Abstract
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.
Highlights
Sclerotium rolfsii Sacc. is a serious ubiquitous soilborne phytopathogenic fungus, causing Southern blight of a wide range of agricultural and horticultural crops (Aycock, 1966 and Anahosur, 2001 and Galdames and Diaz, 2010 and Kwon et al, 2013 and Shen et al, 2014 and Mahadevakumar et al, 2015)
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
All S. rolfsii isolates showed optimum mycelial growth on the basal medium amended with ammonium chloride (20.08 - 20.45 mm/day) but complete growth inhibition occurred on ammonium acetate treated medium
Summary
Sclerotium rolfsii Sacc. is a serious ubiquitous soilborne phytopathogenic fungus, causing Southern blight of a wide range of agricultural and horticultural crops (Aycock, 1966 and Anahosur, 2001 and Galdames and Diaz, 2010 and Kwon et al, 2013 and Shen et al, 2014 and Mahadevakumar et al, 2015). The fungus is notorious for its ability to induce dark stem rot, during any plant growth stages, followed by drooping and wilting of leaves and gradually wilting of the whole plant Such wilted plants show white cottony fungal thread girdling the basal part of the stem and moving below the stem to roots (Kator et al, 2015 and Sun et al, 2020 and Punja et al, 1985). These compounds affect cell walls, hydrolyze pectin and alter host defensive responses (Bateman and Beer, 1965 and Kritzman et al, 1977 and Punja, 1985 and Ferrar and Walker, 1993) This fungus is widely distributed and causes heavy economic losses on many crops (Aycock, 1966 and Gurha and Dubey, 1983 and Fery and Dukes, 2002 and Billah, 2017 and Sun et al, 2020). This study was undertaken to examine the effect of different nitrogen and carbon sources on the mycelial growth, sclerotial production and germination of three Tunisian S. rolfsii isolates
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