Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2007
Publication Date: 5/1/2008
Citation: Montero-Astus, M., Hartung, J.S., Aguilar, E., Chacon, C., Li, W., Albertazzi, F., Rivera, C. 2008. Genetic diversity of xylella fastidiosa isolates from Costa Rica, Sao Paulo and the United States of America. Phytopathology. 97(10):1338-1347. Interpretive Summary: The bacterium Xylella fastidiosa causes important diseases of grapevines in the USA and of sweet orange and coffee in São Paulo, Brazil. The bacteria that cause these diseases are quite different, though they belong to the same species, and the sweet orange strain is the subject of very great concern to the citrus industry and government of the USA. Interestingly, this bacterium has recently been discovered in Costa Rica, causing disease on grapevines, coffee and sweet orange. Have the grapevine strain from the USA and the sweet orange and coffee strains from São Paulo been introduced into Costa Rica, or have the strains in Costa Rica evolved naturally there? We analyzed DNA from strains of Xylella fastidiosa isolated from grapevine and other hosts in the USA, sweet orange and coffee in São Paulo and grapevine, sweet orange and coffee in Costa Rica. Our results demonstrate that the strains in Costa Rica have evolved there and have not been introduced into Costa Rica from either the USA or São Paulo. Our results are of interest to the scientific community because it represents an example of independent origins of the same diseases of grapevine, coffee and sweet orange, and is consistent with the view that Xylella fastidiosa is naturally widely spread and apparently harmless in the vegetation of the new world but causes disease on horticulturally important crops introduced from the old world. Our results are also of interest to federal regulatory officials because we now have two distinct strains of a Xylella fastidiosa capable of causing disease in sweet orange.
Technical Abstract: Forty two Xylella fastidiosa isolates from Costa Rica, São Paulo and the United States of America were analyzed by variable number of tandem repeat (VNTR) analysis and by restriction fragment length polymorphisms (RFLP) of a specific PCR-amplification product using enzyme CfoI. The PCR-RFLP produced two patterns of DNA bands. One pattern included the citrus strains and two out of four coffee strains from São Paulo. The two remaining coffee strains presented an alternative pattern common to all strains from Costa Rica and the USA. A total of 32 amplification products were scored in the VNTR analysis. The total variation observed among the X. fastidiosa isolates had significant (P<0.001) contributions from both geography and host origin as inferred by Nei’s values of genetic diversity and AMOVA statistics. The strains from Costa Rica were isolated from diseased grapevines, coffee and sweet orange, and these strains grouped together and were readily distinguished from strains from grapevine from the USA or from either coffee or sweet orange from São Paulo. The strains from Costa Rica are evidently of local origin, and have not been introduced there from either São Paulo or the USA, and therefore are examples of independent selection of strains of X. fastidiosa affecting grapevines, coffee and sweet orange. A dendrogram generated with all marker data showed three clusters, corresponding to the geographic regions of origin, São Paulo, Costa Rica and the USA. The data showed greater genetic similarity between isolates from Costa Rica and the USA than with those from São Paulo.