Soil fertility and arbuscular Mycorrhiza: Impact on herbivore induced plant volatiles in tomato

Arbuscular mycorrhizae fungi (AMF) are naturally occurring, beneficial fungi that grow in mutualism with many plants by colonizing their roots. Associations between host plants and AMF enhance plant chemical defense responses, including production of volatile organic compounds (VOCs). Our study tested the hypothesis that AMF mutualism improves plant volatile signaling under conditions of phosphorus limitation, following exposure to insect herbivory.
We used a model system consisting of consisting of tomato plant and the herbivorous pest, Manduca sexta. To isolate mechanisms of AMF mutualisms, we used two tomato genotypes a) Myc, mycorrhizal wild-type tomato, easily colonized by AMF; and b) Rmc, reduced mycorrhizal mutant, resists colonization by AMF. Tomato were grown under low- and high-phosphorous soils. Volatiles were collected from undamaged, mechanically damaged and herbivore damaged plants. To induce the production of herbivore-induced volatiles, four, 4^th instar M. sexta larvae fed on tomato plants 48 hours prior to volatile collection. Volatiles were collected using solid phase microextraction and identified using gas chromatography mass spectrometry.
Results showed that soil fertility and mycorrhizal colonization affected the emissions of herbivore-induced VOCs in tomato. As predicted, VOC emissions differed by genotype, with AMF colonized plants in low fertility responding strongest to herbivory. The implications of this should be considered, particularly in the use of AMF to manage agricultural pests, as many herbivores and their natural enemies are known to use plant VOCs as host location cues. This work is important because it could help identify novel approaches to pest management.