In vitro studies were conducted on Potato Dextrose Agar using different carbon (C) and nitrogen (N) sources to evaluate their effects on the mycelial growth, and the sclerotial development of three Tunisian Sclerotium rolfsii Sacc. isolates. Radial growth was optimum on basal medium supplemented with ammonium chloride (0.48 gram of nitrogen per liter (g of N.L-1)) as N source but was restricted on L-Arginine and completely inhibited on ammonium acetate amended media (0.48 g N.L-1). Sclerotial initiation occurred from the 3rd to the 12th day of incubation for all tested isolates. Potassium nitrate was the most suitable N source for sclerotial formation whereas sclerotial development was completely inhibited on ammonium acetate amended medium. Optimal sclerotial germination was recorded using L-Arginine (78-80%) followed by L-Asparagine (46-94%) and ammonium chloride (46-88%) as N sources. Nevertheless, the lowest sclerotial germination rate was noted on sodium nitrate and ammonium acetate amended media. As for C sources (16 gram of carbon per liter (g of C.L-1)), optimal radial growth occurred using D-mannitol for Sr1 and Sr2 isolates and maltose for Sr3, but no mycelial growth was recorded using sodium citrate for all isolates. All C sources tested, except sodium citrate, were suitable for sclerotial formation, production, and germination. Mature sclerotia became brownish after 6 to 12 days of incubation and sclerotial production was highest using D-mannitol, maltose, and D-glucose, depending on isolates used, as C sources. Optimal germination of sclerotia was noted using D-glucose, D-mannitol and maltose for Sr1 isolate, maltose for Sr2 and D-glucose and maltose for Sr3. It was concluded that N and C sources are both important factors for the growth of S. rolfsii and its survival.

Four endophytic fungal isolates, naturally associated with Solanum tuberosum L., were evaluated for their antagonistic activity against Rhizoctonia solani and their ability to suppress black scurf disease of potato tubers. To identify the potential implication of antifungal compounds in their inhibitory activity, cell-free culture filtrates were produced and tested for their antifungal potential against R. solani mycelial growth and for their protective effect against development of on potato tuber slices.  Results showed that percent inhibition of R. solani mycelial growth, based on in vitro antibiosis tests, ranged between 16 to 59%. Hyphal damage and lysis were the most frequent stress responses exhibited by the target pathogen during its in vitro interactions with the potato-associated fungi tested. All Cell-free culture filtrates of tested fungi had significantly inhibited the radial growth of Rhizoctonia solani Rs20. The cell-free culture filtrates of Penicillium chrysogenum and Aspergillus niger had decreased pathogen growth by more than 60% over control. These two filtrates (P. chrysogenum and A. niger) were found to be the most effective in decreasing the decay incidence in potato slices by 36 and 40%, respectively, as compared to pathogen-inoculated and untreated control. Thus, the present study clearly demonstrated that fungal isolates, occurring ubiquitously within potato plants, may be explored as potent biocontrol agents against potato-associated fungal pathogens and as source of bioactive metabolites for R. solani suppression.