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Citrus canker is a disease of citrus and closely related species, caused by the bacterium Xanthomonas citri subsp. citri. This disease, previously exotic to Australia, was detected on a single farm [infested premise-1, (IP1). IP is the terminology used in official biosecurity protocols to describe a locality at which an exotic plant pest has been confirmed or is presumed to exist. IP are numbered sequentially as they are detected] in Emerald, Queensland in July 2004. During the following 10 months the disease was subsequently detected on two other farms (IP2 and IP3) within the same area and studies indicated the disease first occurred on IP1 and spread to IP2 and IP3. The oldest, naturally infected plant tissue observed on any of these farms indicated the disease was present on IP1 for several months before detection and established on IP2 and IP3 during the second quarter (i.e. autumn) 2004. Transect studies on some IP1 blocks showed disease incidences ranged between 52 and 100% (trees infected). This contrasted to very low disease incidence, less than 4% of trees within a block, on IP2 and IP3. The mechanisms proposed for disease spread within blocks include weatherassisted dispersal of the bacterium (e.g. wind-driven rain) and movement of contaminated farm equipment, in particular by pivot irrigator towers via mechanical damage in combination with abundant water. Spread between blocks on IP2 was attributed to movement of contaminated farm equipment and/or people. Epidemiology results suggest: (i) successive surveillance rounds increase the likelihood of disease detection; (ii) surveillance sensitivity is affected by tree size; and (iii) individual destruction zones (for the purpose of eradication) could be determined using disease incidence and severity data rather than a predefined set area.

Several species of Xanthomonas cause bacterial leaf spot, a disease that affects solanaceous crops worldwide. The diversity of 64 Australian isolates of Xanthomonas spp. associated with bacterial leaf spot in tomato, capsicum and chilli crops in eastern Australia was determined using multi-locus sequence analysis of atpD, dnaK, efp and gyrB genes, species-specific PCR assays and biochemical analyses. At least five species of Xanthomonas associated with bacterial leaf spot were identified in Australian tomato, capsicum and chilli crops and their pathogenicity assessed. Phylogenetic and biochemical analyses identified X. euvesicatoria, X. perforans and X. vesicatoria as the most frequently recovered pathogenic species. Non-pathogenic and weakly pathogenic species were also identified. The suitability of the identification methods used and the implications of the detection of these species will be discussed.Keywords amylolytic . pectolytic . Solanaceae . disease management IntroductionBacterial leaf spot (BLS) is a disease of solanaceous crops that occurs worldwide, especially in warm and humid climates (Jones et al. 2014). Several species of Xanthomonas are reported to cause BLS of tomato (Solanum lycopersicum), capsicum and chilli (Capsicum annuum) . The symptoms of BLS are small, brown, angular, water-soaked lesions on leaves, stems and fruit, and result in defoliation and direct fruit damage. Severe infection may result in extensive damage to crops with significant yield losses (Pernezny et al. 2003). Species reported to cause BLS all produce similar symptoms on their hosts, making precise diagnosis difficult from visual symptoms alone. The impact of pathological convergence and importance of phylogenetic testing in the case of BLS are further highlighted by Hajri et al. (2009). The causal bacteria are spread by wind and water, and may survive in crop residues, weeds and volunteer plants (Jones et al. 1986). A link between field disease and seed contamination has Eur J Plant Pathol (2018) 150:595-608

A previously published partial sequence of pineapple bacilliform virus was shown to be from a retrotransposon (family Metaviridae) and not from a badnavirus as previously thought. Two newly discovered sequence groups isolated from pineapple were associated with bacilliform virions and were transmitted by mealybugs. Phylogenetic analyses indicated that they were members of new badnavirus species. A third caulimovirid sequence was also amplified from pineapple, but available evidence suggests that this DNA is not encapsidated, but more likely derived from an endogenous virus.

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