Infection and Development of the Obligate Parasite Catenaria Allomycis on Allomyces Arbuscula

SUMMARY

Catenaria allomycis occurs as an endobiotic parasite of Allomyces arbusculo. Light and electron-microscopic observations on the establishment of the parasite are described. The encysted zoospore produces a germ tube which attaches to the Allomyces hypha by an appressorium. An infection tube arises from the appressorium and penetrates the host wall. A double-layered papilla is produced by the host in response to invasion by the parasite. The plasma membrane and the papilla are ruptured by continued growth of the infection tube resulting in direct contact of the Catenaria with the host cytoplasm. The thallus released from the cyst into the cytoplasm is surrounded by a wall throughout development. It undergoes rapid growth with a corresponding deterioration of the host cytoplasm. Sporangium development culminates in the formation of discharge tubes which penetrate the host wall and the release of the posteriorly uniflagellate zoospores shortly thereafter.