Prediction of Phyllosticta citricarpa using an hourly infection model and validation with prevalence data from South Africa and Australia. (September 2015)

• Record Type: Journal Article
• Authors: Magarey, Roger D.; Hong, Seung Cheon; Fourie, Paul H.; Christie, David N.; Miles, Andrew K.; Schutte, Gerhardus C.; Gottwald, Timothy R.
• Is Part Of: Crop protection. Volume 75(2015)
• Page Start: 104
• Page End: 114
• Publication Date: 2015-09
• Subjects: Risk analysis -- Modeling -- Validation; Plants, Protection of -- Periodicals; 632.05
• DOI: 10.1016/j.cropro.2015.05.016
• Languages: English
• ISSNs: 0261-2194

Abstract

Abstract: An hourly infection model was used for a risk assessment of citrus black spot (CBS) caused by Phyllosticta citricarpa . The infection model contained a temperature-moisture response function and also included functions to simulate ascospore release and dispersal of pycnidiospores. A validation data set of 18 locations from South Africa and Australia was developed based on locations with known citrus black spot prevalence. An additional 67 sites from Europe and the United States with unknown prevalence were also identified. The model was run for each location with 9 years of hourly weather data from the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR) database. The infection scores for the sites with known prevalence where ranked and a threshold for suitability in a given year was derived from the average score of the lowest ranked moderate prevalence site. The results of the simulation confirm that locations in Florida were high risk while most locations in California and Europe were not at risk. The European location with the highest risk score was Andravida, Greece which had 67% of years suitable for ascosporic infection but only 11% of years were suitable for pycnidiosporic infection. There were six other sites in Europe that had frequency of years suitable for ascosporic infection greater than 22% including Pontecagnano, Italy; Kekrya, Greece; Reggio Calabria, Italy; Cozzo Spadaro, Italy; Messina, Italy; and Siracusa, Italy. Of these six sites only Reggio Calabria had a frequency of years suitable for pycnidiosporic infection greater than 0%. These six sites are predicted to have prevalence similar or less than Messina, South Africa, i.e. low and occasional. Other sites in Europe would best be described as likely to have no prevalence based on very low simulated scores for both spore types. Although Andravida had a similar risk of infection to moderate locations in South Africa there was a difference in the seasonality of infection periods. The ascosporic infection period score was similar between the two sites, but Andravida had a much lower pycnidiosporic infection score in the middle of the period of fruit susceptibility than Addo, South Africa. In Europe favorable climatic conditions are discontinuous, i.e., there is a low frequency of suitable seasons. This raises doubts about the ability of the pathogen to persist at a location and cause disease loss when favorable seasons reoccur. These results suggest that Europe is less suitable for CBS than suggested by an earlier study produced by the European Food Safety Authority using a similar model. The findings from our model simulations suggest that only a few isolated locations in the extreme south of Europe are likely to have a low to marginal risk of P. citricarpa establishment. Highlights: An hourly infection model was used for a risk assessment of citrus black spot (CBS) caused by Phyllosticta citricarpa . A validation data set of 18 locations with known citrus black spot prevalence was used to predict CBS for 36 locations with unknown prevalence in Europe. The results confirm that Europe is not at risk except a few isolated locations in the extreme south that have low to marginal suitability. In Europe, a low frequency of suitable seasons raises doubts about the ability of the pathogen to persist.