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Etiology

The Effect of Free Water on the Potential Germinability of Cold-Dormant Urediniospores of Puccinia graminis f. sp. tritici. J. S. Melching, Research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Bldg. 1301, Frederick, MD 21702; M. R. Bonde, and W. M. Dowler. Research plant pathologist, and research leader, respectively, U.S. Department of Agriculture, Agricultural Research Service, Foreign Disease-Weed Science Research, Ft. Detrick, Bldg. 1301, Frederick, MD 21702. Phytopathology 81:734-738. Accepted for publication 4 February 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/Phyto-81-734.

Germination of fresh urediniospores of Puccinia graminis f. sp. tritici, race 56, always was greatly reduced after storage at –196 C (“cold-dormant” spores). Immersing cold-dormant spores in water or buffer solution for 1–2 h at room temperature caused irreversible injury to a majority of the population but, contrary to published reports, up to 32% of the spores survived as judged by subsequent germination tests on water agar. When cold-dormant spores were heat-shocked at 40 C for 5 min before incubation on water agar at 18 C, their germinability was comparable to that of fresh nonfrozen spores of the same lot. Following liquid immersion of cold-dormant spores, subsequent heat-shocking did not reverse dormancy; if heat-shocked in liquid, further injury to spores occurred, but drying spores before heat-shock provided protection against further damage. Both freshly collected and cold-dormant spores, regardless of preincubation treatments, germinated at higher levels on water agar than in water or buffer medium during 2-h incubation at 18 C in the dark.