An Established Arbuscular Mycorrhizal Symbiosis Positively Impacts Potato Aphids

The symbiosis between arbuscular mycorrhizal (AM) fungus and plant roots aid plants in nutrient acquisition (i.e. phosphate) leading in some instances to enhanced vegetative and reproductive growth. Recent evidence has unveiled another side to this mutualism, known as mycorrhiza-induced resistance (MIR) and seems to be effective against certain pathogens and arthropods. While the majority of phytophagous insects studied so far are negatively affected when feeding on mycorrhizal plants, the impact of the AM symbiosis on aphids is inconsistent. Our research focuses on potato aphids (Macrosiphum euphorbiae), potato (Solanum tuberosum cv. Desiree), and the generalist AM fungus Glomus intraradices. The research objectives were: a) to examine the effects of above-ground aphid herbivory and below-ground AM fungus root colonization on plant physiology, and assess organism performance in this tripartite interaction, and b) to determine the impact of MIR in potato against aphids. Our results showed that the level of G. intraradices root colonization positively affected aphid fitness with distinguishable impacts over longer feeding times. In this study, there were no significant alterations in plant physiology (i.e. plant water status, chlorophyll content, and photosynthetic rate) on aphid infested leaves and non-infested systemic leaves. Assessment of plant gene expression focusing on aphid- and mycorrhiza-induced genes is underway, and the results would provide a better understanding of the plant alterations that in this case lead to aphid susceptibility.