Anti-herbivore resistance changes in tomato with elevation

Local adaptations of host plants to climatic conditions along an elevation gradient can affect insect-plant interactions. Using local accessions sampled from different elevations within South America, plant defense responses and herbivore growth were evaluated on two host plants: a) cherry tomato, Solanum lycopersicum var. cerasiforme, and b) wild tomato, Solanum pimpinellifolium. The elevational origin of the accessions ranged from 100 to 3000 m above sea level. We hypothesized a higher level of defensive compounds in plants originating from lower elevations and, consequently, stronger resistance to insect herbivory. Interestingly, plant resistance to insect herbivory, as demonstrated by a reduction in Helicoverpa zea growth, was stronger for middle and high-elevation accessions. Total phenolic content increased with elevation in both herbivore-damaged and undamaged leaves, augmenting plant resistance. However, an elevational gradient was not evident for plant defensive proteins (polyphenol oxidase and trypsin protease inhibitors) or the density of leaf trichomes. Tradeoffs between constitutive and induced defenses were evident in both tomato genotypes. Future studies should test the role of plasticity in plant defense systems in restricting or facilitating range expansion of insect herbivores with climate change.