The epidemiology and management of cladosporium on raspberry

Cladosporium is a genus of fungi that causes dark mycelial lesions on raspberries, rendering fruit unmarketable. As Cladosporium is an opportunistic pathogen, its prevalence varies across years, and there is insufficient research on its epidemiology and management. This study aimed to investigate the epidemiology of Cladosporium on raspberries and to elucidate which management strategies could be effective. Isolates of Cladosporium were obtained from raspberries, with C. cladosporioides being the most predominant, and was therefore used in further experiments. The susceptibility of raspberry fruit development was determined, with ripening and ripe fruit found to be susceptible to skin lesions; this stage of development was subsequently targeted in management studies. The effects of ripening and fruit location (fruit location within a tunnel vs. across a farm) on the inoculum load on the surface of raspberries were investigated using metabarcoding studies. The fungal and bacterial microbiomes were also investigated to better elucidate the ecology of Cladosporium on the fruit surface. Cladosporium was more abundant on green fruit than ripening fruit; perhaps due to organisms such as Rouxiella present on the fruit’s surface. Fungal α diversity increased during ripening while bacterial diversity decreased. The Cladosporium inoculum load in the air was also investigated, with more spores trapped inside a raspberry polytunnel than an open field. The efficacy of commercial Biological Control Agents (BCAs) and resistant varieties to control Cladosporium skin lesions were tested across two years in field applications. The Trichoderma sp. was the most effective at reducing the incidence of Cladosporium on raspberry than compared to the other tested products. The variety resistance study was inconclusive, but results indicate further testing will reveal which varieties are more susceptible. This research will inform potential management strategies against Cladosporium on raspberries that will aid growers in reducing food waste sustainably