Studies on the Isolation and Growth of Plant Rusts in Host Tissue Cultures and Upon Synthetic Media. I. Gymnosporangium

SUMMARY

Through the use of a tissue-culture technique, systemically infected dual-membered callus cultures have been established from the telial galls of Gymnosporangium juniperi-virginianae produced on Juniperus, and maintained for several years by periodic transfer. Seven strains of this rust have been isolated from these tissue cultures and grown in axenic culture in the complete absence of the host cells. They are able to survive continuous transfer on various synthetic media. All of these strains after axenic culture proved able to reinfect their alternate rosaceous hosts in tissue culture and under field conditions, and four of them, which were presumably dikaryotic, were also capable of infecting Juniperus. Infection studies on various hosts indicate that one strain is atypical in attacking both Crataegus and Pyrus and showing the characteristics of G. globosum when parasitizing Crataegus.