Comparative Germination of Culture-Produced and Plant-Produced Sporangia ofPythium ultimumin Response to Soluble Seed Exudates and Exudate Components

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Abstract
Sporangia of Pythium ultimum were produced in vitro on culture media commonly used for the cultivation of Pythium spp. and on media amended with germinating seeds and excised radicles of various plant species. Their responses to seed exudates and selected sugars and amino acids were determined. On synthetic media, sporangia germinated in response to certain sugars and amino acids as well as cotton seed exudate. However, when produced in association with plant tissue or on media amended with .alpha.-phosphatidyl choline, sporangia failed to germinate in response to any sugar or amino acid tested individually or in combination, despite their ability to germinate in response to cotton seed exudate. Because sporangia reared in vitro more closely reflect the nature of those in soil when produced on plant-tissue-amended media than when produced on other conventional media, we concluded that molecules other than sugars or amino acids are responsible for activating sporangia of P. ultimum and establishing host-pathogen interactions under natural conditions.