Nuclear behavior and evolution of two populations of the western gall rust fungus

Vogler, D. R., Epstein, L, and Cobb, F. W., Jr. 1997.

Department of Environmental Science, Policy, and Management, University of California, Berkeley.

Mycological Research 101(7):791-797.


Peridermium harknessii, cause of western gall rust of pines, comprises two populations of multilocus electrophoretic types (zymodemes) in the western United States. When stained with a DNA-specific fluorochrome, mature, ungerminated aeciospores from zymodeme I were found to be predominantly binucleate (70%), as were those of the related macrocyclic species, Cronartium quercuum (74%), whereas aeciospores from zymodeme II were predominantly uninucleate (93%). Within each zymodeme, aeciospores with two nuclei had significantly (P = 0.01) more DNA than spores with one nucleus, and numbers of nuclei in germlings increased arithmetically over time. These data suggest that aeciospore nuclei in both zymodemes I and II divide mitotically, not meiotically, as is consistent with an asexual life cycle.

Photometric measurements also indicated that the amount of DNA in one nucleus of a uninucleate zymodeme II aeciospore was similar to the total amount of DNA in a binucleate zymodeme I aeciospore. These data, coupled with recent isozyme studies, suggest either that zymodeme II evolved after karyogamy of zymodeme I and an unidentified zymodeme, or that zymodeme I evolved after haploidization of zymodeme II.

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