Mycelial growth, pathogenicity, aggressiveness and apothecial development of Sclerotinia sclerotiorum isolates from Brazil and the United States in contrasting temperature regimes

Authors: GODOY, CLAUDIA VIEIRA - Embrapa; KOGA, LUCIMARA JUNKO - University Of Illinois; NEVES DE OLIVEIRA, MARIA CRISTINA - Embrapa; HILL, CURTIS - Agricen Sciences; Hartman, Glen

Submitted to: Summa Phytopathologica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2017
Publication Date: 12/1/2017
Citation: Godoy, C., Koga, L., Neves De Oliveira, M., Hill, C.B., Hartman, G.L. 2017. Mycelial growth, pathogenicity, aggressiveness and apothecial development of Sclerotinia sclerotiorum isolates from Brazil and the United States in contrasting temperature regimes. Summa Phytopathologica. 43(4):263-268.

Interpretive Summary: Fungi can adapt to environmental conditions and produce different physiological responses. The fungus that causes Sclerotinia stem rot of soybean is considered a cool season disease primarily occurring in the northern states in the United States. This study verified the existence of fungal (Sclerotinia sclerotiorum) temperature ecotypes in isolates from Brazil and the United States. Ten fungal isolates from tropical and subtropical regions of Brazil and six isolates from the United States were used to measure mycelial growth, pathogenicity and aggressiveness of the fungus on bean, canola and soybean, as well as formation of a fruiting in contrasting temperatures. For mycelial growth, regardless of the origin, all isolates grew faster at 20°C, compared to 27°C. For pathogenicity and aggressiveness, disease severity was greater at 20°C than at 30°C for all isolates. For spore production, only Brazilian isolates were capable of producing the fruiting structure without preconditioning. None of the 16 isolates was capable of producing fruiting structures at 30oC after 40 days. Results indicated that there was no adaptation of isolates from Brazil to grow or colonize leaflets at higher temperatures, whereas isolates from the United States did adapt to higher temperatures. Only isolates from Brazil were capable of forming fruiting structures without preconditioning. This information is important to scientists (plant pathologists, ecologists, mycologists, soybean breeders) interested in soybean diseases and adaptation of fungi to different temperature conditions.

Technical Abstract: Fungi can adapt to environmental conditions and produce different physiological responses. The aim of this study was to verify the existence of Sclerotinia sclerotiorum temperature ecotypes in isolates from Brazil and the USA. Ten S. sclerotiorum isolates from tropical and subtropical regions of Brazil and six isolates from the USA were used to measure mycelial growth, pathogenicity and aggressiveness on bean, canola and soybean, as well as apothecial formation at contrasting temperatures. For mycelial growth, regardless of the origin, all isolates grew faster at 20°C, compared to 27°C. For pathogenicity and aggressiveness, disease severity was greater at 20°C than at 30°C considering all isolates. As regards apothecial production, only Brazilian isolates were capable of producing apothecia with no preconditioning. After preconditioning at 4°C during 40 days, isolates from Brazil and the USA produced apothecia. None of the 16 isolates was capable of producing apothecia at 30oC after 40 days. Results indicated no adaptation of S. sclerotiorum isolates from Brazil to grow or colonize leaflets at higher temperatures, compared to isolates from the USA. Only sclerotia from S. sclerotiorum isolates from Brazil were capable of germinating carpogenically without preconditioning.