Sour rot, an emerging postharvest disease on stone fruit in the Ebro Valley

Stone fruit-producing areas in Spain have experienced severe outbreaks of sour rot, whereas before 2016, sour rot had not been reported. The main microorganism causing sour rot is Geotrichum candidum , and fruit symptoms include characteristic soft lesions of digested tissue as a white layer of mycelial growth with a sour odor. Currently, there are no effective treatments for sour rot control in stone fruit. In this study, we have documented the incidence of fruit affected by G. candidum under commercial conditions and its proportion compared to other main postharvest pathogens of stone fruit. Moreover, we investigated the main sources of G. candidum inoculum in postharvest and its risk for fruit infection. Finally, inoculum sources in the field were also identified. Our results confirmed Monilinia spp. as the main postharvest pathogen causing disease on peaches and nectarines, followed by Rhizopus spp. Importantly, G. candidum was detected as a cause agent of fruit disease at both sampled packinghouses. Inoculum sources of G. candidum were found in packinghouse facilities, but no conidia were detected in the air samples. When inoculum sources were simulated, for water samples, the risk for healthy fruit infection ranged from 7% to 21% in ‘Angeleno’ plums and 0–5% in ‘Tardibelle’ peaches. In the case of handling line surfaces, 21% of infected fruit was observed on healthy ‘Sweet Dream’ peaches. In the field, all samples evaluated presented G. candidum inoculum, including soil, leaves, and fruits. This information suggests that the origin of the disease is in the field, although the main losses occur after harvest. This study provides novel evidence that G. candidum is a causal agent of disease in stone fruit in Ebro Valley and offers essential epidemiological knowledge to understand sour rot behaviour, which will be essential for developing sustainable control strategies.