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Abstract Detail

Mycological Section

Masi, Marco [1], Meyer, Susan E. [2], Clement, Suzette [2], Cimmino, Alessio [3], Andolfi, Anna [3], Evidente, Antonio [3].

Phytotoxin production by the pathogen Pyrenophora semeniperda and its possible role in pathogenesis on Bromus tectorum seeds.

The ascomycete seed pathogen Pyrenophora semeniperda is abundant in Bromus tectorum (cheatgrass) seed banks, where it can cause mortality of up to 50% of the seeds produced each year. As a necrotrophic pathogen, it produces phytotoxic compounds as part of pathogenesis on host seeds. We first investigated phytotoxin production by this pathogen in traditional media: wheat seed solid culture and potato dextrose broth (PDB). We confirmed earlier findings that the fungus produces large quantities of cytotoxic cytochalasin B in wheat seed culture, along with smaller quantities of the related compounds cytochalasins A, F, and deoxaphomin. These compounds were also produced in similar quantities in solid culture on host (cheatgrass) seeds, but were not produced in PDB culture. The fungus also produces pyrenophoric acid, a novel sesquiterpenoid penta-2, 4-dienoic acid structurally related to abscisic acid, in both wheat seed and cheatgrass solid culture. We studied the phytotoxicity of these compounds in cheatgrass seedling bioassays. All induced growth suppression of both radicles and coleoptiles, but had no effect on germination per se. Cytochalasin A proved to be the most toxic compound overall and pyrenophoric acid the least toxic. However, when pyrenophoric acid was combined in pairwise tests with each cytochalasin, a synergistic interaction increased toxicity to seedling coleoptiles, especially with cytochalasins A and B. Interestingly, we did not observe this synergistic growth suppression effect for radicles. In studies to investigate the effect of medium on cytochalasin B production, we found that liquid media that contained components derived from grass seeds could stimulate the production of this compound, suggesting that it has a specific role in in seed pathogenesis. The compounds produced in PDB culture belonged to the spirocyclic lactam group, and included the new compound spirostaphylotrichin W. Spirocyclic lactams are also produced by the wheat tan spot pathogen P. tritici-repentis. These compounds had little effect on cheatgrass seedlings but caused necrosis in leaf puncture bioassays, suggesting that their production by P. semeniperda may be a legacy of its descent from a group of primarily foliar pathogens.  

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1 - Brigham Young University, Department of Plant and Wildlife Sciences, Provo, UT, 84602
3 - University of Naples Federico II, Department of Chemical Sciences, Naples, Italy

Pyrenophora semeniperda
Bromus tectorum
pyrenophoric acid.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Eyrie/Boise Centre
Date: Monday, July 28th, 2014
Time: 5:30 PM
Number: PMY001
Abstract ID:168
Candidate for Awards:None

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