Inoculum dynamics and environmental factors associated with the preharvest contamination of citrus fruits by Geotrichum citri-aurantii

Abstract

The aim of this study was to establish the methodology and determine the relationships between climatic factors and contamination of citrus fruit by the soil-inhabitant pathogenic fungus Geotrichum citri-aurantii. This pathogen causes sour rot decay of citrus. The field trial was set up in a ‘Murcott’ mandarin experimental orchard in Salto, Uruguay. Fruit sampling was conducted weekly from March to June 2022. Six fruits from 2-3 trees per experimental unit were arbitrarily selected within 50 cm from the orchard floor. Rainfall, air temperature, wetness and relative humidity sensors were placed in the center of the orchard. Wind sensors were placed at each sampling location. The mean number of epiphytic spores of G. citri-aurantii per fruit (abundance) and the proportion of fruits positive for G. citri-aurantii (incidence) were determined in the laboratory by washing and plating serial dilutions. Climatic factors were related to G. citri-aurantii abundance or incidence through generalized linear models specifying the normal or binomial error structure, respectively. For both incidence and abundance, a significant negative relationship was observed with rainfall and wind speed. In contrast, the relationship was significantly positive for wind gusts. The variables wetness and maximum temperature were negatively and significantly related only to abundance. Further field trials are necessary to validate the models and confirm the results obtained in this first year of the study.