SOME UREDOSPORE CHARACTERISTICS OF IMPORTANCE IN EXPERIMENTAL EPIDEMIOLOGY,
ARMY BIOLOGICAL DEFENSE RESEARCH CENTER FREDERICK MD
Pagination or Media Count:
The experimental initiation of stem rust epidemics with uredospores of Puccinia graminis var. tritici is a valuable technique for the epidemiologist. Successful utilization of the technique requires that sufficient quantities of uredospores of the desired race be available for timely application and that the infectivity of these spores be properly assessed prior to their employment. Moisture content of spores and their storage temperature have a major influence on viability retention. Reducing spore moisture to about 10 and storing at 4 C will generally retain satisfactory germinability in most cultures for 1 to 2 years. Uredospores vacuum-dried and stored in the absence of oxygen and water vapor may retain viability for at least 5 years. Spores at ultra-low temperatures in liquid nitrogen -196 C may remain viable indefinitely however, they require heat shock at 40 C to restore maximum germinability. Rate of cooling and subsequent thawing are not critical for survival, nor is moisture content below 25. Laboratory germination tests have most frequently been used to assess the infectivity of spores. By themselves these are inadequate, however, because germination is but the first in a series of sequential events required for infection. These events are modified by factors inherent in the spore, by those peculiar to the host plant, and by the environment.