First report of Fusarium sporotrichioides causing root rot of Erigeron breviscapus in China

In China, Erigeron breviscapus is used extensively as a traditional herbal drug to improve brain circulation and enhance cerebral function. In August and September of 2005, root rot of E. breviscapus was observed in greenhouses in Mile County, Yunnan province of China. The initial symptoms of brown necrosis began in lateral roots, then advanced to the base of the stems. Plants withered, dried and died within 1-2 weeks (Fig. 1 & 2). The disease spread rapidly to neighbouring plants through irrigation water.

Tissue fragments taken from the diseased roots, at the edge of necrotic areas, were surface sterilised, transferred to potato dextrose agar and incubated at 27°C in the dark. Cultures from single-spore isolates formed characteristic pale pink colonies. Abundant single-celled microconidia and some macroconidia with 2 to 3 partitions (39-51 x 4-5 µm) were observed. Abundant chlamydospores were formed on water agar. The fungus was identified as Fusarium sporotrichioides based on its micro-morphology and cultural features (Booth, 1977; Nelson et al., 1983). For pathogenicity testing, a conidial suspension (5 x 10⁶ conidia per ml) was dropped onto wounded roots of 5-month-old E. breviscapus plants (10 ml per plant) in the field. Control plants were treated with water. The inoculated plants and controls were planted in the same field and observed daily for symptom development. All the inoculated plants showed root rot 14 days after inoculation. None of the wounded control plants developed symptoms. F. sporotrichioides was successfully re-isolated from all the inoculated plants, thus fulfilling Koch's postulates.

No records on F. sporotrichioides causing root rot of E. breviscapus have been found. To our knowledge, this is the first report of this disease in the world.