Jasmonic acid is associated with resistance to twospotted spider mites in diploid cotton (Gossypium arboreum)

The twospotted spider mite (Tetranychus urticae Koch) is capable of dramatically reducing the yield of cotton crops and is often difficult and expensive to control. This study investigated and compared two important plant hormones, jasmonicacid(JA)andsalicylicacid(SA),asconstitutiveand/orinduceddefenceresponsecomponentsinamitesusceptible commercialcottoncultivar,Sicot71(GossypiumhirsutumL.)andaresistantdiploidcottonBM13H(Gossypiumarboreum L.). Foliar application of JA and methyl jasmonate (MeJA) reduced the mite population and leaf damage but application of other potential elicitors, SA and methyl salicylate (MeSA) did not. The concentrations of JA and SA in leaf tissues of inducedandnon-inducedSicot71andBM13Hwerequantifiedbyliquidchromatographycoupledtoelectrosprayionisation tandem mass spectrometry (LC-ESI-MS/MS). The JA content was constitutively higher in BM13H than Sicot 71 and also highly induced by mite infestation in BM13H but not in Sicot 71. However, SA was not significantly induced in either BM13H or Sicot 71. The expression levels of JA related genes, LOX, AOS and OPR were measured by quantitative PCR and elevated expression levels of JA related genes were detected in mite-infested BM13H. Therefore, JA and MeJA were implicated as key biochemical components in both the constitutive and induced defence responses of BM13H to spider mites.