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Title: Scientific critique of the paper “Climatic distribution of citrus black spot caused by Phyllosticta citricarpa. A historical analysis of disease spread in South Africa” by Martínez-Minaya et al. (2015)

Author
item FOURIE, P.H. - Citrus Research International (CRI)
item SCHUTTE, G.C. - Citrus Research International (CRI)
item CARSTENS, E. - Citrus Research International (CRI)
item HATTINGH, V. - Citrus Research International (CRI)
item PAUL, I. - Experico, Agri-Research Solutions
item MAGAREY, R.D. - North Carolina State University
item Gottwald, Timothy
item YONOW, T. - Csiro European Laboratory
item KRITICOS, D.J. - Csiro European Laboratory

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2016
Publication Date: 9/29/2016
Citation: Fourie, P., Schutte, G., Carstens, E., Hattingh, V., Paul, I., Magarey, R., Gottwald, T.R., Yonow, T., Kriticos, D. 2016. Scientific critique of the paper “Climatic distribution of citrus black spot caused by Phyllosticta citricarpa. A historical analysis of disease spread in South Africa” by Martínez-Minaya et al. (2015). European Journal of Plant Pathology. DOI: 10.1007/s10658-016-1056-x.

Interpretive Summary: This manuscript the scientific critique recently published by Martínez-Minaya et al. concerning climatological conditions for the fungus that causes black spot of citrus can exist. The unfortunate impact of Martínez-Minaya et al. is that the authors predict that the black spot fungus can exist in European citrus growing areas where it has never been found before. This then supports the European Union to establish severe trade restrictions on citrus produced in the United States that is exported to Europe. After close examination of this manuscript, we have found fatal flaws in the analysis and conclusions by Martínez-Minaya et al. that invalidate the study. We have found flaws in analytical methods, in their climatological assessments and climate data, and fatal scale differences in the kinds of data they utilize. Based on our critique, we conclude that the Martínez-Minaya et al. (2015) study is procedurally flawed and therefore cannot credibly contribute to the scientific knowledge of black spot, including its invasion dynamics and potential distribution. The impact of this critique is that it is highly supportive of US citrus trade and provides justification for arguments by the European Food Security Agency (EFSA) that would greatly curtailed or prohibit import of US citrus fruit to the EU.

Technical Abstract: The global potential distribution of Phyllosticta citricarpa, the causal organism of citrus black spot (CBS), is at the heart of an ongoing debate on the level of potential pest risk posed by P. citricarpa to citrus producing orchards within the European Union (EU). The EU currently regulates the importation of citrus fruit sourced from CBS-affected areas, requiring orchards to be managed to control P. citricarpa, and harvested fruit to be free of CBS symptoms. Under the International Standards for Phytosanitary Measures, the justification for these phytosanitary measures depends critically upon whether the citrus-growing areas within the EU fall within the endangered area from CBS (FAO, 2006). Martínez-Minaya et al. (2015) presents an argument that significant portions of the EU and the broader Mediterranean basin are climatically suitable for P. citricarpa persistence and CBS development, and that the potential distribution of P. citricarpa is less constrained by climatic factors than spatial contagion. We herewith expose significant logical and methodological flaws in the analyses and arguments presented in Martínez-Minaya et al. (2015) that lead to an overstatement of the pest risk posed by P. citricarpa to the EU.