SUMMARY: Sporidesmin production by 37 recently isolated strains and one heavily sporing laboratory isolate of was assayed by toxicity to tissue culture cells and related to sporulation and growth. Under standard cultural conditions strains varied greatly in their ability to produce Sporidesmin and spores. Heavily sporing cultures produced most sporidesmin and the level of sporidesmin production by a strain could be changed by manipulation of cultures in ways which also stimulated or depressed sporulation. Ultraviolet radiation increased sporulation and sporidesmin production in 33 strains. Shaken cultures, in which growth was good but sporulation suppressed, produced no sporidesmin. The close association of sporidesmin production with sporulation supports the reliability of spore counts as an index of pasture toxicity. Most and probably all strains of are potentially able to produce moderate to high levels of sporidesmin. Ultraviolet radiation may stimulate production of sporidesmin by the growing fungus but destroys it in aqueous solutions leached from the senescent mycelium.


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