The axenic culture of Puccinia species from uredospores: experiments on nutrition and variation

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Abstract
Eighteen isolates of Puccinia were compared for ability to grow as saprophytes. After incubation of uredospores until growth ceased, six isolates developed an extensive mycelium, nine isolates formed a limited mycelium, and three isolates produced only scant saprophytic hyphae.The following factors were tested for their effect on the growth of P. graminis tritici race 126 Anz 6,7: inoculation from different uredosori; mode of application of the inoculum; density of the inoculum; composition of the medium. Using a dense inoculum it was found that yeast extract and peptone may be replaced by aspartic acid and a sulphur amino acid such as cysteine, and that glucose, fructose, mannose, or mannitol will substitute for sucrose as principal carbon source. However, no medium or method of inoculation was found to be completely reliable. A study of thinly seeded cultures showed that although 20–80% of sporelings could initiate saprophytic growth, only 3–6% eventually formed macroscopically visible colonies. It was found that frequencies of growth initiation and colony formation were highest on the thinnest layer of nutrient agar tested, and that sporelings mutually stimulated one another's growth. We conclude that the success of present culture techniques depends on an adequately high inoculum density, and other processes which are not understood.

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