Species of the Castanea genus (chestnuts) are used in the production of chestnut fruit (nuts). This edible product is incorporated into various food products and has become popular among consumers with demand and consumption increasing. Few fungal pathogens are reported to cause nut decay and negatively impact nut production. To identify the fungal species affecting the yield and postharvest quality of nuts, 1,814 samples from 11 Michigan orchards were collected and assessed. Rot symptoms were observed from 16% of the samples with 20 fungal species isolated from nut kernels. Gnomoniopsis sp. 1 was most frequently isolated, while Gnomoniopsis smithogilvyi was associated with severe disease symptoms. Seven species were evaluated for pathogenicity and two were confirmed as nut rot pathogens. While the other species are known to cause rot, they were not significantly different from the control. To evaluate the effect of cold storage on disease development, nuts from the cultivars Labor Day, Colossal, and Benton Harbor were inoculated with G. smithogilvyi, the pathogen that causes brown rot on chestnut. Following inoculation, the nuts were stored for various periods of time at 4 °C in three experiments conducted from 2019 to 2021. The cultivar Colossal was most susceptible to brown rot and cold storage treatments suppressed rot symptoms. Cultivar susceptibility, the pathogens that cause rot of nuts, and postharvest storage conditions should be considered in the development of IPM strategies.
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