Fungal plant pathogen Colletotrichum shisoi identified as a potential biological control agent of invasive Perilla frutescens in the United States

ABSTRACT

Perilla frutescens (L.) Britton, an annual plant in the mint family, is considered invasive in the United States where it excludes native vegetation in natural areas and can cause respiratory illness in livestock. An effective biological control agent would improve perilla management, but none have been developed or proposed. This study investigated the biocontrol potential of a fungal pathogen, Colletotrichum shisoi, recently found infecting perilla in North America. The growth rates and morphology of seven Colletotrichum shisoi isolates were recorded. A virulence assay was performed on two perilla accessions, and the number and size of foliar lesions produced were used to select a single isolate, Colletotrichum shisoi isolate 21-072, exhibiting consistently high virulence for further evaluation of biocontrol efficacy and host specificity. Treatment with 0.5 mL of 1 × 10⁷ spores/mL H₂O caused a 52% reduction in shoot height and 84% reduction in root length of invasive perilla seedlings compared to a control treatment (P < 0.001). Seedlings treated with 1 × 10⁸ spores/mL had a 100% mortality rate. Formulation of inoculum in a 1:1 water:oil emulsion reduced dew period requirements for causing >50% plant mortality from 48 to 24 h, but oil emulsions exhibited a mild phytotoxic effect on seedlings. Four additional perilla accessions were susceptible to C. shisoi, and none of 34 other species included in host range experiments developed disease symptoms following inoculation. These results suggest C. shisoi 21-072 could be an effective antagonist of perilla and likely poses a low risk of non-target impacts.

KEYWORDS:

• Invasive
• weed
• pathogen
• fungus
• perilla
• Colletotrichum

Acknowledgements

The preparation of this manuscript was supported by the U.S. Department of Agriculture, Agricultural Research Service through Project 8044-33000-047-000-D. The findings and conclusions in this publication are those of the authors and should not be construed to represent any official USDA or U.S. Government determination or policy. Mention of trade names or commercial products in this report is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. Pathogen isolates were collected from the Chesapeake and Ohio Canal National Historic Park under permit CHOH-2021-SCI-0023 and in collaboration with A. Landsman and L. Strickler.

Data availability

Data and computer software code used in the preparation of this manuscript will be made available upon reasonable request to the corresponding author.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The preparation of this manuscript was supported by the U.S. Department of Agriculture, Agricultural Research Service through Project 8044-33000-047-000-D.