Exploring the Feasibility of Sclerotium rolfsii VrNY as a Potential Bioherbicide for Control of Swallowworts (Vincetoxicum spp.)

Abstract

Pale swallowwort (PSW) and black swallowwort (BSW) are two viney milkweeds native to Europe that have increasingly become problematic and noxious weeds in eastern North America. An indigenous fungal isolate, Sclerotium rolfsii VrNY, was discovered causing significant mortality in a dense stand of PSW in a park in upstate New York. Although this fungus is a known pathogen with a broad host range, we evaluated the host potential of S. rolfsii VrNY on a limited range of related and nonrelated U.S. species as a critical first step to assess its suitability as a mycoherbicide for PSW and BSW. In addition, PSW and BSW produce the specific stereoisomer (−)-antofine, a compound with antimicrobial and phytotoxic activity that could inhibit the pathogen. Tests revealed this compound had no effect on S. rolfsii VrNY. This isolate caused significant mortality on all broadleaf plants tested (Asclepias syriaca, Asclepias curassavica, Apocynum cannabinum, Monarda fistulosa, Rudbeckia hirta, PSW, BSW) with the exception of Glycine max, and had no effect on the monocots Schizachyrium scoparium and Zea mays. Although these laboratory studies indicate that most broadleaf vegetation may be susceptible to the pathogen, S. rolfsii might have potential as a mycoherbicide in natural eco-niche environments where invasive PSW and BSW have already become the predominant vegetation. Further laboratory testing of S. rolfsii and limited field testing at the initial discovery site are needed in order to prevent premature rejection of this isolate as a potential management tool against these highly invasive weeds.

Tolerance of Swallowworts (Vincetoxicumspp.) to Multiple Years of Artificial Defoliation and Clipping

“…Several candidate insect and pathogen agents have been assessed to varying degrees (Berner et al 2011;Dolgovskaya et al 2014;Gibson et al 2014;Hazlehurst et al 2012;Leroux 2014;Maguire et al 2011;Casagrande 2010, 2011;Weed et al 2011a,b). Given the frequency with which leaf-feeding insects have been used in other programs (Winston et al 2014), it was reasonable to assume that a similar type of agent would be used against swallowworts.…”

Temporal dynamics of plant–soil feedback and root‐associated fungal communities over 100 years of invasion by a non‐native plant

“…Observed localized population declines of V. rossicum in North America (Gibson ; Fletcher Wildlife Garden ; Gibson et al . ) may not be related to pathogen accumulation over time. For example, a fungal strain of S. rolfsii causes wilting and mortality at one site in New York state (Gibson ; Gibson et al .…”

“…For example, a fungal strain of S. rolfsii causes wilting and mortality at one site in New York state (Gibson ; Gibson et al . ), but V. rossicum was not observed at that site until after 1995 (C. Southby & L. R. Milbrath personal communication with NJD). This pathogen has not been observed in Ontario and was not detected in our fungal DNA sequences.…”

“…A potential pathogen on V. rossicum was defined as an OTU in a genus that contained at least one species identified as a plant pathogen on any plant species in the literature. This coarse categorization was required because few studies have explicitly tested pathogens on V. rossicum or its close relatives (Berner et al 2011;Gibson 2012;Gibson et al 2014). We searched for occurrences of potential pathogens in two ways.…”

“…We chose this highly invasive species because it is a perennial with a dense root system and its roots are colonized by fungal pathogens and AM fungi in North America (Couture, Brisson & Emond 2003;). In addition, a fungal stem pathogen, Sclerotium rolfsii VrNY, has recently been shown to be causing population declines at a site in New York state in the USA (Gibson 2012;Gibson et al 2014), and there is anecdotal evidence for localized population declines in Ottawa, Ontario, Canada, where it has been present since the 1950s (McNeill 1981;Fletcher Wildlife Garden 2014). First, we identified 20 sites with similar environmental and soil conditions that had been invaded by V. rossicum ranging in time from zero to c. 100 years.…”