Genetic structure and biology of Xylella fastidiosa causing disease in citrus and coffee in Brazil

Department of Environmental Science, Policy and Management, University of California, Berkeley; Departamento de Entomologia, Fitopatologia e Zoologia Agrícola, ESALQ/USP, Piracicaba, SP, Brazil; Departamento Científico, Fundecitrus, Araraquara, SP, Brazil

^* To whom correspondence should be addressed. Email: rodrigo{at}nature.berkeley.edu.

	Abstract

Xylella fastidiosa is a vector-borne plant pathogenic bacterium that causes disease in citrus (Citrus variegated chlorosis, CVC) and coffee (Coffee leaf scorch, CLS) in Brazil. CVC and CLS occur sympatrically and share leafhopper vectors, thus determining if X. fastidiosa isolates can be dispersed from one crop to another and cause disease is of epidemiological importance. We sought to clarify the genetic and biological relationships between CVC- and CLS-causing X. fastidiosa. We used cross-inoculation bioassays, microsatellite and multilocus sequence typing (MLST) approaches to determine the host range and genetic structure of 26 CVC and 20 CLS isolates collected from different regions in Brazil. Our results show that citrus and coffee X. fastidiosa are biologically distinct. Cross-inoculation tests showed that isolates causing CVC and CLS in the field were able to colonize citrus and coffee, respectively, but not the other host, indicating biological isolation between the strains. The microsatellite analysis separated most X. fastidiosa populations tested based on host plant from which they were isolated. However, recombination among isolates was detected and a lack of congruency observed among phylogenetic trees was observed for the loci used in the MLST scheme. Altogether, our study indicates that CVC and CLS are caused by two biologically distinct strains of X. fastidiosa that have diverged but are genetically homogenized by frequent recombination.