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United States Department of Agriculture

Agricultural Research Service


item Groth James V
item Mccain John W
item Roelfs Alan P

Submitted to: Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/1994
Publication Date: N/A
Citation: N/A

Interpretive Summary: Plant pathogenic fungi are genetically variable organisms. Their genetic variation helps them adapt to their environment. It also allows them to adapt to man's attempts to control them by breeding disease resistant crops. Therefore, it is important to understand what factors promote genetic variation in fungi that cause diseases in crops. One such factor is commonly thought to be sexual reproduction, because sex produces new combinations of genes. Fungi with sexual reproduction in their life cycles are generally assumed to have more genetic variation than fungi that reproduce only with asexual spores. We tested this assumption by comparing two sexual populations of the bean rust fungus with two populations of the fungus that are unable to produce sexual spores. We found that the asexual populations were no less variable than the sexual populations. This unexpected result shows that other factors can be as important as sexual reproduction in maintaining the adaptability of plant pathogenic fungi. This knowledge will stimulate scientists to find what those factors are. Once the important factors are known, it may be possible to counteract their effects. That would make disease control more effective in the long run.

Technical Abstract: Organisms that reproduce sexually have been assumed to be more genetically diverse (have more phenotypes with a more even frequency distribution) than those that are clonal. Rust fungi usually have regular sexual reproduction, but asexual species or populations are not uncommon. Two field collections of the bean rust fungus from sexually-reproducing populations were compared with two collections from apparently nonsexual populations. Neither virulence on ten differential lines of beans nor isozyme band patterns of five enzymes, as compared by the Gleason, Shannon, or Rogers indexes of difference or with simple matching coefficients, supported the hypothesis of less population polymorphism in the asexual collections. The distribution of virulence differences among isolates in one of the asexual collections suggested that sexual reproduction was occurring at a low frequency which was, nevertheless, sufficient to maintain genetic variability.

Last Modified: 10/20/2017
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