Browsing by Author "Hattingh, V."

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    First report of Phyllosticta citricarpa and description of two new species, P. paracapitalensis and P. paracitricarpa, from citrus in Europe
    (Elsevier, 2017) Guarnaccia, V.; Groenewald, J. Z.; Li, H.; Glienke, C.; Carstens, E.; Hattingh, V.; Fourie, P. H.; Crous, P. W.
    The genus Phyllosticta occurs worldwide, and contains numerous plant pathogenic, endophytic and saprobic species. Phyllosticta citricarpa is the causal agent of Citrus Black Spot disease (CBS), affecting fruits and leaves of several citrus hosts (Rutaceae), and can also be isolated from asymptomatic citrus tissues. Citrus Black Spot occurs in citrus-growing regions with warm summer rainfall climates, but is absent in countries of the European Union (EU). Phyllosticta capitalensis is morphologically similar to P. citricarpa, but is a non-pathogenic endophyte, commonly isolated from citrus leaves and fruits and a wide range of other hosts, and is known to occur in Europe. To determine which Phyllosticta spp. occur within citrus growing regions of EU countries, several surveys were conducted (2015–2017) in the major citrus production areas of Greece, Italy, Malta, Portugal and Spain to collect both living plant material and leaf litter in commercial nurseries, orchards, gardens, backyards and plant collections. A total of 64 Phyllosticta isolates were obtained from citrus in Europe, of which 52 were included in a multi-locus (ITS, actA, tef1, gapdh, LSU and rpb2 genes) DNA dataset. Two isolates from Florida (USA), three isolates from China, and several reference strains from Australia, South Africa and South America were included in the overall 99 isolate dataset. Based on the data obtained, two known species were identified, namely P. capitalensis (from asymptomatic living leaves of Citrus spp.) in Greece, Italy, Malta, Portugal and Spain, and P. citricarpa (from leaf litter of C. sinensis and C. limon) in Italy, Malta and Portugal. Moreover, two new species were described, namely P. paracapitalensis (from asymptomatic living leaves of Citrus spp.) in Italy and Spain, and P. paracitricarpa (from leaf litter of C. limon) in Greece. On a genotypic level, isolates of P. citricarpa populations from Italy and Malta (MAT1-2-1) represented a single clone, and those from Portugal (MAT1-1- 1) another. Isolates of P. citricarpa and P. paracitricarpa were able to induce atypical lesions (necrosis) in artificially inoculated mature sweet orange fruit, while P. capitalensis and P. paracapitalensis induced no lesions. The Phyllosticta species recovered were not found to be widespread, and were not associated with disease symptoms, indicating that the fungi persisted over time, but did not cause disease.
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    Probabilistic risk-based model for the assessment of Phyllosticta citricarpa-infected citrus fruit and illicit plant material as pathways for pathogen introduction and establishment
    (Elsevier Ltd., 2020) Gottwald, T.R.; Taylor, E.L.; Amorim, L.; Bergamin-Filho, A.; Bassanezi, R.B.; Silva, G.J.; Fogliata, G.; Fourie, P.H.; Graham, J.H.; Hattingh, V.; Kriss, A.B.; Luo, W.; Magarey, R.D.; Schutte, G.C.; Sposito, M.B.
    Citrus Black Spot (CBS), caused by the ascomycete, Phyllosticta citricarpa, is a fruit, foliar, and twig spotting fungal disease affecting the majority of commercial cultivars of citrus. The disease causes cosmetic lesions, may cause fruit drop and P. citricarpa is considered a quarantine pathogen by some countries, impacting domestic and international trade of citrus fruit. Regulatory requirements affecting fruit trade exist even though there is no documented case of disease spread via infected fruit into previously disease-free areas. To clarify the risk of fruit as a potential pathway for the spread of CBS, we developed a quantitative, probabilistic risk assessment model. The model provides an assessment of all steps in the fruit pathway, including production, packinghouse handling, transportation, export-import distribution channels, and consumer endpoints. The model is stochastic and uses Monte Carlo simulation to assess the risk of P. citricarpa moving through all steps in the pathway. We attempted to use all available literature and information to quantitate risk at each point in the potential pathway and by sequentially linking all steps to determine the overall quantitative risk. In addition, we assessed climatological effects on incidence of diseased fruit at production sites and on fungal reproduction and infection, as well as criteria for establishment at endpoints. We examined ten case studies between exporting and importing locations/countries. Model results indicated fruit to be an epidemiologically insignificant means for CBS spread, even between producing countries where CBS occurs and CBS-free importing countries with disease-conducive climates. We created a second model to examine the introduction of infected plant material from countries where CBS occurs. This model demonstrated significant probability of introduction via such infected material. However, pathogen establishment and disease development was still restricted only to areas with conducive climatological conditions. We created a tool to quantitatively explore the viability of various potential pathways via combinations of CBS-present production sites and corresponding pathway endpoints, including environments conducive and non-conducive to CBS. The tool is provided to aid decision makers on phytosanitary risk relative to international trade of citrus fruit.