Sequence similarities in the ITS region between <i>Cryptostroma corticale</i> and <i>Biscogniauxia</i> spp. complicate detection of the sooty bark disease agent

<i>Cryptostroma corticale</i>, the fungus causing sooty bark disease, is a threat to <i>Acer</i> species in Europe and North America. Furthermore, the conidiospores of this fungus are a threat to the health of highly exposed persons or immunocompromised humans. For the detection of <i>C. corticale</i>, species-specific primer pairs ccITS1f/ccITS1r and ccITS2f/ccITS2r were developed and published in 2017. Here we show that these primers are not completely specific for <i>C. corticale</i>. They detect also the closely related species <i>Biscogniauxia grenadensis</i> var. <i>macrospora</i> and <i>B. cinereolilacina</i>. These species are distributed in similar regions to <i>C. corticale</i>, and furthermore <i>B. grenadensis</i> var. <i>macrospora</i> has a similar host range to <i>C. corticale</i>. Therefore, for an unambiguous diagnosis of <i>C. corticale</i>, positive results of the primers ccITS1f/ccITS1r and ccITS2f/ccITS2r should be verified with a sequence analysis of the ITS region or a morphological investigation.