理时间的变化,桑枝挥发物组分及总释放速率也随之发生改变。处理24 h后,桑枝释放出18种组分,比对照多11种组分,其总释放速率也明显提高,为对照的8.2倍;48 h后桑枝释放出22种组分,比对照多15种组分,其总释放速率进一步提高,为对照的44.6倍;72 h后桑枝释放出13种组分,比对照多6种组分,其总释放速率大幅降低,为对照的3.9倍,但与对照无显著差异。【结论】随着茉莉酸浓度的提高,桑枝对桑天牛卵啮小蜂的引诱活性逐渐增强。茉莉酸能诱导桑枝挥发物的大量释放及新组分的产生。

Attractiveness of jasmonic acid-treated Morus alba branches to Aprostocetus prolixus (Hymenoptera: Eulophidae) and analysis of their volatile compounds

Aim] This study aims to explore the effects of volatiles from Morus alba branches treated with jasmonic acid (JA) on the behaviors of Aprostocetus prolixus,and to investigate the dynamic changes of the volatiles,so as to provide the theoretical basis for clarifying the mechanism of JA-induced indirect resistance to insects in M.alba.Methods] In this study,the olfactometer was employed to investigate the attractiveness of M.alba branches to A.prolixus at 24,48 and 72 h post treatment with different JA concentrations.The dynamic changes of chemical components of volatiles from M.alba branches treated with 1 000 μmol/L JA were analyzed by GC-MS at different time points.Results] The results demonstrated that M.alba branches had no significant attractiveness to A.prolixus at any time point when treated with 10 μmol/L JA.Treated with 100 μmol/L JA,M.alba branches displayed significant attractiveness to A.prolixus only at 48 h post treatment.However,the attractiveness of volatiles from M.alba branches to A.prolixus was significantly higher than that of the control at 24 h (P ＜ 0.05) and 48 h (P ＜0.01) post treatment with 1 000 μmol/L JA.At 72 h post treatment,the attractiveness gradually disappeared.Spearman's correlation analysis revealed a significantly positive correlation between JA concentration and the attractiveness of branches to A.prolixus (p =0.791,P =0.006).Identified by GC-MS,the volatiles of M.alba branches treated with 1 000 μmol/L JA consisted of alcohols,easters,terpenoids,aromatic compounds and nitrogenous compounds.Among them,the terpenoids were predominant and contained 13 components.It was also found that the components and the total emission rate of volatiles altered with extension of the duration of jasmonic acid treatment.At 24 h post treatment,18 chemical components were emitted from the treated M.alba branches (with 11 more components than those of the control),and their total emission rate was 8.2-fold as high as that of the control.The M.alba branches emitted 22 chemical components at 48 h post treatment (with 15 more components than those of the control),and the total emission rate of these components was 444.6-fold as high as that of the control.At 72 h post treatment,13 chemical components,six more than those of the control,were detected from the treated M.alba branches,and their total emission rate sharply decreased (3.9-fold as high as that of the control) but was not significantly different from that of the control.Conclusion] The attractiveness of M.alba branches to A.prolixus gradually enhances with the increase of JA concentration.JA can induce the synthesis of volatile chemical components and great emission of volatiles in M.alba branches.