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 an d R. obtusifolius causing premature senescence and leaf death. We inve stigated the effect of infection on nutritional quality of leaves with respect to the chrysomelid beetle Gastrophysa viridula and measured l arval survival and growth on rusted and unrusted plants. 2. A smaller biomass of G. viridula was produced and a greater area of leaf consume d 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. Inf ection changed the partitioning to different carbohydrates, increasing the proportion of starch in R. crispus and decreasing it in R. obtusi folius. 4. The concentration of total nitrogen, both in the pustule an d the inter-pustule area, decreased in both species with time after ru st infection. 5. In both species, considerably higher oxalate concentr ations occurred in the interpustule area and significantly lower conce ntrations in the uninfected leaves of these plants. Calcium concentrat ions 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 oth er invertebrate herbivores.