Abstract
Xylella fastidiosa subsp. pauca causes citrus variegated chlorosis (CVC) disease in Brazil, resulting in significant production losses in the citrus industry. X. fastidiosa subsp. pauca is mainly transmitted by three species of sharpshooters (Hemiptera: Cicadellidae) in Brazil; Dilobopterus costalimai (Young), Acrogonia citrina Marucci & Cavichioli and Oncometopia facialis (Signoret). We identified bacterial communities associated with the heads of surface-sterilized insect vectors of X. fastidiosa subsp. pauca that were collected from CVC affected citrus groves in Brazil. Bacteria were isolated and analyzed by amplified ribosomal DNA restriction analysis (ARDRA) and sequencing, revealing the presence, among the most abundant genera, of the well-known citrus endophytes Methylobacterium spp. and Curtobacterium spp. Specific PCR systems for the detection of these genera indicated high frequencies of presence of these bacteria in sharpshooters. The remaining bacterial community was compared in distinct vector species and at different period of the year by denaturing gradient gel electrophoresis (DGGE), showing its responsiveness to the climate change over the year. These results represent a new basis for the knowledge about the interaction symbiotic-pathogenic bacteria inside insect vectors and provide a basis for further work on the biocontrol of plant bacteria like X. fastidiosa.
Highlights
Citrus variegated chlorosis (CVC) was first reported in Brazil in 1987 [1,2] and by 2000, the disease affected already 34% of the 200 million sweet orange trees in state of São Paulo
These colonies were classified into three distinct morphological groups; G1) pinkpigmented colonies which appear on plates after seven days of incubations, typically Methylobacterium spp.; G2) dark pink or orange fast grower colonies, typically Curtobacterium spp.; G3) other colonies
The role of associated microbial community in the pathogenic potential of X. fastidiosa has been discussed in the literature [12,14,17,18,37], where authors state that these microorganisms can partially inhibit or promote the growth of X. fastidiosa inside the citrus plants
Summary
Citrus variegated chlorosis (CVC) was first reported in Brazil in 1987 [1,2] and by 2000, the disease affected already 34% of the 200 million sweet orange trees in state of São Paulo. Biocontrol activity of the endophytic bacterial community may be through the synthesis of structural compounds, such as siderophores and extracellular enzymes [16,17], and the induction and expression of general molecular-based plant immunity [16]. They may act by niche competition, preventing pathogens from becoming established in a host [18]
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