Archivio Journal of Plant Pathology

Sclerotinia sclerotiorum is a destructive pathogen and has a wide range of hosts, including sunflower. The fungus produces sclerotia, which is a dormant structure and plays a vital role in the infection cycle of S. sclerotiorum. The initiation and maturation of sclerotia can be influenced by many factors. In this study, S. sclerotiorum isolate X-8, was collected from a diseased sunflower plant, and used to determine the role of H2O2 and cyclic adenosine 3', 5'-monophosphate (cAMP) in the sclerotia initiation and maturation. Results showed that the transition of S. sclerotiorum from vegetative growth to the initial stage of sclerotia is accompanied by a decrease of H2O2 and exogenously supplying H2O2 or diphenyleneiodonium chloride (DPI), an inhibitor of NADPH oxidase, in the culture medium promoted or inhibited the initiation of sclerotia, respectively. In addition, the cAMP-induced inhibition of sclerotia initiation and maturation were also accompanied by significantly decrease of H2O2. This was achieved by down- regulating the transcripts of Nox1 and Nox2 genes, the isoform of NADPH oxidase. Additionally, a decreased enzymatic activity of both superoxide dismutase (SOD) and catalase (CAT) were also detected in S. sclerotiorum after cAMP treatment. We concluded that H2O2 not only regulates the formation of sclerotia, but also cross-talks with cAMP in regulating the inhibition of sclerotial initiation and maturation.