Soybean responses to defensive phytohormone applications and its effects on thrips and fall armyworm performance

ROMERO, BERENICE; DILLON, FRANCISCO M.; ZAVALA, JORGE A.

Conferencia; The 1st International Electronic Conference on Entomology; 2021

Soybean crops can be severely damaged by different insect herbivore species. Two of the most common pests that attack and reduce crop yields belong to different feeding guilds Spodoptera frugiperda (Lepidoptera) and Caliothrips phaseoli (Thysanoptera). However, soybean responds to insect attack upregulating defences, such as proteinase inhibitors (PI) and phenolic compounds, modulated mainly by the phytohormones, jasmonic acid (JA), ethylene (ET), and salicylic acid (SA). It is not clear whether the activation of any of these signalling pathways plays a role in soybeans defensive response and if such response is insect-specific. In this study we determined the responses of Spodoptera larvae and thrips to two different commercial soybean varieties (DM 4210 and DM 5.8i) after the phytohormone application. JA and the precursor of ET ACC applied on leaves 72hs prior to the start of the experiments reduced fall armyworm survival in both soybean genotypes. Interestingly, although larval mass was similar among the different treatments in DM 5.8i, larvae that fed on JA- or SA-treated DM 4210 leaves had higher masses than those that fed on untreated leaves. Thrips´ preference and performance were affected by phytohormone application as well. In DM 4210, SA increased thrips´ attraction, while ACC had the opposite effect, and JA reduced their performance. In addition, JA application increased PI activity when compared to treatments with ACC and SA in DM 421, while no differences among treatments were observed in DM 5.8i. Moreover, manoly-genistin levels were increased following ACC application in DM 4210. These results suggest that not only activation of major signalling pathways by defense hormone application in soybean leads to differential defensive responses against insect attack in a genotype-specific manner, but also responses of herbivores to induced soybean defences are species-specific.