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 Godoy, C.V.; Koga, L.J.; Oliveira, M.C.N.; Hill, C.B.; Hartman, G.L. Mycelial growth, pathogenicity, aggressiveness and apothecial development of Sclerotinia sclerotiorum isolates from Brazil and the United States in contrasting temperature regimes. Summa Phytopathologica, v.43, n.4, p.263-268, 2017.Keywords: carpogenic germination, white mold, temperature, ecotypes ABSTRACT 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 30 o C 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. RESUMOOs fungos podem se adaptar a condições ambientais e produzir diferentes respostas fisiológicas. O objetivo deste estudo foi verificar a existência de ecótipos de temperatura para Sclerotinia sclerotiorum em isolados do Brasil e dos EUA. Dez isolados de S. sclerotiorum de regiões tropicais e subtropicais do Brasil e seis dos EUA foram avaliados para crescimento micelial, patogenicidade, agressividade em feijão, canola e soja e formação de apotécio em temperaturas contrastantes. Palavras-chave: germinação carpogênica, mofo-branco, temperatura, ecótipoThe fungus Sclerotinia sclerotiorum (Lib.) de Bary is an important pathogen which is distributed worldwide and attacks over 600 plant species, including important crops such as sunflower, soybean, oilseed rape, dry bean, peanut, lentil, various vegetables and numerous weeds (3, 7,18). This fungus produces sclerotia as survival structures that can germinate either carpogenically, to form apothecia which in turn release ascospores for infection, or myceliogenically, to directly infect host plants (20). For most diseases caused by S. sclerotiorum, ascospores produced through carpogenic germination are the primary source of epidemics (1). Development of diseases caused by S. sclerotiorum is strongly dependent on environmental factors. High soil moisture is required for apothecial development, while dry periods can prevent car...