Colletotrichum coccodes

(Black dot)

• Causal agent and transmission

The agent causing black dot on potato tubers is the fungus Colletotrichum coccodes, besides damaging tubers, it can also affect roots, stolons and stems.

The sources of infection are essentially plant debris (potato and tomato vines), infected weed hosts (Solanum nigrum, Physalis peruviana, Datura stramonium), and microsclerotia carried by seed tubers or in a free state in the soil.

Microsclerotia that are present in the soil can be infectious for more than 2 years.

• Significance

Black dot is present in many areas of the world but its direct effect on yield is usually alleviated by adequate fertilisation and good irrigation management.

However, in favourable soils and when fresh ware tubers are washed before selling, black dot is a surface-blemishing disease which may downgrade marketable yield and thus cause economic loss.