Abstract
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.
Highlights
Fungi can adapt to environmental conditions and produce different physiological responses
For most diseases caused by S. sclerotiorum, ascospores produced through carpogenic germination are the primary source of epidemics [1]
High soil moisture is required for apothecial development, while dry periods can prevent carpogenic germination [1, 23]
Summary
Fungi can adapt to environmental conditions and produce different physiological responses. Sclerotia from S. sclerotiorum isolates from Brazil were capable of germinating carpogenically without preconditioning. Somente isolados do Brasil foram capazes de produzir apotécio sem pré-condicionamento. Com pré-condicionamento a 4oC por 40 dias, os isolados do Brasil e dos EUA produziram apotécio. The 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]. Sclerotia of S. sclerotiorum were reported to require a preconditioning period under wet and low temperature conditions [15, 16, 21] and germinate
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