Host colonization differences between citrus and coffee isolates of Xylella fastidiosa in reciprocal inoculation

Simone De Souza Prado,João Roberto Spotti Lopes,Rodrigo Piacentini Paes De Almeida,Clarice Garcia Borges Demétrio,Adriano Ferreti Borgatto

doi:10.1590/s0103-90162008000300005

Abstract

Citrus variegated chlorosis (CVC) and coffee stem atrophy (CSA) are important diseases in Brazil associated with closely-related strains of Xylella fastidiosa, but little is know about host aoverlappingnd importance of citrus and coffee as inoculum sources of these strains. In this study, reciprocal-inoculation experiments were performed to determine if CVC and CSA isolates are biologically similar within citrus and coffee plants. These two hosts were mechanically inoculated with a CVC and a CSA isolate of X. fastidiosa at four concentrations ranging between10³ and 10(9) colony forming units CFU mL-1. At two, four and eight months after inoculation, the infection efficiency and bacterial populations of the isolates in each host were determined by culturing. The CVC isolate infected both citrus and coffee plants, but developed lower populations in coffee. The CSA isolate did not colonize citrus. Inoculation of coffee plants with the CVC isolate resulted in low rates of infection and required an inoculum concentration ten-fold higher than that necessary to obtain a similar (25%) rate of infection in citrus. The relatively low infection rates and bacterial numbers of the CVC isolate in coffee plants compared with those observed in citrus suggest that coffee is not a suitable host to serve as a source of inoculum of the CVC strain for primary spread to citrus or within coffee plantations.

Highlights

Two plant diseases caused by the bacterium Xylella fastidiosa, citrus variegated chlorosis (CVC) and coffee stem atrophy (CSA) emerged in São Paulo State, Brazil, in 1987 and 1995, respectively, suggesting that they were caused by the same pathogen strain (Paradela Filho et al, 1997)
The culturing method based on homogenization of infected plant tissue in PBS and subsequent dilution plating onto solid periwinkle gelrite (PWG) medium (Sands et al, 1988) was found to be suitable for primary isolation and quantification of X. fastidiosa in coffee plants
The analyses of infection rates, effective doses and bacterial populations in citrus and coffee plants carried out in these reciprocal-inoculation experiments indicate that these CVC and CSA isolates of X. fastidiosa are biologically different

Summary

Introduction

Two plant diseases caused by the bacterium Xylella fastidiosa, citrus variegated chlorosis (CVC) and coffee stem atrophy (CSA) emerged in São Paulo State, Brazil, in 1987 and 1995, respectively, suggesting that they were caused by the same pathogen strain (Paradela Filho et al, 1997). Li et al (2001) were able to infect coffee plants and observe CSA-like symptoms after inoculation with an isolate originally from citrus, suggesting the possibility of cross-infection by these strains. Li et al (2002) showed that both CVC and CSA isolates can cause symptoms of Pierce’s Disease in grapevine. Lopes et al (2003) demonstrated that CVC and CSA isolates had similar colonization patterns in various weed host plants. It is important to understand the host range of proposed X. fastidiosa isolates through biological assays

Methods

Results

Conclusion