Submitted to: Revista Mexicana de Fitopatologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2002
Publication Date: 5/1/2002
Citation: PEREZ, L., OLALDE, V., VANDEMARK, G.J., MARTINEZ, O., MARTINEZ, J., VAZQUEZ, G., LARA, J. GENETIC RELATIONSHIPS AMONG ISOLATES OF SCLEROTIUM CEPIVORUM BERK. BASED ON RAPD ANALYSIS. REVISTA MEXICANA DE FITOPATOLOGIA, 20:187-192. 2002.
Interpretive Summary: Sclerotium cepivorum Berk. is a soilborne fungus that causes `white rot¿ diseases of several Allium species, including onions and leeks. In Mexico, many garlic producing areas are so infested with the pathogen that production losses approaching 100% have been reported. Isolates of the fungus collected from different fields often are indistinguishable based on visually observable characteristics such as the color of the fungus, or the shape of fungal spores used for long-term survival. The ability to distinguish between different isolates of the pathogen is an extremely important prerequisite for studies focusing on the identification of garlic or leek breeding materials having resistance to white mold disease. Identifying resistant breeding materials is critically important for profitable garlic production, since alternative disease control approaches such as the application of fungicides are prohibitively expensive. We chose to examine diversity in isolates of S. cepivorum collected from Mexico, Spain and Venezuela by looking at differences in the `DNA fingerprints¿ among different fungal isolates. Based on the results of the DNA fingerprint analysis, it is possible to develop a `family tree¿ for the isolates examined in the study. We determined that the isolates of S. cepivorum from Mexico exhibited considerable genetic diversity. An isolate from Venezuela was closer to the Mexican isolates than was an isolate collected from Spain. Now that we know the DNA fingerprints for each isolate, it may be possible to compare the isolates for the severity of disease they cause on garlic, and identify specific DNA sequences that are associated with causing severe disease. This will make it possible to identify specific genes within the fungus that are responsible for severe disease.
Technical Abstract: Sclerotium cepivorum Berk. is the causal agent of `white rot¿ diseases of several Allium species, including onions and leeks. Genetic relationships among isolates of S. cepivorum from different regions of Mexico and also from Spain and Venezuela were assessed based on analysis of randomly amplified polymorphic DNA (RAPDs). Five different oligonucleotide primers were used to detect genetic polymorphisms among 31 isolates from the three countries. A dendrogram based on pair-wise dissimilarities indicated that the Mexican isolates formed two distinct groups. One group consisted of the majority of the isolates collected from a single field. The other group included isolates collected from different regions of Mexico and the isolate from Venezuela. The isolate from Spain occupied a unique terminal branch on the dendrogram, suggesting it was the most divergent of the isolates studied. These results indicate that considerable genetic diversity is present among different isolates of S. cepivorum in Mexico.