Interactions Between Rumex spp., Herbivores and a Rust Fungus: The Effect of Uromyces rumicis Infection on Leaf Nutritional Quality

1. The rust fungus Uromyces rumicis infects leaves of Rumex crispus and R. obtusifolius causing premature senescence and leaf death. We investigated the effect of infection on nutritional quality of leaves with respect to the chrysomelid beetle Gastrophysa viridula and measured larval survival and growth on rusted and unrusted plants. 2. A smaller biomass of G. viridula was produced and a greater area of leaf consumed per unit biomass gained, by egg batches reared on rusted compared to unrusted R. obtusifolius, although no difference was observed between larvae reared on rusted or unrusted R. crispus. 3. Concentrations of total non-structural carbohydrates were not changed in the pustule and non-infected leaves but were increased in the inter-pustule area. Infection changed the partitioning to different carbohydrates, increasing the proportion of starch in R. crispus and decreasing it in R. obtusifolius. 4. The concentration of total nitrogen, both in the pustule and the inter-pustule area, decreased in both species with time after rust infection. 5. In both species, considerably higher oxalate concentrations occurred in the interpustule area and significantly lower concentrations in the uninfected leaves of these plants. Calcium concentrations altered similarly and were correlated with oxalate concentrations. 6. We conclude that rust infection does not improve the nutritional quality of the leaves for G. viridula and is unlikely to do so for other invertebrate herbivores.