Phytohormone Profiling of Cultivated Cotton (Gossypium hirsutum) Inoculated with Entomopathogenic Endophytes and Challenged By Insect Herbivory

     Fungal endophytes are defined as microorganisms living within plant tissues for all or part of their life cycle that remain symptomless to the host. Research shows pathogen attack can lead to profound changes in the metabolism of host plants. Defense responses are regulated by interconnecting signal transduction networks in which plant hormones play a central role. Several signaling cascades involved in herbivore and pathogen signaling responses have been elucidated, with some as jasmonic acid (JA) and salicylic acid (SA) pathways studied more intensively than others. The use of entomopathogenic fungal endophytes for insect control has been well documented in recent years. Our laboratory has shown negative effects of  endophytic Beauveria bassiana and Purpureocillium lilacinum on cotton aphid reproduction under both greenhouse and field conditions. The mechanisms by which entomopathogenic endophytic fungi may protect plants from insect herbivores are unknown. The literature suggests a systemic response in the plant can be induced by the presence of some entomopathogenic endophytes including B. bassiana that confers resistance against plant pathogens. Whether an induced systemic response accounts for the negative effects on insects observed in our study remains to be determined. In this experiment we aimed to investigate which acidic hormones are activated in cotton plants (i) when colonized by two entomopathogenic endophytes, and (ii) when challenged by the cotton aphid. Insects were left to feed for five different points in time at two different cotton plant stages: 3^rd and 5^th true leaf. The experiment was replicated twice in time.