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

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.