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Influence of Fusarium palustre, drought, and DMSO on herbivory of Spartina alterniflora by marsh crabs.
W. H. ELMER (1). (1) The Connecticut Agricultural Experiment Station, New Haven, CT, U.S.A.

Recovery from Sudden Vegetation Dieback (SVD) in New England salt marshes has been hindered by the herbivorous purple marsh crab, <i>Sesarma reticulatum</i>. We hypothesized that inoculation of <i>Spartina alterniflora</i> (SA) with the stem rot pathogen, <i>Fusarium palustre</i> (FP), and/or drought may increase herbivory. SA were exposed to different irrigation regimes and inoculated with FP or left un-inoculated. Pairwise combinations of SA plants were placed in bins with marsh crabs and photographed over a 1-2 day period for visual estimates of loss due to consumption. Herbivory was greatest on drought-stressed plants and/or plants that were inoculated with FP. Plants exposed to the same treatments and transplanted into a crab-infested SVD site were similarly consumed. In other published studies, it was shown that stressed SA plants had higher levels of dimethylsulfoxide (DMSO) than healthy plants. To determine if DMSO was an attractant for the marsh crab, we drenched healthy SA and other grass species with DMSO (20 micromoles) to determine if it increased herbivory when compared to untreated plants. Consumption of SA was significantly greater in the first 4 hr. on DMSO-treated SA plants than on controls, but did not increase herbivory on other grass species. These findings suggest that plant stress, whether by disease or drought may increase the attractiveness of SA to herbivory by marsh crabs and that DMSO might function as a chemo-attractant in SA. <p><p>Keywords: Fungus

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