Abstract
Formation of sclerotia in a strain of Sclerotinia libertiana Fuckel using Czapek-Dox agar medium was highest at pH 4.0_??_6.0 and at 22_??_25°C. The response was better under darkness than under light. However, when a potato-extract medium was used the optimum temperature range extended, and even at 15_??_27°C mature sclerotia formed. The addition of indole-3-acetic acid (IAA) to the Czapek-Dox medium containing riboflavine stimulated the formation of sclerotia under fluorescent light. Though iodoacetic acid, a -SH reagent, also had a stimulatory effect, cysteine had little inhibitory effect on sclerotial formation. Formation was markedly inhibited by p-aminobenzoic acid (PABA), especially in the presence of tyrosine or tryptophan, and excess ammonium salts in the medium also produced an inhibitory effect. It was assumed that accumulation of an intermediary metabolite with high reactivity with -SH groups was necessary for sclerotial formation, but PABA and excess ammonium salts inhibited the accumulation.
