Conidia of Glomerella cingulata did not germinate under crowded conditions. This was not due to limiting effects of concentration of oxygen or carbon dioxide. The ill effect of crowding on germination was alleviated by adding large amounts of twice-crystallized bovine serum albumin. Nearly 88 % conidia germinated in redistilled water when they were present in amounts less than 100/mm.2; but on addition of the washings and exudates of conidia into such suspensions, germination as well as length of germ tubes was markedly decreased. Germination of conidia was increased by prolonged leaching of the conidia by soaking in redistilled water. More than 30% of the thoroughly leached conidia germinated in redistilled water under crowded conditions (3000/mm.2), whereas less than 2% of the conidia sampled before leaching germinated under similar conditions. It is concluded that diffusible inhibitory compounds from the conidia appear to be responsible for the inhibition of germination. Several solubility classes of inhibitory compounds have been extracted from the cultures of G. cingulata. Among them, a basic fraction was relatively more toxic to G. cingulata than to Bacillus subtilis.
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