New disease of coriander in Australia associated with a Microdochium species

Coriander (Coriandrum sativum) is a winter field crop in southern Australia which provides spice seed to export markets (Lillecrapp et al., 2001). In October 1998, a new disease was identified at Mundulla, South Australia. Infected plants had extensive light grey, irregularly shaped, sunken lesions up to 1cm long on the upper stems (Fig. 1). Umbels and branches were distorted or dead above points where lesions had coalesced to cause total or almost complete stem girdling. The disease initially occurred as scattered foci but rapidly spread through the crop causing significant yield loss. The disease reappeared in the same region in 2001, producing severe damage in several crops.

Lesions contained abundant non-septate spores 10-15 μm long (Fig. 2) without obvious conidiophore structures. Single spore cultures on potato dextrose agar (PDA) produced slow growing, white septate hyphae with short conidiophores (Fig. 3), although most reproduction was by direct division of spores (Fig. 2). Cultures were identified by the New South Wales Department of Agriculture Herbarium as an unknown species of Microdochium and filed as specimen DAR 74129 (March, 1999).

Coriander plants at bud emergence were sprayed with a water suspension of spores (1 x 10⁴/ml), covered in plastic bags and incubated in a glasshouse at approximately 25˚C for 3 days. Lesions similar to those on field samples developed on the stems and leaves of the test plants 9 days after inoculation. There were abundant spores in the lesions which produced typical cultures on PDA. A range of Umbelliferae species (fennel, dill, aniseed, cumin, carrot, caraway and celery) and crop species grown in rotation with coriander (canola, peas, beans, barley and clover) were also inoculated but were not susceptible.

While Microdochium species are known to cause foliar diseases of broad leaf crops (Wicks et al., 1994; Anonymous, 2001), no other reports of this disease were found during an extensive literature review. This is the first record of a new foliar disease of coriander caused by a Microdochium species which is only known to occur in the south-east of South Australia.