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

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 overlapping and 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 between10 3 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. Key words: citrus variegated chlorosis, coffee leaf scorch, inoculum concentration, bacterial population, epidemiology DIFERENÇAS EM COLONIZAÇÃO DO HOSPEDEIRO POR ISOLADOS DE Xylella fastidiosa DE CITROS E CAFEEIRO EM INOCULAÇÕES RECÍPROCASRESUMO: Clorose variegada dos citros (CVC) e atrofia dos ramos do cafeeiro (ARC) são doenças importantes no Brasil, associadas a estirpes de Xylella fastidiosa que são geneticamente próximas. Entretanto, pouco se sabe a respeito de plantas hospedeiras em comum e da importância de citros e cafeeiro como fontes de inóculo dessas estirpes. Neste estudo, realizaram-se experimentos de inoculação recíproca para determinar se isolados de X. fastidiosa de CVC e de ARC são biologicamente semelhantes em plantas de citros e café. Estes dois hospedeiros foram mecanicamente inoculados com um isolado de CVC e um isolado de ARC, em quatro concentrações que variaram de 10 3 a 10 9 unidades formadoras de colônias UFC mL -1 . Aos dois, quatro e oito meses após a inoculação, a eficiência de infecção e a população bacteriana dos isolados em cada hospedeiro foram determinadas por cultura. O isolado de CVC infectou tanto plantas de citros quanto de café, mas desenvolveu populações mais baixas em cafeeiro. O isolado de ARC não colonizou citros. A inoculação de plantas de café com o isolado de CVC resultou em baixas taxas de infecção e exigiu uma concentração de inóculo dez vezes mais alta que a necessária para obter uma taxa de infecção semelhante (25%) em citros. A reduzida taxa de infecção e a baixa população bacteriana do isolado de CVC em cafeeiro em relação a citros sugerem que cafeeiro não é um hospe...

Background matching behaviour and pathogen acquisition: plant site preference does not predict the bacterial acquisition efficiency of vectors

“…It should be acknowledged that X. fastidiosa transmission is rather complex and it may be simplistic to assume that evaluating acquisition and/or inoculation levels per se are enough to explain transmission efficiencies of different vectors. For example, the bacterial strain and its interactions with the host (Prado et al 2008) and/or the number of the inoculation events by vectors ) are factors that can influence transmission efficiency. Moreover, from a biochemical point of view, higher populations of X. fastidiosa cells in plant tissue result in elevated levels of diffusible signaling molecules (DSF), which induce an adhesive phase of the pathogen (Newman et al 2004;Chatterjee et al 2008a)-a crucial stage for vector colonization (Chatterjee et al 2008b;Killiny and Almeida 2009a).…”

Genetic Structure and Biology of Xylella fastidiosa Strains Causing Disease in Citrus and Coffee in Brazil

“…We cultured X. fastidiosa from samples, following standard protocols (2), and triply cloned each isolate prior to freezing cells at Ϫ80°C. We recovered frozen samples by plating suspensions on PWG medium (20) to extract DNA for molecular analyses (37) and to mechanically inoculate citrus and coffee plants for pathogenicity tests (see below). All samples were tested with the diagnostic primer set RST31-33 to confirm their identification as X. fastidiosa (31).…”

“…We conducted two tests to determine if CVC-and CLS-causing isolates collected from symptomatic plants in commercial coffee plantations and citrus orchards were able to colonize citrus and coffee plants under greenhouse conditions. Although citrus plants infected with X. fastidiosa readily show diagnostic CVC symptoms under greenhouse conditions (2), typical symptoms of CLS (e.g., shortening of internodes, leaf size reduction, leaf scorch, and yellowing) are not evident in less than 1 to 2 years if the pinprick inoculation method is used (37). Therefore, we focused our assays on determining X. fastidiosa colonization of host plants and not symptom development (i.e., disease); -CFU/ml X. fastidiosa suspensions, following methods previously described (2, 37); plants were maintained in 1-liter pots containing a mixture of soil, manure, and sand (3:2:1), inside an insect-free greenhouse at ESALQ, University of Sao Paulo, Piracicaba, Brazil.…”

“…Li et al (26) showed that CLS can be caused by both coffee and citrus X. fastidiosa isolates. On the other hand, another study showed that a CVC isolate of X. fastidiosa colonized coffee plants but died off over time, whereas no colonization of citrus plants was observed for a CLS isolate (37). Therefore, previous research has not resolved whether CVC and CLS are caused by the same strain or by different strains of X. fastidiosa.…”

Spatial Genetic Structure of Coffee-Associated Xylella fastidiosa Populations Indicates that Cross Infection Does Not Occur with Sympatric Citrus Orchards

“…Based on cross-infection assays, citrus strains were able to persistently infect coffee plants but no coffee strain was detected infecting citrus plants. Almeida et al (2008) and Prado et al (2008) also did not detect citrus strains infecting coffee plants over time, even after an initial infection was detected. Early colonization and detection of X. fastidiosa in host plants that is not followed by systemic and persistent infection is common for this pathogen (Purcell and Saunders 1999).…”