Impact of maize hormonal interactions on the performance of Spodoptera frugiperda in plants infected with Clavibacter michiganensis subsp. nebraskensis

Abstract

In nature, plants interact with multiple organisms, below and aboveground. Although interactions of plants with single biotic stressors are well characterized, knowledge of how the immune system responds to multiple biotic stressors is lacking. It is known that the two most important pathways involved in the plant immune defenses are jasmonic acid (JA) and salicylic acid (SA). The crosstalk between these plant hormonal signaling pathways seems to fine-tune the plant responses to different stressors. In this study, we characterized maize (Zea mays) hormonal interactions under the attack of two economically important pests: the bacterial pathogen that causes Goss’s bacterial wilt and leaf blight (Clavibacter michiganensis subsp. nebraskensis), and the chewing insect, fall armyworm (Spodoptera frugiperda). Our results indicate that the Goss’s wilt-resistant maize plants when pretreated with bacteria became more vulnerable to the subsequent attack by the fall armyworm larvae. Furthermore, plant hormone analysis demonstrated that the antagonistic interactions of JA-Isoleucine (JA-Ile), biologically active form of JA, and SA in maize plants contributed to enhanced plant susceptibility to herbivory. Collectively, our results suggest that plant hormonal interactions may play a major role in maize defense against multiple biotic stressors. Furthermore, this study will improve our understanding and ability to predict plant-induced hormone responses in an economically important crop.