Interaction between Xylella Fastidiosa and Curtobacterium Flaccumfaciens

Xylella fastidiosa (Xf) is a fastidious gram-negative, xylem-limited bacterium that causes diseases in many crops of economic importance, such as grape (Pierce’s disease), almond, peach, coffee, plum and citrus. Xf can infect all known Citrus sinensis cultivars and causes Citrus variegated chlorosis (CVC). One major endophyte isolated from CVC-asymptomatic plants is the bacterium Curtobacterium flaccumfaciens (Cf). Catharanthus roseus (Cr) plants were inoculated together with Cf and Xf and in a similar experiment, plants were inoculated alone with Xf and Cf. Three phytopathology parameters, including number of flowers, height of plants, and disease symptoms were evaluated. Primers for Cf were designed to detect this endophytic bacterium in plant tissue when inoculated with Xf. These primers were able to detect Cf in the presence of Xf after inoculation in Cr. In planta interaction studies where Cf was inoculated together with Xf showed that there was an inhibition of disease symptoms caused by Xf. INTRODUCTION Endophytes are microorganisms that do not visibly harm the host plant but can be isolated from surface-disinfected plant tissue or the inner parts of plants (Hallmann et al. 1997). Since they colonize an ecological niche similar to that of phytopathogens, endophtytes are candidates for biocontrol agents (Hallmann et al. 1997). Members of the genus Curtobacterium have been isolated as endophytic bacteria from many plants, including red clover (Sturz & Christie, 1998), rice (Elbeltagy et al. 2000), potato (Sturz & Matheson, 1996), yam (Tor et al. 1992), citrus (Araújo et al. 2002; Lacava et al. 2004), and are associated with control of plant diseases in tobacco (Park & Kloepper, 2000), cucumber (Raupach & Kloepper, 2000) and potato (Sturz & Matheson, 1996); and plant growth-promotion of red clover (Sturz et al. 1997) or interacting with other bacteria in plant growth-promotion (Bent & Chanway, 1998). CVC is a disease of sweet orange trees (Citrus sinensis L.) caused by one strain of the xylem-limited bacterium Xf (Hartung et al. 1994). Xf is transmitted by xylem-feeding sharpshooter leafhoppers (Homoptera: Cicadellidae, Cicadellinae; Roberto et al., 1996; Brlansky et al., 2002) or through seeds (Li et al., 2003). In Brazil, CVC is responsible for losses to the citrus industry of US $ 100 million per year (Coletta-Filho et al., 2001). In spite of the fact that Xf was the first plant pathogen to have its genome completely sequenced (Simpson et al. 2000), much remains to be learned about its pathogenesis, biology and ecology. Araújo et al. (2002) and Lacava et al. (2004) demonstrated that Cf is isolated more frequently from CVC-asymptomatic than CVC-symptomatic orange and tangerine plants. Also, Lacava et al. (2004) found, through the use of in vitro interaction experiments that the growth of Xf could be inhibited by the presence of endophytic Cf. OBJECTIVES 1. Evaluate, in planta, the interaction between Xf and Cf and the potential use of this endophytic bacterium in biological control RESULTS Sixty days after the inoculation of Cr seedlings, Cf was detected by PCR using primers CFC1 and CFC2. Xf was also specifically detected using primers 271-int and 272-int on extracts of Cr inoculated with Xf. In seedlings simultaneously inoculated (doubly-inoculated), Cf was detected by PCR with primers CFC1 and CFC2 and Xf with primers 271-int and 272int respectively. The first parameter analyzed to check the effects of inoculation of Xf and Cf was the number of flowers. Plants inoculated with sterile PW medium (negative control) and plants inoculated with Cf did not demonstrate a statistically significant difference (< P 0.05) in the number of flowers. Plants inoculated with Xf alone had a reduced number of flowers (< P 0.05)