In the Netherlands, approximately 30% of organic apples are made up of scab-resistant cultivars such as Topaz and Santana. However, Topaz organic apples show a high incidence of rot after storage. The hot water treatment (HWT) of fresh apples before placing them in units for months is an important strategy to control post-harvest infections, especially in the organic sector.
Treatment temperature and length vary depending on the cultivar in relation to the risk of heat damage to the peel. In January 2016, Topaz apples from an organic orchards showed slight superficial damage caused by this treatment. In addition, up to 15% of apples showed typical rot lesions - brown irregular necrosis and were slightly sunken - caused by an unknown fungal agent
Researchers from the University of Wageningen identified the fungus from both a morphological and molecular point of view, confirming that it was Truncatella angustata.
"T. angustata has a worldwide distribution and has also been reported on rosa canina, blueberries and plives. This is the first report of T. angustata causing rot on apples during the post-harvesting stage. Important: we have noticed that the infection can be favoured by the presence of wounds, which in this case were caused by the hot water treatment."
Source: M. Wenneker, K. T. K. Pham, L. C. Boekhoudt, F. A. de Boer, P. J. van Leeuwen, T. C. Hollinger, B. P. H. J. Thomma, 'First Report of Truncatella angustata Causing Postharvest Rot on 'Topaz' Apples in the Netherlands', 2017, Plant Disease, Vol. 101 (3), pag. 508.