Combined effects of Cry1Ab toxin and methyl jasmonate improve resistance of transgenic tomato plants against Helicoverpa armigera larvae

Helicoverpa armigera is one of the most harmful pests of tomato. Due to its effectiveness on non-target organisms and increased probability of resistance induction in Helicoverpa armigera, chemical discipline is not a sustainable approach. Moreover, expression of transgenes gradually reduces and finally results in declining the pest resistance in plants. Hereby for the first time, as an integrated pest management strategy, we established that treating the transgenic tomatoes harboring Cry1Ab under control of MPI inducible promoter by methyl jasmonate (MeJA), as a hormonal elicitor stimulating plant defense system, is more effective approach to overcome the pest attack. Cry1Ab integration, its expression, and the presence of Cry1Ab protein were confirmed in T₃ transgenic lines. Applying various concentrations of MeJA increasing ROS levels and SOD activity in MeJA treated transgenic (MTT) leaves. The bioassay data indicated that feeding the larvae with MTT leaves resulted in the weakness of digestive system and immunity of Helicoverpa armigera larvae, and subsequently increased the larval mortality rate. The inefficiency of the insect’s digestive and immune system in larvae feeding on MTT leaves led to a decrease in larval growth and development, which was shown in the nutritional indices (Relative Growth Rate [RGR], Relative Consumption Rate [RCR], and Efficiency of Conversion of Ingested Food [ECD]). Finally, utilizing the combination of transgene Cry1Ab with 1 mM MeJA on T₃ plants induced 47% larvae death and 53% decrease in larval growth and development during the bioassay. Therefore, the application of MeJA on transgenic plants harboring Cry1Ab could properly enhance tomato resistance against the Helicoverpa armigera via increasing ROS accumulation in transgenic leaves.