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Genetic Diversity of Xylella fastidiosa Strains from Costa Rica, Sao Paulo, Brazil, and United States

First, third, and fourth authors: Centro de Investigación en Biología Celular y Molecular (CIBCM), Universidad de Costa Rica (UCR), San Pedro 2060, Costa Rica; second author: U.S. Department of Agriculture (USDA)-Agricultural Research Service Fruit Laboratory, 10300 Baltimore Ave., Beltsville, MD 20705; fifth author: USDA-APHIS-PPQ, Beltsville, MD; sixth author: CIBCM and Escuela de Biología, UCR; and seventh author: CIBCM and Facultad de Microbiología, UCR.

The diversity of 42 Xylella fastidiosa strains from Costa Rica, São Paulo, Brazil, and the United States were analyzed using the sequence of the 16S rRNA gene by variable number of tandem repeat (VNTR) fragment analysis and by restriction fragment length polymorphisms (RFLP) of a specific polymerase chain reaction (PCR)-amplification product using enzyme CfoI. Limited variability in the sequence of the 16S rRNA gene was observed and, although the separation was not absolute, most strains from Costa Rica clustered with strains from the United States and not with strains from São Paulo. The PCR-RFLP produced different patterns of DNA bands. The same pattern was shared by strains from Costa Rica, the United States, and two coffee strains from São Paulo, but a different pattern was observed in six coffee and orange strains from Brazil. In all, 32 amplification products were scored in the VNTR fragment analysis. The total variation observed among the X. fastidiosa strains had significant (P < 0.001) contributions from both geography and host origin as inferred by Nei's values of genetic diversity and WINAMOVA statistics. The strains from Costa Rica were isolated from diseased grapevines, coffee, and sweet orange and these strains grouped together and could be distinguished from strains from grapevine from the United States or from either coffee or sweet orange from São Paulo. The strains tested from Costa Rica are most likely of local origin, although the possibility that they have been introduced along with horticultural crops cannot be excluded. In either case, they are examples of independent selection of strains of X. fastidiosa affecting coffee and sweet orange. Greater genetic similarity was observed between strains from Costa Rica and the United States than with those from São Paulo.

Additional keywords:citrus variegated chlorosis, coffee leaf scorch, Pierce's disease.