| Cassava Manihot esculenta is a globally important food crop and industrial raw material,fodder,energy and relief crop,one of the three major yam crops and seven major crops in the world.Tetranychus urticae(two-spotted spider mite,TSSM for short)is one of the world’s most dangerous mites,and its infestation often leads to50%-70% yield reduction in cassava.The selection and utilization of insect-resistant varieties is recognized as the most economical,effective and simple way to effectively prevent and control the pest at source.Jasmonic acid(JA)and salicylic acid(SA)signaling pathways are known to be important signaling pathways for crop regulation of their own defense responses and play an important role in crop insect resistance.It was found that exogenous application of methyl jasmonate(Me JA)and methyl salicylic acid(Me SA)as signaling molecules can produce similar induction patterns as phytophagous insect pests and can induce plants to develop defense systems against pests.However,few studies have been reported so far on the effect of exogenous application of both substances to induce activation of cassava defenses against mites.Therefore,in this study,the optimal concentration of Me JA or Me SA was firstly determined by the dose effect of external application of different concentrations of Me JA or Me SA on the development and reproduction of mites,and then further analyzed the effect factors,protective enzymes,detoxifying enzymes,and digestive enzymes of mites after feeding on external application of Me JA or Me SA on the basis of this study.Then,we analyzed the changes of effectors,protective enzymes,detoxifying enzymes,digestive enzymes,and synthetic gene expression,synthetic enzyme activity,endogenous JA or SA content,and total phenol,flavonoid,lignin and tannin content of insect-resistant secondary metabolites in cassava varieties resistant and susceptible to mites after external application of Me JA or Me SA,and analyzed the mechanism of defense effect of exogenous Me JA or Me SA-induced activation of cassava against mites.The main findings were as follows:1.Topical application of Me JA or Me SA significantly inhibited the development and reproduction of mites and population growth,and the appropriate concentrations of topical Me JA and Me SA were determined to be0.2 m M and 0.5 m M,respectively.Compared with the control,the development and reproduction of mites were significantly inhibited,egg production and adult longevity were significantly reduced,and developmental calendar and net growth rate were also significantly reduced after mites were treated with five concentrations of Me JA at 0.008,0.04,0.2,1.0 and 5.0m M or Me SA at 0.004,0.02,0.1,0.5 and 2.5 m M on mite resistant and mite susceptible cassava varieties.The development and reproduction of mites were significantly inhibited by external application of Me JA or Me SA on mite resistant cassava varieties,and the development and reproduction of mites were significantly better than those of mite susceptible cassava varieties.Since there was no significant difference in the development and reproduction of mites after feeding on 0.2,1.0and 5.0 m M Me JA-treated cassava,and all of them were significantly better than0.008 m M and 0.04 m M,while there was no significant difference in the effect of external application of Me SA 0.5 and 2.5 m M on the development and reproduction of mites,and all of them were significantly better than 0.004,0.02 and 0.1 m M,it was determined that 0.2 m M and 0.5 m M were determined as the appropriate concentrations of Me JA and Me SA for external application.2.Topical application of Me JA or Me SA significantly induced up-regulated expression of mite effectors Tu28,Tu84 and Tu90 and increased activities of antioxidant enzymes,detoxifying enzymes and digestive enzymes,and the effect of mite resistant cassava variety C1115 was significantly better than that of mite susceptible cassava variety KU50,and the duration of induction effect was 8 d for both varieties.Compared with the control,the expression of mite effectors Tu28,Tu84 and Tu90 genes were significantly up-regulated after feeding on mite resistant and mite susceptible cassava treated with 0.2 m M Me JA or 0.5 m M Me SA;digestive enzymes(amylase,protease,sucrase),antioxidant enzymes(superoxide dismutase,catalase),detoxifying enzymes(cytochrome P450 enzymes,glutathione S-transferase,carboxylesterase)activities were significantly increased,and the expression of effectors and the fold increase of enzyme activities were significantly higher in C1115 than in KU50,and the holding time of induction effect was 8 d in all cases.3.Topical application of Me JA or Me SA significantly affected the expression of cassava JA and SA synthesis genes,synthetase activity and the content of endogenous JA and SA,and the induction effect of mite resistant cassava variety C1115 was significantly better than that of mite susceptible cassava variety KU50,and the holding time of the induction effect was 8 d for both.Compared with the control,the expressions of JA synthesis genes AOS and OPR3 were significantly up-regulated,the expressions of ACX and LOX were significantly down-regulated,and the activities of JA synthesis enzymes AOS,OPR3 and LOX enzymes were significantly increased after external application of 0.2 m M Me JA to both mite resistant and mite susceptible cassava varieties,and the trends of the expressions of AOS,OPR3 and AOS and OPR3 enzyme activities were consistent,but the The expression of LOX and LOX enzyme activity showed opposite trends.The expressions of SA synthesis genes EDS5,ICS,PAL and PBS were significantly up-regulated after external application of 0.5 m M Me SA to mite resistant and mite susceptible cassava varieties,and the activities of SA synthesis enzymes ICS and PAL enzymes were significantly increased,and the expressions of ICS and PAL were consistent with the trends of the activities of ICS and PAL enzymes;both external application of Me JA and Me SA increased the The contents of endogenous JA and SA were increased by external application of Me JA and Me SA.In addition,except for the induction effect of ACX,which was not significantly different among mite resistant and mite susceptible cassava varieties,the induction effect of external application of Me JA or Me SA on the expression of AOS,LOX,OPR3 and EDS5,ICS,PAL and PBS,the activities of AOS,OPR3,LOX and ICS and PAL enzymes and the contents of endogenous JA and SA of mite resistant and mite susceptible cassava varieties C1115 was significantly superior to the mite susceptible cassava variety KU50,and the duration of induction effects were all up to 8 days.4.Topical application of Me JA or Me SA significantly increased the content of total phenols,flavonoids,lignin and tannins in mite resistant and mite susceptible cassava varieties,and topical application of Me JA induced tannins and flavonoids and topical application of Me SA induced tannins and lignin in mite resistant cassava variety C1115 better than mite susceptible cassava variety KU50,and the duration of induction effect was up to 8 days in both varieties.Compared with the control,the contents of total phenols,flavonoids,lignin and tannins in the leaves of mite resistant and mite susceptible cassava varieties were significantly higher after external application of 0.2 m M Me JA and 0.5 m M Me SA than before spraying,and the duration of induction effect was 8 days for both varieties.Topical application of Me JA induced tannins and flavonoids significantly better in mite resistant cassava variety C1115 than mite susceptible cassava variety KU50,but induced no significant difference in total phenols and lignin between resistant and susceptible cassava varieties;topical application of Me SA induced tannins and lignin significantly better in mite susceptible cassava variety KU50 than mite resistant cassava variety C1115,but induced no significant difference in total phenols and flavonoids between resistant and susceptible cassava varieties There were no significant differences between the mite resistant and susceptible cassava varieties. |
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