GENERAL INFORMATION project1 project2

Sclerotinia sclerotiorum and Botrytis cinerea are the two most closely related ascomycetes in the family Sclerotiniaceae. The next most closely related family member is Monilinia, which causes diseases of many stone fruits. All members of the Sclerotiniaceae can produce sclerotia, which are survival structures that can persist in soils for years.

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When grown in culture, S. sclerotiorum produces black sclerotia once it hits the edge of the Petri plate and depletes the nutrients. This fungus does not produce asexual spores. Instead, sclerotia can give rise to fruiting bodies, called apothecia, which produce ascospores. Once released, these spores infect plants in the field during bloom. Systemic infections lead to the formation of more sclerotia, which can form in organs such as bean pods shown above. Infected pods contain few and poorly developed seeds.
B. cinerea produces asexual spores, called conidia, in culture. The sclerotia it produces are much smaller in comparison to S. sclerotiorum. The example above shows that conidia infect tomato plants in the greenhouse or growth chambers when humidity is high and temperatures are cool. The sexual form of B. cinerea is called Botryotina fuckeldiana.
 

PROJECT 1

Spray inoculation of tomato with conidia of B. cinerea results in expanding lesions and petiole collapse.

Spray inoculation of the nightshade Solanum lycopersicoides with B. cinerea triggers primarily localized lesions that do not spread.

The two plant species shown above are cross-compatible. S. lycopersicoides is significantly more resistant to B. cinerea than tomato and a potential resource for crop improvement. We recently demonstrated that resistance of S. lycopersicoides to B. cinerea is associated with induced hyphal death. Conversely, the fungus continues to proliferate on susceptible tomato leaves. In order to determine the basis of this variation, we are currently investigating differences in plant defense activation between tomato and the nighshade. The genetic basis of resistance is another important goal of our research program. The gray mold fungus is primarily a problem for greenhouse-grown and fresh market tomatoes.

 

PROJECT 2
B. cinerea and S. sclerotiorum are necrotrophic pathogens that kill host cells in advance of colonization. These fungi do so by producing non-selective toxins and enzymes that degrade plant cell walls. Oxalic acid can be regarded as a non-selective toxin. It causes foliar wilting symptoms and is an essential virulence factor of S. sclerotiorum. B. cinerea also produces oxalic acid but its role is less clear because smaller amounts of it are produced during later stages of infection relative to S. sclerotiorum. We have gained support for the hypothesis that oxalate-induced wilting is at least partially controlled through deregulation of guard cell physiology. Our data suggest that opening of stomatal pores also facilitates the emergence of hyphae from the uninoculated leaf surface to promote secondary colonization.

This image shows green fluorescent protein-tagged S. sclerotiorum during infection of a Vicia faba leaf. Our model suggests that this pathogenic fungus secretes oxalic acid, which induces opening of stomatal pores by increasing the osmotic pressure of guard cells.

PowerPoint presentation of Sclerotinia data