Fitness of Cuscuta salina (Convolvulaceae) parasitizing Beta vulgaris (Chenopodiaceae) grown under different salinity regimes

The distribution of saltmarsh dodder (Cuscuta salina) worldwide is restricted to areas of high salinity, where it parasitizes a variety of salt-tolerant plants. Because dodders do not maintain root connections to the soil, this pattern of parasitization may be related to the effects of salt stress on the host that increase the ability of attached dodders to more easily transfer host contents. This study explored whether a saline host environment is required for successful infection and whether stem contents of potential hosts become more concentrated in response to salinity. Fecundity of dodder was highest when hosts (Beta vulgaris) were grown either without salt or at high (250 mmol/L) salinity; it produced significantly fewer flowers and fruit at intermediate salinities. Stem constituents of two unparasitized host species had high conductivity and elevated levels of dissolved sugars at increasing salinities. Nitrate content of stems was also increased by salinity, but declined at the extreme salinity (400 mmol/L). Salinity effects on host suitability may partially explain differences in growth and vigor of C. salina in certain areas of salt marsh, but information on nonrandom dispersal of C. salina seeds may be needed to fully explain this parasite's distribution.