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POSTERS: Pathogen dispersal and survival

Dead twigs: a reservoir for Phyllosticta citricarpa inoculum leading to citrus black spot (CBS)
Megan Dewdney - University of Florida. Nan-Yi Wang- Gulf Coast Research and Education Center, University of Florida, Jeffrey Rollins- University of Florida, Collin Solomon- CREC University of Florida

Phyllosticta citricarpa, the causal agent of CBS, is an emerging fungal pathogen of citrus causing heavy yield loss and a reduction in fruit marketability. New research has determined the heterothallic nature of the fungus, mating gene structure, and population structure in Florida. Currently, only one mating type is present in Florida leading to new questions about the mechanism for disease progression. Our objective was to assess dead twigs as a potential inoculum source contributing to new secondary infections. Field collection of twigs was conducted in Immokalee, FL from 2016 to 2018, to determine the presence of P. citricarpa. Citrus trees were sampled biweekly and a total of 10,176 twigs were evaluated. DNA obtained from conidia and bark samples had a positive correlation with CBS fruit severity ratings (P<0.0001). Conidia production was negatively affected by growing degree-day (base 10°C) accumulation over a 7-day period (gdu7) and number of days with measurable precipitation (>0.254 mm) over a 28-day period (rainday28). However, the interaction between gdu7 and rainday28 increased conidia production. Similarly, P. citricarpa DNA titers obtained from bark samples were negatively affected by average temperature and rainday28 but the interaction between them increased fungal growth. To conclude, P. citricarpa DNA was correlated with CBS development and fungal inoculum production occurred with increasing temperature in the presence of precipitation.