Effect of Salinity, Temperature and Carbon Source on the Growth and Development of Sclerotia of Sclerotinia sclerotiorum Isolated from Semi-arid Environment

Studies were conducted to determine the effects of temperature, solute potential and carbon source on the mycelial growth, sclerotia development, and apothecium production of an isolate of Sclerotinia sclerotiorum. Mycelial growth rate was greatest at 25 degrees C on potato dextrose agar (PDA) medium amended with up to 2% NaCl (psi s <= 1.91 MPa) and thereafter, growth rate declined. The least number of sclerotia were produced at 20 degrees C on both PDA and malt extract agar (MEA) amended with 8% NaCl (psi s=6.62 MPa). With increasing temperature and decreasing solute potential the number and size of sclerotia were significantly reduced. The combined effect of temperature, solute potential and carbon source on sclerotia production were highly significant and had an impact on the development of the rind layer cells of sclerotia. These cells lacked a transparent cell wall which was surrounded by a compact melanized layer, and some of these cells appeared to be devoid of cell contents or were totally vacuolated. The survival of the sclerotia with increase in salinity and temperature appeared to affect melanization and the nature of the rind cells. The observations of this study re-enforces the need for an integrated disease management to control S. sclerotiorum.