Leaf UV-B irradiation and mycorrhizal symbionts affect lettuce VOC emissions and defense mechanisms, but not aphid feeding preferences

Arbuscular mycorrhizal fungi (AMF) and ultraviolet-B radiation (UV-B) play important roles in plant–insect interactions by altering plant physiology and histology. We hypothesized that UV-B induced oxidative stress was mitigated by AMF symbiosis. In this study, we conducted a multifactorial experiment to explore lettuce plant response to AMF inoculation and UV-B exposure (0.4 W m-2; 16 h d-1; 2 weeks), either together or individually, as well as the interaction with the polyphagous insect pest Myzus persicae (Sulzer). Lettuce plants subjected to UV-B radiation showed an increase in callose and oxidative stress indicators, as well as a decrease in stomatal density. Mycorrhizal colonization cancelled out the effect of UV-B on stomatal density, while the symbiosis was not affected by UV-B treatment. The plant volatile emission was significantly altered by UV-B treatment. Specifically, the non-terpene 1-undecene abundance (+M/+UVB: 48.0 +- 7.78%; -M/+UVB: 56.6 +- 14.90%) was increased, whereas the content of the non-terpene aldehydes decanal (+M/+UVB: 8.50 +- 3.90%; -M/+UVB: 8.0 +- 4.87%) and undecanal (+M/+UVB: 2.1 +- 0.65%; -M/+UVB: 1.20 +- 1.18%) and the sesquiterpene hydrocarbons (+M/+UVB: 18.0 +- 9.62 %; -M/+UVB: 19.2 +- 5.90%) was decreased. Mycorrhization, on the other hand, had no significant effect on the plant volatilome, regardless of UV-B treatment. Aphid population was unaffected by any of the treatments, implying a neutral plant response. Overall, this study provides new insights about the interactions among plants, UV-B, and AMF, outlining their limited impact on a polyphagous insect pest.