Annual Brome Control after Wildfire Using a Native Fungal Seed Pathogen

Final Report – JFSP 2007-1-3-10

Principal Investigators:

Susan E. Meyer - USFS RMRS Shrub Sciences LabJulie Beckstead - Gonzaga UniversityPhil S. Allen - Brigham Young University

Sagebrush Steppe

Cheatgrass Monoculture

Recurring Fire

The Problem

• Naturally occurring fungal seed bank pathogen• Generalist with wide host range • Abundant in annual brome seed banks• Targets dormant seeds in the carryover seed bank• Sometimes kills a large fraction of carryover seeds• Has potential for use as a mycoherbicide

in an IPM strategy for use in conjunction with range restoration seedings

Part of the Solution?Introducing

Black Fingers of Death(Pyrenophora semeniperda)

Project Objectives

1) To determine the effectiveness of this pathogen as a biocontrol organism for annual bromes, alone and in combination with other control measures.

2) To evaluate the risk to non-target organisms, including seeded species.

3) To develop strategies for minimizing identified risks.

Study Components

• Field in situ seed bank studies• Field inoculum persistence studies• Laboratory virulence screening• Bulk inoculum technology development• Host range studies• Fungicide trials• Field inoculation trials

Seed Bank Studies

• What fraction of seed production germinates the first year?•What fraction of ungerminated seeds is killed by black fingers of death?• How do these fractions change according to habitat

and weather?

A drier climate means lower germination and more potential seed carry over

More potential carryover means higher seed mortality

Inoculum Persistence Study

How long can pathogen inoculum persist in the absence of host seeds?

Virulence Screening

Do different strains of the pathogenvary in their ability to kill brome seeds?

How are more virulent strains different from less virulent strains?

Host Range Studies

Crested Wheatgrass Prairie Junegrass Indian Ricegrass

Can the pathogen infect seeds of other grass species?

How much of a problem will this create for use of the pathogen as a biocontrol organism?

At VERY high inoculum loads, most grass species are susceptible

But, even at these very high inoculum loads, seed mortality is often not very high.

Fast-germinating seeds can usually escape, and slow germinating species often have high resistance.

At inoculum loads achievable with biocontrol, dormant cheatgrass seeds show high mortality.

Indian ricegrass and needle and thread grass are resistant, and show little or no mortality at these loads,

even though they germinate slowly.

Even highly susceptible grasses like bluebunch wheatgrass and squirreltail can escape completely

through fast germination at inoculum loads that give high dormant cheatgrass seed mortality

Protecting Native Seeds with Fungicide

Bulk Inoculum Development

Field Inoculation Trials

Residual Effects on Non-target Host Seeds

Residual Effects on Non-target Host Seeds

How does black fingers of death kill so many nondormant cheatgrass seeds in the field?

Where do we go from here?

•Develop a delivery system that is lightweight , economical, and effective at low inoculum loads, and work toward a commercially viable biocontrol product.

•Select pathogen strains that are more effective as biocontrol agents.

•Carry out comprehensive evaluation of non-target host effects in realistic field restoration settings.

•Explore whether this pathogen might also be effective for seed bank biocontrol of other annual grass weeds, including medusahead and ventenata.

Some Recent PublicationsBeckstead J, Meyer SE, Molder CJ, Smith C. 2007. A race for survival: can Bromus tectorum seeds

escape Pyrenophora semeniperda-caused mortality by germinating quickly? Annals of Botany 99:907–914.

Meyer SE, Quinney D, Nelson DL, Weaver J. 2007. Impact of the pathogen Pyrenophora semeniperda on Bromus tectorum seed bank dynamics in North American cold deserts. Weed Research 47:54–62.

Meyer SE, Beckstead J, Allen PS, Smith DC. 2008. A seed bank pathogen causes seedborne disease: Pyrenophora semeniperda on undispersed grass seeds in western North America. Canadian Journal of Plant Pathology 30: 525–533.

Smith DC, Meyer SE, Anderson VJ. 2008. Factors affecting Bromus tectorum seed bank carryover in western Utah. Rangeland Ecology and Management 61:430–436.

Meyer SE, Allen PS. 2009. Predicting seed dormancy and germination timing for Bromus tectorum in a semi-arid environment using hydrothermal time models. Seed Science Research 19:225-139.

Leger EA, Espeland EK, Merrill KR, Meyer SE. 2009. Genetic variation and local adaptation at a cheatgrass (Bromus tectorum) invasion edge in western Nevada. Molecular Ecology 18:4366-4379.

Beckstead J, Meyer SE, Street L, Huck M, Connelly B. 2010. Cheatgrass facilitates spillover of a seed bank pathogen onto native grass species. Journal of Ecology 98:168-177.

Stewart TE, Allen PS, Meyer SE. 2009. First report of Pyrenophora semeniperda in Turkey and Greece. Plant Disease 93:1351.

Meyer SE, Stewart TE, Clement S. 2010. The quick and the deadly: Growth versus virulence in a seed bank pathogen. New Phytologist DOI: 10.1111/j.1469-8137.2010.03255.x.

Meyer SE, Leger EA. 2010. Inbreeding, genetic variation, and invasiveness: The strange case of Bromus tectorum. Rangelands 32:6-11.

Scott JW, Meyer SE, Merrill KR, Anderson VJ. 2010. Local population differentiation in Bromus tectorum in response to habitat-specific selection regimes. Evolutionary Ecology. DOI 10.1007/s10682-010-9352-y

Thanks to Team BFOD!Botanical Society of America Meeting

Snowbird July 2009

Cheatgrass RIP

For more information: www.cheatgrassbiocontrol.org