Multiple species of Asteraceae plants are susceptible to root infection by the necrotrophic fungal pathogen Sclerotinia sclerotiorum

Authors: Underwood, William; GILLEY, MICHELLE - North Dakota State University; Misar, Christopher; GULYA, THOMAS - Retired ARS Employee; Seiler, Gerald; MARKELL, SAMUEL - North Dakota State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2021
Publication Date: 4/4/2022
Citation: Underwood, W., Gilley, M., Misar, C.G., Gulya, T.J., Seiler, G.J., Markell, S.G. 2022. Multiple species of Asteraceae plants are susceptible to root infection by the necrotrophic fungal pathogen Sclerotinia sclerotiorum. Plant Disease. 106:1366-1373. https://doi.org/10.1094/PDIS-06-21-1314-RE.
DOI: https://doi.org/10.1094/PDIS-06-21-1314-RE

Interpretive Summary: The fungus Sclerotinia sclerotiorum is a destructive plant pathogen that can infect many important crop plants and cause significant economic losses. Infection of most crop plants occurs on above-ground tissues and is initiated by airborne fungal spores. However, basal stalk rot of cultivated sunflower is caused by root infection initiated by mycelium arising from germination of fungal propagules known as sclerotia beneath the soil surface. Reports of root infection by S. sclerotiorum are uncommon, but not limited to sunflower. Most plant species with documented susceptibility to root infection by S. sclerotiorum belong to the Asteraceae family of flowering plants. In this study, we evaluated eight Asteraceae plant species for root susceptibility to S. sclerotiorum infection. We also compared the effects of root inoculation of sunflower with those of canola and dry edible bean, two crop hosts of S. sclerotiorum that do not exhibit root infections. We found that all tested Asteraceae species developed visible disease symptoms, while no visible symptoms of disease were observed on canola or dry edible bean. Infection of sunflower progressed through the roots to the base of the stem but was restricted in canola and dry edible bean. These results expand the host range for S. sclerotiorum root infection and highlight the relevance of root infection to important Asteraceae crop and weed species. Future research comparing root physiology and defense responses of Asteraceae species to non-Asteraceae crop plants may reveal the basis for susceptibility among members of this important family of flowering plants.

Technical Abstract: The necrotrophic fungal pathogen Sclerotinia sclerotiorum can cause disease on numerous plant species, including many important crops. Most S. sclerotiorum-incited diseases of crop plants are initiated by airborne ascospores produced when fungal sclerotia germinate to form spore-bearing apothecia. However, basal stalk rot of sunflower occurs when S. sclerotiorum sclerotia germinate to form mycelia within the soil which subsequently invade sunflower roots. To determine if other plant species in the Asteraceae family are susceptible to root infection by S. sclerotiorum, cultivated sunflower (Helianthus annuus) and seven other Asteraceae species were evaluated for S. sclerotiorum root infection by inoculation with either sclerotia or mycelial inoculum. Additionally, root susceptibility of sunflower was compared to that of dry edible bean and canola, two plant species susceptible to S. sclerotiorum but not known to display root-initiated infections. Results indicated that multiple Asteraceae family plants are susceptible to S. sclerotiorum root infection after inoculation with both sclerotia and mycelium. These observations expand the range of plant hosts susceptible to S. sclerotiorum root infection, elucidate differences in root inoculation methodology, and emphasize the importance of soil-borne infection to Asteraceae crop and weed species.