Molecular detection of <i>Helicobasidium purpureum</i> on carrots

Abstract

Helicobasidium purpureum (anamorph Rhizoctonia crocorum) is the causal organism of the carrot disease violet root rot, common in the Ohakune region of New Zealand. Helicobasidium purpureum has proven a difficult organism to isolate and grow in culture, confounding diagnosis of early infections. To enable early diagnosis of the disease, a conventional PCR assay was developed with the primer sequences (HelicoPurp1 and HelicoPurp2, 101bp amplicon) targeting part of the internal transcribed spacer (ITS) region of the organism. The assay detected all 15 H. purpureum isolates collected and maintained by our laboratory in pure culture. The assay was also robust enough to detect the fungi’s full range of inoculum types from the field (sclerotia, hyphae, mycelial mats and ‘black sheaths’), and was also able to detect the fungus when it was in association with plant tissues. Samples required washing, as soil inhibited this assay.