Showing papers by "Wade H. Elmer published in 2012"

Association Between Fusarium spp. on Spartina alterniflora and Dieback Sites in Connecticut and Massachusetts

Abstract: Sudden vegetation dieback (SVD) is defined as the loss and lack of recovery of smooth cordgrass (Spartina alterniflora) in salt marshes. A new species of a moderately pathogenic fungus called Fusarium palustre is consistently found in SVD sites, but greenhouse tests revealed that it is not capable of causing mortality of healthy plants. Similarly, root-knot nematodes (Meloidogyne spartinae) are also found in SVD sites, but their incidence in marshes affected by SVD is not known. To understand more about the ecology of F. palustre and M. spartinae, salt marshes along Connecticut's Long Island Sound and Massachusetts' Cape Cod that exhibited SVD and those that did not, were visited during the summers of 2007, 2008, and 2009. Belowground and aboveground tissues of smooth cordgrass plants from 18 marshes were removed, washed, and assayed for Fusarium spp. to determine if patterns between the incidence of the different species of Fusarium, their virulence on S. alterniflora, root-knot nematodes (M. spartinae), and the health of the marsh could be revealed. There were significantly more colonies of Fusarium growing from plants in SVD sites (6.1%) than in healthy marshes where no SVD was present (<1.0%). The incidence of Fusarium spp. from plants at the perimeter of the SVD site was not statistically different from asymptomatic plants 10-20 m from the SVD edge. The majority of isolates could be assigned to one of two species, F. palustre or another slightly pathogenic group called Fusarium cf. incarnatum (88% in 2007, 62% in 2008, and 96% in 2009). The ratio of F. palustre to F. cf. incarnatum was 6.7, 2.7, or 2.1 for 2007, 2008, or 2009, respectively. Greenhouse tests on healthy S. alterniflora revealed that isolates of F. palustre were more virulent than F. cf. incarnatum, regardless of whether they were recovered from plants in healthy marshes or in SVD sites. Root-knot nematodes were found sporadically and could not be associated with SVD. Factorial greenhouse experiments did not demonstrate any interaction between F. palustre and M. spartinae providing no experimental evidence that combining Fusarium and root-knot nematodes could cause mortality. The presence of Fusarium on S. alterniflora in healthy marshes also suggests an endophytic relationship that may subsequently function in the breakdown of tissue when plants are compromised.

First Report of Crown Rot of Bloodroot (Sanguinaria canadensis) Caused by Fusarium oxysporum in the United States.

Abstract: Bloodroot (Sanguinaria canadensis L [Papaveraceae]) is a native herbaceous perennial in eastern North America, found from Nova Scotia to Florida. Although it is a common wildflower, rhizomes of double-flowered forms are sold commercially. Rhizomes planted into a wooded area in Guilford, CT produced healthy stems and flowers for a few years and then began to collapse and die in 2008. The same symptoms were observed with a new planting in 2011. Initially, leaves were dull green and were more leathery than healthy leaves. Eventually, the leaves collapsed at the junction of the petioles and the rhizomes. Vascular discoloration, if present, was obscured by the red pigmentation in the rhizome. A Fusarium sp. sporulated on the discolored tissue at the junction between healthy and rotted tissue. Stem pieces were surface disinfested (0.53% NaClO for 1 min), rinsed, and placed on Peptone-PCNB agar (2) at room temperature for 5 days. Colonies originating from single spores were subcultured on carnation leaf agar (2) and identified as Fusarium oxysporum based on falcate, thin-walled, three-septate macroconida borne in monophialides on doliform conidiophores (2). Four rhizomes of double-flowered bloodroot were planted in potting mix in the greenhouse in October 2010; sprouts were observed in March 2011. Two plants were inoculated in March 2011 by drenching the soil with 100 ml of a conidial suspension (106 spores/ml) and two control plants were treated with deionized water. Two months later, the inoculated plants were smaller than the controls. The treated plants subsequently collapsed and F. oxysporum was reisolated. Control plants remained healthy and F. oxysporum was not isolated. DNA extracted from the F. oxysporum isolates was used to obtain partial sequences of the translational elongation factor 1-alpha (tef1) gene, which were then blasted against the GenBank database. We observed a 100% similarity with F. oxysporum f. sp. lycopersici. The bloodroot isolates were compared with a known F. oxysporum f. sp. lycopersici isolate for their ability to cause disease on 2-week-old tomato seedlings (cv. Brandywine), using pathogenicity tests as described above. The known F. oxysporum f. sp. lycopersici isolate caused severe wilt and stunting of the tomato seedlings, but the bloodroot isolate caused no symptoms in inoculated seedling compared with those not inoculated. These results suggest that there may be more hosts for isolates in the F. oxysporum f. sp. lycopersici species complex than previously thought (1). An isolate (O-2603) has been deposited at the Fusarium Research Laboratory at Pennsylvania State University, University Park. Since bloodroot is now being sold commercially as an ornamental, disease management strategies may be needed. To our knowledge, this is the first report of a Fusarium crown rot of bloodroot. References: (1).V. Edel-Hermann et al. Online publication. doi:10.1111/j.1365-3059.2011.02551.x. Plant Pathology, 2011. (2) J. Leslie and B. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006.