Changes in the prevalence of fungal species causing post-harvest diseases of carrot in Finland

Post-harvest diseases cause significant economic losses in the carrot production chain. In this study, storage losses and fungal pathogens causing them were analysed in the carrot yield from 52 different field plots in four areas in Finland in 3 years (2016–2018). Over 30,000 carrots were sampled and analysed at three time points during cold storage at 0–1°C. In March, after 5–6 months' storage, the average loss due to diseases was 20%–21% every year. Decay of the root tip was the most common disease symptom, followed by pits on the side and black rot in the crown, detected in 69.2%, 15.0% and 9.0% of the symptomatic samples, respectively. Both intensive carrot cultivation practice and early timing of harvest increased storage losses. Pathogens in 3057 symptomatic carrot tissue samples were isolated by culturing, and fungal species were identified. The most common fungal species detected were Mycocentrospora acerina, Botrytis cinerea and Fusarium spp., especially F. avenaceum. However, the frequency of different pathogens varied between the different years and time points during storage. Species-specific PCR tests revealed that M. acerina and F. avenaceum were present in many early time-point samples where they could not yet be detected by the culturing method. In Finland, this study on carrot post-harvest diseases is the first large-scale survey in which the fungal pathogens were isolated and identified by laboratory tests. In comparison with the previous studies, Fusarium spp. were detected more frequently in this study, while grey mould and Sclerotinia rot were less frequent.