Etiology and management of black rot on ‘Forelle’ pears in the Western Cape

This study was conducted due to an increase in black rot reports in stored South African pears. This disease is not well documented and studied in South Africa. It has been reported that Diplodia seriata and Botryosphaeria dothidea are the main causal organisms. This study was performed to: 1) determine the distribution and presence of the disease in the Western Cape region of South Africa; 2) to confirm the main causal organism(s); and 3) to test the effectiveness of immersing fruit in currently registered and applied postharvest fungicides such as fludioxonil and pyrimethanil. To determine the incidence of black rot disease, a survey was conducted in 11 orchards in the Western Cape with 500 ‘Forelle’ pears being harvested from each orchard over two production seasons. The fruit was stored at -0.5°C under regular atmosphere conditions for three months. Black rot was confirmed in all sampled areas with a mean incidence of 1.7% and a maximum incidence of 9.2%. Fungal cultures collected from black rot pears were identified using species specific primers. The main causal organism for black rot was determined to be D. seriata. Isolates were collected in regions previously thought to be free of this pathogen. Notably, no Botryosphaeria dothidea cultures were collected from the survey. The fungicide trials using fludioxonil and pyrimethanil were performed with ‘Forelle’ pears inoculated with D. seriata. Results showed that a fludioxonil application was effective in controlling black rot at the registered dosage of 300 mg L-1. Conversely, pyrimethanil did not effectively control black rot even at double the recommended dosage of 1000 mg L-1.

Martin-John Richard won the ISHS Young Minds Award for the best oral presentation at the XIV International Pear Symposium in South Africa in January 2023.

Martin-John Richard, Department of Plant Pathology, Stellenbosch University, 7600 Stellenbosch, South Africa, e-mail: 20714580@sun.ac.za

The article is available in Chronica Horticulturae