Moldy core is a fungal disease of apple fruits that is characterized by mycelial growth in the seed locules and is sometimes accompanied by penetration of the immediate surrounding flesh. The disease can go undetected until the fruit is cut open, as no external symptoms appear on the fruit. Alternaria, Aspergillus, Cladosporium, Coniothyrium, Epicoccum, Phoma and Stemphylium are some of the common pathogens associated with moldy core.
The disease is more common in apple cultivars with an open calyx, where spores may initiate infections during the growing season or at the post-harvest storage stage. In 2018, a shipment of Sweet Tango apples from New Zealand to Scotian Gold Co-operative Ltd., Nova Scotia, Canada, was found to be affected by moldy core. Moderate to severe moldy core symptoms were observed when the apples were cut open. In comparison, Sweet Tango apples grown in Nova Scotia showed no moldy core symptoms when random fruits were cut open.
Symptoms of moldy core of Sweet Tango apples caused by Alternaria arborescens. A) Non-infected fruit; B) Naturally-infected fruit (mild infection); C) Naturally-infected fruit (moderate infection); D) Naturally-infected fruit (severe infection.
Scientists at Agriculture and Agri-Food Canada, Kentville Research and Development Centre (Nova Scotia, Canada) have isolated the pathogen from small pieces of the diseased fruit tissue from the core region and have identified the isolated pathogen species by morphological analyses, DNA sequencing and pathogenicity test.
"These isolates produced colonies of regular shape, tan black with prominent white gray margin and gray colour conidia. Based on the size and shape of conidia and other morphological characteristics the isolated fungi were identical to Alternaria species. The identity of the isolated pathogen species was assessed by DNA sequencing, which showed 100% identity to A. arborescens, the same results were confirmed by pathogenicity test. Two strains of A. arborescens were isolated and both isolates produced visible moldy core symptoms on the inoculated Sweet Tango fruits. To our knowledge, this is the first report of Alternaria arborescens causing moldy core disease in Sweet Tango apples from New Zealand," the scientists explained.
Source: Shawkat Ali, Pervaiz Abbasi, Sajid Rehman, Walid Ellouze, 'First Report of Moldy Core of Sweet Tango Apples from New Zealand Caused by Alternaria arborescens', 24 Marzo 2021, Plant disease.