Relative Contribution of Windbreak, Copper Sprays, and Leafminer Control for Citrus Canker Management and Prevention of Crop Loss in Sweet Orange Trees.

The management of citrus canker, caused by Xanthomonas citri subsp. citri, has been widely studied in endemic areas because of the importance of the disease in several citrus-producing countries. A set of control measures is well established, but no study has investigated the efficiency of each measure individually and their combination for disease suppression. This study comprised a 3-year field study to assess the relative contribution of three measures for the control of citrus canker and reduction of crop losses. Windbreak (Wb), copper sprays (Cu), and leafminer control (Lc) were assessed in eight different combinations in a split-split plot design. The orchard was composed of 'Valencia' sweet orange trees grafted onto 'Rangpur' lime. Casuarina cunninghamiana trees were used as Wb. Cu and Lc sprays were performed every 21 days throughout the year. Individually, Cu showed the highest contribution for canker control, followed by Wb. Lc had no effect on reducing citrus canker. Wb+Cu showed the highest efficiency for control of the disease. This combination reduced the incidence of diseased trees by approximately 60%, and the incidence of diseased leaves and fruit by ≥90% and increased the yield in 2.0- to 2.6-fold in comparison with the unmanaged plots. Cu sprays were important for reducing disease incidence and crop losses, whereas Wb had an additional contribution in minimizing the incidence of cankered, non-marketable fruit. The results indicated that the adoption of these measures of control may depend on the characteristics of the orchard and destination of the production.

CitrusKB: a comprehensive knowledge base for transcriptome and interactome of Citrus spp. infected by Xanthomonas citri subsp. citri at different infection stages.

Citrus canker type A is a serious disease caused by Xanthomonas citri subsp. citri (X. citri), which is responsible for severe losses to growers and to the citrus industry worldwide. To date, no canker-resistant citrus genotypes are available, and there is limited information regarding the molecular and genetic mechanisms involved in the early stages of the citrus canker development. Here, we present the CitrusKB knowledge base. This is the first in vivo interactome database for different citrus cultivars, and it was produced to provide a valuable resource of information on citrus and their interaction with the citrus canker bacterium X. citri. CitrusKB provides tools for a user-friendly web interface to let users search and analyse a large amount of information regarding eight citrus cultivars with distinct levels of susceptibility to the disease, with controls and infected plants at different stages of infection by the citrus canker bacterium X. citri. Currently, CitrusKB comprises a reference citrus genome and its transcriptome, expressed transcripts, pseudogenes and predicted genomic variations (SNPs and SSRs). The updating process will continue over time by the incorporation of novel annotations and analysis tools. We expect that CitrusKB may substantially contribute to the field of citrus genomics. CitrusKB is accessible at http://bioinfo.deinfo.uepg.br/citrus. Users can download all the generated raw sequences and generated datasets by this study from the CitrusKB website.

Novel insights into the genomic basis of citrus canker based on the genome sequences of two strains of Xanthomonas fuscans subsp. aurantifolii.

BACKGROUND: Citrus canker is a disease that has severe economic impact on the citrus industry worldwide. There are three types of canker, called A, B, and C. The three types have different phenotypes and affect different citrus species. The causative agent for type A is Xanthomonas citri subsp. citri, whose genome sequence was made available in 2002. Xanthomonas fuscans subsp. aurantifolii strain B causes canker B and Xanthomonas fuscans subsp. aurantifolii strain C causes canker C. RESULTS: We have sequenced the genomes of strains B and C to draft status. We have compared their genomic content to X. citri subsp. citri and to other Xanthomonas genomes, with special emphasis on type III secreted effector repertoires. In addition to pthA, already known to be present in all three citrus canker strains, two additional effector genes, xopE3 and xopAI, are also present in all three strains and are both located on the same putative genomic island. These two effector genes, along with one other effector-like gene in the same region, are thus good candidates for being pathogenicity factors on citrus. Numerous gene content differences also exist between the three cankers strains, which can be correlated with their different virulence and host range. Particular attention was placed on the analysis of genes involved in biofilm formation and quorum sensing, type IV secretion, flagellum synthesis and motility, lipopolysacharide synthesis, and on the gene xacPNP, which codes for a natriuretic protein. CONCLUSION: We have uncovered numerous commonalities and differences in gene content between the genomes of the pathogenic agents causing citrus canker A, B, and C and other Xanthomonas genomes. Molecular genetics can now be employed to determine the role of these genes in plant-microbe interactions. The gained knowledge will be instrumental for improving citrus canker control.

[Natural infectivity of Xylella fastidiosa Wells et al. in sharpshooters (Hemiptera: Cicadellidae) from coffee plantations of Parana, Brazil]. / Infectividade natural por Xylella fastidiosa Wells et al. de cicadelíneos (Hemiptera: Cicadellidae) de lavouras cafeeiras do Paraná

Xylella fastidiosa Wells et al., a gram-negative and xylem limited bacterium, causes significative economic on several crops, such as the leaf scorch in coffee. It is transmitted by xylem feeding insects and four sharpshooters species have been reported as vectors of X. fastidiosa in coffee. The objective of this study was to determine the natural infectivity of X. fastidiosa in five species of sharpshooters from coffee trees: Acrogonia citrina Marucci & Cavichioli, Bucephalogonia xanthophis (Berg), Dilobopterus costalimai Young, Oncometopia facialis (Signoret) and Sonesimia grossa (Signoret). Samples were collected from coffee plantations in five counties of the North and Northwest regions of the State of Parana, Brazil, from October 1998 through November 2001. A total of 806 samples containing three to five insects were examined for the presence of X. fastidiosa by using PCR and nested PCR tests. X. fastidiosa was present in samples of all five species of sharpshooters collected in the two coffee regions. The average level of natural infectivity potential was 30.4%. However, this natural infectivity ranged from 2.2% for O. facialis to 68.8% for A. citrina. Sharpshooters collected in the spring tended to have lower natural infectivity of X. fastidiosa as compared to those collected in other seasons. The results obtained showed the high potential of dissemination of X. fastidiosa by different insect vectors in coffee trees in Parana.

Outbreaks of Bacterial Spot Caused by Xanthomonas gardneri on Processing Tomato in Central-West Brazil.

Severe epidemics of bacterial spot have been observed in central-west Brazil in fields of processing tomato. Several xanthomonads, Xanthomonas axonopodis pv. vesicatoria, X. vesicatoria, or X. gardneri, can cause the disease; therefore, attempts were made to identify the pathogen species present in this region. A total of 215 strains were obtained from 10 commercial areas in 1997, 1998, and 2000. The strains were characterized using pulsed-field gel electrophoresis (PFGE) and by their amylolytic and pectolytic activities. Representative strains from each PFGE haplotype then were tested for pathogenicity on tomato and pepper, carbon source utilization, and whole protein sodium dodecyl sulfate-polyacrylamide gel electrophoresis. rRNA sequence comparisons also were performed. All strains recovered from six fields were classified as X. gardneri, whereas X. vesicatoria and X. axonopodis pv. vesicatoria also were detected in the remaining four fields. Strains of X. gardneri, which could be grouped into two PFGE haplotypes, were unable to hydrolyze starch and pectate and to utilize gentiobiose and maltose. They expressed the ß protein of 27 kDa and were pathogenic on tomato but variable on pepper. This is the first report of outbreaks of bacterial spot on tomato caused by X. gardneri.